POSITIVE DISPLACEMENT PUMP WITH FRANGIBLE PRESSURE RELIEF DISC ASSEMBLY

Abstract: A frangible pressure relief disc assembly is disclosed which is adapted to fit into a positive displacement pump on the suction side of each cylinder. The disc assembly (1) provides a pressure relief when the fluid passing through the pump encounters a closed valve or other obstruction in the line. The disc assembly (1) comprises: (a) a support member (2) having a first side and second side which is penetrated by a passage (5) (e.g., a bore) providing fluid communication from the first side to the second side, and (b) a pressure frangible disc (3) fixedly attached to the support member (2) and positioned to form a fluid-tight seal covering the passage.

Description: FRANGIBLE PRESSURE RELIEF DISC ASSEMBLY AND POSITIVE DISPLACEMENT PUMPS CONTAINING THE DISC ASSEMBLY This invention pertains to a novel pressure relief disc assembly which is useful as a safety valve when it is in operative communication with a positive displacement pump. Positive displacement pumps are widely used items of commerce. Such pumps have a power source driving at least one piston (and usually an odd number of pistons) in a reciprocating path within the confines of a cylinder. The piston(s) usually is connected to the power source by way of a crankshaft or camshaft. In operation, the reciprocating piston alternately creates a vacuum (on the back-stroke) and a pressure (on the forward stroke) within the cylinder and any chamber in fluid communication with a cylinder. This principle is utilized to draw a fluid into the cylinder chamber through an inlet port while the piston makes its back-stroke by suction (vacuum) and to discharge the fluid from the clyinder chamber through an outlet port while the piston makes its forward stroke by pressure. The flow of fluid through the inlet and outlet ports is usually controlled by operation of certain valves movably seated in each of these ports, which are pressure actuated. If the positive displacement pump has more than one cylinder, then the movement of the reciprocating pistons are usually timed by operation of the camshaft or crankshaft so as to provide a uniform flow of fluid through the pump at a substantially constant pressure. Usually the fluid pulled into the positive displacement pump is from a common fluid reservoir located on the 1,suction side of the pump. Likewise, the fluid discharged is usually discharged into a common reservoir or conduit located on the "discharge side or "pressure side of the pump. Positive displacement pumps are quite efficient and operate essentially trouble-free in most instances. However, a severe safety problem can (sand does) occur when the fluid is discharged from the pump into a closed vessel or conduit. This occurs, for example, when the fluid'is pumped against a closed valve in a conduit. In such instance, the pressure build-up is dramatic and can result in a catastrophic rupture of the pump, the conduit, and/or the receiving vessel. To alleviate this problem, it has been attempted to place pressure sensitive "pop valves" and the like on the conduit or vessel and external to the workings of the pump. While such pop valves may be effective to prevent rupture of the system, they pose another safety problem when they are released under excess pressure. Namely, a stream of pressurized fluid is released to the surroundings through the ruptured pop valve which can cause injury to personnel in the surrounding area. Accordingly, a need exists for a new type of pressure relief device for use with a positive displacement pump that can effectively protect personnel and equipment when the pressure side of the pump system is closed or blocked. The present invention generally resides in a frangible pressure relief disc assembly which is uniquely effective in preventing catastrophic rupture of positive displacement pumps and equipment located on the pressure side of such pumps. More particularly, the invention resides in a frangible pressure relief disc assembly comprising: (a) a support member having a first side and a second side which is penetrated by a passage providing fluid communication from said first side to said second side, and (b) a pressure frangible disc fixedly attached to said support member and positioned to form a fluid-tight seal covering said passage. The disc assembly of the invention is advantageously located in each cylinder of a positive displacement pump in fluid communication with a cylinder chamber and a fluid reservoir from which the fluid is being pumped. When the disc assembly is positioned in this manner, the fluid merely circulates from the fluid reservoir into the cylinder chamber and back into the fluid reservoir when the frangible disc ruptures. The disc assembly is most useful when used as a pressure actuated valve, movably seated in the inlet port of each cylinder of a displacement pump to control the flow of fluid into the cylinder chamber. The disc assembly is easily installed in the positive displacement pump and requires a minimum amount of space. The disc assembly of the invention will be more fully understood upon reference to the accompanying drawings and the following description, wherein: Figure 1 is a side view of one embodiment of a disc assembly of the invention. Figure 2 is a top view of the disc assembly illustrated in Figure 1. Figure 3 is a side view, in cross-section, of another embodiment of the disc assembly which is provided with a plurality of rigid legs. Figure 4 is a top view of the disc assembly shown in Figure 3. Figure 5 is a schematic view, in cross-section, of a positive displacement pump having the disc assembly of Figure 3 positioned in an inlet port thereof. With particular reference to the embodiment illustrated in Figure 1, the disc assembly is generally identified by reference numeral 1 and comprises a disc-shaped support member 2 having an upper surface 2a and a lower surface 2b. Either or both of the surfaces 2a and 2b may be beveled or have a concave configuration which can serve as sealing surface to allow the disc assembly to be seated in a sealing relationship with a similarly beveled or concavely shaped seating surface in the cylinder of the positive displacement pump. The disc assembly is provided with a passageway 5 extending generally through the center of the disc assembly from the upper surface to the lower surface thereof. A pressure frangible disc member 3 is held in position in a passageway 5. Preferably, the frangible disc member is fixedly attached to the support member 2 by means of a sealing member 4 to form a fluid-tight seal for the passageway 5. The disc member may be constructed of any material which ruptures upon the application of a predetermined pressure. Preferably, the disc member 3 is formed of a ductile metal such as aluminum, copper, alloys of aluminum or copper, or the like. The frangible disc member may be constructed of a flat planar shape or it may be formed in the shape of a spherical segment with the concave side of the disc member positioned towards the cylinder chamber of a positive displacement pump. In such position, the hemispherical shape of the disc member is better able to resist normal operating pressures exerted by the piston of the pump during repeated forward strokes thereof, which result in increased pressure surges applied to the concave side of the disc member 3. With particular reference to Figure 3, there is illustrated another embodiment of a disc assembly 1 in which the same reference numbers are employed to identify the same structural features of the disc assembly illustrated in Figure 1. The disc assembly 1, in Figure 3, generally comprises a disc-shaped support member 2 of a similar configuration as the support member of Figure 1, except that the peripheral portion of the support member adjacent the lower surface thereof is provided with a sealing gasket 8 having a sealing surface 8a which is adapted to seat against an opposing sealing surface in the inlet port of a cylinder head. The support member is provided with a plurality of legs 9, which extend from the lower surface 26 of the support member. The legs are generally uniform in length and have outwardly facing guide surfaces 9a. The guide surfaces are adapted to slide along the internal surface of the inlet port to the cylinder chamber of a displacement pump as the piston of the pump reciprocates within the cylinder to produce positive and negative pressure surges of fluid entering through the inlet port into the cylinder chamber. The upper portions of the rigid legs 9 and the support member 2 define a region of a concave configuration 10 which terminates in passageway 5 extending generally through the center of the support member 2. A pressure frangible disc member 3 provides a closure for the passageway 5 and is preferably mounted adjacent the upper surface 2a of the support member 2. The disc member may be constructed of a unitary tubular section 3a with the spherical segment forming the frangible disc closing off the tubular section. The disc member 3 is preferably frictionally mounted on the upper surface of the support member 2 and held in sealing engagement therewith by means of a sealing member 4. The disc and sealing members can be made as a one-piece unit or as a multiple-piece unit. However, it has been found that a two-piece unit is more economical and more easily replaced in case of rupture of the disc member 3. As shown in Figure 3, the tubular section 3a of the disc member 3 is positioned in alignment with the passageway 5 and is preferably held in frictional engagement in a counterbore 3c provided in the support member 2. It will be understood that the tubular portion of the disc member could also be provided with screw threads for threaded engagement with similar threads provided in the counterbore 3a of the support member. Preferably, the tubular portion of the disc member 3 extends into the counterbore on upper surface of the support member and is held thereby in a frictionally restrained position against lateral or longitudinal movement of the disc member 3 with respect to the counterbore. The sealing member 4, as a separate member, is provided with a central bore to receive the tubular portion of the disc member 3. The sealing member 4 may be constructed of the same material as the disc member 3 or it may be constructed of a synthetic. resinous material, or the like. It being sufficient that the sealing member be constructed of a material to withstand the physical and mechanical stresses imparted to it by the reciprocating piston during operation of the displacement pump. As shown in Figure 4, the support member 2 is provided on its upper surface 2a with a retainer means 7 for retaining a spring 6 in an aligned and centered position with respect to the support member 2. The retainer means, in the embodiment illustrated in Figure 3, is in the form of a plurality of tabs for holding a terminal end of the spring 6 in a seated position on the support member The opposite terminal end of the spring 6 is in engagement with an abutment surface 14 for positively biasing the disc assembly 1 in a direction away from the abutment surface. Figure 5 more clearly illustrates the cylinder 11 of a positive displacement pump having a disc assembly 1, as illustrated in Figure 3, positioned in an inlet port 12 in the cylinder. The disc assembly serves a dual function as a check valve for controlling the flow of fluid into the cylinder during the operation of the displacement pump and as an internal safety valve. As shown, the disc assembly is pressure actuated and is movably positioned within the inlet port of the cylinder. A piston 16 is reciprocally movable in the piston bore 18 of the cylinder 11 and is operative in moving the disc assembly 1 between open and closed positions in the inlet port 12. The disc assembly 1 is retained in position in the cylinder chamber 14 for limited reciprocal movement by means of a removable abutment or retainer member 13. As is more clearly shown in Figure 3, the spring 6 is in engagement with the abutment surface 11 of the abutment member 13 and thus positively biases the disc assembly towards a position wherein the sealing surface 8a of the support member 2 is in sealing engagement with a seating surface provided in an inlet port insert 12a. In operation, when the piston 16 moves to its flback-stroke" position in the piston bore 18, a vacuum or suction is created within the cylinder chamber 14 causing the disc assembly 1 to move upwardly against the pressure of the spring 6 to disengage the sealing surface of the support member from the seating surface on the insert 12a. With the disc assembly in an open or unseated position, fluid which is communication with the inlet port 12 is allowed to enter the cylinder chamber 14 by flowing between the legs 9 and the lower surface 2b of the support member 2. At the instant the piston 16 starts its forward or "compression" stroke, the pressure within the cylinder chamber 14 becomes a positive pressure which allows the spring 6 to bias the disc assembly towards the seated position on the insert 12a. Fluid is discharged from the cylinder chamber 14 through outlet port 15 in check valve 17. The check valve 17 may be any conventional type of valve such as a spring biased ball valve, as illustrated. In the event of a failure of the system downstream of the check valve 17, the pressure of the fluid in the cylinder chamber 14 increases to the point where it exceeds the burst pressure of the disc member 3 in the disc assembly. Accordingly, when the burst pressure is exceeded, the disc member ruptures and the fluid in the cylinder chamber 14 is discharged back through the inlet port 12 into the fluid supply reservoir on the suction side of the pump. If the pump continues to operate after the disc member is ruptured, the piston 16 will merely cycle the fluid between the reservoir and the cylinder chamber 14 without causing damage to the system downstream of the check valve or injury to operators of the equipment due to bursting components such as pipelines, valves, and the like. Conventional electronic and/or mechanical indicator means (not shown) can be used to signal to the operator that the fluid is no longer being pumped through the positive displacement pump. The operator is therefore alerted to a malfunctioning of the system which can then be shut off. Any obstruction on the downstream side of the system can then be corrected. The ruptured disc member in the pump can be readily replaced by removing the removable abuttment member 13 from the cylinder 11 which provides for ready access to the cylinder chamber 14. In accordance with the teachings of the present invention, a commercial positive displacement pump having three cylinders was modified so that each cylinder contained a disc assembly (of the embodiment illustrated in Figure 3) in its inlet port. Each disc assembly was provided with a frangible disc member designed to rupture at a pressure of about 665 kg/cm2 (9500 psi). This pressure was well below the pressure limit of the pump and associated equipment. The pump was started and used for several hours to pump water at an elevated pressure from one reservoir to another. The pump operated at its designated pressure and capacity without failure and the disc assembly operated well as an internal check valve. After the system had operated flawlessly for a period of time, a valve was closed in a conduit on the discharge side of the pump to cause a sudden increase in pressure in the cylinder chamber of the displacement pump. Each disc member immediately ruptured on the forward "compression stroke of each piston and at the designated rupturing pressure of each frangible disc. Thereafter, the water in the system circulated harmlessly back and forth between each cylinder chamber of the pump and the supply reservoir. Similar results were obtained when the positive displacement pump, containing the disc assembly of the invention, was used to pump a cement slurry at an elevated pressure. No undue erosion of the disc member was observed over a period of time, and the disc member ruptured at its designated rupturing pressure when a valve on the discharge side of the pump was closed. The invention has been described with reference to the particular embodiments illustrated in the drawings, which are presently preferred. It will be apparent, however, to the skilled artisan that various obvious modifications can be made such as, fo example, in the materials that can be used in the construction of the disc-shaped support member or the disc and sealing members. Various modifications may also be made in the manner in which the disc member and/or sealing member may be mounted on the disc-shaped support member. It is, therefore, apparent that the invention is not to be limited to the specific embodiments illustrated in the drawings.

Claims: 1. A frangible pressure relief disc assembly comprising: (a) a support member having a first side and a second side and a passageway providing fluid communication between said first and said second side7 and (b) a pressure frangible disc member mounted in said support member and positioned to form a fluid-tight seal for said passage. 2. The assembly of Claim 1 including guide means on said support member. 3. The assembly of Claim 2 wherein said guide means comprise a plurality of spaced legs extending from said support member. 4. The assembly of Claim 1 wherein said support member has a sealing surface. 5. The assembly of Claim 1 including a sealing gasket positioned in a peripheral portion of the support member. 6. The assembly of Claim 1 wherein said disc member is fixedly attached to said support member. 7. The assembly of Claim 1 wherein said frangible disc member comprises a tubular section having a frangible disc closing off said tubular section, and said tubular section being removably mounted on the support member and forming a fluid tight seal for said passage. 8. The assembly of Claim 7 including a sealing member having a bore diameter larger than, but approximately the same as, the outer diameter of the tubular section of the disc member for restraining lateral movement of the disc member with respect to the passageway. 9. The assembly of Claim 1 including a spring retainer means on the support member. 10. The assembly of Claim 9 wherein said spring retainer means comprises a plurality of spaced tabs extending radially outwardly over an upper surface of the support member. 11. An assembly comprising a positive displacement pump having at least one cylinder, a piston slideably mounted within a bore of said cylinder, a power source connected to the piston for moving the piston in a reciprocating manner within the bore, a cylinder chamber in fluid communication with said piston bore, and fluid inlet and outlet means, said chamber being alternately filled with a fluid and evacuated upon reciprocating movement of the piston, and the frangible disc assembly of Claim 1 located in said inlet means and in operative fluid communication with said cylinder chamber.

Inventors: CAMERON, DONALD C., SHIREMAN, PAUL M.
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1984
Main classification: F04B21
IPC codes: F04B53