Abstract:
A constant-head soil permeameter for determining hydraulic conductivity of earthen materials is inserted into a borehole at the desired test depth. A calibrated reservoir, disposed on the ground surface, is attached thereto with a suitable length of hose. Water is added to the calibrated reservoir and allowed to flow freely into the borehole until an equilibrium level is reached in the borehole and inside the soil permeameter. The water flowing to the permeameter is throttled by buoyant float pressure that is greatly increased by a single lever, lever-lever, or lever-link-lever valve control assembly which provides considerable versatility and mechanical advantage, thereby allowing more constant head control and much greater depths of testing than previously attained by known permeameters. A filtered vent system, backflow check valve, and seals restrict entry of soil particles and debris, thereby minimizing cleaning and maintenance of the invention. The soil permeability is determined by solving appropriate mathematical equations which utilize the equilibrium height of water, rate of water flow, and dimensions of the borehole as input parameters.

Description:
RELATED INVENTION 
   This invention is a continuation-in-part of U.S. Utility patent application Ser. No. 09/764,375, filed Jan. 19, 2001 of Larry K. Johnson that will issue on Jun. 3, 2003 as U.S. Pat. No. 6,571,605. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to the hydraulic conductivities of liquids through permeable materials and particularly relates to the conductivity of water through earth. It also relates to testing such conductivity from the surface of the earth to great depths beneath the surface and above the water table while preventing contamination by falling soil and debris. It more particularly relates to instruments that establish a static head of water within a borehole and maintain the water at this predetermined level by use of a float and valve system. It specifically relates to a highly versatile permeameter having a float and valve system that provides a mechanical advantage enabling use of the permeameter at any selected depth up to such great depths. 
   2. Review of the Prior Art 
   It is often important to estimate the hydraulic conductivities of porous materials, such as various types of earth, for solving many agricultural, hydrological, and environmental problems. In a practical sense, these conductivities are needed in order to safely and economically develop lands for urban and agricultural uses. Hydraulic conductivity values are also important considerations in design and construction of building and roadway foundations, on site sewage wastewater treatment systems, and storm water infiltration facilities. These hydraulic conductivity values are important for design of constructed wetlands and for estimating the rate of transport of liquid contaminants from waste disposal sites and leaking storage tanks. Hydraulic conductivity values are additionally important in design of irrigation systems and drainage of agricultural lands. 
   Soil hydraulic conductivity can be used to describe the ability of earthen materials to transmit water. Darcy&#39;s Law describes the relationship of the volume of water, moving through a cross sectional area of soil (commonly known as flux) along the hydraulic gradient of the water flow path, to the hydraulic conductivity. Under saturated conditions, such as below a water table, hydraulic conductivity is referred to as saturated hydraulic conductivity. Even though Darcy&#39;s law was originally developed to describe saturated flow, the principles of the law can be applied to water movement in partially saturated soils above the water table. 
   The determination of hydraulic conductivity under field conditions can be complicated because of the natural variation of soil properties and the specific need for which the test is being conducted. Soils typically contain multiple contrasting layers and often exhibit significantly differing hydraulic conductivity values along preferential flow paths within the soil matrix. 
   Prior art instruments developed for measuring hydraulic conductivity of soils above the water table in the field have generally fallen into three groups. The first group introduces either a ponded static (i.e., constant) or a variable (i.e., falling) head of water into the bottom of an unlined borehole below the ground surface or into a confining ring in contact with the ground surface. Instruments that establish a static head of water within a borehole maintain the water at a predetermined level, usually by use of either a float and valve system or a marriotte tube system. The rate of water flow necessary to maintain a constant water level in the borehole at the predetermined level is utilized to estimate hydraulic conductivity of the soil. 
   Methods used to measure the saturated hydraulic conductivity in a borehole utilizing a constant head of water have been referred to as the shallow well pump-in technique or constant-head well permeameter. Instruments in this first group that utilize a falling head procedure usually measure the drop of water from a predetermined level in a lined or unlined borehole as it dissipates into the soil to estimate hydraulic conductivity. 
   The second group of instruments applies water through a semi-permeable membrane to a soil surface, which is under negative pressure (tension), to measure unsaturated hydraulic conductivity. The third group of instruments utilizes various methodologies, which include electrical resistivity procedures and gas or liquid injection into the soil through penetrating probes. The instruments in the third group typically require a power source, fluid or gas pumps, multiple chambers, borehole packers, electronic data loggers, and/or complex analysis procedures. 
   U.S. Pat. No. 6,212,941 of G. Cholet describes a permeameter, designed particularly for measuring the air permeability of cigarette paper, which comprises a measuring head having two chambers opening onto two sides of a test piece, one of these chambers being connected to a measuring circuit successively comprising at least one flow meter and a pumping means capable of generating pressure or a partial vacuum in the circuit, an adjusting means for maintaining the circuit at a given pressure, and an electronic circuit comprising plural calibrated amplifiers having inputs connected to the output of the flowmeter and outputs connected to the inputs of a multiplexer whose output is connected to a processor via an analog-to-digital converter. 
   U.S. Pat. No. 6,178,808 of X. Wang et al relates to a method for measuring hydraulic conductivity of geological samples, using a closed volume pumping system that ensures constant volume of test liquid within the sample and a shaped tube of mercury to provide a constant pressure difference across the sample for eliminating second order influences on the hydraulic conductivity measurement and to speed measurement. 
   U.S. Pat. No. 6,105,418 of T. Kring discloses a constant-head float valve assembly which includes a J-shaped fluid conduit for intermittently delivering water from a supply container to a borehole. As the float moves downward with dissipating water levels, a shutoff valve is contacted and thereby opened to replenish the water in the borehole. The rising water moves the float upward and away from the valve, thereby allowing pressure of the incoming water to close the valve again. 
   U.S. Pat. No. 6,098,448 of W. Lowry et al describes an apparatus and method for discrete soil gas and saturated liquid permeability measurements with direct push emplacement systems, such as a cone penetrometer rod. Gas or liquid is injected into the soil at a predetermined location of the penetrometer rod after such a system, having at least one injection port and at least two measurement ports, has penetrated the soil to a predetermined depth. A pressure response is recorded from each measurement port, which is at a known distance from the injection port on the same penetrometer rod, thereby providing differential pressure response data allowing calculation of the soil permeability directly by using a one-dimensional, spherical, steady-state, porous flow model to measure the effective permeability of the soil, without substantially disturbing the surrounding soil. 
   U.S. Pat. No. 4,561,290 of Jewell utilizes a float valve assembly, connected to a water supply reservoir, to regulate water inflow and obtain a constant water level within a borehole. The float responds to a rising water level by regulating water flow through a valve and thereby maintaining a constant water level as the water in the test bore percolates away from the bore through the soil around it at a steady rate. 
   U.S. Pat. No. 6,055,850 of D. Turner et al describes a multi-directional permeameter comprising a mold which is removably secured to a base and having a removably secured lid. A porous plate circumferentially disposed around the midsection of the mold and another porous plate at its bottom are connected to the interior of the mold by filter papers. The interior of the mold is filled with a soil sample to be tested. This soil sample may be selectively compressed. Water is introduced above the soil sample through an inlet port. After percolation through the soil, the filter papers, and the porous plates, the water leaves through drainage ports, whereby the coefficients of permeability of the soil sample may be determined either horizontally, vertically, or simultaneously horizontally and vertically. 
   U.S. Pat. No. 5,520,248 of J. Sisson et al discloses an apparatus for determining the hydraulic conductivity of an earthen material. This apparatus comprises: a) a semipermeable membrane having a fore earthen material bearing surface and an opposing rear liquid receiving surface; b) a pump connected to the semipermeable membrane rear surface and capable of delivering liquid to the membrane rear surface at a plurality of selected variable flow rates or at a plurality of selected variable pressures; c) a liquid reservoir connected to the pump and containing a liquid for pumping to the membrane rear surface; and d) a pressure sensor connected to the membrane rear surface to measure pressure of liquid delivered to the membrane by the pump which preferably comprises a pair of longitudinally opposed and aligned syringes operated so that one syringe is filled while the other is simultaneously emptied. 
   U.S. Pat. No. 5,161,407 of M. Ankeny et al relates to a soil desorption device and method utilizing a pressure cell which contains soil samples, the pressure cells being attachable to pneumatic pressure manifolds and selectively being independently valved. The cells may be connected to collection containers for any desorbed fluid. Each cell utilizes a cylindrical container having rubber gaskets at opposite ends thereof for sealable attachment of top and bottom plates. A thin nylon membrane having small pores is positioned at the bottom of the container, and the bottom plate has apertures, whereby fluid forced through the membrane can pass to fluid collection devices. 
   U.S. Pat. No. 4,984,447 of J. Phillips describes a soil testing apparatus having a hollow shaft for insertion into a test hole. The shaft includes vertically adjustable wedging blades for centering alignment in the test hole. A hand pump evacuates water from the test hole to a predetermined null point, whereupon vertical movement of a float and float rod supported and guided within the shaft over a finite period of time yields a direct percolation absorption rate. 
   U.S. Pat. No. 4,884,436 of M. Ankeny et al discloses an automated tension infiltrometer having a soil contacting base to which a porous plate is attached for interfacing the infiltrometer with the soil to be analyzed. A Marriotte column is positioned in the base so that its open bottom end abuts the porous plate, and a bubble tower is also positioned in the base with a bubbling tube operatively connecting its interior and the interior of the Marriotte column. The bubble tower is adjustable to provide variable tension to the Marriotte column. Pressure changes in the upper and lower parts of the Marriotte column are continuously measured by first and second transducers while water from the column infiltrates into the soil. 
   U.S. Pat. No. 4,829,817 of L. Koslowski describes an apparatus for taking soil percolation tests which comprises a threaded shaft having a plurality of marking discs that can be selectively positioned along the shaft at predetermined gradations, a positioning brace that overlies the shaft for securing the shaft in vertical alignment, a mounting disc affixed near a base end of the shaft that becomes flush with the soil when the shaft is inserted into a percolation test hole, and a receiving disc near a top end of the shaft for receiving the positioning brace as it straddles the test hole. 
   U.S. Pat. No. 4,561,290 of D. Jewell discloses a float valve apparatus for soil percolation measurements. This apparatus comprises a float valve assembly, integral with a water supply system, which responds to changes in a predetermined water level inside a test bore to regulate water flow through the float valve into the bore to maintain this water level. The float valve assembly is positioned at different depths below ground level by suspension at the lower end of a premarked flexible hose hanging freely inside the test bore. The float valve housing is open at its lower end so that water around it in the test bore can raise the float therewithin to throttle the water flowing down through a reducer at the end of the hose and directly above the float. After an initial transient stage, the water in the test bore percolates away from the bore through the soil around it at a steady rate. 
   U.S. Pat. No. 4,520,657 of H. Marthaler discloses an apparatus for determining the pressure of capillary water in soil, comprising a probe tube and a pressure measuring device that measures pressure by means of an elastically deformable membrane. The probe tube is closed and pneumatically coupled to the pressure measuring device by a pierceable and self-sealing closure member. A hollow needle suitable for piercing the closure member is attached to the pressure measuring device. Mechanical-electrical transducers measure the pressure corresponding to the deformation of the membrane. 
   U.S. Pat. No. 4,341,110 of P. Block relates to a percolation testing apparatus for automatically recording the rate of fluid absorption of the soil surrounding a test hole. This apparatus includes three subsystems: a) a tubular housing having a plurality of perforations at its lower end; b) a float subassembly which includes a float member, a float rod, and a channel-shaped float rod extension; and c) a clock-marker subassembly which includes a guide member for the channel extension of the float rod. During a test procedure the rate of descent of a float is recorded on a tape by a timer controlled marker. 
   U.S. Pat. No. 4,182,157 of R. Fink describes a soil percolation testing apparatus comprising an elongated guide rod having one end to be driven into the bottom of a test hole for supporting a rod along which a gauge rod is slidable by means of guide brackets on the gauge rod and a scale strip which is attached to the upper end of the gauge rod for vertical movement relative to a reference marker supported adjustably upon the upper portion of the guide rod. A float is connected to the lower end of the gauge rod for vertical floating movement in the test hole that moves the scale strip relative to the reference marker which is stationary on the guide rod. 
   In U.S. Pat. No. 3,954,612, A. Wilkerson disclosed septic tank systems buried below the ground level and having a cover to minimize rainwater soaking into its drainage bed. The gravel-filled ditch is then covered with dirt. An indicator above the ground surface shows the water level in tributaries so that excess liquid can be pumped out before upstream sewage is backed up. 
   In U.S. Pat. No. 3,926,143, H. Hothan describes an upright gauge that detects and gives visual indications of the presence of free water at a predetermined depth in the ground. The gauge has a tubular housing in which a spherical float, with an attached float stem, is enclosed. Water applied to the nearby soil enters the gauge, moves the float upwardly, and causes the stem to rise and signal water penetration of the soil. 
   In U.S. Pat. No. 3,892,126 of J. Curtin, a test hole in soil is filled with a predetermined amount of liquid and has a calibrated measuring stick extending up from a support member having a float member disposed in the liquid to indicate up and down movement of the liquid level. 
   In U.S. Pat. No. 2,949,766, D. Kirkham et al describe an annular water reservoir which has an inlet tube as its inner wall that enters the ground. Water is in the annular space, and a graduated cylinder that fits within the annular space is inverted and suspended by its content of air, thereby maintaining a constant pressure. As air enters the soil, the float falls accordingly. 
   In an article published in  Soil Science Society of America Journal , Vol. 53, No. 5, pp. 1356–1361, Sept.–October 1989, by A. Amoozegar, entitled “A Compact Constant-Head Permeameter for Measuring Saturated Hydraulic Conductivity of the Vadose Zone”, a compact constant-head permeameter is described for maintaining a constant height of water (&gt;5 cm) at the bottom of a 4- to 10-cm-diameter hole in the unsaturated zone, and measuring the amount of water flowing into the hole, thereby measuring K S  from the soil surface to a depth of two meters. 
   In another article published in the same issue of the same journal, pp. 1362–1367, by A. Amoozegar, entitled “Comparison of the Glover Solution with the Simultaneous-Equations Approach for Measuring Hydraulic Conductivity”, the Glover solution and the simultaneous-equations approach for determining the saturated hydraulic conductivity (K S ) of the vadose zone by the constant-head well permeameter technique are examined. The uncertainty associated with calculating K S  by the simultaneous-equations approach, as compared with using the Glover solution, is then discussed. 
   However, neither of these devices incorporates an apparatus for magnifying the vertical force of the float body that is necessary for valve regulation at large depths and flow volumes, nor do they incorporate a backflow check valve to prevent incident entry of suspended soil particles and other contaminates into the float chamber. In addition, neither of these devices includes a means for eliminating the entry of contaminants through its air equalizing passage into the interior of the device. 
   Soil hydraulic conductivity has been historically measured on a smaller scale in the laboratory, utilizing a falling or constant head of water applied to soil core samples retrieved from the field or on remolded soil samples. Laboratory centrifugal force methods are also utilized to estimate hydraulic conductivity. Laboratory measurements are often significantly at variance with in situ field measurements because of the differing methodologies and the inherent difficulty of obtaining undisturbed soil samples and replicating natural environmental and stress conditions in the laboratory. 
   It is desirable to have the capability to conduct hydraulic conductivity tests at any depth in earthen materials above the permanent water table. Such depths may range from zero to many meters below the ground surface. In addition, it is desirable to have adequate flow capacity for maintaining flow equilibrium in a wide range of soils. Clay and marl strata often have slow permeability, whereas sandy or gravelly soils often have high permeability and, therefore, a greater equilibrium flow rate. 
   Not infrequently, when clay or marl strata are at or near the surface, it is necessary to prepare a hole through such strata into underlying layers having adequate permeability for receiving septic tank fluids and the like, whereby a tract of land may be developed by building single-family homes thereon. 
   Another matter of developing concern is the disposal of urban area rainwater into the ground in order to maintain the water table. With such large areas in urban areas and suburban areas being covered with roofs, parking lots, sidewalks, streets, and highways, there is very little opportunity for rainwater to be absorbed into the ground. It is instead gathered into storm sewers for transport into the nearest lake, river, or ocean, thereby bypassing underground strata that are pervious enough to water to receive and transport the wasted rainwater. 
   Prior art inventions that utilize a float system alone do not provide a mechanical advantage ratio, thereby limiting testing to relatively shallow depths. Inventions utilizing the marriotte tube principle to establish a constant water level are also limited to relatively shallow depths of testing. 
   A buoyant force is provided by a float in accordance with Archimedes&#39;s Principle which states that the buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced by that body. The displacement volume of any float of practical geometric shape that can fit in a small-diameter borehole is relatively small; therefore, the depth at which such a float can provide throttling of a valve by direct buoyant force alone is limited to relatively shallow depths and small flow rates. 
   There is accordingly a need for an apparatus that is sufficiently rugged and versatile to measure hydraulic conductivities of soils inside a borehole at a variety of depths above the water table, ranging from shallow to deep. None of the prior art apparatuses having a float utilize a magnifying means, such as a lever arm, to increase the available force for shutting off the flow of water into the apparatus. 
   There is also a need for a device that can be used inside a borehole, wherein the device is subject to being struck by falling soil particles and debris, without contamination by such particles and debris through the air vent hole at its top or through water outlets at its bottom. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a simple, sturdy, and versatile apparatus which functions as a constant-head soil permeameter for estimating saturated hydraulic conductivity of in situ earthen materials above the water table by establishing a constant head of water at a predetermined level in a borehole that is dug below the ground surface with ordinary hand auger equipment or with power equipment. 
   It is a further object to provide a constant-head soil permeameter that can, without incorporation of electronics, be effectively used to estimate hydraulic conductivity at desired test depths normally encountered above the water table and at depths much greater than the depths at which known devices that utilize a float system can be employed. 
   It is a still further object to provide a constant-head soil permeameter utilizing a float therewithin and leveraging principles for magnifying the upward thrust, created by the float when the water level rises within the permeameter. 
   It is an important object to provide principles for constructing a constant-head soil permeameter that utilizes at least one lever arm and at least one pivot for magnifying the upward thrust created by a float therewithin when the water level rises within the permeameter, whereby many variations may be constructed to meet a variety of measurement demands in the field. 
   It is an additional object to provide a constant-head soil permeameter that can be effectively used to determine hydraulic conductivities within a wide range of soil permeabilities. 
   It is also an object to provide a constant-head soil permeameter that avoids malfunction in the field by minimizing contamination from soil particles and debris falling from the side of the borehole. 
   It is another object to provide a constant-head soil permeameter that avoids malfunction in the field by minimizing contamination through outlets at its bottom from floating or suspended dirt and other particles in the water at the bottom of a borehole. 
   In accordance with these objects and the principles of the invention, the constant-head soil permeameter of this invention is an apparatus which incorporates a float, at least one lever arm, and at least one pivot that selectively increase the forces created by the float for the purpose of throttling water flow at the inlet valve. 
   The constant-head soil permeameter of this invention seeks to overcome disadvantages of prior art float systems by selectively multiplying the buoyant force resulting from submergence of a float alone. The permeameter increases the buoyant force by use of at least one lever arm that contacts the top of its float assembly while revolving around a fixed pivot and applying a leveraged force to the water inlet valve. 
   The one lever-arm embodiment, which utilizes one pivot and two pairs of lugs, has a mechanical advantage of approximately 4.3:1 at full closure, stoppers flow at a hydrostatic pressure of approximately 121 KPa and a buoyant force of 0.33 Kg-force. The float becomes almost totally submerged at this point. 
   The lever arm may be pivotally combined with an additional lever arm to form a compound two-lever assembly in sliding relationship while utilizing two pivots and four pairs of lugs. This embodiment has a mechanical advantage of approximately 11:1 at full closure and stoppers flow at a hydrostatic pressure of approximately 410 KPa and a buoyant force of 0.28 Kg-force. 
   As the preferred embodiment, the lever arm may be combined with another lever arm and an intervening link to form a compound lever-link-lever assembly, utilizing four pivots and seven pairs of lugs, which provides a mechanical advantage ratio ranging from approximately 10:1 at full valve opening up to approximately 60:1 at full valve closure at a hydrostatic pressure of approximately 410 KPa and a required buoyant force of 0.105 Kg-force. The resultant available maximum throttling force can, therefore, be approximately 60 times greater than simple buoyant force at full valve closure, depending upon the selected locations of the four pivots and the selected lengths of the lever arms and the link arm. The effective testing depth range of the permeameter is from 15 centimeters to about 30 meters. The permeability testing range of the apparatus is from 10 −6  centimeters/second to 10 −2  centimeters/second. The range of water flow volume through the apparatus is from zero to 2000 milliliters/minute or more at depths greater than one meter. 
   All of these embodiments of the constant-head soil permeameter comprises a tubular cylinder having a top end, a bottom end, means for introducing a liquid into the top end, means for selectively closing the bottom end, and means for preventing falling debris and soil from entering the top end while enabling air to flow into and out of the cylinder, the top end and the bottom end being defined in relation to usage within a vertically disposed borehole in materials permeable to the liquid, such as soil. The cylinder contains a leverage system that provides a mechanical advantage ratio for shutting off the introduction of liquid. 
   This leverage system comprises at least one lever arm that functions as a valve control assembly and is hereinafter thus identified. It is particularly operative when:
         A) the liquid is water, the materials are earthen, and the borehole has a bottom disposed above a water table in the earthen materials; and   B) the mechanical advantage ratio ranges from approximately 10:1 at full valve opening to approximately 60:1 at full valve closure.       

   When utilizing the lever-link-lever assembly, the valve control assembly, described hereinafter with water as the liquid, comprises the following components:
         A) a valve support bracket which is longitudinally disposed and rigidly supported within the cylinder, adjacent to the inner side thereof;   B) an actuating lever arm, having a contact end and a pivot end, which is attached at the pivot end to a first pivot which is rigidly attached to the valve support bracket, the contact end resting upon the top end of a float which is axially movable within the cylinder;   C) a link, having two ends, which is attached at its lower end to a second pivot which is attached to but spaced apart by a selected distance from the first pivot; and   D) a valve seat retaining lever arm, having two ends, which is pivotally attached at one end to the valve support bracket and is pivotally attached at its other end to a third pivot attached to the upper end of the link.       

   The top end of the cylinder comprises a top stopper, having an upper side and a lower side, which is rigidly attached to the cylinder and is encircled by an o-ring in sealing contact with the cylinder. The means for introducing water into the top end of the cylinder comprises a reservoir for containing water which is disposed on the surface of the ground, a hose connection which is rigidly attached to the top stopper and projects outwardly from its upper side and has a bore therewithin, a hose for connecting the reservoir to the hose connection, and a valve body which is rigidly attached to the lower side of the stopper and has a bore therewithin in fluid communication with the bore within the hose connection. 
   The valve seat retaining lever arm comprises a valve seat which is attached thereto in facing relationship to the valve body and is adapted for selectively shutting off the introducing of water into the cylinder from the reservoir. 
   The cylinder additionally contains a buoyant float body that is axially movable within the cylinder and has upper and lower surfaces. The upper surface exerts pressure against the contact end of the actuating lever arm when the float is supported by water within the cylinder. 
   The constant-head soil permeameter may be described as comprising the following lever-link-lever assembly within its cylinder which provides a mechanical advantage ratio:
         A) a valve support bracket, rigidly attached to the top stopper, having an upper pair and a lower pair of spaced-apart lugs attached perpendicularly thereto and projecting toward the center of the cylinder;   B) an actuating lever arm, comprising a contact end and a pivot end, having one pair of spaced-apart lugs attached perpendicularly thereto at its pivot end and projecting upwardly, being attached to the lower pair by a first pivot;   C) a link having upper and lower ends and a pair of spaced-apart lugs attached perpendicularly thereto at each end thereof which project toward the valve support bracket, the pair at the lower end being attached by a second pivot to the pair of spaced-apart lugs on the pivot end of the actuating lever arm, the second pivot being spaced from the first pivot by a selected distance; and   D) a valve seat retaining lever arm having two pairs of spaced-apart lugs attached perpendicularly thereto at the ends thereof and projecting in opposite directions, one pair being pivotally attached to the pair of spaced-apart lugs on the upper end of the link by a third pivot and the other pair of lugs being pivotally attached to the upper pair of lugs on the valve support bracket.       

   The means for preventing falling debris and soil from entering the top end of the cylinder while enabling air to flow into and out of the cylinder comprises an inverted J-shaped tube, having a long portion which passes through the stopper and a short portion having a filter screen at its outer end, the filter screen being disposed to face toward the upper side of the stopper and being spaced from the upper side. The short portion is downwardly enlarged, whereby falling debris and soil is dispersed outwardly and a clear space is left beneath the screen. 
   The means for selectively closing the bottom end of the cylinder comprises a bottom stopper, having an upper surface and a lower surface, which is rigidly attached to the cylinder, an o-ring encircling the stopper and in sealing contact with the cylinder, an axially disposed bolt attached to the stopper and extending upwardly beyond its upper surface, at least one longitudinally disposed hole extending through the bottom stopper, and a check valve disposed beneath the lower surface, whereby reverse flow of water from the borehole toward the stopper lifts the check valve and closes the hole and the bottom end. 
   This constant-head soil permeameter, adapted for operational use within a borehole in earthen materials, comprises a cylindrical housing having a top end and a bottom end which has a flow-through means for allowing water entering the top end to form a first water level within the housing and then to flow through the bottom end into the borehole to form a second water level therewithin when the second water level is lower than the first water level and having a closing means for preventing water from flowing into the cylindrical housing when the second water level is higher than the first water level. 
   This flow-through means comprises a bottom stopper which is rigidly attached to the cylindrical housing, has a countersunk bottom surface forming a downwardly extending skirt that contacts the bottom of the borehole when the permeameter is resting thereupon, has at least one longitudinally disposed hole through the stopper, and has at least one laterally extending hole through the skirt. 
   This closing means comprises a check valve guide which is axially and rigidly attached to the countersunk bottom surface of the stopper, a disk-shaped check valve which is loosely and axially fitted to the check valve guide, and a disk-shaped baffle, having a plurality of longitudinally disposed holes therethrough, which is rigidly and perpendicularly attached to the check valve guide and disposed beneath the check valve, whereby backflow of water from the borehole toward the bottom stopper passes through the plurality of holes in the baffle and lifts the check valve to block the at least one longitudinally disposed hole in the bottom stopper. 
   The method of using the permeameter of the invention is as follows:
         1) The rate of water flow into the borehole that is necessary to maintain the constant head is recorded at appropriate intervals during the test period; and   2) The information recorded during the test, which also includes height of constant water column, rate of flow, and borehole geometry, is factored into an appropriate mathematical equation to provide an estimate of hydraulic conductivity.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric and partial cutout view of the preferred embodiment of the constant-head soil permeameter in place in a shallow borehole dug in earthen materials. 
       FIG. 2  is an isometric and partial cutout view of the upper part of the soil permeameter shown in  FIG. 1 , showing the top stopper, the valve control assembly in its fully closed position, and a portion of the float valve assembly. 
       FIG. 3  is an isometric and partial cutout view of the lower part of the constant-head soil permeameter shown in  FIGS. 1 and 2 , showing the base assembly and the check valve in its open position. 
       FIG. 4  is a sectional view of the upper part of the same soil permeameter showing the top stopper, the filter vent assembly, and the air vent pathway into the interior of the cylinder, taken along line  4 — 4  in  FIG. 2 . 
       FIG. 5  is a fully sectioned view of the upper part of the constant-head soil permeameter shown in  FIGS. 1–3 , illustrating the top stopper, its o-ring, the filter vent assembly, the air vent assembly, and the valve control assembly in its fully opened position, a flow arrow emanating from the valve body representing the flow of water into the interior of the cylinder. 
       FIG. 6  is a sectional view of the upper part of the constant-head soil permeameter showing the same components as in  FIG. 5  but with the valve control assembly in its fully closed position, as in  FIG. 2 . 
       FIG. 7  is an enlarged sectional view of the middle part of the constant-head soil permeameter showing the same components as in  FIGS. 5 and 6  with the valve control assembly in its fully opened position, and illustrating the force components acting at their respective pivots and the imaginary lines of action connecting the pivots. 
       FIG. 8  is an enlarged sectional view of the middle part of the soil permeameter showing the same components as in  FIG. 7  but with the valve control assembly in its fully closed position, the force components and the imaginary lines of action being in their changed positions. 
       FIG. 9  is a sectional view of the lower part of the soil permeameter showing the base assembly and its check valve in its fully opened position, with flow arrows indicating the flow of water from the interior of the cylinder into the borehole. 
       FIG. 10  is a sectional view of the lower part of the soil permeameter, showing the base assembly and its check valve in its fully closed position and with the buoyant float body in a lowered position, in contact with a bolt attached to the base assembly, as a flow arrow indicates attempted movement of water from the borehole toward the interior of the cylinder. 
       FIG. 11  is a sectional view of the buoyant float body and the surrounding cylindrical housing of the constant-head soil permeameter. 
       FIG. 12  is a plan view of the float assembly, taken along line  12 — 12  in  FIG. 11 , and a sectional view of the surrounding cylindrical housing of the constant-head soil permeameter. 
       FIG. 13  is a plan view of the filter vent assembly and hose connection at the top end of the cylinder and a partial sectional view of the suspension bracket, taken along line  13 — 13  in  FIG. 5 . 
       FIG. 14  is a bottom view of the base assembly, taken along line  14 — 14  in  FIG. 10 , of the constant-head soil permeameter. 
       FIG. 15  is an isometric and partial sectional exploded view of the base assembly, taken generally along line  15 — 15  in  FIG. 14 . 
       FIG. 16  is a sectional view of the top stopper, taken along line  16 — 16  in  FIG. 6 , of the constant-head soil permeameter. 
       FIG. 17  is a sectional view, looking upwardly, of the base assembly of the soil permeameter, taken along line  17 — 17  in  FIG. 9 . 
       FIG. 18 , taken along the line  18 — 18  in  FIG. 6 , is a top view of the actuating lever arm, the three lug pairs, the two lower pivots, and the upper float guide of the float assembly, plus cross sections of the valve support bracket, the stabilizing bracket, and the link, the relative distances apart of the three lug pairs also being isometrically illustrated in  FIG. 2 . 
       FIG. 19 , taken along the line  19 — 19  in  FIG. 6 , is a sectional side view of the third pivot, both pairs of lugs which rotate around it, and the valve seat retaining lever arm, as well as a side view of the upper portion of the link. 
       FIG. 20  is a graph of the mechanical advantage ratio, provided by the valve control assembly within the housing. 
       FIG. 21  is a graph containing permeameter test depth-curves for the preferred embodiment of the constant-head soil permeameter of the invention undergoing permeameter flow rates from zero to 2,000 ml/min. 
       FIG. 22  is a sectional view of the middle part of the constant-head soil permeameter, as the preferred embodiment of this invention, showing the valve control assembly in its fully closed position as in  FIG. 8 , including applied forces, resultant forces, and angles therebetween. 
       FIG. 22A  is a force diagram which resolves the vertically aligned applied force, at the point of application thereof by the float assembly onto the heel of the actuating lever arm, into a force along the first imaginary line of action between the point of application to the axis of the first pivot and a force aligned perpendicularly thereto. 
       FIG. 22B  is a force diagram which resolves the force resulting from the torque produced at the second pivot, exerted perpendicularly to a second imaginary line of action between the first and second pivots, into a force aligned with this second line of action and a force aligned with a third imaginary line of action connecting the second and third pivots. 
       FIG. 22C  is a force diagram which resolves the force aligned with this second line of action, when applied to the third pivot connecting the link and the valve retaining lever arm, into a force applied perpendicularly to a fourth imaginary line of action between the third pivot and the fourth pivot, which connects the valve retaining lever arm to the valve support bracket, and a force aligned with this fourth imaginary line of action. 
       FIG. 22D  is a force diagram which resolves the force applied at the center of the valve seat, as the valve seat retaining arm revolves around the fourth pivot and multiplies the force applied perpendicularly to the fourth imaginary line of action by the ratio of the length of the fourth imaginary line of action to the length of a fifth imaginary line of action between the fourth pivot and the center of the valve seat, into a force aligned with this fifth imaginary line of action and a resultant force which is aligned vertically. 
       FIG. 23  is a sectional view of the middle part of the constant-head soil permeameter, as a second embodiment of this invention having its second pivot displaced a short distance away from the valve support bracket and approximately in parallel with the first imaginary line of action, showing the valve control assembly in its fully closed position as in  FIG. 8 , including applied forces, resultant forces, and angles therebetween. 
       FIG. 23A  is a force diagram which resolves the vertically aligned applied force in the same manner as for  FIG. 22A . 
       FIG. 23B  is a force diagram which resolves the force resulting from the torque produced at the displaced second pivot in the same manner as for  FIG. 22B . 
       FIG. 23C  is a force diagram which resolves the force aligned with this second line of action in the same manner as for  FIG. 22C . 
       FIG. 23D  is a force diagram which resolves the force applied at the center of the valve seat in the same manner as for  FIG. 22D . 
       FIG. 24  is a sectional view of the middle part of the constant-head soil permeameter, as a third useful embodiment of this invention having its second pivot displaced a relatively large distance away and upwardly from the valve support bracket, showing the valve control assembly in its fully open position as in  FIG. 8 , including applied forces, resultant forces, and angles therebetween. 
       FIG. 24A  is a force diagram which resolves the vertically aligned applied force in the same manner as for  FIG. 22A . 
       FIG. 24B  is a force diagram which resolves the force resulting from the torque produced at the displaced second pivot in the same manner as for  FIG. 22B . 
       FIG. 24C  is a force diagram which resolves the force aligned with this second line of action in the same manner as for  FIG. 22C . 
       FIG. 24D  is a force diagram which resolves the force applied at the center of the valve seat in the same manner as for  FIG. 22D . 
       FIG. 25  is a sectional view of the middle part of the constant-head soil permeameter, as a fourth useful embodiment of this invention having its second pivot displaced a relatively large distance away from the valve support bracket, showing the valve control assembly in its fully closed position as in  FIG. 8 , including applied forces, resultant forces, and angles therebetween. 
       FIG. 25A  is a force diagram which resolves the vertically aligned applied force in the same manner as for  FIG. 22A . 
       FIG. 25B  is a force diagram which resolves the force resulting from the torque produced at the second pivot in same manner as for  FIG. 22B . 
       FIG. 25C  is a force diagram which resolves the force aligned with this second line of action in the same manner as for  FIG. 22C . 
       FIG. 25D  is a force diagram which resolves the force applied at the center of the valve seat in the same manner as for  FIG. 22D . 
       FIG. 26  is a sectional view of the middle part of the constant-head soil permeameter, as a fifth useful embodiment of this invention having its second pivot in the same position as in  FIG. 25  and its third pivot displaced a medium distance away from the valve support bracket, showing the valve control assembly in its fully closed position as in  FIG. 8 , including applied forces, resultant forces, and angles therebetween. 
       FIG. 26A  is a force diagram which resolves the vertically aligned applied force in the same manner as for  FIG. 22A . 
       FIG. 26B  is a force diagram which resolves the force resulting from the torque produced at the second pivot in same manner as for  FIG. 22B . 
       FIG. 26C  is a force diagram which resolves the force aligned with this second line of action in the same manner as for  FIG. 22C . 
       FIG. 26D  is a force diagram which resolves the force applied at the center of the valve seat in the same manner as for  FIG. 22D . 
       FIG. 27  is a sectional view of a simplified embodiment of the invention that utilizes two lever arms in sliding relationship, the first pivot supporting the actuating lever arm being attached to a valve support bracket and stabilizing bracket on the opposite side of the cylindrical housing to the brackets supporting the second pivot on which revolves the valve seat retaining lever arm having a curved end in sliding contact with the actuating lever arm, with the valve seat being in open position. 
       FIG. 28  is a sectional view corresponding to  FIG. 27  except that the valve seat is in closed position. 
       FIG. 28A  is a force diagram which resolves the vertically aligned applied force, upon the heel of the lower lever arm, into a force aligned with a first imaginary line of action, between the first pivot and the line of contact of the top of the float body and the heel of the lever arm, and a force aligned perpendicularly thereto. 
       FIG. 28B  is a force diagram which resolves the force resulting from the torque produced at the line of sliding contact between the two lever arms into a force exerted perpendicularly to a second imaginary line of action between the this line of sliding contact and the second pivot and a force aligned with this second imaginary line of action. 
       FIG. 28C  is a force diagram which resolves the force applied at the center of the valve seat, as the valve seat retaining arm revolves around the second pivot and multiplies the force applied perpendicularly to the second imaginary line of action by the ratio of the length of the second imaginary line of action to the length of a third imaginary line of action, between the second pivot and the center of the valve seat, into a force aligned with this third imaginary line of action and a resultant force which is aligned vertically at the center of the valve body. 
       FIG. 29  is a sectional view of the middle part of a greatly simplified embodiment of the constant-head soil permeameter, showing a single lever arm as the valve control means in its fully closed position. 
       FIG. 29A  is a force diagram which resolves the vertically aligned applied force, exerted upon the heel of the lever arm by the rising top of the float, into a force aligned with an imaginary line of action, between this line of contact and the center of the single pivot, and a force which is aligned perpendicularly thereto. 
       FIG. 29B  is a force diagram which resolves the force aligned perpendicularly to a third imaginary line of action, between the center of the single pivot and the center of the valve body, into a force aligned with this line of action and the resultant force which is aligned vertically at the center of the valve body. 
       FIG. 30  is a sectional view of the middle portion of the soil permeameter, with a greatly modified valve seat retaining lever arm in order to simulate the prior art in which no leverage is used. 
       FIG. 31  shows two tables, the upper table providing six calculated forces for each of five embodiments of the invention, identified by figure numbers, and for the instance (identified by **) when the actuating lever arm has moved one degree upwardly after closing the valve, as it compresses the neoprene valve body, and the lower table providing the same calculated forces, where applicable, for the two-lever, single lever, and prior art embodiments. 
       FIG. 32  shows two drawings of the float body used in all embodiments of the invention, as well as in  FIG. 30  that illustrates prior art forces, to illustrate the float submersion required to stopper the valve at various pressure heads of water for the lever-link-lever and for the two-lever embodiments (left float), and for the single lever and prior art embodiments (right float) as the float bodies are submerged in surrounding water within the cylindrical housing, with depths of float submergence and corresponding borehole depths being given for each float. 
       FIG. 33  is a semi-logarithmic graph for the hydraulic pressure at the valve seat (pressure head, as in  FIG. 1 ) versus the buoyant force required to stopper the valve, the four curves representing the lever-link-lever embodiment, the two-lever embodiment, the single-lever embodiment, and the prior art embodiment. 
       FIG. 34  is a semi-logarithmic graph for the downward force at the valve seat, calculated as the hydrostatic pressure only and not including the momentum and other fluid-flow forces, versus the buoyant force required to stopper the valve. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1–21  are drawings from the parent application that describe the preferred embodiment, having two lever arms and a connecting link, referred to as the lever-link-lever embodiment.  FIGS. 22–30  are drawings that show additional embodiments, including a prior art embodiment for comparative purposes, illustrating the versatility and broad usefulness of the invention.  FIGS. 31–34  are tables, illustrative drawings, and graphs that provide information enabling the embodiments to be compared with each other and with the prior art. 
   As shown in  FIG. 1 , constant-head soil permeameter  10  of this invention comprises cylindrical housing  19 , means  21  for venting air from housing  19  and preventing dirt from entering the top of housing  19 , means  17  for providing a mechanical advantage ratio for shutting off water flow into housing  19 , and means  60  for preventing debris and fallen earth particles from entering the bottom of housing  19 . More specifically, valve control assembly  17 , float assembly  18 , base assembly  60 , and portions of the flow control assembly are inside of housing  19 . 
   Permeameter  10  also comprises suspension bracket  13  and utilizes a lifting and/or support means connected thereto. Cable  12  has snap connection  71  at its lower end which is secured through hole  99  in bracket  13  and is attached at its upper end to any suitable anchoring mechanism above ground surface  101 . Permeameter  10  is connected to calibrated reservoir  15 , which is disposed on ground surface  101  near borehole  11 , by hose  14  which is attached to hose connection  28  at its lower end. Hose  14  has a suitable length for the testing depth. Hose connection  28 , as a part of flow control assembly  59 , provides the entry port for water into housing  19  during tests. 
   Housing  19  consists of a tubular cylinder suitable for isolation and protection of interior components of the permeameter. Permeameter  10  may rest on bottom  11   b  of borehole  11  or may be supported at any desired height above bottom  11   b  by cable  12 . 
   Top stopper  16 , as shown in  FIGS. 2 ,  4 ,  5 , and  6 , provides a rigid mounting base for valve control assembly  17 , suspension bracket  13 , filter vent assembly  21 , and hose connection  28 . Top stopper  16  incorporates an o-ring  30  to provide a seal between stopper  16  and housing  19 , thereby preventing soil particles and debris from entering the invention in the annular space between top stopper  16  and housing  19 . 
   Hose connection  28  and valve body  44  are hydraulically connected and secured through top stopper  16  by commercial pipe  57 , as shown in  FIGS. 5 ,  6 ,  7 , and  16 . Suspension bracket  13  and valve control assembly  17  are additionally secured to top stopper  16  by commercial bolt  55  and commercial nut  56 . Top stopper  16  is secured to housing  19  by commercial machine screws  43 , as seen in  FIGS. 2 and 16 . 
   Filter vent assembly  21 , as shown in  FIGS. 2 ,  4 ,  5 ,  6 , and  13 , comprises commercial pipe nipple  51 , commercial pipe elbows  52 , filter housing  53 , filter screen  31 , and filter retaining snap ring  54 . Pipe nipple  51  is threadably fastened to top stopper  16  in a manner that allows free movement of air through vent pathway  68  in filter vent assembly  21  and top stopper  16 . Filter vent assembly  21  is constructed as an inverted J-shape to discourage entry of soil particles into the cylinder chamber through gravitational action while allowing free passage of atmospheric gas and excluding soil particles and other debris. Because filter screen  31  faces downwardly and is spaced from the upper side of stopper  16 , there is substantially no opportunity for soil and debris to pass through screen  31  into vent pathway  68 , whereby contamination of the apparatus is substantially impossible. 
   Valve control assembly  17 , as shown in  FIGS. 2 ,  5 ,  6 ,  7 , and  8 , comprises valve body  44 , valve seat  45 , valve seat retaining lever arm  38 , valve support bracket  35 , stabilizing bracket  48 , link  37 , and actuating lever arm  36 . Valve support bracket  35  and stabilizing bracket  48  are fastened together by commercial bolts  49  and  46  and by commercial nuts  50 . Stop heel  102  at the pivot end of lever arm  38 , by contacting bracket  35 , prevents arm  38  from dropping too far and thereby prevents heel  67  on lever arm  36  from moving to the right beyond the center of nut  100 . 
   Valve support bracket  35 , actuating lever arm  36 , link  37 , and valve seat retaining lever arm  38  comprise pairs of spaced apart and perpendicularly extending support lugs, shown in  FIGS. 2 ,  5 ,  6 ,  7 , and  8 . Each lug pair  90 ,  91 ,  92 ,  93 ,  94 ,  95 ,  96  has a hole drilled completely through both lugs, and a pivot  39 ,  40 ,  41 ,  42  is inserted completely through each drilled hole of the lug pairs, thereby serving as an axis of rotation. The pivots are crimped on the outsides of the lugs to ensure retention. These pivots are parallel to each other and provide a nearly frictionless connection between actuating lever  36 , link  37 , valve seat retaining lever arm  38 , and stationary valve support bracket  35 . 
   The pivots allow actuating lever arm  36 , link  37 , and valve seat retaining lever arm  38  to move freely in a plane parallel to the longitudinal axis of stationary valve support bracket  35 . 
   Actuating lever arm  36 , which comprises a single lug pair  90 , revolves around pivot  39 , which is also connected to lug pair  91  that is rigidly attached to valve support bracket  35 . Link  37 , which comprises two lug pairs  92  and  93  extending in opposite directions, is connected at pivot  40  to actuating lever arm  36  and at pivot  41  to valve retaining lever arm  38 . Link  37  revolves around both pivots  40  and  41  in response to the rising and lowering of float assembly  18 . Valve seat retaining lever arm  38 , which comprises two lug pairs  94  and  95  extending in opposite directions, revolves around pivot  42  which is also connected to lug pair  96  that is rigidly attached to valve support bracket  35 . 
   Valve support bracket  35  provides a rigid stationary connection between valve seat retaining lever arm  38  and actuating lever arm  36 . Link  37  provides a movable rigid connection between valve seat retaining lever arm  38  and actuating lever arm  36 . Valve control assembly  17  is shown in a fully opened position in  FIG. 5  and in a fully closed position in  FIGS. 2 and 6 . 
   Float assembly  18 , as shown in  FIGS. 11 and 12 , comprises buoyant float body  72 , upper and lower float end guides  27 , commercial threaded rod  58  and commercial nuts  50  and  100 . Water flow channels  23  are disposed opposite to each other on the perimeter of float body  72  and extend longitudinally through float body  72  and both float end guides  27 , as seen in  FIGS. 11 and 12 . 
   Base assembly  60 , as shown in  FIGS. 3 ,  9 ,  10 ,  14 , and  15 , comprises bottom stopper  20  which provides a rigid mounting body for o-ring  30  which is in sealing contact with housing  19 , commercial bolt  29 , check valve  32 , check valve guide  34 , baffle  25 , longitudinally disposed holes  24  through stopper  20 , laterally disposed holes  26  in the skirt of bottom stopper  20 , and commercial nuts  56  and  98 . Check valve  32  moves freely in a vertical direction on check valve guide  34 . Bottom stopper  20  is secured to housing  19  by commercial machine screws  43 , as shown in  FIG. 17 . 
   Check valve  32  rests on baffle  25  and remains open during normal operation, as illustrated in  FIG. 9 , when water is flowing through base assembly  60  to borehole  11 . However, check valve  32  rises into contact with countersunk bottom surface  20   c  and closes holes  24  to prevent backflow, as seen in  FIG. 10 , if forced upward by reverse water flow, shown by flow arrow  69  through hole  33  in baffle  25 . 
   Valve control assembly  17  and float assembly  18  provide flow control of water from reservoir  15  to maintain a constant head of water in borehole  11 . This constant head of water is established by the preset level of the permeameter within borehole  11  and the resultant equilibrium of the pressure head induced by the height of water  70  in reservoir  15  and the rate of water absorption  47  into earthen material  11   a , as depicted in  FIG. 1 . The force provided by any float assembly to effectively stop or throttle the flow through a valve must be sufficient to exceed hydrostatic pressures produced by the height of water  70  through hose column  14  and resultant pressure of water flow at control valve components  44  and  45  in the constant-head soil permeameter. 
   As the depth of testing increases, the increasing hydrostatic pressure at control valve components  44  and  45  of valve control assembly  17  requires progressively greater water displacement by float assembly  18  to throttle and maintain flow equilibrium. Other constant head devices utilizing a float alone with a float displacement equivalent to displacement of float assembly  18  become fully submerged and, therefore, ineffective at deep depths, as illustrated in  FIG. 32 . Indeed, prior art devices become fully submerged at a depth of one meter. In addition, the float assemblies of other constant-head devices, not having a mechanical advantage means, displace a greater volume of water than the present invention at any given depth while maintaining equilibrium, thereby causing a correspondingly greater transient rise of the water level, H, within the borehole. This complicates determining the constant height of water for permeability test determinations. 
   The entire constant-head soil permeameter of this invention is constructed of stainless steel except for: a) o-rings  30 , check valve  32 , and valve seat  45  which are made of neoprene; b) top stopper  16 , bottom stopper  20 , baffle  25 , and upper and lower float end guides  27  which are made of polycarbonate plastic; and c) float  72  which is made of a closed-cell foamed plastic. 
   Explanation of Forces Exerted Within Valve Control Assembly  17   
   The mechanical advantage ratio that is necessary for hydraulic testing at considerable depths is provided by the lever-link-lever action of valve control assembly  17 . A force along a line of action is required to make any body rotate about an axis. The perpendicular distance from the line of action of the force to the axis of rotation is the moment arm of the force and the product of the force and the moment arm of the force is the torque. 
   As seen in  FIGS. 7 ,  8 ,  22 ,  22 A,  22 B,  22 C, and  22 D, buoyant or applied force  74 , which has a line of action parallel to the longitudinal axis of valve support bracket  35 , can be resolved into force components  75  and  76 , which are, respectively, perpendicular and parallel to imaginary line  77  which joins the point of application of force  74  to the axis of actuating lever arm  36 , as illustrated in  FIG. 22A . Line  77  is, therefore, a moment arm of force  75  about pivot  39 . The torque applied at pivot  39  is equal to the product of force  75  and the length of moment arm  77 . Force  76  is directed toward the axis at pivot  39  and does not cause rotation. 
   As actuating lever arm  36  revolves around pivot  39 , every point on actuating lever arm  36 , including pivot  40  on lugs  90 , sweeps out the same angle at any time. The torque produced at pivot  39  from force  75  results in force  78  at pivot  40 , which acts in a line of action perpendicular to moment arm  79 . Force  78  is proportional to the ratio of the length of moment arm  77  to the shorter length of moment arm  79 , thereby greatly exceeding force  75 . Force  78  can be resolved into force  81  and force  80  along moment arm  79 , as illustrated in  FIG. 22B . 
   Force  81  lies along line of action  87 , which is an imaginary line connecting pivot  40  and pivot  41  of link  37 , all parts of which act as a rigid plate. Force  80  is directed toward pivot  39  and does not cause rotation. Forces  81  and  80  can be determined by two-dimensional equilibrium equations. The maximum ratio of force  81  to force  78  is achieved just before pivot  40  and line of action  87  of force  81  move across line  73 . Line of action  87 , however, is prevented from crossing line  73  by bolt  46 , which limits the rotational travel of link  37 . 
   Force  81  can be resolved into force components  82  and  83  which are, respectively, perpendicular and parallel to imaginary line  84  which joins the point of application of force  81  at pivot  41  with pivot  42 , as illustrated in  FIG. 22C . All parts of valve retaining lever arm  38 , similarly to link  37  and actuating lever arm  36 , act as a rigid plate. Line  84  is, therefore, a moment arm of force  82  about the axis of pivot  42 . 
   The torque applied at pivot  42  is equal to the product of force  82  and the length of moment arm  84 . Force  83  is directed either toward or away from the axis at pivot  42 , depending on the degree of closure of valve control assembly  17 , and does not cause rotation in either case. Force component  82  is nearly superimposed on line of force  87 , as seen in  FIG. 7 , because this line of force is nearly perpendicular to moment arm  84  at the fully open position. 
   As valve seat retaining lever arm  38  revolves around pivot  42 , every point on valve retaining lever arm  38 , including valve seat  45 , sweeps out the same angle at any time. Force  86  is perpendicular to moment arm  85  and is a result of the torque at pivot  42  acting along the length of moment arm  85 . Force  86  is proportional to the ratio of the length of moment arm  84  to the shorter length of moment arm  85 , thereby greatly exceeding force  82  which applies the initial torque. Force  86  can be resolved into component force  88  that is perpendicular to face  89  of valve seat  45  and another force (neither shown nor numbered) that is parallel thereto, as illustrated in  FIG. 22D . 
   Force component  88  of force  86  has a line of action through the center of and perpendicular to face  89  of valve seat  45 . Force  88 , applied at the surface of valve seat  45 , provides the force necessary to throttle or stop fluid flow from valve body  44 . The mechanical advantage ratio of resultant force  88  to buoyant force  74  ranges from approximately 10:1 at full valve opening ( FIG. 7 ) to approximately 60:1 at full valve closure ( FIG. 8 ). The mechanical advantage (MA) increases as a result of the cumulative mechanical advantages of actuating lever arm  36 , link  37 , and valve seat retaining lever arm  38 . As can be seen in  FIG. 20 , the mechanical advantage ratio becomes larger at an increasing rate as pivot  40  and line of force  87  approaches, but does not cross, line  73 . As the mechanical advantage ratio moves beyond 60:1, the neoprene material in valve seat  45  becomes increasingly compressed. 
   Within the confines of housing  19 , the distance between pivots  39  and  40  is the principal factor controlling amplification of the mechanical advantage ratio beyond 60:1. If the distance of 7.75 mm between pivots  39  and  40 , as in the preferred embodiment herein described, is reduced, the torque about pivot  39  is increased in accordance with the ratio of the length of moment arm  77  to the length of moment arm  79 , thereby correspondingly increasing resultant force  78 . In addition, reduction in distance between pivots  39  and  40  simultaneously increases resultant force component  81  along line of action  87 . However, this increased mechanical advantage and increased resultant force comes at a cost because the valve does not open as much as formerly and the maximum fluid flow is less. 
   The lugs and lever arms are quite rigid while using the preferred 14-gauge stainless steel materials, with a significant safety factor at a depth of even 40 meters. Consequently, the mechanical advantage ratio can be further increased, and the testing depth can thereby be significantly increased beyond 30 meters. The maximum depth of testing for the preferred embodiment described herein is limited to some undetermined depth greater than 40 meters because of limitations imposed by float capacity, fluid pressure, and turbulence created by the incoming water. 
   Valve control assembly  17  controls the water flow through the permeameter. At the beginning of a typical hydraulic conductivity test, water flows into hose connection  28  of valve control assembly  17  as shown by flow arrow  61  in  FIG. 5 . Valve control assembly  17  is initially in a fully open position, thereby allowing water flow through valve body  44  and through the opening between valve body  44  and valve seat  45  as shown by flow arrow  62  in  FIG. 5 . 
   This water falls on upper float end guide  27  and passes through water flow channels  23  of float assembly  18  and holes  24  of base assembly  60  and continues to flow beneath bottom stopper  20  and into borehole  11 , as indicated by flow arrows  63 ,  64 ,  65 ,  66 , as seen in  FIG. 9 . 
   The water rises at equal corresponding levels in borehole  11  and inside housing  19 . As the water level continues to rise, nut  100  of float assembly  18  strikes heel  67  of actuating lever arm  36 , which is pivotally connected to valve support bracket  35  at pivot  39 , and initiates upward rotation of actuating lever arm  36  around pivot  39 . As float assembly  18  continues to rise, forcible contact at heel  67  of actuating lever arm  36  is transferred from nut  50  to float end guide  27 , which maintains continuous sliding contact until partial or full valve closure is attained, as seen in  FIGS. 1 ,  2 , and  6 . 
   As actuating lever arm  36  rotates upwardly around pivot  39 , link  37 , which is pivotally connected to pivot  40 , revolves around pivot  40  and transfers the buoyant force provided by float assembly  18  to pivot  41  of valve seat retaining lever arm  38 . This arm  38  is pivotally connected to valve support bracket  35  at pivot  42 . It consequently revolves upwardly and progressively closes the valve opening between valve body  44  and valve seat  45 . The mechanical advantage imparted by actuating lever arm  36 , link  37 , and valve seat retaining lever arm  38  increases with progressive valve closure, as shown in  FIG. 20 . 
   Line  73  is an imaginary straight line passing through the centers of pivot  39  and pivot  41 , as depicted in  FIG. 7 . As float assembly  18  rises, heel  67  of actuating lever arm  36  slides from nut  100  onto upper float end guide  27  and continues to slide across guide  27  as actuating lever arm  36  revolves upwardly around pivot  39 , thereby moving pivot  40  and link  37  toward line  73 . The maximum mechanical advantage is attained just before pivot  40  reaches line  73 . Pivot  40 , however, is prevented from crossing line  73  by bolt  46 , which limits the travel of link  37 . The preferred embodiment provides a mechanical advantage ratio of approximately 60:1 at full valve closure. 
   Float assembly  18  provides the buoyant force required by valve control assembly  17  to throttle water flowing through bore  97  in hose connection  28 , pipe  57 , and valve body  44 . Float assembly  18  moves freely inside housing  19  and is maintained in alignment by both float end guides  27 , as shown in  FIGS. 5 ,  6 ,  11 , and  12 . The upward travel range of float assembly  18  is limited by contact with valve control assembly  17  and the downward travel range is limited by contact with bolt  29 . Prior to application of water during a hydraulic conductivity test, threaded rod  58  of float assembly  18  is at rest on bolt  29 , as shown in  FIG. 10 . 
   Water added to reservoir  15  during a typical test flows freely around float assembly  18  through flow channels  23  that are disposed longitudinally on float body  72  and float end guides  27 , as well as in the annular space between float body  72  and housing  19 , as shown in  FIG. 12 . Bolt  29 , which limits downward travel of float assembly  18 , prevents float assembly  18  from resting on the upper surface of bottom stopper  20 , thereby allowing water applied during the test to flow freely through holes  24 , as illustrated in  FIGS. 9 and 17  by flow arrows  63 ,  64 ,  65 , and  66 , through bottom stopper  20  and also allowing the water to contact the entire lower surface of float assembly  18  when the water is rising inside housing  19 . 
   Float assembly  18  rises with the rising water and displaces a volume of water equal in weight to the weight of float assembly  18 . Float assembly  18  continues to rise in response to the rising water level and strikes heel  67  of actuating lever arm  36  and initiates upward revolution of actuating lever arm  36  around pivot pin  39 , as illustrated in  FIG. 5 . As float assembly  18  continues to rise, contact at heel  67  of actuating lever arm  36  is transferred from nut  100  to upper float end guide  27 , which maintains continuous sliding contact until valve throttling control or full valve closure is attained, as seen in  FIG. 6 . Float assembly  18  becomes partially submerged in proportion to the buoyant force required to throttle water flow from the contact orifice of valve body  44  by valve seat  45 , as illustrated in  FIG. 32 . 
   As float assembly  18  rises initially, valve seat  45  almost contacts valve body  44  to close bore  97  and stop the flow of water from reservoir  15 ; then valve seat  45  lowers slightly to establish an equilibrium fluid level in borehole  11  with only a slight fluctuation. 
   It is desirable to prevent inadvertent backflow entry of water, which may contain suspended soil particles or other debris, into the permeameter. Potential for reverse water flow, as shown by flow arrow  69  in  FIG. 10 , may occur if the permeameter is placed in a borehole already containing water, if the borehole is advanced further after initial testing and water is not removed, or if the sidewall of the borehole collapses during the test and displaces a sufficient volume of water to cause backflow. Check valve  32  remains closed by pressure differential as long as the water level remains higher in the borehole than in the chamber of housing  19 . 
   During normal operation, water flows through holes  24  in base assembly  60 , as shown by flow arrow  63  in  FIGS. 3 and 9 , then into the space above check valve  32  and around the annulus between baffle  25  and bottom stopper  20 , as shown by flow arrow  64 . Water continues to flow through lateral holes  26  of base assembly  60  into the annulus between housing  19  and borehole  11 , as shown by flow arrow  65 , and into the cavity below baffle  25  as shown by flow arrow  66  in  FIG. 9 . 
   Baffle  25  and check valve  32  physically block direct entry of loose soil and other debris into the chamber of housing  19  when the permeameter of the invention is initially placed in the borehole. Bottom stopper  20  also incorporates o-ring  30  to provide a seal between bottom stopper  20  and housing  19 , thereby further preventing entry of suspended soil particles and debris. Bottom stopper  20  is countersunk at its bottom  20   c  to leave a narrow circular rim  20   b  having a bottom edge  20   a , as shown in  FIGS. 3 and 9 , thereby minimizing the contact area with borehole bottom  11   b  and providing negligible smearing or blockage of the absorptive soil surface at the bottom of the borehole. 
   During field operations to determine hydraulic conductivity, an unlined borehole  11  is drilled into the earth to a desired test depth with a suitable drilling or digging device to remove earthen materials and provide an approximately level surface at the bottom of the borehole. The constant-head soil permeameter of the invention is then lowered in a vertical position by cable  12  to rest upon bottom  11   b  of borehole  11 , as shown in  FIG. 1 . Water is poured into reservoir  15  and flows by gravity through hose  14  and bore  97  in hose connection  28 , as shown by flow arrow  61  in  FIG. 5 , into valve control assembly  17 , as shown by flow arrow  62  in  FIG. 5 . Valve control assembly  17  is initially in a fully open position, thereby allowing water to flow, as shown by flow arrow  62 , through the opening between valve body  44  and valve seat  45 . 
   Water then flows onto and around float assembly  18  through channels  23 ., as seen in  FIGS. 2 and 12 , into the annular space between float assembly  18  and housing  19  and into the lower part of housing  19 . Water next flows through holes  24  in bottom stopper  20 , as shown by flow arrow  63  in  FIGS. 3 and 9 . During normal test procedures, check valve  32  is in its open position which allows water to flow freely through holes  24  in bottom stopper  20  into the space above check valve  32  and around the annulus between baffle  25  and bottom stopper  20 , as shown by flow arrows  63  and  64  in  FIG. 9 . Water then continues to flow through lateral holes  26  in skirt  20   b  into the annulus between housing  19  and the perimeter of borehole  11 , as shown by flow arrow  65  and into the cavity below baffle  25  as shown by flow arrow  66 . 
   Filter vent assembly  21  allows exhausting of air as water rises within housing  19  and maintains atmospheric pressure equally inside and outside of housing  19  within borehole  11  at all times; this pressure equalization between level  22  within housing  19  and height of water H within borehole  11  is essential for maintaining equal water levels inside and outside of housing  19 . Filter screen  31  of filter vent assembly  21  also stops entry of loose soil particles into housing  19 . 
   Water rises freely at equal levels within constant-head permeameter  10  and in the annular space between cylindrical housing  19  and the borehole sides until float assembly  18 , which is buoyed by the rising water, engages valve control assembly  17 . Water flow through valve body  44  is progressively throttled by valve seat  45  of valve control assembly  17  as float assembly  18  continues to rise until water level  22 , as seen in  FIG. 1 , is approximately attained. After a suitable period of time that may vary from several minutes to one-half hour or more depending on soil characteristics, while water from borehole  11  is being transported radially into the surrounding soil matrix  11   a , as shown approximately by permeation arrows  47  in  FIG. 1 , equilibrium water levels H and  22 , which are equal, are attained. 
   The wetting front continues to develop radially from borehole  11  as water levels H and  22  are maintained above the bottom of borehole  11  during the testing period. Water moves radially from borehole  11  through interparticle pores and along voids and fissures that are unique to any particular borehole in response to pressure induced by the constant head of water H, gravitational forces, and capillary forces within the earthen materials. The saturation that occurs within the wetting front during the test period is sometimes referred to as field saturation because some of the voids and pores may contain entrapped air and thereby reduce the potential flow that may occur under fully saturated conditions below the water table. An approximate steady state flow is attained in soil matrix  11   a  after a period of initial saturation and equilibrium is developed. Water level H is the resultant equilibrium level maintained by permeameter  10  in response to water absorption by soil and a pressure head of water level  70  in reservoir  15 , as illustrated in  FIG. 1 . Once equilibrium of flow is approximately attained, reservoir  15  is filled approximately to initial level  70  in preparation for recording test data. 
   After initial flow equilibrium is attained, the steady state flow of water absorbed by the soil is determined by recording at discrete time intervals the dropping water levels observed at graduations on reservoir  15 . The optimum recording interval varies with the soil type and permeability and is determined by the user. For example, the optimum recording interval for highly permeable sandy soils may be approximately 5 minutes, but for slowly permeable clayey soils may be one-half hour or more. The total time during which observations are recorded may typically vary from on-half hour to 2 hours or more. The flow rate is derived from observations recorded during the selected time period. Level H of water in the borehole may be determined from direct observations or by the use of  FIG. 21 , which determines level  22  as a function of water flow rate and depth of the permeameter below ground surface  101 . The estimated hydraulic conductivity is determined by factoring the steady state flow rate, water depth, and borehole geometry into an appropriate analytical solution. 
   Solution to Hydraulic Conductivity Values 
   The depth of water, indicated as level H in the borehole, may be determined from direct observations by use of a measuring tape or may be estimated by use of the Flow Rate/Test Depth Chart in  FIG. 21 . Test depth curves for placement of the permeameter below ground surface  101  range from 0.5 to 30.0 meters, as shown in  FIG. 21 . The test depth curves of  FIG. 21  represent the mean of all observations, 95% of which are within +/−0.5 cm as determined by using an embodiment of the present invention. The test depth curves denote the height of water in the borehole if the permeameter rests on the bottom of the borehole. Alternatively, the permeameter can be suspended at any desired distance above the bottom of the borehole, and the suspended distance beneath rim  20   a  can be added to the height determined in  FIG. 21  to obtain H. 
   The chart in  FIG. 21  can be used to estimate the depth of water within the borehole at any flow rate of the invention ranging from zero to 2000 ml/min. For example, if the permeameter is placed on the bottom of the borehole, the depth of water in the borehole is 10.0 meters, and the flow rate is 500 ml/min., then the estimated depth of the static water level H is approximately 15.2 cm. Where test depths are intermediate to the depth curves of  FIG. 21 , an appropriate interpolation is made. 
   The estimated hydraulic conductivity is determined by factoring the steady state flow rate of water into the soil, height of water within the borehole, and borehole geometry into an appropriate analytical solution. One example of an analytical solution has been developed by R. E. Glover (Zangar, 1953). This equation, suggested by Amoozegar and Warrick (1986) for use where the distance between the bottom of the borehole and an impermeable layer is at least twice as large as H, is:
 
 K   S   =Q[sinh   −1 ( H/r )−( r   2   /H   2 +1)· 5   +r/H]( 2π7 H   2 )  [Equation 1]
 
   Where
         K S =Saturated hydraulic conductivity,   Q=Steady-state flow rate of water into the soil,   H=Constant height of water in a cylindrical borehole, indicated as level H, and   r=Radius of the cylindrical borehole.       

   Use of this equation is illustrated in the two following examples. 
   EXAMPLE 1 
   A cylindrical borehole  11  with diameter of 9.5 cm is augured to a depth of 0.6 meters. It is desired to establish a minimum height H of water equalling 25 cm above the bottom of the borehole, so that the permeameter is suspended 10 cm above the bottom of the borehole. During the test, in which volumetric readings of falling water levels in reservoir  15  are recorded at discrete time intervals spanning a two-hour period, it is determined that the steady-state flow rate of water Q into soil  11   a  is 5 ml/min. The constant height H of water is, therefore, 25.1 cm (15.1 cm from  FIG. 21 , plus 10 cm of suspended height). The radius r of borehole  11  is 4.75 cm, and the saturated hydraulic conductivity, K 8 , from Equation 1 is 3.2×10 −5  cm/sec. This is a low hydraulic conductivity value, typical of silt and clay soils. 
   EXAMPLE 2 
   A circular borehole  11  with diameter of 9.5 cm is augured to a depth of 10.0 meters. It is desired to establish a minimum height H of water equalling 25 cm above the bottom of the borehole and to suspend the permeameter at a height of 10 cm above the bottom of the borehole. During a test period of one-half hour, it is determined that the steady-state flow rate of water Q into soil  11   a  is 900 ml/min. The constant height H of water is, therefore, 25.1 cm (15.1 cm from  FIG. 14 , plus 10 cm of suspended height). The radius r of the borehole is 4.75 cm and the saturated hydraulic conductivity from Equation 1 is 5.8×10 −3  cm/sec. This is a high hydraulic conductivity value, typical of sandy soils. 
   In the event that water covers bottom  11   b  of borehole  11  at the time of inserting the permeameter in borehole  11 , check valve  32  of base assembly  60  closes and stops water and suspended soil particles from entering housing  19 , as seen in  FIG. 10 . It is desirable to prevent inadvertent entry of water, which may contain suspended soil particles or other debris, into the permeameter. 
   This situation may occur if seepage water enters the borehole after it is drilled or if the borehole is advanced to a deeper depth after an initial test has been performed and the remaining water has not been removed during drilling or has not drained completely away into the soil. Water must be removed from the borehole if the initial water levels exceed the equilibrium height of the permeameter. If the water level is a result of seepage or groundwater inflow, the test procedure is invalid because the permeameter is designed to measure hydraulic conductivity as a result of outflow to the soil. Potential reverse water flow may also occur if the sidewall of the borehole collapses during the test and displaces a sufficient volume of water to cause backflow. 
     FIG. 22  shows a section of the preferred lever-link-lever embodiment which is exactly as shown in  FIG. 8  except that the angles, a, b, c, and d are identified therein and are resolved in respective force diagrams,  FIGS. 22A ,  22 B,  22 C, and  FIG. 22D . Vertically applied force  74 , caused by the upward thrust of float assembly  18  upon heel  67 , is resolved into force  75  that is perpendicular to imaginary line of action  77 , as shown in  FIG. 22A . Multiplying force  75  by the length of line  77 , functioning as a moment arm, provides a torque force at pivot  39 . 
   Because second pivot  40  passes through lugs  90 , this torque force sweeps through pivot  40  and at its center produces force  78  which is resolved in  FIG. 22B  into force  81  that is exerted along line of action  87  upon third pivot  41 . In  FIG. 22C , force  81  is resolved into force  82  that is perpendicular to line of action  84  between third pivot  41  and fourth pivot  42 . 
   Multiplying force  82  by the length of line of action  84 , functioning as a moment arm, provides a torque force at the center of pivot  42 . Then multiplying this force by the ratio of the length of line  84  to line  85 , between the center of pivot  42  and the center of valve seat  44 , produces force  86  which is perpendicular to line  85 . It is resolved in  FIG. 22D  into a vertically applied resultant force  88  that performs the critical task of stopping the momentum of inwardly flowing water, closing the valve by contacting body  44  with valve seat  45 . Assuming initial force  74  to be 1.00 kg-force, resultant force  88  is 58.71 kg-force. 
   The equation used is as follows:
 
Force  88 =(Force 74 )(COS  a )( MA 77 /MA 79)(1/COS  b )(COS  c )( MA 84 /MA 85)(COS  d )
 
   When lever arm  36  is moved upwardly beyond the point of closure by one degree past horizontal, the neoprene of valve seat  45  is compressed, causing resultant force  88  to increase to 62.77 kg-force, as given in  FIG. 31  in the line identified by **. 
   In  FIG. 23 , a second embodiment of the lever-link-lever invention is illustrated in which lugs  90  are slightly lengthened and pivot  40  is moved a small distance toward the center of housing  19  to the position indicated as  40   a . The same multiplication of forces by moment arm lengths and resolving of forces in  FIGS. 23A ,  23 B,  23 C, and  23 D occur to produce the resultant force  88  available for closing valve body  44 . Assuming initial force  74  to be 1.00 kg-force, resultant force  88  is 29.20 kg-force. 
   In  FIG. 24 , a third embodiment of the lever-link-lever invention is illustrated in which lugs  90  are extended vertically and pivot  40  is moved upwardly and toward the center of housing  19 , almost parallel to line  73 , to the position indicated as  40   b . The same multiplication of forces by moment arm lengths and resolving of forces in  FIGS. 24A ,  24 B,  24 C, and  24 D occur to produce the resultant force  88  available for closing valve body  44 . Assuming initial force  74  to be 1.00 kg-force, resultant force  88  is 70.31 kg-force. 
   In  FIG. 25 , a fourth embodiment of the lever-link-lever invention is illustrated in which lugs  90  are considerably lengthened to form lugs  90   c  and pivot  40  is moved much further toward the center of housing  19  to the position indicated as  40   c . The same multiplication of forces by moment arm lengths and resolving of forces in  FIGS. 24A ,  24 B,  24 C, and  24 D occur to produce resultant force  88  available for closing valve body  44 . Assuming initial force  74  to be 1.00 kg-force, resultant force  88  is 12.13 kg-force, as given in  FIG. 31 . 
   In  FIG. 26 , a fifth embodiment of the lever-link-lever invention is illustrated in which lugs  90   c  and pivot  40   c  are used, while pivot  41  is moved away from the center of housing  19  to position  41   a . The same multiplication of forces by moment arm lengths and resolving of forces in  FIGS. 26A ,  26 B,  26 C, and  26 D occur to produce resultant force  88  available for closing valve body  44 . Assuming initial force  74  to be 1.00 kg-force, resultant force  88  is 17.27 kg-force, as given in  FIG. 31 . 
     FIGS. 27 and 28  show the two-lever or lever-lever embodiment at open and closed valve positions, respectively. In  FIG. 27 , valve support bracket  35   a  is extended into a upside-down U shape, and an additional stabilizing bracket  48   a  is bolted to it on the left side by identical bolt  49  and nut  50 . Lug pair  91   a  is rigidly attached to the lower end of brackets  35   a ,  48   a , and lug pair  90   a  is attached to lug pair  91   a  by pivot  39   a  which is rigidly attached to lever arm  36   a  having heel  67 . 
   This lever arm  36   a , although on the opposite side of cylinder housing  19  as compared to other embodiments, operates in exactly the same way except that the valve formed by valve body  44  and valve seat  45  is fully opened when heel  67  is past nut  100 , as shown in  FIG. 27 . Valve seat retaining lever arm  38   b  has been modified so that lugs  94  have been removed and the lever arm turned down and then bent slightly upward to provide a rounded sliding contact to act as heel  67   a  for sliding contact with actuating lever arm  36   a . Heel stop  102   a , as it contacts bracket  35   a , prevents lever arm  36   a  from dropping too far. 
     FIG. 28  shows the lever-lever embodiment in its closed position in which lever arm  36   a  has slid across upper float end guide  27  toward housing  19  sufficiently for valve body  45  to contact valve seat  44  and close the valve. 
     FIG. 28A  resolves applied force  74  into force  75 , across an angle of 11.7°, so that force  75  is perpendicular to imaginary liner of action  77  between line of contact  67  and line of contact  67   a  where, as shown in  FIG. 28B , applied force  78  is resolved across an angle of 46.5° into force  82  which is perpendicular to imaginary line of action  84  between line of contact  67   a  and pivot  42 . This results in applied force  86  which is perpendicular to imaginary line of action  85  between pivot  42  and the center of seat  45 . Resolving force  86  across angle d of 7.8° provides resultant force  88 . Assuming initial force  74  to be 1.00 kg-force, resultant force  88  is 11.49 kg-force, as given in  FIG. 31 . 
   In  FIG. 29 , a one-lever embodiment of the invention is illustrated in which lugs  95 ,  96  and pivot  42  are used to support valve seat retaining arm  38   c  which has been modified to have a heel like heel  67  in lever arm  36 . Arm  38   c  functions as does arm  36  in other embodiments by initially resting on nut  100  and then sliding across upper float end guide  27  as float  18  rises.  FIG. 29  shows the valve  44 ,  45  in fully closed position. The same multiplication of forces by moment arm lengths and resolving of forces in  FIGS. 29A and 29B  occur to produce resultant force  88  available for closing valve body  44  with valve seat  45 . Assuming initial force  74  to be 1.00 kg-force, resultant force  88  is 4.33 kg-force, as given in  FIG. 31 . 
     FIG. 30  is an embodiment utilizing all of the components of the constant-head permeameter, particularly as shown in  FIG. 29 , except that lever arm  38   d  has been drastically modified. Lever arm  38   d  comprises a dipper-shaped arm which is rigidly attached to lug pairs  95  that are in movable engagement with lug pairs  96  through both of which pivot  42  passes. The bottom of lever arm  38   d  contacts the top surface of float end guide  27 , and its cup pivotably supports valve seat  45 , so that valve  44 ,  45  controlling the water inlet means is fully closed when float  18  has sufficiently risen, but without application of any closing leverage other than force  74 , thus simulating the prior art, because applied force  74  and resultant force  88  are equal and in vertical alignment. As shown in  FIG. 31 , if initial force  74  is 1.00 kg-force, resultant force  88  is also 1.00 kg-force. 
     FIG. 31  contains two tables of calculated data to show the relationship of forces. The upper table relates to the lever-link-lever embodiments in which the second pivot is in four selected positions and the third pivot is in one different position in combination with one of the alternate positions for the second pivot. The first line for  FIG. 22  represents the preferred embodiment. 
   The lower table in  FIG. 31  contains calculated data for the two-lever, the single lever, and the prior art embodiments. The wide range of magnification that is obtainable by using the principles of this invention is amply demonstrated in these two tables. 
     FIG. 32  shows two drawings of the float body used in all embodiments of the invention, as well as in the prior art embodiment shown in  FIG. 30 , to illustrate the float submersion required to stopper the valve at various pressure heads of water for the lever-link-lever and the two-lever embodiments at the left float and for the single lever and prior art embodiments at the right float as the float bodies are submerged in surrounding water within the cylindrical housing, with depths of float submergence in centimeters being indicated by the central scale and the pressure heads of water in meters being marked on each side of each float. 
     FIG. 33  is a semi-logarithmic chart on which curves for four types of valve control assemblies are displayed. These are: 1) lever-link-lever, 2) two-lever, 3) single lever, and 3) prior art. Each of these four embodiments was constructed as hereinbefore descibed and tested. The prior art has not used any lever to provide a mechanical advantage for stoppering the valve seat, and this prior art embodiment illustrates that fact. 
   On the left ordinate is the hydrostatic pressure at the valve seat in kilopascals. On the right ordinate is the comparable pressure head of water at the valve seat in meters. On the abscissa is the buoyant force (kilogram-force or kg-force) required to stopper fully the flow from the valve seat at various depths ranging from 0.75 meter to approximately 41 meters. 
     FIG. 34  is a semi-logarithmic graph which also displays curves for the four valve control assemblies. These curves, which are based on the same empirical test results as shown in  FIG. 33 , show the downward resultant forces of the hydrostatic pressure at valve  44 ,  45  that must be overcome to fully stopper flow from the valve for each embodiment. The valve body bore diameter is 0.715 cm, and the valve seat composition is the same for all embodiments. The downward resultant force at the valve seat is shown on the ordinate in kg-force, and the corresponding buoyant force to stopper the downward flow is also shown on the abscissa in kg-force. 
   The values for each embodiment and for the prior art were determined empirically, using water pressure available in Fairfax county, Va., in simulated tests. The same housing  19 , float assembly  18 , float body  72 , and orientation were used for each test. Float assembly  18  comprised a buoyant core  72 , rigid end caps  27 , bolt  58  through the center of float body  72 , and channels  23  for free water flow. The float was approximately 11 cm in length, including the end caps (each 0.318 cm or ⅛ inch in thickness). The diameter of buoyant core  72  was approximately 6.9 cm. The cross-sectional area of core  72  was 36.33 sq. cm. 
   A column of water within a 10.16-cm (4-inch) diameter cylinder was used to establish the pressure head for a height ranging from 0.75 m to 1.25 m. A water line source (tap water), with three pressure regulators of different ranges and a bank of three pressure gauges of different ranges, was used to establish a pressure head equivalent to a height of up to approximately 41 meters. The gauges were positioned in elevation to provide correct pressure readings for depths corresponding to the bottom of permeameter housing  19 . However, for these comparative tests shown in the graph, an adjustment of 0.31 meter was used to determine the pressure at as close to the face of valve body  44  as possible. 
   Float assembly  18  became submersed to a depth of 1.5 cm under its own weight. The net buoyant force required to stopper the valves for each embodiment and depth was provided by the buoyant force of the float, as water rose and increased the buoyant force until pressure at the seat of valve body  44  became sufficient to stopper the inward flow completely. The submersed depth was measured and then converted to volume. Archimedes Principle was then used to determine the net resultant buoyant force. The net buoyant force is shown on the abscissa of the graph. 
   As seen in the graph of  FIG. 33 , the lever-link-lever embodiment, which has a mechanical advantage of approximately 60:1 at full closure, stoppered flow at a hydrostatic pressure of approximately 410 KPa and required a buoyant force of 0.105 Kg-force. The lever-lever embodiment, which has a mechanical advantage of approximately 11:1 at full closure, stoppered flow at a hydrostatic pressure of approximately 410 KPa and a buoyant force of 0.29 Kg-force. The maximum pressure attainable in the local water service was just over 410 KPa so that higher hydrostatic pressures might have been achieved if higher water pressures had been available. 
   The one-lever embodiment, which has a mechanical advantage of approximately 4.3:1 at full closure, stoppered flow at a hydrostatic pressure of approximately 121 KPa and a buoyant force of 0.33 Kg-force. The float became almost totally submerged at this point. 
   The no-lever embodiment (prior art), which has no mechanical advantage, stoppered flow at a hydrostatic pressure of approximately 9 KPa and a buoyant force of 0.33 Kg-force. The float became almost totally submerged at this point. The maximum effective depth was approximately one meter. It was also noticeable that it took several minutes for the water to stop flowing and for the valve  44 ,  45  to stabilize. 
   The water was introduced into each of the cylinders  19  at a moderate flow rate. During previous tests, it was noted that the flow of the lever-link-lever permeameter pulsed somewhat at high flow rates, such as higher than 2,000 ml/minute, and at high pressures corresponding to depths greater than approximately 30 meters for the lever-link-lever embodiment. This phenomenon was probably due to the dynamics caused by the high pressure and flow rate. 
   The lever-link-lever embodiment is the most efficient of the embodiments, because its mechanical advantage dynamically changes in a manner that allows full valve openings over a range of pressures, yet it provides the maximum mechanical advantage at full closure where it is most necessary. 
   Because it will be readily apparent to those skilled in the constant-head soil permeameter art that innumerable variations, modifications, applications, and extensions of the principles hereinbefore set forth can be made without departing from the spirit and the scope of the invention, what is hereby defined as such scope and is desired to be protected should be measured, and the invention should be limited, only by the following claims.