US2740357A - Pump pressure control system - Google Patents

Description

April 3, 1956 Filed Nov. 13 1.95]

N. PLANK PUMP PRESSURE CONTROL SYSTEM 2 ShetsSheet 1 H. Plank.

His Arforneg April 3, 1956 N. PLANK 2,740,357

PUMP PRESSURE CONTROL SYSTEM Filed NOV. 13, 1951 2 Sheets-Sheet 2 \nvenhar: N. Pkmk By- His ArTorneg United States Patent PUMP PRESSURE CONTROL SYSTEM Norris Plank, East Chicago, Ind, assignor to ShellDeve'lopment Company, Emeryville, Calih, a-corporation of Delaware Application November 13,1951, Serial No. 256,085 7 Claims. (Cl. .10337) This invention relates to the control of pumps and pertains more particularly to a control system for readily varying the over-all capacity of a reciprocating pump without loss of efficiency.

Reciprocating plunger pumps are presently used instead of centrifugal pumps in many large pipe line pumping stations because of the greater efficiency realized. When constant-speed electric motors are used to drive the reciprocating pumps, the operator encounters the difficult problem of varying the capacity of the pump in a simple manner without excessive loss of efliciency.

At present, motor-driven reciprocating pipe line pumps may be controlled by (1) providing speed variation of the pump, (2) mechanically varying the stroke of the pump operating at a fixed speed, or ('3) by by-passing liquid from the discharge end to the suction end of the pump. All of the above-mentioned methods are subject to important drawbacks; the first and second methods are very expensive in that they require the installation of additional equipment while the last-named method is very ineflicient as the pump uses the same amount of power while pumping lesser quantities of liquid.

it is therefore a primary object of the present invention to provide a pump control system whereby the capacity of a reciprocating pump may be varied over a considerable range without loss of efliciency.

Another object of the present invention is to provide a pump control system whereby the maximum discharge pressure and minimum suction pressure of 'a reciprocating pump may be set at any desired value.

A further object of this invention is to provide a pump control system for a reciprocating pump driven by a constant speed motor whereby the maximum discharge pressure and/or the minimum suction pressure may be re-set or varied when the pump is in operation.

Another object of this invention is to provide a pump control system capable of effectively eliminating substantially all pressure surges on the discharge side of a reciprocating plunger pump.

These and other objects of this invention will be understood from the following description taken with reference to the attached drawing, wherein:

Figures 1 and 2 are diagrammatic views, partly in crosssection, illustrating two arrangements of the present pump control system.

A portion of a reciprocating plungerpump 11 is shown in Figure l which includes a pump housing 12 having mounted for reciprocating therein one or more plungers 13. Any suitable type of pressure-tight packing may be arranged around the plunger, such for example as a plurality of packing rings 14 and a follower ring 15 held in place by a gland 16.

The pump barrel 17 communicates with a discharge conduit 18 through a passageway 19, discharge check valve 20 and passageway '21. Similarly, the pump barrel 17 is in communication through passageway 22, suction check valve 23 and passageway 24 with suction pipe line 25. The opening of valves 20 and 23 is limited by adjustable valve plugs 68 and 69 screw-threaded into the housing 12.

Additionally, the pump barrel 17 is also in communication, through passageway 26 and conduit 27, witha fluid-pressure responsive device 28. The pressure responsive device 28 comprisesa closed tank or housing formed by apair of flanged vessels .29 and 30 in face-to-face relationship on either side of a plate 31 whichdivides the housing into closed fluid-tight chambers 32 and33.

The plate 31 forms the central support plate of a damping device or diaphragm means and has formed thereon or attached on either side thereof a pair of raised annular walls or 'fianges 34 and 35-upon which a pair of flexible diaphragms 36 and 37 are positioned or secured in spaced relationship so as to form fluid-tight compartments 38 and 39 on opposite sides of the plate 31. The diaphragms 36 and 37 may be made of any flexible material, such as, for example, rubber, rubberized canvas, sheet metal, or the like, which may be secured in any suitable manner, as by clamping, cementing, soldering, etc., to the flanges 34 and 35. In this embodiment the -diaphragms 36 and 37 are clamped between the flanges 34 and 35 andrings 49 and 41, respectively.

A hole is formed through the center of the transverse plate 31 and a short tubular member 42 fixedly secured therein, as by welding. 'Mountedfor axial movement in the bore 49 of tubular member 42 is a valve stem 43. Secured to the valve stem 43cm opposite sides of said plate 31 and spaced therefrom are suitable valve-closure means, such, for example, as beveled valve plates-45 and 46, formed so as to fit tightly against the beveled valve seats 47 and 48 around the edges of the hole 49 when forced thereagainst. A more .positive seal between the valves and their seats may be secured by the use of rubber ring seals 50 and 51 suitably secured to the valve plates. The overall length of the valve stem 43 including the thickness of plates 45 and 46 is preferably chosen so that the distance between the centers of the diaphragms 36 and 37 is equal to that at the peripheries. Both compartments 38'and 39 of the diaphragm assembly are filled with any suitable clean fluid such as oil, said fluid being relatively incompressible, of reasonably constant viscosity at operating temperatures andhaving a low freezing point.

The upper diaphragm 36 is secured to the valve stem 43 between valve plate 45 and a diaphragm contact disk 52 which is in turnfixedly positioned on stem 43 by a nut 53. In a like manner the lower diaphragm 37 is secured between valve plate 46 and a second diaphragm contact disk 54 which is held in place by a nut 55. If desired, the ends of the valve stem 43 may be slidably mounted and aligned in tubular members or perforate cage members56 and 57 aflixed, as by welding, to the inner walls of the vessels 29 and 30. The two vessels 29 and '30 are secured together in a fluid-tight manner on opposite sides of the plate 31 in any suitable manner, as by bolts While one chamber 33 of the pressure responsive device 28 is in open communication with the pump barrel 17 through conduits 26 and 27, the other chamber preferably communicates through a port 59 and conduit 60 with a large container of high pressure fluid, for-example, a gas reservoir 61. The pump barrei 17 may also communicate at the same time, through conduits 22 and 62, with one pressure chamber of a second pressure responsive device 63 which is identical in construction with the onehereinabove described with regard to numeral 2%. The second chamber in the Vessel 63 is in communication through conduit 64 with a second large container of pressure fluid, such as a gas bottle or tank 65. The tanks 6i. and

'65 preferably have a volume substantially greater, preferably 2 to 10 times greater, than the chambers 32 and similar chamber in device 63 so that compression of the pressure fluid within the system is substantially elimiline 18 is more than 1000 lbs.

forces liquid into chamber 33 at a pressure greater than nated. The reservoir tanks 61 and 65 in turn may be each in communication through conduits 70 and 71 and valves 72 and '73 with a pressure cylinder 74 or 75 by which the two systems (i. e. the chambers 32 and 33 and two similar chambers in the second pressure responsive device 63 and their communicating tanks 61 and 65) may be charged to predetermined pressures. If desired, the

tanks 61 and 65 may be covered with insulation or buried Assuming, for example, that the minimum suction and maximum discharge pressures of the pump 11 were to be 50 and 1000 p. s. i., respectively, tanks 65' and 61 would be precharged with gas from cylinders 75 and 74 to discharge gas at those pressures into the pressure chambers 63 and 28.

At any time when the fluid pressure in the pump discharge line 18 is below 1000 p. s. i., the pressure within the pump barrel 17 and its communicating chamber 33 would also drop to below 1000 p. s. i. Thus, with 1000 p. s. i. gas pressure being exerted on top of diaphragm 36 while a lesser pressure is acting on the lower side of diaphragm 37, both diaphragms 36 and 37 are moved downwardly until the valve plate 45 seats on the beveled valve seat 47 preventing any further flow of fluid from chamber 38 to chamber 39 between the diaphragms 36 and 37.

As long as the discharge pressure of the pump remained below 1000 p. s. i., the valve 45 would remain seated on its seat 47 and no movement of the diaphragms 36 and 37 would take place. pressure rises for some reason above 1000 p. s. i., the present pump control unitoperates to vary the capacity of the pump in the following manner.

As the pump plunger moves downwardly and the pressure in the pump barrel 1'7 exceeds 1000 p. s. i., fluid will be forced into the lower chamber 33 of the pressure unit 28 rather than out through valve 20 if the pressure in Since the plunger 13 1000 lbs., this pressure fluid acts against the lower side of diaphragm 37 to move both diaphragms 36 and 37 and valve stem 43 upwardly until valve plate 46 seats in its seat 48, as shown in Figure l of the drawing.

Preferably, the pressure responsive unit is of a size that the diaphragms 36 and 37 displace an amount of fluid equal to that displaced by one stroke of the pump, say, from 2 to 5 gallons in pipe line pumps. Thus, if the pump discharge pressure was above 1000 lbs. during the entire stroke, the lower chamber of the pressure unit 28 would accept all the fluid discharged by the pump for that stroke. As the plunger 13 withdrew from the pump barrel on its suction stroke, the pressure within the pump barrel 17 would drop and the fluid which was previously forced from the pump barrel 17 to the chamber 33 by the plunger, would be forced from the chamber 33 back into the pump barrel 17 by the gas pressure of 1000 lbs. acting on the top of diaphragm 36. Thus, as long as the pressure in the discharge pipe line 18 or the pump discharge pressure remains above 1000 lbs., the fluid on each stroke of the pump is shuttled back and forth between the pump barrel 17 and pressure chamber 33.

It may, therefore, be seen that when the fluid transmitting or retaining capacity of the pressure chamber 33 equals the displacement of the pump plunger 13, the acceptance of liquid by the pressure chamber 33 com- However, if the pump discharge- 4 pletely offsets the plunger displacement in the pump and hydraulically nullifies the action of the pump plunger stroke entirely. On the other hand, a pressure unit 28 of a capacity which would accept 50 percent of the plunger displacement in its pressure chamber 33 would hydraulically shorten the pump stroke by 50 per cent.

It may be seen that pressure unit 28 is designed to receive fluid pressure surges from the pump 11 rather than allowing them to be transmitted through the discharge line 18. The construction of the pressure unit 28 prevents pressure surges or excessive pressures from damaging the unit. When a 1000 lb. pressure is being exerted on the top diaphragm 36, a pressure greater than 1000 lbs. applied to the lower face of diaphragm 37 causes both diaphragms to .rnove upwardly forcing fluid from compartment 39 through the bore 49 of tubular member 42 and into compartment 38. A continued increase in pressure on diaphragm 37 causes valve plate 46 to seat in its seat 48 thus closing the flow channel 49 and stopping the flow of fluid from compartment 39 to compartment 38 whereby the diaphragm 37 is protected from being ruptured by increased pressure within chamber 33.

The rate at which the valves 45 and 46 open and the diaphragms 36 and 37 are flexed between their extreme positions depends upon the rate of transfer of fluid between compartments 38 and 39 through bore 49. The bore 49 is preferably of a size which prevents a too rapid transfer of fluid so that the diaphragms are protected against rupture and yet of a size suflicient to permit the entire transfer of fluid during the suction stroke of the pump 11.

A second pressure unit 63 connected into the suction side of the pump 11 between the pump barrel 17 and the intake valve 23 operates to vary the capacity of the pump it the suction pressure upstream to the intake valve 23 is less than a predetermined value, say 50 p. s. i. Since the normal operating pressure of the pump 11 is above 50 pounds, an excessive amount of fluid (the amount displaced by one stroke of the plunger 13) is normally.

contained in the lower chamber of the pressure unit 63. Whenever the suction pressure upstream of theintake valve 23 is less than 50 lbs., the diaphragm unit within the pressure unit 63 feeds liquid back to the pump barrel. This same liquid is forced back and forth between the pump barrel 17 and the pressure unit 63, thus effectively hydraulically shortening the stroke of the plunger. As in the case of pressure unit 28, the fluid receiving and transmitting capacity of pressure unit 63 is preferably equal to the fluid displaced by one stroke of the pump plunger 13.

From the foregoing description it may be seen that comprises frictional losses involvedin the fluid flow between the pressure chambers and the pump barrel. The high efficiency realized by the present pump control system is due to the fact that the power used in pushing the diaphragms in one direction (against the gas reservoir pressure) is only stored, being returned to the pump on the suction stroke by the gas pressure from the reservoir pushing the diaphragms in the opposite direction which forces fluid back into the pump barrel to help raise the pump piston.

An advantage of the present pump control system is that the maximum pump discharge pressure and/or the minimum intake pressure may be readily varied at any time, even when the pump is in operation, by simply 1 pressure chambers -chamberscontrolling either the intake or discharge preschanging the pressure in tanks 61 and 65 so that more or less fluidpressure'is applied to the diaphragms in the pressure units. While the present pump control system hasibeen described when applied to a pump l'lhaving a single piston 13, 'it is realized that the control system '.may also "be utilized for controlling duplex or triplex "pumps, or a pumphaving any desired number of pistons,

single-acting or "double-acting. If either the maximum discharge pump pressure or the minimum intake pressure is "to "be controlled, a separatepressure chamber such as 28 or 63 must be in open communication with each pump barrel or working end thereof. If both the discharge and intake pressures of the pump are to be controlled,

it is necessarytha'ttwo pressure chambers, such as 28 and 63, be connected in open communication with each pump barrel 17. Thus, if boththe discharge and intake j pressures of a triplex single-acting pump areto be controlled, -it would be necessary to employ a total of six 28. However, all three pressure pressure vessel-80 comprises a fluid-tight tank divided into three pressure chambers 82, 83 and 84 by transverse plates 85 and 86. The plates 85 and 86 are identical in design to plate 31 of Figure 1 and form the central plates of two diaphragm units.

The upper diaphragm unit comprises a pair of diaphragms 87 and 88 secured to and movable with a valve stem 89 and valve plates 90 and 91. Similarly the lower diaphragm unit comprises diaphragms 92 and 93, valve stem 94, and valve plates 95 and 96. One chamber, for example the upper chamber 82, may be in communication through conduit 97 with a high pressure bottle 98 while the lower chamber 84 is connected to a low pressure bottle 99 through conduit 100. The bottles 98 and 99 may be pre-charged from pressure bottles in a manner similar to that described with regard to Figure 1.

The chamber 83 in the pressure vessel intermediate the two diaphragm units is in open communication at all times with the pump barrel 101. In the following example it is assumed that the pressure fluid is being discharged from the high and low pressure bottles 98 and 99 at pressures of 1000 and 50 p. s. i. When the pressure in the pump barrel 101 exceeds 1000 p. s. i., fluid is forced by the plunger 102 from the barrel 101 through conduit 106 into the central chamber 83 of the pressure vessel 80. The diaphragms 87 and 88 are forced upwardly against the 1000 p. s. i. pressure fluid from the bottle 98 until valve 91 is closed, as shown. On the suction stroke the excess fluid pumped to chamber 83 is withdrawn into the pump barrel 101. As soon as the discharge pressure of the pump drops below 1000 p. s. i. this fluid is pumped out the pump discharge valve 103 into the discharge pipe line 104. At that time the valves 90 and 95 of the two diaphragm units are closed.

In the event that the intake pump pressure upstream of its intake valve 105 drops below 50 p. s. i., the 50 p. s. i. pressure fluid acting on diaphragm 93 causes valve 95 to open, forcing fluid from chamber 83 into the pump barrel 101. On the discharge stroke of the pump, this fluid is returned to the chamber 83. The 1000 p. s. i. pressure fluid acting on diaphragm 87 at this time is ineflective as valve 90 has been closed preventing any further movement of the diaphragms 87 and 88.

I claim as my invention:

1. A displacement pump control system comprising in combination with a pump having at least one pump barrel and a plunger reciprocating therein, a closed vessel, diaphragm means fixedly mounted in said vessel dividing said chambers comprising two spaceddiaphragms, rigid plate means fixedly connected within the housing parallel to said diaphragms and dividing the space therebetween into two fluid-tight compartments adapted to contain a pressure fluid, fluid conduit means through said plate means in communication between said compartments and valve means in said conduit means for stopping the flow of fluid therethrough when thediaphragms are at their extreme position of travel in either direction.

2. A displacement pumpcontrol system comprising in combination with a pump having at least one pump barrel and a plunger reciprocating therein, a closed vessel, a wall member dividing said vessel into two chambers, said wall member having an opening therethrough, flexible partition "elements aflixed about said opening on either side of said wall member to form a fluid-tight variable-volume compartment within each of said chambers, said compartments being in communication with each other-through said opening, an outside fluid pressure source, and fluid .conduit means comprising orifices through the walls of said vesselincommunication between said vessel, .saidpressure'source and said pump to apply the pressure of said source to one of the chambers in said vessel and the pump barrel pressure to the other chamber, said pressures being applied to said chambers exteriorly of the variable-volume compartments therein.

3. A displacement pump control system comprising in combination with a pump having at least one pump barrel and a plunger reciprocating therein, a pair of closed vessels, a wall member dividing each vessel into two chambers, said wall member having an opening therethrough, flexible partition elements aflixed about said opening on either side of said wall member to form a fluid-tight variable-volume compartment within each of said chambers, said compartments being in communication with each other through said opening, an outside source of a high and a low pressure fluid, and fluid conduit means comprising orifices through the walls of said vessels in communication between said vessel, said source of pressure fluids and said pump to apply the high pressure fluid to one of the chambers in one vessel, the low pressure fluid to one of the chambers of the other vessel and the pump barrel pressure to the second chamber of both vessels, said pressures being applied to said chambers exteriorly of the variable-volume compartments therein.

4. A displacement pump control system comprising in combination with a pump having at least one pump barrel and a plunger reciprocating therein, a closed vessel, a wall member dividing said'vessel into two chambers, said wall member having an opening therethrough, flexible partition elements aflixed about said opening on either side of said wall member to form a fluid-tight variable-volume compartment within each of said chambers, said compartments being in communication with each other through said opening, a rod member extending through said opening and attached at each end to one of said flexible partitions to maintain a fixed spacing therebetween, valve means carried by said rod, said valve means being adapted to close said opening, an outside fluid pressure source, and fluid conduit means comprising orifices through the walls or" said vessel in communication between said vessel said pressure source and said pump to apply the pressure of said source to one of the chambers in said vessel and'the pump barrel pressure to the other chamber, said pressure being applied to said chambers exteriorly of the variablevolume compartments therein.

5. A displacement pump control system comprising in combination with a pump having at least one pump barrel and a plunger reciprocating therein, a pair of closed vessels, a wall member dividing each vessel into two chambers, said wall member having an opening therethrough, flexible partition elements affixed about said opening on either side of said wall member to form a fluid-tight variable-volume compartment within each of said chambers, said compartments being in communication with each other through said opening, a rod member extending through said opening and attached at each end to one of said flexible partitions to maintain a fixed spacing therebetween, valve means carried by said rod, said valve means being adapted to close said opening, an outside source of a high and a low pressure fluid, a first fluid conduit in communication between said high pressure source and one of the chambers in one vessel, a second fluid conduit in communication between said low pressure source and one of the chambers in the other vessel, and a third fluid conduit in communication between said pump barrel and the second chamber of both said vessels.

6. The device of claim including valve means in said first and second fluid conduits whereby the pressure from said high and low pressure fluid sources may be varied to adjust the minimum intake pressure and maximum discharge pressure of the pump to any desired value.

7. A displacement pump control system comprising in combination with a pump having at least one pump barrel and a plunger reciprocating therein, a closed vessel, a pair of diaphragm assemblies spaced parallel to each other dividing said vessel into three fluid-tight variablevolume fluid-tight chambers, plate means positionedon either side of said diaphragm assemblies limiting the movement thereof, an outside source of a high anda low pressure fluid, fluid conduit means in communicationbetween the center chamber of said fluid-tight vessel and the pump for applying the pump barrel pressure tov said chamber, a conduit in communication between thehigh pressure fluid source and one of the end chambers of said vessel and a second conduit in communication between the low pressure fluid source and the other end chamber of said vessel.

References Cited in the file of this patent UNITED STATES PATENTS 315,485 Davies Apr. 14, 1885 684,806 Enzinger Oct. 2, 1901 910,292 Krichbaum Jan. 19, 1909 1,452,223 Smith Apr. 17, 1923 1,932,921 Bizzarri a--' Oct. 31, 1933 2,055,578 Hurst Sept. 29, 1936 2,265,232 Hotter Dec. 9, :1941 2,517,501 Mennesson Aug, 1, 1950 2,570,965 Meyers Oct. 9, 1951 2,619,907 Paterson Dec. 2, 1952 2,711,697 Gibbs June 28, 1955 FOREIGN PATENTS 319,758 Italy Apr. 5, 1934

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