Abstract:
A liquid level control unit having a permanent magnet mechanism for translating displacements of a displaces element in the liquid of a container to an actuator device that actuates a control system for a regulated device such as a supply water control valve in a boiler system the control unit utilizing concentrically positioned annular magnet assemblies that are separated by a tube to shield the environment of one magnet assembly from the other.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a liquid level control unit that has particular application in regulating the level of water in a feedwater receiver of a boiler system. The liquid level control unit is adapted to translate changes in the level of a liquid of several inches into small displacements of 3 or 4 thousandths inch. In the preferred embodiment, the translated displacement operates an air valve that controls an air-operated, water control valve for adding make-up water to the feedwater receiver. 
     The liquid level control unit of this invention is suitable for isolated liquid systems. In a feedwater receiver for a boiler system, the water in the receiver is circulated to a boiler in a circuit that avoids contact with air. In order to translate movement of a internal water displacer device within the receiver tank to an external air valve actuator, the control unit utilizes a magnetic motion transfer mechanism. With this mechanism the internal displacement apparatus is isolated from the external actuator apparatus. The unit does not utilize seals or diaphragms that wear and may eventually leak. Also, the unit is entirely mechanical in operation. In this manner the unit is suitable for use in systems such as a boiler systems where auxiliary components must have a high degree of reliability. It is desirable that the control system be operable during a temporary electrical power failure. Therefore, the unit utilizes a mechanical permanent magnet actuation mechanism to actuate changes in a pressurized air circuit which regulate the water control valve of the boiler system supply water. 
     SUMMARY OF THE INVENTION 
     This invention relates to a liquid level control unit that in its preferred embodiment regulates a water supply valve for make-up water in a boiler system. The preferred embodiment of the liquid level control unit includes an actuator mechanism with an air valve to regulate an air-controlled water valve. The air-controlled water valve operates when the water level in a receiver tank for the boiler feedwater drops below a predetermined level. During such state the water valve opens to connect a water supply source to the receiver tank and supplies water until the water level rises and the liquid control unit determines that the appropriate level has been reached, causing the water valve to close. 
     In a boiler system the feed water receiver tank provides for storage of treated water supplied to the boiler. The receiver tank is partially filled with conditioned and deaerated water that is returned to the tank from the boiler as condensate. During continuous cycling of water to and from the boiler, losses occur that necessitate replenishment as make-up water from a supply source. In order to provide for deaeration of the make-up water and to accommodate for surges in the water supply, the receiver tank is not filled to capacity and the water level is maintained at an optimized level during operation. 
     The liquid level control unit of this invention includes a displacer element that is suspended in the receiver tank and partially immersed in the water. The displacer element is preferably made of a sinkable material, although a floatable material may be suitable in certain environments. 
     The preferred displacer element is a cylindrical weight suspended by a rod that is connected to a spring. The rod and spring connection preferably places the spring in compression. The rod has a distal end with a permanent magnet assembly that includes a pair of annular magnets that sandwich a Teflon® guide washer. The guide washer has a slightly greater diameter than the annular magnets and allows displacement of the magnet assembly in a stainless steel tube. The tube has an open end in communication with the receiver tank through which the rod and magnet assembly are installed and a closed end that isolates the displacer components from the external environment. 
     The cylindrical tube projects from the receiver tank with the closed end contained in a housing. The housing also encases a magnetic actuator mechanism with an external permanent magnet assembly having a pair of annular magnets mounted on a displacement plate and concentrically positioned over the cylindrical guide tube at the location of the pair of magnets within the tube. 
     The displacement plate functions as a cantilevered balance beam with linear displacements of the immersed displacer element translated into small arcuate displacements of the displacement plate. The displacement plate is supported on a pair of spaced springs against a pivot and acts as an actuator lever against an air release valve. 
     The air release valve forms part of a pressurized air circuit that includes an air supply, a constricted flow orifice, a pressure gauge, and an air regulated water control valve. 
     In the preferred embodiment the housing has a base plate with two alternate locations for mounting the air release valve, so that the system can be used with a direct acting or reverse acting valve. The liquid level control unit includes an adjustment mechanism for limited adjustment of the flow rate of the makeup water by altering the applied force of the displacement plate on the air release valve. These and other features will become apparent on a consideration of the detailed description of the preferred embodiment that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the liquid level control unit of this invention incorporated on a feedwater receiver tank for a boiler system. 
     FIG. 2 is a cross sectional view of the liquid level control unit of FIG.  1 . 
     FIG. 3 is a top view of the liquid level control unit of FIG. 2 with a cover removed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The liquid level control unit of this invention, designated generally by the reference numeral  10 , is particularly adapted for regulating the level of a liquid in an environment that is isolated from the control system. In the preferred embodiment described, the liquid level control unit is utilized to regulate the level of water within a feedwater receiver tank of a boiler system. 
     Referring to FIG. 1, a feedwater receiver tank  12  stores conditioned and deaerated water for a boiler (not shown). Water  18  is drawn from the receiver tank  12  through a boiler supply conduit  14  and returned as a condensate through return conduit  16 . Water is maintained at a predefined optimal level, shown in dotted line with a space  20  above the water that is filled with steam or water vapor during the deaeration process and operation of the boiler. 
     Because of inevitable losses during circulation of water in its forms as a liquid and gas, makeup water is periodically supplied from a water supply, designated schematically by the reference numeral  22  in FIG.  1 . Supply water under pressure is delivered through a supply line  24  regulated by a water control valve  26 . In the embodiment shown the water control valve  26  is regulated by pressurized air from an air supply  28 . Preferably the water supply  22  and air supply  28  for the boiler system comprise pressurized storage tanks, which are functional during temporary losses of electrical power. The liquid level control unit  10  is operable with other electrical or hydraulic liquid supply controls by modification of the regulator device being actuated by the control unit. 
     In FIG. 1 the control unit  10  includes air regulator apparatus  30  and a magnetic actuator device  32 . The magnetic displacer device utilizes a displacer element  34  shown in dotted line in FIG. 1, partly immersed in water  18  in the receiver tank  12 . The displacer element  34  is a cylindrical weighted member that is suspended on a rod  36  that extends into a housing  38 . 
     Referring to FIG. 2, the housing  38  includes a cylindrical cover  40  mounted on a circular base platform  42  and retained by a cap nut  44 . The cap nut  44  is threaded on a threaded post  46  top of a cylindrical tube  48 . 
     The cylindrical tube  48  has a closed end  50  and an open end  52  that communicates with the environment inside the receiver tank  12  shown in FIG.  1 . In this manner the components inside the receiver tank  12  are isolated from the external components by the capped tube  48  which forms a shield. The tube  48  is welded to a threaded sleeve  54  which in turn is fixed to a threaded reducer  56  form that together a tube assembly  57 . The threaded sleeve  54  projects through an opening  60  in the base plate  42  and is engaged by a retainer nut  62 , which secures the tube assembly  57  to the housing. 
     The reducer  56  connects to a short standpipe  58  threaded into a port on the receiver tank  12  to position the magnetic actuator device  32  over the tank  12  as shown in FIG.  1 . The rod  36  of the displacer element  34  has an extension segment  64  connected to a segment  66  fixed to the displacer element by a gimbal coupler  68  to insure the displacer element is vertically suspended in the tank. The extension segment  64  has an end  70  located within the closed tube  48  with a first magnet assembly  72  comprising a pair of annular permanent magnets  74  with a Teflon® washer  76  therebetween. The Teflon® washer has a slightly larger diameter than the annular permanent magnets to provide a slidable positioning guide that maintains the magnets  74  displaced from the tube  48 . The magnet assembly is held by cotter pins  78  and  80 . The lower pin  80  also positions a spring retainer  82  for a compression spring  84 . The compression spring  84  is seated on a second spring retainer  86  held in place by a clip  88  that engages a groove  90  within the tube. 
     The compression spring  84  and rod length are preselected to position the first magnet assembly  72  at a predefined calibration position when the displacement element  34  is immersed at the predefined optimal water level at approximately one-half its length. 
     With reference to this optimum position, a second magnet assembly  92  is concentrically positioned relative to the calibration position of the first magnet assembly  72 . The second permanent magnet assembly  92  is mounted on a balance beam in the form of an actuator plate  94  with a first annular magnet  96  mounted on one side of the plate  94  and a second annular magnet  98  on the opposite side of the plate  94 . The plate  94  is supported above the platform  42  with the magnet assembly  98  located around the closed-end tube  48  by a pivot assembly  100 . The pivot assembly  100  includes a pair of spaced support bolts  102  extending through the plate  94 . Each bolt  102  is fastened to the base platform  42  by a bottom nut  104  and a clamping nut  106 . An adjustment nut  108  supports a compression spring  110  on each bolt  102  against the underside of the actuator plate  94 . The actuator plate  94  is biased against a pair of spaced pivot points  112  threaded into a cross member  114  connected to the two bolts  102 . The cross member  114  is pressed against the bolt heads  116  by the action of the compression springs  110  against the underside of the actuator plate  94  as applied to the pivot points  112 . 
     The cantilevered actuator plate  94  floats on an adjustment spring  118  projecting from a location bolt  120 . The spring  118  seats on an adjustment nut  122  on the bolt, which is threaded to a swing arm  124  of a pivot knob  126 . By twisting the pivot knob  126  the adjustment spring can be repositioned toward or away from the pivot points  112  forming the pivot axis of the actuator plate  94 . This change in the effective moment arm, changes slightly the degree of angular displacement of the actuator plate for a given drop in liquid level. 
     The actuator plate  94  acts on an air relief or bleed valve  128  shown in cross section in FIG.  2 . The air valve  128  has a passage  130  with a contact ball  132  that is actuated by angular displacements of the actuator plate  94 . The air valve  128  is attached to the base platform  42  by nuts  134  and  135 . The air valve  128  may be located in either of two positions depending whether the valve an indirect bleed valve as shown in cross section, or a direct valve as shown in the alternate position in dotted line. The indirect bleed valve  128  releases pressurized air when the ball  132  is depressed when the actuator plate  94  is downwardly pivoted upon lowering of the liquid level. 
     The pressurized air is supplied, through the air circuit  136  which includes an elbow  138  connected to the air valve  128  and with a nipple  140  connecting the elbow to a cross  142 . The cross  142  interconnects the control unit  10  to a pressurized supply with a flow restriction  144 , a pressure gauge  146  and a line to the liquid control valve  26  shown in FIG.  1 . 
     The air pressure is supplied at 20 p.s.i. and because of the flow restriction, is quickly reduced in the down flow side of the restrictor  144  by release through the air valve  128  of the control unit  10 . In operation, when the water level is lowered, typically by periodic losses during cycling, the effective weight of the displacer element  34  is greater causing the displacement element  34  to compress the support spring  84  and perceptively lower. The lowering of the displacer element and the attached first magnet assembly  72  through magnetic attraction causes the second magnet assembly  92  to follow. Displacement of the second magnet assembly and the attached actuator plate  94  acts like a lever arm and actuates the ball  32  of the air valve, depressing the ball and releasing air from the air circuit. The lowered air pressure in the down flow side of the flow restrictor regulates the air regulated water control valve, (typically a diaphragm and spring control) partially opening the valve and allowing water to flow into the tank until the water level raises the displacement element and the actuator plate to release the ball to an air blocking position. The pressure in the down flow side of the restriction rises and closes the water control valve. 
     Adjustment in the response time of the modulated liquid level control unit is accomplished by the positioning of the adjustment spring. Initial calibration is accomplished using the adjustment nut  122  for the adjustment spring, and operational adjustments are made using the pivot knob which has a hex recess (not visible) for convenient use of an Allen wrench. 
     The use of the two permanent magnet assembles allows motion in the environment of the receiver tank to be translated to the environment external to the receiver tank. Although the function in the preferred embodiment is to prevent the conditioned and deaerated water from the receiver tank from being contaminated by air, the function could equally well be the protection of the external environment from toxic liquid and gas within the receiver tank. 
     While, in the foregoing, embodiments of the present invention have been set forth in considerable detail for the purposes of making a complete disclosure of the invention, it may be apparent to those of skill in the art that numerous changes may be made in such detail without departing from the spirit and principles of the invention.