US3266426A

US3266426A - Pump control

Info

Publication number: US3266426A
Application number: US346274A
Authority: US
Inventors: Virgil A Brunson
Original assignee: Dover Corp
Current assignee: Dover Corp
Priority date: 1964-02-20
Filing date: 1964-02-20
Publication date: 1966-08-16
Anticipated expiration: 1983-08-16

Description

6 v. A.YBRUNSON 3,266,426

PUMP CONTROL Filed Feb. 20, 1964 2 Sheet s-Sheet 1 INVENTOR. VIRGIL A. BRUNSON aHoh nagg- United States Patent 3,266,426 PUlVIP CONTROL Virgil A. Brunson, Grand Rapids, Mich., assignor, by mesne assignments, to Dover Corporation, New York, N.Y., a corporation of Delaware Filed Feb. 20, 1964, Ser. No. 346,274 6 Claims. (Cl. 103-42) This invention relates to pumps and pump controls.

Positive displacement pumps have been used extensively for pumping liquids or fluids into confined spaces having ample storage capacity, such as tanks partially filled with air. However, the use of such pumps for pumping into systems having little or no storage capacity has not been completely satisfactory and has required relatively complicated systems. An example of such a system having little or no storage capacity is a fuel oil delivery truck pumping system in lwhich it is desired to operate a pump at high pressures while the delivering nozzle is open and liquid is flowing through the system and to have a low bypass pressure in the pumping system when the nozzle is closed and fluid motion stops. A major difliculty when pumping into a closed system having little or no storage capacity is the difficulty of control of the pumping rate when the outlet of such system is throttled or closed.

It is sometimes desirable in the above fuel oil de' livery truck pumping system to have the pump independent of the truck motor speed controls, i.e., it is sometimes desirable to have a low shut-off pressure and high pumping pressure regardless of the speed of the truck mot-or. An example of such a pump which is tied in 'with the truck motor speed controls is shown in US. application Ser. No. 280,841 filed May 16, 1963, now Patent No. 3,183,839,- in the names of Virgil A. Brunson and Harold L. Vanden Hoek.

Accordingly,the objects of this invention areito improve pumping systems, to simplify such systems, to provide such a system for pumping fuel oil from a delivery truck in which the pump is independent of the truck -mo tor speed controls and that has a low regulated pressure when there is no or very low fiotw in the discharge system and a higher regulated pressure when flow higher than said very low fiow exists in the discharge system, to provide a positive displacement pump with control means responsive to fiow produced by the pump for adjusting valve means in the pump by liquid pressure to produce said regulated pressures, to provide such a pump with a built-on fiow responsive control means, to provide such a pumphaving superior simplicity, and to use liquid pressure, in a pump regulating valve, to select one of two fixed positions for the normally fixed end of a regulator spring in the valve.

One embodiment of this invention enabling the realization of these objects is a pump control for. a discharge system which includes a positive displacement pump having a housing with inlet and outlet ports, means in the housing for forcing fiuid from the inlet port to the outlet port, a passage in the housing connecting the ports, a valve in the passage for controlling the flow therethrough, the housing defining an opening in a wall thereof' in communication 'with the passage between the valve and the inlet port, a diaphragm closing the opening, means forming a chamber over the diaphragm, and resilient means between the diaphragm and the valve urging the valve toward its closed position. Motion sensing control means is mounted at the outlet port and is responsive t-o fiow from such port. When a hose nozzle at the end of the discharge system is closed and liquid does not fiow, the chamber over the diaphragm is opened by the control means to drain into the low pressure section of the pump. The resilient means is then extended and the pump bypasses at low regulated pressure. When the nozzle is open, the chamber over the diaphragm is closed by the control means and a constant bleed of pressure enters the diaphragm chamber-through a pressurizing orifice causing the resilient means to be compressed and thus raising the regulated operating and bypass pressure. When the hose nozzle is closed, the liquid is drained from the diaphragm rapidly. However, when the hose nozzle is opened, the diaphragm chamber is filled with liquid under pressure slowly. The low and high regulated pressure both are adjustable.

In accordance with the above, one feature of this invention resides in improved motion sensing control means which is responsive to liquid flow and which permits the use 'of the pump control in a fuel oil delivery truck pumping system in which it is desired to have the pump independent of the truck motor speed controls.

Still another feature resides in using liquid pressure to select one of two fixed positions for the normally fixed end of the resilient means.

A further feature resides in the quick-pressure-release of the diaphragm chamber and slow-pressure-recovery of the diaphragm chamber. When the hose nozzle is opened, the operating pressure builds up slowly so that the hose is not jerked out of the operators hand. However, when the hose nozzle is closed, the high operating pressure is reduced quickly to prevent damage to the system components. The above and other objects and features of this invention will be appreciated more fully from the following detailed description when read with reference to the accompanying drawings wherein:

FIG. 1 is a vertical section of a positive displacement pump incorporating a built-in liquid controlled bypass and a motion sensing control means mounted at the outlet port of the pump for controling the liquid controlled bypass; and

FIG. 2 is a schematic diagram of an improved pumping system constructed according to the invention.

Referring to the drawings, a rotary sliding vane pump 10 includes a housing 11 having an inlet port 12 and an outlet port 13. A shaft 14, extending transversely through the pump housing 11, carries a circular cylindrical rotor 15 that fits withinv a rotor chamber 16 in the housing 11.

Therotor chamber 16 includes, as a wall thereof, an interior partition 17 of the housing 11 having a cylindrical surface concentric with the shaft 14 at a radius equal to the radius of the rotor 15. Diametrically opposite the partition 17, the rotor chamber 16 is formed by a portion 18 of the bottom Wall of the housing 11. This portion is concentric with respect to the shaft 14 at a radius sufiiciently greater than the radius of the rotor 15 to provide pumping chambers in the space between the rotor 15 and the Wall portion 18.

The rotor 15 has a plurality of radial slots 19 extending parallel to the shaft 14 to receive sliding vanes 20 which in cooperation with the exterior surface of the rotor 15 and interior surface of the chamber 16 provides a series of pockets or chambers for transporting fluid from the inlet port 12 to the discharge port 13.

The rotor'15 has axially extending pockets 22 at the base of each of the slots 19 and the forwardly facing sides of the vanes 20 are grooved as indicated by the dotted lines 23 to form communicating passages between the pockets or chambers formed ahead of the vanes 20 and the rotor pockets 22. The grooves 23 provide free communication between the pumping chambers ahead of the vanes 20 and the pockets 2-2 so that the vanes 20 may :freely slide radially in the slots 19. Furthermore, by letting each of the .pockets 22 communicate with the chamber ahead of the vane the pressure in the chamber is 3 employed to hold the vane against the exterior wall of the rotor chamber 16.

To further assist the centrifugal force, as the rotor turns, in throwing the vanes outwardly into contact with the wall of the chamber 16 a plurality of push rods 24 extending diametrically through the rotor 15 are provided so that as one of a pair of vanes is pushed inwardly by contact with a contracting portion of the chamber wall the diametrically opposite vane is .pushed outwardly to keep it in contact with an expanding portion of the wall of the chamber 16.

A bypass duct 25 leading from the outlet port 13 past a disk valve 26 to the inlet port 12 is provided in the housing 11. The valve 26 controls the flow through the .passage 2'5. The valve 26 is shown as a disk valve althuogh other types such as piston valves, ball seat valves or angular seat valves may be employed as long as the outlet pressure of the pump tends to open the valve. The disk valve 26 seats at 27 and is carried on a valve guide 28 that is axially slidable in the bypass duct 25.

A flexible diaphragm 29, which, like a piston, is a pressure responsive member, is clamped between a marginal face of a ring 30 and a rim 3]. of a cap or cup 32 enclosing a diaphragm chamber 33. The central portion of the diaphragm 29 is clamped between a .pair of disks 34 mounted on a stem 35. A nut 36 on the stem engaging the left hand disk 34 as viewed in FIG. 1 holds the right hand disk 34 against a spring mounting 37 carried by the right hand end of the stem 35. A second spring mounting 3-8 is carried by the valve disk 26 and the ends of a regulator coil spring 39 receive the mountings 37 and 38, the regulator spring 39 being compressed between the respective diaphragm disk 34 and the valve disk 26 urging the valve towards its seat 27, i.e., toward its closed position.

The diaphragm stem 35 is axially slidable in an opening 40 in the cup 32. An adjustment nut 41 on the lefthand end of the stem 35 exterior of the cup 32 acts as a stop limiting movement of the stem 35 to the right by engaging the cup 32. A lock nut 42 maintains the adjusted position of the adjustment nut 41. Washers 21 act as'a stop limiting movement of the stem 35 to the left by engaging the nut 36. The ring 30 and the cup 32 are held in place by means of screws 43, only one of which is shown, at an opening 44 defined by a wall of the housing 11. The opening 44, which is closed by the diaphragm 29, is in communication with the passage 25 and is between the valve 26 and the inlet port 12.

The valve 26 is a liquid pressure adjusted relief valve, its body being made up of the ring 30, the cup 32 and that part of the pump housing 11 at the valve 26, the valve seating at 27 in the pump. The diaphragm 29 is movable under the influence of liquid under pressure (liquid supplied to the chamber 33 through tubing 45) in opposition to the regulator spring 39 to a position determined by engagement of the stop, i.e., adjustment nut 41, with the valve body to compress the regulator spring for high pressure valve operation and is returned by the regulator spring in the absence of the liquid pressure to permit low pressure valve operation. The stop 41 is adjustable to select the desired high pressure. The number or the thicknesses of the washers 21 is varied to select the desired low pressure. The stop 41 and its lock nut 42 are covered by a hollow nut 46 threaded on the cup 32, there being a rubber O-ring 47 between the hollow nut 46 and the cup 32 to prevent leakage.

The pressure of the fluid in the outlet port 13 acts against the face of the valve disk 26 enclosed within the valve seat 27 and this force is opposed by the force of the regulator spring 39 and the liquid pressure in the chamber 33 acting against the diaphragm 29. The pump 10 is particularly well suited for use in a fuel oil delivery truck pump system. Such a system has little or no storage capacity. The liquid pressure adjusted relief valve 26 gives good control of the pumping rate when the outlet of such system is throttled or closed. Control means, hereinafter described, are provided which communicate with the chamber 33 through the tubing 45 and are rcspsonive to the flow in the discharge system for supplying liquid under pressure to the chamber 33 to drive the diaphragm toward the valve seat .27 compressing the regulator spring 39 between the diaphragm disk 34 and the valve disk 26 when substantial flow exists in the discharge system and to exhaust or dump liquid from the chamber 33 permitting the regulator spring 39 to expand and push the diaphragm 29 away from the valve seat 27 when there is no or very low flow in the discharge system. The regulator spring 39 in its compressed condition maintains a high regulated pressure in the outlet port 13 and in its expanded condition maintains a low regulated pressure in the outlet port 13. The system has a low regulated pressure, when there is no or very flow in the discharge ystem and a higher regulated pressure when higher flow exists in the discharge system.

The :above control means which communicates with the chamber 33 through the tubing 45 includes a pilot valve or motion sensor 50 mounted on the discharge port connection of the pump, the sensor 50 having an outlet port 51 which is threaded internally for the reception of the end of a pipe 52 (FIG. 2). The pilot valve 50 includes a body member 53 which is mounted on the discharge port connection of the pump and which defines the outlet port 51 and an orifice defining member 54 which fits into an opening in the top of the body member 53. The member 54 is provided with a vertical hole 55 which receives a valve stem 56 for sliding action, a generally horizontal hole 57 which communicates at one end with the vertical hole 55 and at its other end with a tubing 58, a second generally horizontal hole 59 which communicates at one end with the vertical hole 55 and at its other end with the tubing 45, and a pressurizing orifice 60 leading from the outlet port 51 to the second generally horizontal hole 59. The tubing 45 is connected at one end to the diaphragm chamber 33 and at its other end in the generally horizontal hole 59. The tubing 58 is connected at one end to the low pressure section of the pump to the right of the diaphragm 29 as viewed in FIG. 1 and at its other end in the generally horizontal hole 57. This connects spaces on opposite sides of the diaphragm 29, liquid being dumped as hereinafter described from the diaphragm chamber 33 through the tubing 45, holes 59, 55 and 57, and tubing 58 into the low pressure section of the pump, and also connects the pressurizing orifice 60 to the diaphragm chamber 33, liquid under pressure being admitted through the pressurizing orifice 60 from the discharge system into the diaphragm chamber 33 as hereinafter described.

The pilot valve 50 also includes a disk 61 on the lower end of the valve stem 56 which seats in the body member 53 and controls the flow from the outlet port 13 and a coil spring 62 that surrounds the valve stem 56 and is compressed between the orifice defining member 54 and the valve disk 61. The spring 62 urges the pilot valve 50 toward its closed position in opposition to the liquid flow through the outlet port 13. The function of the pilot valve 50 is to sense and respond to flow produced by the pump, i.e., to flow from the outlet port 13, and adjust the diaphragm 29 to produce, when no or very low flow exists in the discharge system, a low regulated pressure in the outlet port 13 and to produce, when flow higher than said very low flow exists in the discharge system, a regulated pressure in the outlet port 13 which is higher than said low regulated pressure. When a hose nozzle 63 (FIG. 2) at the end of the discharge system is closed and liquid does not flow or is nearly closed and liquid flows slowly, the spring 62 closes the valve disk 61 and moves the upper end 64 of the valve stem 56 into the position shown in FIG. 1 in the first instance or nearly closes the valve disk 61 in the second instance, and the valve stem 56 uncovers the entrance of the generally horizontal hole 57 into the vertical hole 55. This opens the diaphragm chamber 33, i.e., spaces on opposite sides of the diaphragm 29 are connected, and liquid drains through the tubing 45, holes 59, 55 and 57, and tubing 58 into the low pressure section of the pump. As above described, dumping of liquid from the chamber 33 permits the regulator spring 39 to expand and push the diaphragm 29 away from the valve seat 27 (no or very low flow in the discharge system) to maintain a low regulated pressure in the outlet port 13, i.e., the pump bypasses at low pressure. The bypass being at low pressure condition at very low flow rates allows a slow topping oif process. When the hose nozzle 63 is open wider than the above nearly closed condition and liquid flows relatively fast, the flow out of the outlet port 13 forces the pilot valve disk 61 open in operation to the spring 62 moving the upper end 64 of the valve steam 56 upward into a position well above the entrance of the generally horizontal hole 57 into the vertical hole 55. This closes the diaphragm chamber 33 with respect to the low pressure section of the pump and a constant bleed of pressure enters the diaphragm chamber 33 through the pressurizing orifice 60 (tubing 45 connects the pressurizing orifice 60 to the diaphragm chamber 33). As above described, liquid under pressure in the chamber 33 drives the diaphragm 29 toward the valve seat 27 compressing the regulator spring 39 between the diaphragm disk 34 and the valve disk 26 (relatively high flow exists in the discharge system) to maintain a high regulated pressure in the outlet port 13.

One feature of this invention resides in, when the motion sensor 50 is used, for example, in a fuel oil delivery truck pumping system, having the pump independent of the truck motor speed controls. Low shut off pressure and high pumping pressure are obtained regardless of the truck motor speed simply by sensing the liquid flow and supplying liquid under pressure to the chamber 33 or dumping such liquid from the chamber 33 to maintain the desired regulated pressure.

The pump control is particularly useful in a fuel oil truck pumping system to cause a pump to operate at high pressures while thedelivering nozzle is wide open and liquid is flowing through the system and have a low bypass pressure in the pumping system when the nozzle is closed and liquid motion ceases or when the nozzle is nearly closed and liquid is flowing slowly.

Another feature resides in a quick pressure-release of the diaphragm chamber 33 and a slow-pressure-recovery of the diaphragm chamber 33. When the hose nozzle is opened, the operating pressure builds up slowly so that the hose is not jerked out of the operators hand. However, when the hose nozzle is closed, the high operating pressure is reduced quickly to prevent damage to the system components. This is accomplished by making the area of the pressurizing orifice 60 smaller than any crosssectional area of the generally

horizontal holes

57 and 59. As shown in FIG. 2, the diameters of the smaller portions of the

holes

57 and 59 are twice that of the diameter of the pressurizing orifice 60. Accordingly, liquid can be dumped more rapidly from the diaphragm chamber 33 through the

holes

59 and 57 into the low pressure section of the pump when the pilot valve 50 is closed (FIG. 1 position) than it can be supplied to the chamber 33 through the pressurizing orifice 60 when the pilot valve 50 is open.

The fuel oil delivery truck pump system is shown in FIG. 2. When the truck driver arrives at a customers house, before he gets out of the cab he puts the pump in gear. The pump 10 then will be bypassing at a low pressure setting (system pressure about 35 p.s.i.), since as described above there is no liquid pressure on the diaphragm 29. The driver pulls a hose 65 from a reel 66 in a low pressure condition. It is preferred that there be a certain minimum pressure always present in the system so that the hose 65 will wind on the reel 66 in an extended condition. A completely flat hose, when wound on a reel, provides a restriction to the flow on the next usage if the entire hose is not removed from the reel. The above minimum pressure is obtained because the regulator spring 39 does not go to a completely relaxed position when liquid pressure is exhausted from the diaphragm chamber 33. When the driver puts the hoses nozzle 63 in the customers tank, he opens the nozzle 63. Flow of fuel oil through the system is sensed by means of the motion sensor 50 as described above and the high regulated pump output pressure is built up and then maintained. When the delivery is complete, the driver closes the nozzle 63 and the no flow condition is sensed by the motion sensor 50, and the liquid is dumped from the diaphragm chamber 33 allowing the pump 10 to recirculate at low pressure as described above. The inlet port 12 of the pump 10 communicates through a strainer 67 with a truck fuel oil tank 68 and the outlet port 51 of the pilot valve 50 is attached to the pipe 52 which carries the fuel oil through an air eliminator 69 and a meter 70 to a pipe 71 communicating with the hose 65. The air eliminator 69 is provided with a float-operated valve 72 which is mechanically connected to a float 73. At the start, the valve 72 is open exhausting any air under pressure through a vent pipe 74 to the atmosphere. When the fuel oil is pumped through the pipe 52, it rises in the air eliminator 69 and air bubbles on top of the oil break and the air is exhausted to the atmosphere. Eventually, the oil rises to a point where it lifts the float 73 closing the valve 72. Air-free oil then flows into the meter 70. To assist in blowing air through the air eliminator 69, a spring loaded poppet type check valve, like the valve 51 shown in the above U.S. application Ser. No. 280,841, can be included in the system immediately following the meter 70. Being spring loaded, such a check valve provides a back pressure to the meter 70 and the air eliminator 69 which assists in blowing air through the air eliminator vent 74. Without the back pressure, after the tank 68 is drained, air tends to run through the meter and the hose. The check valve provides a barrier for the flow of air forcing it to go through the vent tube 74.

Flow of fuel oil through the system is sensed by means of the pilot valve 50 which, when there is substantial oil flow, allows oil to be supplied under pressure to the tubing 45, and which, when there is no or little oil flow, causes oil to be dumped from the diaphragm chamber 33. The oil under pressure is supplied through the tubing 45 to the diaphragm chamber 33 forcing the diaphragm 29 and the end of the regulator spring 39 remote from the valve disk 26 to a position fixed by the nuts 41 and 42 on the threaded stem 35 and in this position the regulator spring 39 holds the valve disk 26 closed until the desired high regulated pressure is reached at the pump discharge. If the pressure tends to rise above such regulated pressure, the valve disk 26 lifts sufficiently to bypass the excess fluid flow and maintains the preset pressure (preset by adjustment nut 41). The housing surrounding the valve disk 26 is so designed that little additional pressure is required to hold the valve open for any bypass flow there-by holding a substantially constant maximum pressure when the pump is operating at intermediate flow rate-s. When the liquid pressure is released, as a result of the action of the pilot valve 50 sensing a no or very low flow condition, the diaphragm 29 is allowed to move thus releasing the coil spring 39. The limit of travel of the diaphragm 29 as determined by the washers 21 is such that the coil spring 39 is not completely released. If the pressure tends to rise above the low regulated pressure, the valve 26 lifts sufficiently to bypass the excess fluid flow and maintain the preset pressure.

Accordingly, the liquid pressure adjusted relief valve controls the pump 10 and, thus, controls the discharge system, there being in the pump control for the discharge system a pump having inlet and outlet ports, a passage in the pump connecting the ports, valve means in the passage controlling the flow therethrough, and the control means 50 of the invention responsive to flow produced by the pump for adjusting the valve means by liquid pressure to produce, when no or very low flow exists in the discharge system, a low regulated pressure in the outlet port and to produce, when flow higher than said very low flow exists in the discharge system, a regulated pressure in-the outlet port which is higher than said low regulated pressure.

It is to be understood that the above description is illustrative of this invention and that various modifications thereof can be utilized without departing from its spirit and scope.

Having described the invention, I claim:

1. A system for supplying liquid selectively at either of two controlled pressures comprising, in combination, a positive displacement pump, a relief valve which is biased toward closed position and is connected between the outlet and inlet'side of the pump to divert liquid from the through flow produced by the pump upon attainment of a pressure on the outlet side that is sufficient to open the valve, a chamber having an expansible Wall that is operatively connected to the relief valve to control the closing bias of the valve, a bleed connecton for supplying to the chamber liquid discharged from the pump, to establish an elevated pressure in the chamber and thereby establish an increased valve-closing bias, a discharge valve which is connected to the chamber and which has a capacity for discharging liquid from the chamber that is substantially greater than the capacity of the bleed connection, and a flow-sensing member located in the path of the through flow of liquid produced by the pump, which is operatively connected to the discharge valve and is movable between a normal flow-sensing position in which it holds the discharge valve closed and a non-fiowsensing position in which it holds the discharge valve open.

2. A system as claimed in claim 1 wherein the flowsensing member responds to highly throttled flow by remaining in a position in which it holds the discharge valve open.

3. A system as claimed in claim 2 wherein the flowsensing member is in the form of a valve through which passes the through flow of liquid produced by the pump and which is biased toward closing position with a force that is insufficient to hold such valve closed when a path is open for through flow of liquid produced by the pump.

4. A system as claimed in claim 3 wherein the flowsensing member is located on the downstream side of the pump.

5. A system as claimed in claim 1 wherein the discharge valve forms a connection leading from the chamber to the inlet side of the pump. 7

6. A system as claimed in claim 1 wherein the bleed connection for supplying to the chamber liquid discharged from the pump is so restricted that the pressure in the chamber drops rapidly when the discharge valve opens and rises slowly when the discharge valve closes.

References Cited by the Examiner UNITED STATES PATENTS 1,367,452 2/1921 Bolton 137543.19 2,160,028 5/1939 Moore 10342 2,409,975 10/1946 Curtis 103--42 2,625,108 1/1953 Logan 10342 2,671,409 3/1954 Wright 103-42 2,683,418 7/1954 Smith 10342 2,747,598 5/1956 Wooldridge 10321 X 2,804,878 9/1957 FisherWood et al. 137522 2,829,664 4/ 1958 Mountford 10342 2,944,564 7/ 1960 Pettey 137--529 2,958,291 11/1960 Rizttenhouse 10342 3,021,790 2/1962 Brunson 10342 3,103,891 9/1963 Fulton et al. 10342 MARK NEWMAN, Primary Examiner.

W. J. KRAUSS, Assistant Examiner.

Claims

1. A SYSTEM FOR SUPPLYING LIQUID SELECTIVELY AT EITHER OF TWO CONTROLLED PRESSURE COMPRISING IN COMBINATION, A POSITIVE DISPLACEMENT PUMP, A RELIEF VALVE WHICH IS BIASED TOWARD CLOSED POSITION AND IS CONNECTED BETWEEN THE OUTLET AND INLET SIDE OF THE PUMP TO DIVERT LIQUID FROM THE THROUGH FLOW PRODUCED BY THE PUMP UPON ATTAINMENT OF A PRESSURE ON THE OUTLET SIDE THAT IS SUFFICIENT TO OPEN THE VALVE, A CHAMBER HAVING AN EXPANSIBLE WALL THAT IS OPERATIVELY CONNECTED TO THE RELIEF VALVE TO CONTROL THE CLOSING BIAS OF THE VALVE, A BLEED CONNECTED FOR SUPPLYING TO THE CHAMBER LIQUID DISCHARGED FROM THE PUMP, TO ESTABLISH AN ELEVATED PRESSURE IN THE CHAMBER AND THEREBY ESTABLISH AN INCREASED VALVE-CLOSING BIAS, A DISCHARGE VALVE WHICH IS CONNECTED TO THE CHAMBER AND WHICH HAS A CAPACITY FOR DISCHARGE LIQUID FROM THE CHAMBER THAT IS SUBSTANTIALLY GREATER THAN THE CAPACITY OF THE BLEED CONNECTION, AND FLOW-SENSING MEMBER LOCATED IN THE PATH OF THE THROUGH FLOW OF LIQUID PRODUCED BY THE PUMP, WHICH IS OPERATIVELY CONNECTED TO THE DISCHARGE VALVE AND IS MOVABLE BETWEEN A NORMAL FLOW-SENSING POSITION IN WHICH IT HOLDS THE DISCHARGE VALVE CLOSED AND A NON-FLOW-SENSING POSITION IN WHICH IT HOLDS THE DISCHARGE VALVE OPEN.