Abstract:
An on-off valve that operates between an open position and a closed position, particularly with high-pressure working fluids. has a valve body that defines a valve cavity. A valve poppet is slidably mounted within the valve cavity. A bushing is mounted with respect to the valve body and divides the valve cavity into a first chamber and a second chamber. One end of the valve poppet is positioned within the first chamber and an opposite end of the valve poppet is positioned within the second chamber. A spring urges the valve poppet into the first chamber. An actuating pin is slidably mounted with respect to the valve body. In the closed position, the actuating pin seals the passage of the valve poppet. An actuator is used to operate the actuating pin between the open position and the closed position of the on-off valve.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an on-off valve which instantly operates between an open position and a closed position. The on-off valve of this invention is particularly suitable for high-pressure fluid systems and/or those that operate with an incompressible fluid. 
     2. Description of Prior Art 
     On-off valves are commonly used to control fluid flow. There are many types of valves suitable for fluids, gas or liquid, operating at low fluid pressures. As the fluid pressure increases, the availability of suitable valves narrows. At high fluid pressures, the selection of suitable conventional valves is significantly restricted. At pressures above 10,000 psi, which are common in water jetting processes, the suitable conventional on-off and pressure-regulating valves are reduced to a few needle valves, poppet valves, stem valves, and ball valves. These valve names indicate the shape of an internal key valving element. When the water pressure is further increased to above 20,000 psi, only stem valves, needle valves, and poppet valves can withstand the high stresses induced by the pressurized fluid. 
     There are several reasons why high-pressure fluid, particularly water, pose problems for valves. On-off valves commonly include a valve cavity having an inlet and an outlet, an elongated valve stem having one end inside the valve cavity and an other end outside the valve cavity, a valve port shaped to mate with the internal end of the valve stem and connected to the valve outlet, and a source of outside force connected to the external end of the valve stem, as shown in FIG.  1 . The outside force is used to raise or lower the valve stem so as to close or open the valve port. One common outside force is generated by a human hand working on a lever to rotate the valve stem, which is supported by threads between the valve stem and the valve body. To close the valve, the valve lever is rotated clockwise, for example, to lower the valve stem until a tip of the valve stem tightly engages the valve port. To open the valve, the valve lever is rotated counterclockwise to raise the valve stem and to open the port. Because of the hand motion involved, the valve lever generally is rotated a quarter turn at a time. If the threads around the valve stem are fine, the valve port is generally opened quite slowly. Thus the fluid will gush out of the valve port when first opened. When the fluid is water at very high pressures, severe erosion of valve stem and valve port can occur. Once eroded, a greater outside force is required to close the valve. This excessive force can deform valve parts and if so, the valve will not perform its duty. To avoid such situation, the valve port should be opened more quickly, particularly when the fluid pressure is very high and the fluid is incompressible, such as water. In other words, the on-off valve should be open or closed instantly. 
     Providing a fast on-off valve operation requires a linear motion on the valve stem and the slow rotation will not suffice. This linear motion can be easily applied to a valve stem at low fluid pressures. At very high fluid pressures, this task becomes very difficult. For example, a 0.125 inch diameter valve stem positioned in a valve cavity filled with 30,000-psi water will be pushed out by a force of about 368 lb f . To push this valve stem into the valve cavity, an outside force greater than 368 lb f  must be applied to the external end of this 0.125 inch diameter valve stem. This force is practical if compressed air or pressurized oil is the source and is applied by an actuator, but impractical if it is applied by a hand of a human operator. Further, the strength and support of this valve stem also become critical factors. The pounding between the valve stem and its mated port is also a concern if the valve has frequent operation. As a result, there is no good conventional instant on-off valve for use with water at very high pressures. It is one object of this invention to solve these problems by providing suitable valves. 
     In water jetting operations, a valve must frequently interrupt the water stream. To minimize the outside force required, the diameter of the valve stem is often very small. For example, a waterjet at 55,000 psi is currently used in industrial material-cutting operations and the waterjet must be interrupted frequently with an instant on-off valve having a compressed air operated actuator. The valve stem is commonly about 0.078 inches in diameter and mates with a valve port about 0.045 inches in diameter. This diameter ratio results in a cross-sectional area of about 0.003 square inches available for generating a valve stem lifting force necessary to open the valve, if compressed air is used only in closing the valve. This valve-lifting force fades away as the valve stem and the valve port become worn. Further, the small valve port required by a small valve stem is incompatible with many water jetting processes that require high flow rates, such as cleaning ship hulls with waterjets. It is another object of this invention to provide on-off valves without such flow rate restrictions. 
     SUMMARY OF THE INVENTION 
     Another problem with conventional on-off valves used in high-pressure water jetting processes is a frequent pounding between the valve stem and the valve port. Because the valve operating force is applied directly to the valve stem and then transmitted to the valve port upon contact, failure of these two parts will occur soon if the contact is frequent. It is highly desirable to soften the contact to eliminate severe pounding of the valving parts, particularly at high fluid pressures. It is another object of this invention to provide on-off valves that have no pounding or that significantly reduce pounding of valve parts. 
     Automatic pressure regulating valves are very useful in pressurized fluid systems and are often a safety valve of the system. In water jetting operations, water flow is often interrupted while the pump is driven by a diesel engine that typically operates at a constant speed. Therefore, a reliable bypass valve that can sense system pressure changes and automatically bypass a predetermined amount of water to maintain a constant system pressure is of significant value. In many waterjet cleaning operations, the water flow must be interrupted frequently. Thus, the bypass valve will also be frequently operated on and off. A conventional spring-operated pressure regulating valve is illustrated in FIG. 2, which is similar in construction to the conventional manual on-off valve illustrated in FIG. 1, except that a constant outside force from a compressed spring is applied to the valve stem. The valve stem has a diameter greater than the diameter of the valve outlet port to create a cross-sectional area differential and to generate a prescribed valve lifting force F f . When the compression spring is set against a prescribed fluid pressure P f , the valve port is closed. When the fluid pressure is increased beyond P f , the fluid induced force F f  is increased, thus causing the valve stem to move up and to release some fluid. As soon as the fluid pressure is restored to below P f , the valve stem will again move down to close the valve port. This conventional setup is a main component of pressure-relief valves used in water jetting processes, despite its many known shortcomings. One serious shortcoming is the change and ultimately loss of the valve opening capability from erosion and wear of the valve stem and its mated valve seat, a situation shared by manual on-off valves. 
     It is one object of this invention to provide an on-off valve for use with all types of fluid, particularly incompressible fluids, at a wide range of operating pressures. 
     It is another object of this invention to provide an on-off valve that can be easily operated by forces generated by a human hand or foot, even at very high operating fluid pressures. 
     Another object of this invention is to provide an automatic valve for pressure regulating applications in high-pressure water jetting processes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention can be better understood when the specification is taken in view of the drawings, where: 
     FIG. 1 is a partial cross-sectional view of a conventional on-off valve; 
     FIG. 2 is a partial cross-sectional view of a conventional on-off valve with a mechanical actuator; 
     FIG. 3 is a partial cross-sectional view of an on-off valve and an actuator, shown in a closed position, according to one preferred embodiment of this invention; 
     FIG. 4 is a partial cross-sectional partial view of an actuator, according to one preferred embodiment of this invention; 
     FIG. 5 is a partial cross-sectional view of the on-off valve with the actuator as shown in FIG. 3, but in an open position; 
     FIG. 6 is a partial cross-sectional view of an on-off valve and an actuator, in a closed position, according to another preferred embodiment of this invention; 
     FIG. 7 is a partial cross-sectional view of an on-off valve and an actuator, according to another preferred embodiment of this invention; 
     FIG. 8 is a partial cross-sectional view of an on-off valve and an actuator, according to another preferred embodiment of this invention; 
     FIG. 9 is a partial cross-sectional view of an on-off valve and an actuator, according to another preferred embodiment of this invention; and 
     FIG. 10 is a partial cross-sectional view of an on-off valve and an actuator, according to yet another preferred embodiment of this invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 3 shows one embodiment of this invention as a lever-operated on-off valve suitable for human hand operation, even at a wide range of fluid pressures. Valve  100  of this invention has valve body  101 , cylindrical valve cavity  102  divided by bushing  103  into upper chamber  104  and lower chamber  105 . A cylindrical valve poppet  106  straddles bushing  103  and has end portion  107  positioned in chamber  104  and opposite end portion  108  positioned in chamber  105 . Valve inlet  109  is in communication with chamber  105 . Valve seat  110  inside chamber  105  has a bore in communication with valve outlet  111 . Spring cylinder  112  is engaged by threads or other connection means to valve body  101  at end  113  to plug or seal chamber  104  in a fluid-tight manner. Cam housing  114  is attached to an opposite end of spring cylinder  112 . Compression spring  115  is positioned inside chamber  104  around valve poppet  106  and urges valve poppet  106  into a position disengaged from valve seat  110 . Compression spring  116  is positioned inside spring cylinder  112  and abuts spring piston  117  at one end and abuts a cam piston  118  at an opposite end. Valve actuating pin  119  has tapered end  120  positioned inside chamber  104  and the other end abutting spring piston  117 . Cam disk  121 , positioned inside cam housing  114 , is rotatable around axial element  122  and constantly contacts cam disk  118 . Valve lever  123  is attached to cam disk  118 . Slot  124  within cam disk  119  accommodates axial element  122 . Seal assembly  125  is positioned around actuating pin  116 . 
     Still referring to FIG. 3, cam disk  121  of valve  100  of this invention is shaped so that its rotation around axial element  122  results in a linear movement of cam piston  118  along a central axis of valve cavity  102 . Cam piston  118  moves between a high position and a low position. In the high position spring  116  is extended and in the low position spring  116  is compressed. Movement of cam piston  118  causes spring piston  117  to move accordingly, which causes valve actuating pin  119  to move in and out of chamber  104 . At the high position, pin  119  is retracted from chamber  104 . At the low position, pin  119  is extended into chamber  104  and engages end portion  107  at a central location. Valve poppet  106  has a central fluid passage  126  that extends from end portion  107  to end portion  108  and has check valve  127  therebetween to limit the fluid flow only from chamber  104  to chamber  105  but not from chamber  105  to chamber  104 . Tapered end  120  of valve pin  119  engages fluid passage  126  so that passage  126  is closed when these two parts are engaged and open when disengaged. Bushing  103  is positioned around valve poppet  106  snugly but not in a fluid tight manner, allowing valve poppet  106  to slide up and down and a fluid to slowly flow across bushing  103 . A bore within bushing  103  can be sized and/or dimensions of valve poppet  106  can be sized to allow a selected or predetermined amount of the working fluid to flow from chamber  105 , between bushing  103  and valve poppet  106 , and into chamber  104 . End portion  108  may be tapered to fit within valve seat  110  in a fluid-tight fashion. 
     Still referring to FIG. 3, cam disk  121  of valve  100  of this invention may have a simple round hole to accommodate axial element  122  so that cam disk  121  is stable only at one position, or cam disk  121  may have slot  124  within which axial element  122  is positioned to provide two stable positions. As shown in FIG. 3, valve  100  is in an assembled condition, a condition in which there is no working fluid in the valve cavity. In this position, spring  116  is slightly compressed and cam piston  118  is at its high position and spring piston  117  is at its low position, forcing pin  119  to engage valve poppet  106  and to push valve poppet  106  down to close valve outlet  111 . FIG. 3 shows valve  100  in a normally closed position. However, if spring  115  is of sufficient strength to exert a force strong enough to overcome the downward force from spring  116 , then valve outlet  111  can be open at this position. This is simply a design option, allowing valve  100  to be normally open or normally closed. 
     Referring to FIG. 4, the cam disk arrangement of valve  100  is illustrated in more detail. Cam housing  114  is attached to spring cylinder  112 , preferably by a threaded arrangement at one end. Cam housing  114  has center hole  128  to accommodate cam piston  118 , and slot  129  across the diameter at the other end accommodates cam disk  121 . Bolt  122  serves as a rotating axis for cam disk  121 . FIG. 4 shows cam piston  118  at its lowest position and spring  116  is compressed. 
     Referring to FIG. 5, when a pressurized fluid enters into valve  100  at a pressure P f , it flows into chamber  104 , between bushing  103  and valve poppet  106  and pushes pin  119  upward, thus allowing valve poppet  106  to move up and to open valve outlet  111 . Valve  100  is now at its open position and the fluid flows freely through the valve cavity. At this position, pin  119  is retracted fully by the fluid force and spring piston  117  is pushed up to compress spring  116 . Spring piston  117  may abut cam piston  118  if necessary. The technical requirements of compression of spring  116  depend on the spring involved, the fluid pressure, and the size of pin  119 . This is a stable position as cam disk  121  is at rest. Valve lever  123  can be positioned vertically or horizontally depending on the preference. To close valve  100 , lever  123  is rotated a quarter turn, or at a specified angle depending on the design of cam disk  121 . 
     Referring to FIG. 6, valve  100  is in a closed position when cam disk  121  is rotated to push cam piston  118  to its lowest position, thus compressing spring  116 , which exerts a force upon spring piston  117  and pin  119 . Pin  119  thus enters into chamber  104 , engages valve poppet  106  at the entrance of passage  126 , and pushes valve poppet  106  down to close outlet  111 . At this position, pin tip  120  closes passage  126  and end portion  108  closes outlet  111 . The fluid in chamber  104  exerts a full force on valve poppet  106  to close outlet  111 . The force required to close passage  126  with pin  119  is supplied by spring  116 , which travels a distance t, as shown in FIG.  6 . To assure secured valve closure, the bias force of spring  116  must be adequate. Thus, the selected spring material must have a spring rate so that a compression distance t produces a force greater than the force exerted on pin  119  by pressurized fluid in chamber  104 . Once a suitable spring  116  is installed, the required compression distance t can be readily supplied by movement of a small cam disk and a relatively short lever. By having a suitable slot within cam disk  121 , pushing valve lever  123  from right to left, as shown in FIG. 6, will position cam disk  121  at a stable position and lock valve  100  in a closed position. With this invention, valve actuating pin  119  is not subjected to excessive forces that can cause damage. The pin assembly essentially floats between spring  116  and the fluid inside the valve cavity, unlike the rigid valve stems of conventional valves shown in FIG.  1 . This invention allows an on-off valve to be actuated by forces generated from a human hand very quickly even at very high fluid pressures. There is no need to limit the flow rate as a relatively large valve outlet can be installed in a relatively small valve assembly. 
     Still referring to FIG. 6, to open valve  100  requires only lifting valve lever  123  to its vertical position shown in FIG.  3 . Then the pressurized fluid in chamber  104  pushes pin  119  upward and flows through passage  126  to the outside of outlet  111 . Chamber  104  thus loses its pressure and the force holding down valve poppet  106 . Simultaneously, the fluid inside chamber  105  is still at full pressure and exerts a considerable force on end portion  108  in an upward direction. Therefore, valve poppet  106  will quickly move up, thus opening valve outlet  111 . The check valve arrangement  127  inside valve poppet  106  prevents the fluid from flowing back into chamber  104 , through passage  126 . The fluid travels around bushing  103  to reach chamber  104 , which takes more time because of the flow restrictions. This time delay allows valve poppet  106  to move up fully before it is balanced again in the fluid. Spring  115  assists this effort. 
     Still referring to FIG. 6, a close examination of valve  100  shows that it is a pilot-operated valve in which there is a pilot fluid circuit linking the two fluid chambers  104  and  105 . By manipulating the pressure inside the two chambers  104  and  105 , a force inbalance is created to move a relatively large valve poppet. The pilot circuit comprises central fluid passage  126  of valve poppet  106 , chamber  104 , the fluid passage around bushing  103 , and chamber  105 . Valve actuating pin  119  controls the pilot circuit flow in a prescribed direction. Valve poppet  106  should slide smoothly at all times. Thus bushing  103  is preferably made of a relatively soft bearing material and is smooth. Restricted fluid flow across bushing  103  is not preferred, particularly with incompressible fluid such as water at high pressures. It is possible to have a separate channel for flow from chamber  105  to chamber  104 . 
     Referring to FIG. 7, valve  200  represents another embodiment of this invention having a dedicated pilot fluid passage. Valve  200  is a manually operated on-off valve capable of high pressure operations. Valve  200  is similar to valve  100 , except that the valve poppet and the valve bushing are different. Valve  200  has a bushing assembly comprising bushings  203  and seal  230 . This assembly separates valve cavity  202  into upper chamber  204  and lower chamber  205 . The fluid does not flow from chamber  205  to chamber  204  through the bushing assembly. Instead, the fluid flows through a relatively small fluid passage  231  within valve poppet  206 , which can be parallel to central fluid passage  226 . Fluid passage  231  is long enough to always connect the two chambers  204  and  205  but it is comparatively smaller to allow chamber  104  to lose pressure momentarily when passage  226  is opened. With this arrangement, valve poppet  206  can be made with a relatively hard material while bushing  203  is made of a relatively softer material. Seal  230  prevents erosion of the soft bushings. Seal  230  can be made of common polymeric seal materials. 
     EXAMPLE 
     To better illustrate details of this invention, valve  300  was constructed according to the embodiment shown in FIG.  7  and illustrated in part in FIG.  8 . Valve  300  had valve poppet  306  straddling bushing assembly  303 . Upper end  307  of valve poppet  306  was 0.312 inches in diameter and lower end  308  was 0.250 inches in diameter and mated with a tapered center hole of valve seat  310 . The contact circle or the sealing circle of valve seat  310  contacting end portion  308  was about 0.188 inches in diameter. 
     Valve poppet  306  had central fluid passage  326  of 0.050 inches in diameter and parallel side passage  331  of 0.020 inches in diameter. Valve actuating pin  319  was 0.078 inches in diameter and had tapered end  320  for engaging a slightly tapered entrance of passage  326 . The sealing circle around pin end  320  when engaged to valve poppet  306  was about 0.060 inches in diameter. When pin  319  engaged passage  326 , an annular cross-sectional surface area of about 0.0016 square inches of pin  319  was exposed to the fluid in chamber  304 . At the same time in chamber  305 , an annular cross-sectional surface area of about 0.0487 square inches of valve poppet  306  was exposed to the pressurized fluid. 
     Further, valve  300  had a 0.750 inch diameter die spring  316  inside spring cylinder  312 . Spring  316  had a spring rate of about 40 lb f  per 0.1 -inch compression. The initial compression of spring  316  during assembling was 0.05 inches, corresponding to an initial valve closing force of 20 lb f  on pin  319 . When water of 20,000 psi entered valve  300 , the water exerted a force of 0.0016×20,000=32 lb f  on pin  319 . This force is greater than the 20 lb f  from spring  316 . Thus pin  319  was lifted. Pin  319  was then exposed fully to the water and a force of 0.0048 square inches×20,000 psi=96 lb f  worked on pin  319  and pushed pin  319  out to compress spring  316 . In the meantime, passage  326  was opened and water in chamber  304  quickly lost pressure as water flowed out through passage  326 , check valve arrangement  327 , and outlet  311 . Valve poppet  306  rapidly moved up until stopped by spring cylinder end  313 . The fluid force inside chamber  305  available for pushing up valve poppet  306  was estimated at 0.0487 square inches×20,000 psi=974 lb f . Thus, valve poppet  306  moved up very quickly. Further, once the sealing circle around the valve seat  310  was broken, the entire cross-sectional area of the valve poppet was exposed to 20,000 psi water. Therefore, the pushing force was increased to about 1,470 lb f . Check valve  327  inside valve poppet  306  prevented water from flowing back to upper chamber  304  through the larger central passage  326 . Once moved up, valve poppet  306  stayed up as the water pressure equalized at its two ends. Valve  300  was then in the open position. The seal  330  prevented valve poppet  306  from dropping down. Thus there was no need for another spring inside the valve cavity to move valve poppet  306 . In high-pressure applications, the valve cavity is relatively small because there may not be room for a relatively large spring around the valve poppet. 
     Still referring to FIG. 8, to close valve  300  required moving pin  319  back into chamber  304 . A spring force greater than 96 lb f  was applied to the outside end. Spring  316  was initially compressed 0.05 inches to create a downward force of 20 lb f , which was subsequently canceled by the water force on pin  319 . A net water force of about 96−20=76 lb f  pushed pin  319  against spring  316 , resulting in compression of about 0.19 inches. Thus, the total compression of spring  316  was 0.19+0.05=0.24 inches. The original overall length of spring  316  was 1.5 inches. The length of compressed spring  316  at the valve-open position was 1.5−0.24=1.26 inches. 
     The cam assembly of valve  300  was designed to provide a vertical travel of 0.3 inches on pin  319 . When the valve lever was rotated down, the cam piston moved down 0.3 inches, thus further compressing spring  319 . A spring force of about 120 lb f  was generated by the 0.3 -inch compression, which was sufficient to overcome the water force of 76 lb f . Thus, valve poppet  306  moved down to close valve outlet  311 . Once seated, the water force working on pin  319  was reduced back to 32 lb f . Thus, spring  316  firmly maintained pin  319  down to close passage  326 . Valve poppet  306  was held down against valve seat  310  by the water force. The net valve closure force from the water was 1470−947=523 lb f , which was very substantial. Valve  300  thus stay closed. This setup of valve  300  accommodates water pressures up to about 25,000 psi. If water pressures greater than 25,000 psi are to be applied, then spring  316  must be changed. For example, a spring with a spring rate of 60 lb f  per 0.10 -inch compression will allow valve  300  to be operated at water pressures up to 35,000 psi. The pressure capability of valve  300  can be increased by installing a cam disk assembly having a vertical travel greater than 0.3 inches. 
     It was clear that valve  300  can be designed with precision to construct on-off valves suitable for use at various pressure ranges. A very high outside force can be generated through the cam assembly to provide fast valve actuation. Yet, the force acting on the valve actuating pin is isolated and controlled to protect this pin. By virtue of a floating valve poppet, a relatively large valve outlet port is possible, without sacrificing valve performance. By using water force to open and close the valve outlet port, positive valve actuations are assured. Valve  300  had all the virtues desired in an on-off valve for use with incompressible fluids such as water at very high pressures. 
     FIG. 9 shows another embodiment of this invention, an improved spring-operated pressure relief valve ideally suited for use with incompressible fluids at high pressures. Valve  400  of this invention is very similar to valve  300  illustrated in FIG. 8, except that it does not have a valve actuating cam disk or lever. Instead, spring cylinder  412  has one end  413  inside valve body  401  and the other end engaged to threaded plug  414  that abuts cam piston  418 , which in turn abuts compression spring  416 . End plug  414  can be rotated with a screw driver or other suitable tools to compress or decompress spring  416 , thus changing the spring force exerted on valve actuating pin  419 . The spring force is set according to the fluid pressure inside the valve cavity. 
     In operation, a fluid such as water enters into valve  400  at a pressure P and flows into chambers  404  and  405 . The water exerts force on and pushes pin  419  out of chamber  404 , thus raising valve poppet  406  and opening outlet  411 . To set valve  400 , end plug  414  is moved into spring cylinder  412  to compress spring  416  until the spring force is increased to a level sufficient to move pin  419  back into chamber  404  and to push down on valve poppet  406  to close valve  400 . Valve  400  is now set for fluid pressure P. When the fluid pressure in the fluid system is increased beyond fluid pressure P, pin  419  will again disengage from valve poppet  406 , causing valve outlet  411  to open and fluid to be released. As a result, the fluid pressure inside valve  400  will drop and valve  400  will again close to repeat another cycle. 
     Comparing valve  400  of FIG. 9 of this invention to the conventional pressure relief valve illustrated in FIG. 2 will show one difference in the presence of the floating valve poppet. In conventional valves, the spring has to be very large and powerful to handle incompressible fluid such as water at high pressures and high flow rates. The powerful spring force is applied directly to the valve stem and to the valve seat. Therefore, there is very much pounding and erosion around the tip of the valve stem and valve seat. The valve will thus have a relatively short life. As a result, spring-operated automatic pressure relief valves are rarely used for water jetting applications above 10,000 psi. Instead, rupture disks are commonly employed at the crankshaft pumps, despite their unreliable performance. 
     Valve  400  of this invention can be reliably used at water pressures above 20,000 psi. By using a valve actuating pin of a moderate diameter, an ordinary die spring can be used to handle water at high pressures. The situation with valve  400  is very similar to that of valve  300 . For example, a 1.0 inch diameter die spring with a spring rate of 50 lb f  per 0.1 -inch compression can be used in valve  400  to handle water at pressures up to 35,000 psi with good sensitivity. Such performance is possible with the design of this invention. 
     FIG. 10 shows yet another embodiment of this invention wherein a spring-operated on-off valve is normally closed and depends on a lever-aided force to open. Valve  500  of FIG. 10 is very similar to valve  300  and valve  400 , except that valve  500  is normally closed by a spring force and its opening depends on a force generated by a human hand or foot. Valve  500  has spring housing  521  attached to valve body  501  directly or indirectly in a fluid-tight manner. Spring housing  521  has cylindrical cavity  535  to accommodate spring piston  517 , compression spring  516 , and end plug  514 . Lever  523  is anchored at one end inside spring housing  521  by anchor bolt  522  through slot  536  in spring piston  517 . The other end of lever  523  extends outside of spring housing  521 . Lever  523  is free to rotate around anchor bolt  522  and the rotation generates a linear travel of spring piston  517  inside cavity  535 . Spring housing  521  is mounted on base  537  from which force is applied to lever  523 . Base  537  can be in the form of a handle to yield a hand-operated on-off valve that is normally closed, which requires a hand force to open. Base  537  can be in the form of a plate to yield a foot-operated on-off valve. Valve  500  is different from valve  200 , which is normally open. Spring piston  517  abuts valve actuating pin  519  that controls the pilot fluid circuit in a way similar to other valves of this invention. End plug  514  is used to adjust the initial compression of spring  516  required for closing valve outlet  511  at the fluid pressure P involved. When an outlet flow from valve  500  is needed, lever  523  is pulled or pressed toward base  537 . When the flow is not needed, lever  523  is released. 
     While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.