US3076417A

US3076417A - Positive displacement pump

Info

Publication number: US3076417A
Authority: US
Inventors: Joseph C Rhodes; John P Segers
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1959-10-29
Filing date: 1959-10-29
Publication date: 1963-02-05
Anticipated expiration: 1980-02-05

Description

J. C. RHODES ETAL POSITIVE DISPLACEMENT PUMP Filed Oct. 29, 1959 s 71:2 .152 15E mmm. I v 1 mg N ,5 a v .3 k l .3 Q S Q E Q v t w R m fiQ \u ww mm, m a m n. n vw |||l|1|||||||I1I|I|||ILII7QAA n u..

Feb. 5, 1963 United States Patent 3,076,417 hOfllTlVE DESPEJACEMENT PUMP Joseph C. Rhodes, Park Forest, and John P. Segers, Crete, E1, assignors to fitandard Oil Company, Chicago, 111., a corporation oi lindiana Filed Oct. 29, 1959, Ser. No. 849,553 2 Claims. (61. 103-23tl) This invention relates to reciprocating, positive displacement pumps. In a more particular aspect it relates to a check valve assembly for a positive displacement pump.

On many occasions it is desirable to accurately and positively displace vapors, gases and liquids in combination or liquids of low vapor pressure from one space into another. In both instances the operability of the pump is affected and the efliciency reduced. The difliculty of pumping liquids is increased where the net postive suction head (NPSH) of the fluid is insuflicient. The NPSH is the excess of pressure at the pump suction over the vapor pressure of the liquid. Where liquids must be pumped under such conditions an excessive pressure drop across the intake valve of the pump may cause the liquid to flash into a vapor on the suction stroke of the pump. The result is an alternate compression and expansion of the vapors and/ or gases, which reduces the pump capacity and negates the accuracy of displacement. Conventional equipment is not suitable for such use because of the existence of large dead spaces at the end of the piston stroke and in the connections to the exhaust valve, and because of the excessive pressure drop across the check valves.

One object of this invention is a pump which is capable of efiiciently pumping liquids, gases and vapors at a constant volumetric rate. Another object is a pump which is capable of displacing such fluids from a container in which the fluid is enclosed at subatmospheric pressures or when the retaining pressure is less than the vapor pressure of the liquid to be pumped. A further object is such a pump which has a long life, with a minimum of maintenance required. A more particular object is such a pump having a minimum pressure drop across the intake valve. Another particular object is such a pump having no pressure drop across the exhaust valve. Still another particular object is such a pump which has a minimum of dead space at the end of the piston exhaust stroke. Other objects will be apparent from the detailed description of the preferred embodiment of the invention.

The above objects are attained in a reciprocating pump provided with a magnetic check valve on the intake stroke, with an exhaust valve adapted to be mechinically unseated by the action of the piston or the fluid pressure produced within the cylinder during the exhaust stroke, and having a minimum volume between the end of the piston at the completion of the exhaust stroke and the exhaust valve ort.

FIGURE 1 is a schematic representation of the positive displacement pump of the invention, and

, FIGURE 2 is a cross-section of the valve head and valve assembly, and FIGURE 3'is a cross-sectional end view of the valve head and valve assembly taken at line A-A, and FIGURE 4 is a plan view of the valve disc employed in the valve assembly.

Referring to FIGURE 1 of the drawings, our improved positive displacement pump 16 is mounted on an appropriate base 11. The pump is provided with a cylinder 12,

within which a piston 13 is mounted. A suitable linkage 14 connects to a driver 16 which imparts a reciprocating motion to the piston 13 by means of a rack and pinion, cam or the like, so that the piston 13 slides within the cylinder 12. The driven end of the pump may be sealed against loss of fluid within the cylinder by graphited pack- 3,075,417 Patented Feb. 5, 1963 "ice ing or the like. The fluid end of the cylinder 12 is provided with a valve head 17 which encloses the fluid, or outer, end of the cylinder. The valve head 17 is joined to the cylinder 12 preferably by threaded engagement therewith. However, this joint may be of flange type or other suitable construction. It is to be understood that the valve head 17 is defined by that portion of the pump outboard from the end of the piston 13 at the completion of the exhaust stroke. The valve head 17 is provided with an inlet conduit 18 which conducts the fluid to be pumped from a reservoir 19 into the cylinder 12. Outlet conduits 21 and 21a serve to conduct away the fluid discharged from the pump. The pump discharge may be passed through only one discharge conduit, however, it has been found to be advantageous to provide two discharge conduits. The upper discharge conduit 21 serves to carry away the discharged vapors and gases, and the bottom conduit 21a carries away the discharged liquids.

FIGURE 2 shows a cross-section of the preferred construction of the valve head 17, the valve assembly 22, the piston 13 and the cylinder 12. The inlet conduit 13 passes the fluid to be pumped through a check valve 23 through flow channels between the valve disc 3 1 and the check valve housing, and through intake port 24 into the bore of the cylinder 12 when the piston 13 is moved from the outer end of the cylinder towards the driven end of the cylinder to produce an intake stroke. When the piston 13 is driven toward the outer (fluid) end of the cylinder 12 in the exhaust stroke, the fluid contained in the cylinder is compressed. The amount of compression which occurs will depend upon the relative amounts of liquid and vapors contained within the cylinder when the exhaust stroke is begun. As a result of this compression the pressure is built up in the cylinder 12. A plunger 26 positioned within the valve head 17 relieves the pressure within the cylinder 12 by compressing a spring 27 so that the plunger 26 moves and allows the fluid under pressure to be discharged from the cylinder 12. This discharge is conducted around the plunger 26 to the valve head 17 and is discharged from the system through the pump outlet 28 and 28a. In the preferred form, the

' plunger 26 is provided with a plurality of raised members or ribs 26', as shown in FIGURE 3, spaced around the periphery of the plunger and extending radially from the plunger to provide flow channels between the plunger periphery and the inner wall of the valve head. The periphery of the plunger 26 or the inner wall of the valve head 17 is relieved to provide flow channels between the plunger and the inner wall communicating with the bore of the cylinder 12 and the pump outlets 28 and 28a. Near the end of the exhaust stroke the end of the piston 13 mechanically unsea-ts the plunger 26 by pushing it from its seat on the shoulder 29 on the end of the cylinder 12. The plunger is displaced about This mechanical unseating relieves the pressure in the cylinder 12 and allows fluid to escape freely into valve head 17. Thus the effective dead space is held to a minimum.

The check valve 23 preferably is mounted Within the plunger 26 and is provided with an inlet port 20 for receiving fluid from conduit 13 and passing it into the valve housing 37, and an outlet port 25. On the suction stroke of the piston 13 fluid from conduit 18 passes into the valve housing to cause the valve disc 31 to become unseated. As the valve disc moves away from the valve seat 32, the incoming fluid passes around the valve disc between it and the inner wall of the valve housing. Flow channels may be provided between the valve disc and the wall of the housing my employing a valve disc having a plurality of ears 31', as shown in FIGURE 4, extending radially from the disc and spaced around its periphery so as to space the disc from the housing wall. The fluid then passes from the valve housing by way of the outlet port 25, through the intake port 24 and into the bore of the pump cylinder. During the exhaust stroke the check valve closes to prevent the escape of fluid after it has entered the pump. It is preferred to use a magnetic type check valve in order to obtain a minimum pressure drop across the intake valve. It has been found that this type of valve opens upon a fraction of an ounce of pressure, i.e., about /2 ounce. Additionally, the magnetic check valve has a desirable snap open action because of the decrease in strength of the magnetic field as the valve disc 31 is unseated from the valve seat 32 and moves away from the magnet 33. In order to obtain a better seal, the valve seat 32 may be provide with an ring of rubber or other material compatible with the fluid to be pumped. While we have described a magnetic check valve it is to be understood that the check valve may be a butterfly type, or of another type suitable for a specific use.

The plunger 26 covers the end of the cylinder bore and is seated against a shoulder 29 provided at the end of the cylinder 12 and acts as the exhaust valve. The spring 27 maintains the plunger 26 in place and prevents the escape of fluid from the cylinder until the plunger 26 is unseated. It is advantageous to employ an outer 0 ring 34 on the face of the plunger 26 in order to provide a better seal. When the pressure with-in the cylinder overcomes the force exerted on the plunger by the spring 27 this seal is broken and the fluid is discharged from the cylinder 12. In the event suflicient pressure is not built up to unseat the plunger near the completion of the exhaust stroke the end of the piston 13 mechanically unseats the plunger from the shoulder and displaces it about /3. This assures that the exhaust valve will be open so as to require no pressure drop, and also provides a minimum of dead space between the end of the piston and the exhaust valve. In order to insure that no fluid is allowed to pass in either direction through the intake port 24 a second inner 0 ring 36 is provided so that the end of the piston seals the entrance port when it contacts the plunger 26.

By mechanically unseating the plunger assembly which acts as an exhaust valve the pressure of the dead space in the system is reduced to the pressure of the system into which the pump discharges. Only the small opening behind the valve disc 31 and the intake port 24 are under compression at the beginning of the intake stroke. If the system is pumping both liquid and gases this space is largely filled with liquid and does not significantly affeet the efliciency of the pump. By placing the assembly so that the intake stroke is upward the entire dead space may be filled with liquid and the efiiciency would be substantially 100%.

One of the advantages of the above described pump is that it combines the features obtainable in a pressure relieving exhaust valve with those of a mechanically relieving exhaust valve. That is, it is capable of pumping from systems with greater intake than exhaust pressures, and the pressure of the dead space is reduced to that of the exhaust system at the end of the exhaust stroke.

The inlet tubing 18 enters the valve head 17 and is rigidly. connected to acheck valve housing 37 which is moved in the direction of the longitudinal axis of the cylinder 12 when the plunger 26 is unseated from the shouldder 29. In order to provide a seal where the inner tubing 18 passes through the valve head 17 a flexible seal 38 is provided around inner tubing 18. For this purpose it is preferred to use a flexible tubing such as neoprene which provides a snug fit over the tubing 18, and which forms a seal at its ends with the outer end of the plunger 26 and the inner wall of the valve head 17 through which the tubing 18 passes. In a preferred construction a spring guide 3 9 is placed against this same wall encircling the inner tubing 18, and provided with a spring guide 0 ring seal 41 adjacent to the wall of the valve head 17. The spring guide is also provided with a cylindrical extension which fits inside of the spring 27 in order to support 4 and guide the spring. When this spring guide 39 is so used the outer end of the flexible seal 38 forms a seal therewith. Although the flexible seal 38 has been so described it is to be understood that the same purpose may be accomplished by the use of a conventional stutling box and packing, a bellows or other type of seals.

A pump constructed as in FIGURES 1 and 2 has satisfactorily displaced a mixture of hydrocarbon gases, vapors and liquids from a chamber at subatmospheric pressure at the rate of 40 ml. per minute of liquid and ml. per minte of gases and vapors.

Having described our invention, what we claim is:

1. In a reciprocating piston pump adapted for pumping liquids, gases and vapors at a substantially constant rate, which pump is provided with valve means for controlling the flow of fluid to and from the bore of a cylinder of said pump, apparatus which comprises: a valve head member positioned to enclose the fluid end of said cylinder; plunger means movably positioned within said valve head member and at the outer end of the cylinder bore, said plunger means being provided with an intake port communicating with said cylinder bore, and further being provided with a surface covering the area of the cylinder bore which surface includes a first outer seating surface adapted to engage in sealing contact with the outer end of the cylinder, and a second inner seating surface located within the periphery of said outer surface encircling said intake port and adapted to engage in sealing contact with the end of the piston; check valve means in flow communication with said intake port, said check valve means comprising a valve housing provided with inlet and outlet ports communicating to permit a flow of fluid into and out of said housing, a magnet rigidly mounted in said housing, a valve seat encompassing said outlet port and a magnetically responsive valve disc movably positioned in said housing between said check valve ports, which valve disc is attracted to said magnet and engages with said seat to close said outlet port during the discharge stroke of said piston and disengages from said seat under inlet fluid pressure influence greater than the attraction of said magnet to open said outlet port during the intake stroke of said piston, means adapted for maintaining said plunger means in sealing contact with said cylinder bore during the intake stroke of said piston and responsive to pressure in said cylinder bore to permit movement of said plunger means away from the end of said cylinder bore at a preselected pressure, conduit means for passing fluid to be pumped to said check valve inlet port, and fluid discharge conduit means communicating with said cylinder bore when said first outer seating surface of said plunger means is disengaged from said outer end of said cylinder during the discharge stroke of said piston.

2. In a reciprocating piston pump adapted for pumping liquids, gases and vapors at a substantially constant rate, which pump is provided with valve means for controlling the flow of fluid to and from the bore of a cylinder of said pump, apparatus which comprises: a valve head positioned to enclose the outer end of said cylinder; a plunger movably positioned within said valve head at the outer end of said cylinder bore and provided with a surface which is adapted to cover the area of said cylinder bore, said surface being provided with an intake port, with a first outer seating surface adapted to engage in sealing contact with the outer end of said cylinder bore, and with a second inner seating surface adapted to engage in sealing contact with the end of said piston, said second inner seating surface being located within the periphery of said outer seating surface and encircling said intake port; a check valve mounted in said plunger and comprised of a valve housing provided with inlet and outlet ports, said outlet port communicating with said intake port, a magnet rigidly mounted in said housing, a valve seat encompassing said outlet port and a magnetically responsive valve disc movably positioned in said housing between said check valve ports, which valve disc is attracted to said magnet and engages with said seat to close said outlet port during the discharge stroke of said piston and disengages from said seat under fluid pressure influence greater than a fraction of an ounce to open said outlet port during the intake stroke of said piston; a helical spring for maintaining said first outer surface of said plunger in said outer end of said cylinder bore during the intake stroke of said piston while permitting said plunger to move away from the outer end of said cylinder bore at a preselected pressure within said cylinder; an inlet conduit passing through a wall of said valve head and rigidly connected to said valve housing for passing fluid to be pumped to said check valve inlet port cylinder bore; sealing means around said inlet conduit adapted to provide a fluid tight seal between said inlet conduit and said valve head; pump outlet means positioned in said valve head; and flow channel means between the inner wall of said valve head and said plunger communicating said cylinder bore with said pump outlet means when said first outer seating surface of said plunger is disengaged from said outer end of said cylinder bore during the discharge stroke of said piston.

References Cited in the file of this patent UNITED STATES PATENTS 737,809 Whitmaker Sept. 1, 1903 1,688,978 McCallum Oct. 23, 1928 2,599,898 Dalrymple June 10, 1952 2,646,071 Wagner July 21, 1953 2,708,944 Modine May 24, 1955 2,775,399 Robinson et a1 Dec. 25, 1956 2,894,526 Booth et a1. July 14, 1959 FOREIGN PATENTS 750,851 France June 6, 1933