WO1988002818A1

WO1988002818A1 - Double acting fluid intensifier pump

Info

Publication number: WO1988002818A1
Application number: PCT/US1987/002620
Authority: WO
Inventors: Thomas Welch Hotchkiss
Original assignee: Thomas Welch Hotchkiss
Priority date: 1986-10-14
Filing date: 1987-10-14
Publication date: 1988-04-21
Also published as: AU8151787A

Abstract

A compressed gas-driven, liquid intensifier pump of the type employing a double acting, reciprocating piston (16). The pump operates in a lower pressure - high flow rate mode until a pre-set, trip point pressure in the discharge conduit (52) is reached. This causes the sequence valve (80) to open and the pump to operate in a high pressure - low flow rate mode.

Description

DOUBLE ACTING FLUID INTENSIFIER PUMP

Related Applications

Application Serial No. 891,318, filed on July 31, 1986, discloses and claims subject matter which is related to the present application.

Field of the Invention

The present invention relates in general to fluid intensifier pumps. More particularly, the invention relates to an improved compressed gas-driven, liquid intensifier pump of the type employing a double acting, reciprocating piston.

Background of the Invention

Many hydraulic systems in use today employ a liquid intensifier pump as a hydraulic source. For instance, it is common to employ this pump to operate the hydraulic power cylinders used in large hydraulic presses and clamps.

A compressed gas such as pressurized air is most commonly employed to operate a liquid intensifier pump. Gas pressure is applied against a large gas piston producing a force which is transmitted to a smaller reciprocating, hydraulic piston. A liquid, e.g., hydraulic oil, is drawn into the pump during the "pull¹¹ stroke of the hydraulic piston while, conversely, the liquid is discharged under pressure through the pump outlet during the ^,rpush" stroke of the piston.

The ratio of output pressure to input pressure is proportional to tke ratio between the hydraulic piston and gas piston surface areas. Thus, a low pressure-compressed gas can be utilized with a relatively large surface area gas piston to drive a pump employing a relatively small surface area hydraulic piston, e.g., a thin rod, and produce high pressures at the outlet of the pump.

Double acting, reciprocating, liquid intensifier pumps are also known in the art wherein liquid is drawn into and discharged from the pump during both the "push" and "pull" stroke of the piston. These pumps inherently have a large displacement and pump output.

In many applications, a liquid intensifier pump may be required to provide relatively low hydraulic pressures at high flow rates. In other applications, on the other hand, the pump may be required to provide relatively high hydraulic pressures at low flow rates. It would be highly desirable to achieve both modes of operation with a single pump.

It is therefore a general object of the present invention to provide an improved fluid intensifier pump.

A more specific object of the present invention is to provide an improved compressed gas-driven, double acting, reciprocating, liquid intensifier pump having a relatively large output capacity but which, at the same time, is small, compact and efficient. Another specific object of the present invention is to provide an improved compressed gas-driven, double acting, reciprocating liquid intensifier pump which can be operated at multiple output ratios for a fixed input pressure.

Description of the Invention

The present invention, in its broadest aspect, resides in a double acting, reciprocating, fluid intensifier pump including a cylinder having slidably mounted therein a piston which divides the cylinder into two chambers. A piston rod extends into tke first of the two chambers and is connected at one end to the piston. Tke other end of the piston rod is connected to an actuator device for reciprocating the piston inside the cylinder. A first and second inlet conduit communicate respectively between the first and second chambers and a fluid reservoir, while a first and second outlet conduit communicate respectively between the first and second chambers and a pump outlet. Valve means are provided in the first inlet conduit and second outlet conduit which allow fluid to flow in one direction only from the fluid reservoir to the first chamber and from the second chamber to the pump outlet during the "push" stroke of the piston. Similarly, valve means are provided in the second inlet conduit and first outlet conduit which allow fluid to flow in one direction only from the fluid reservoir to the second chamber and from the first chamber to the pump outlet during the "pull" stroke of the piston.

A cross-over conduit communicates between the first and second chambers and valve means are provided in the cross-over conduit which when open allows fluid to flow from the second chamber to the first chamber during the "push" stroke of the piston.

The actuator device used in the present invention is preferably a gas pump employing a large surface area gas piston which is connected to the opposite end of the piston rod. In operation, a compressed gas, such as pressurized air, is supplied alternately to each side of the gas piston causing it to move back and forth inside the pump cylinder.

Brief Description of the Drawing

The present invention will now be described in greater detail with particular reference to the accompanying drawing wherein like reference numerals indicate the same or similar parts and wherein:

Figure 1 is a diagrammatical view of a typical compressed air-driven, double acting, reciprocating, liquid intensifier pump embodying the invention;

Figure 2 is a similar view of part of the pump illustrated in Figure 1, showing the rotating air valve in a different position;

Figure 3 is a graph showing the performance of the pump illustrated in Figures 1 and 2 in two different modes of operation. Figure 4 is a diagrammatical view similar to Figure 1 showing part of a liquid intensifier pump employing another embodiment of the invention;

Figures 5 and 6 are graphs showing the performance of the pump illustrated in Figure 4 during one mode of operation;

Figure 7 is a graph showing the performance of the pump illustrated in Figure 4 in its two different modes of operation;

Figure 8 is a diagrammatical view similar .-to Figure 1 showing part of a liquid intensifier pump employing still another embodiment of the invention;

Figure 9 is a graph showing the performance of the pump illustrated in Figure 8 during its three different modes of operation.

Description of the Preferred Embodiments

Although the present invention will be described hereinafter with particular reference to the use of a compressed gas pump, e.g., an air pump, as the actuator device, it will be understood that other actuator means may be employed to reciprocate the hydraulic piston. It will also be understood that while the following description mentions only the use of hydraulic oil as the output medium, the invention is not so restricted and that other liquids may be pumped, e.g., water and various solvents.

Referring now to the drawing in detail, there is shown a compressed air-driven, liquid intensifier pump embodying the present invention. As skown, tke pump comprises a housing 10 having formed therein an air cylinder 12 and a hydraulic cylinder 14, the latter being considerably smaller in size than the former and including a hydraulic piston 16 having a relatively small surface area as shown at 18. The piston 16 is slidably mounted inside tke cylinder 14 and is sealed by an 0-ring 20.

An air piston 22 having a relatively large surface area as shown at 24 is slidably mounted inside the air cylinder 12 and is also sealed by an 0-ring 26. The air piston 22 is connected to the hydraulic piston 16 by an elongated piston rod 28. Th^'e piston rod 28 is slidably mounted within a bore 30 and is sealed by an 0-ring 32.

The piston 16 divides the hydraulic cylinder 14 into two chambers, namely, a first hydraulic chamber 34 on the left hand side of the cylinder 14 and a second hydraulic chamber 36 on the right hand side of the cylinder. The piston rod 28 extends into the first chamber 34 and is connected at one end to the hydraulic piston 16. Similarly, the air piston 22 divides the air cylinder 12 into two chambers, namely, a first air chamber 38 on the left hand side of the cylinder 12 and a second air chamber 40 on^" the right hand side of the cylinder. The opposite end of the piston rod 28 extends into the second chamber 40 and is connected to the air piston 22.

A first and second inlet conduit 42, 44 communicate respectively between the first and second kydraulic ckambers 34, 36 and the inlet port 46. Check valves 48, 50 are provided in the first and second inlet conduits 42, 44 and allow hydraulic oil to flow in one direction, only from the inlet port 46 to each of the two chambers. In the embodiment of the pump shown in Figure 1, the first inlet conduit 42 is connected to the second inlet conduit 44 at a point between the check valve 50 and tke inlet port 46.

In a similar fashion, a first and second outlet conduit 52, 54 communicate respectively between the first and second hydraulic chambers 34, 36 and the discharge port 56. Check valves 58, 60 are provided in the first and second outlet conduits 52, 54 and allow kydraulic oil to flow in only one direction from eack of tke two ckambers to tke discharge port 56. Again in tke embodiment of the pump illustrated in Figure 1, tke first outlet conduit 52 is connected to tke second outlet conduit 54 at a point between tke ckeck valve 60 and tke disckarge port 56. A pair of air conduits 62, 64 are provided and communicate at one end with the first and second air chambers 38, 40, respectively. The air conduits 62, 64 communicate at their opposite ends with a two position, four-way, rotating valve 66. In one position of this valve 66 (the position shown in Figure 1), the first air chamber 38 communicates directly with the air inlet 68 via the air conduit 62 while, on the other hand, the air chamber 40 communicates with the air exhaust port 70 via the air conduit 64. It will be seen that by simply rotating the valve 66 to its second position (the position shown in Figure 2), the second air chamber 40 will communicate with the air inlet port 68 via the air conduit 64 and the first air chamber 38 will communicate with the air exhaust port 70 via the air conduit 62.

Air under low pressure, e.g., 100 psi, from an air compressor or other convenient source is supplied through the air inlet port 68 to the second air chamber 40 via the conduit 64 with the valve 66 rotated 90 degrees to its second position (Figure 2). Tke pressurized air filling tke ckamber 40 forces tke air piston 22 to move in a direction toward tke extreme left kand portion of the air cylinder 12. This movement of the air piston 22 causes the piston rod 28 to be pulled through the bore 30 in turn forcing the smaller hydraulic piston 16 to move in a similar fashion toward the extreme left hand portion of the hydraulic cylinder 14.

During this "pull" stroke of the piston rod 28, hydraulic oil is drawn into the second hydraulic chamber 36 through the second inlet conduit 44. The hydraulic oil is supplied from an external oil reservoir 72 through the inlet port 46.

As soon as the piston 28 completes its "pull" stroke and the second hydraulic chamber 36 is filled with oil, the four-way valve 66 is again rotated 90 degrees to its first position as shown in Figure 1. Air under low pressure is then supplied to the first chamber 38 of tke air cylinder 12 via tke air conduit 62. The pressurized air filling the chamber 38 forces the air piston 22 to move in a direction toward the extreme right hand portion of the air cylinder 12. This movement of the air piston 22 causes the piston rod 28 to be pushed back through the bore 30 in turn forcing the smaller hydraulic piston 16 to move in a similar fashion toward the extreme right hand portion of the hydraulic cylinder 14.

During this "push" stroke of the piston rod 28, oil is discharged from the second hy.draulic chamber 36 and is initially fed under low presstire- to the discharge port 56 via the second outlet conduit 54. The check valve 58 prohibits the flow of oil through the conduit 52 in a direction toward the first hydraulic chamber 34.

An external conduit 74 is connected to the discharge port 56 and includes a pressure gauge 76 and a" needle valve 78. Any oil that is fed through the conduit 74 and needle valve 78 collects in the external oil reservoir 72. The needle valve 78 and reservoir 72 represent a "working load" which, in actual practice, may be a separate hydraulic motor or cylinder performing useful work.

As shown in Figure 1, a remote pilot operated sequence valve 80 is provided within a cross-over conduit 82 connected between the first hydraulic chamber 34 and the second outlet conduit 54. The cross-over conduit 82 communicates between the first and second chambers 34, 36 when the sequence valve 80 is open.

The pump is initially started with the needle valve 78 open. The valve is then gradually ^~ closed to build up a workable pressure In the system, say about 400 psi.

During the first mode of operation, the sequence valve 80 is closed and the pump operates in the following manner: Oil is discharged from tke second kydraulic ckamber 36 and is drawn into tke first kydraulic ckamber 34 from tke oil reservoir 72 via the first inlet conduit 42 during the "push" stroke of the piston rod 28. The oil discharged from hydraulic chamber 36 flows through the second outlet conduit 54 and check valve 60 to the discharge port 56 and then through the needle valve 78, returning to the oil reservoir 72. The check valves 50 and 58 prohibit the flow of oil back to the inlet port 46 and the first hydraulic chamber 34 during the "push" stroke of the piston rod 28.

As soon as the piston rod 28 completes its "push" stroke and the first hydraulic chamber 34 is filled with oil,- the valve 66 is again rotated 90 degrees to its first position (Figure 2) and connects the second air chamber 40 with the air inlet port 68. Pressurized air enters the chamber 40 and forces the piston 22 to move in a direction toward the extreme left hand portion of the air cylinder 12. This movement of the air piston 22 pulls the piston rod 28 back through the bore 30 in turn forcing the hydraulic piston 16 to move in a similar fashion toward the extreme left hand portion of the hydraulic cylinder 14. During this "pull" stroke of the piston rod 28, oil is discharged from the first hydraulic chamber 34 and is drawn into the second hydraulic chamber 36 from the oil reservoir 72 via the second inlet conduit 44. The oil discharged from the first hydraulic chamber 34 flows through the first outlet conduit 52 to the discharge port 56 and then through the needle valve 78, returning to the oil reservoir 72. The check valves 48 and 60 prohibit tke flow of oil back to tke inlet port 46 and tke second kydraulic ckamber 36 during tke "pull" stroke of tke piston rod 28.

Tke two position, four-way, rotating valve 66 is skown in Figures 1 and 2 only for purposes of simplicity. In actual practice, the valve 66 may be biased in either direction between its two operating positions automatically at the end of each direction of piston travel by any suitable means, such as by an indexing linkage, for example. The speed at which the air pump drives the hydraulic piston is determined by several factors including the size of the air piston 22 and the magnitude of the air inlet pressure. Typically, the pump can be operated at speeds ranging from zero to about 6 cycles per second at an inlet air pressure of about 100 psi.

It will be seen that a liquid intensifier pump according to the present invention employs a reciprocating, hydraulic piston which is "double acting," that is to say, liquid such as hydraulic oil is discharged from the pump during both the "push" and "pull" strokes of the piston rod 28. In conventional pumps using a single acting piston, liquid is discharged only during the "push" stroke of the piston.

The ratio of output oil- pressure to input- air pressure is inversely proportional to the ratio of air to hydraulic piston surface areas. Assuming- the air and hydraulic pistons to have surface areas of 10 and 2 square inches, respectively, and the piston rod to have a cross-sectional area of 1 square inch, then the output to input pressure ratio of this pump during the first mode of operation would be 5:1. If the total stroke of the piston rod is assumed to be 3 inches, the displacement would be approximately 6 cubic inches on the "push" stroke and approximately 3 cubic inches on the "pull" stroke.

Tke remote pilot operated, sequence valve 80 is an externally pressure operated valve tkat can be adjusted to open at a predetermined pressure. Tke dotted line skown connected to tke outlet conduit 52 in Figure 1 represents tke external pilot pressure required to operate tke valve. Tke valve is normally closed at zero pilot pressure. As tke kydraulic pressure is increased, tke valve remains closed up to its preset trip point. Witk pressure at or above tkis point, tke valve 80 opens fully to allow full flow in both directions through the valve. The valve will reset or close itself when the pilot pressure is reduced to just below its preset trip point. A spring-loaded set screw 84 or similar means may be provided to adjust the preset trip point of the valve 80. A suitable pilot operated, sequence valve for use in this embodiment is Model No. PSV8-10 manu¬ factured by Modular Controls of Villa Park, 111.

With the pilot operated, sequence valve 80 open, the pump operates in its second mode, i.e., the high pressure-low flow rate mode. In this mode, the hydraulic piston 16 is again "double acting" but the performance characteristics of the pump are different. Oil is discharged from the second hydraulic chamber 36 during the "push" stroke and is forced under pressure through the outlet conduit 54 to the discharge port 56. Some of the oil is also.; : forced into the first hydraulic chamber 34 via the cross-over conduit 82 with the sequence valve 80 open. Conversely, upon rotating the valve 66, the piston stroke is reversed and oil is discharged from the first hydraulic chamber 34. The oil is forced to flow through the outlet conduit 52 to the pump outlet 56. A check valve 86 provided in the outlet conduit 54 prohibits the flow of oil back through the cross-over conduit 82. It should be noted that when the pump is operated in this second mode, the output pressure is determined by the ratio of tke air piston surface area to tke cross-sectional area of tke piston rod (ratker tkan tke surface area tke kydraulic piston) . This is true because the pressure in the two hydraulic chambers 34, 36 is the same and the effective surface area on the push stroke is the difference between the areas on each side of the piston 16, i.e., the difference being tke cross-sectional area of tke piston rod 28. Moreover, it skould be noted tkat tke displacement of tke pump during tke "pusk" stroke is equal to tke volume of oil from tke second ckamber 36 less tke volume of oil tkat by-passes tke pump outlet 56 via tke cross-over conduit 82 to tke first ckamber 34. During tke "pull" stroke, on tke otker hand, the displacement of the pump is equal to the volume of oil discharged from tke first kydraulic ckamber 34. Tkus, witk tke air and kydraulic pistons kaving surface areas of ^"10 and 2 square inckes , respectively, and tke piston rod having a cross-sectional area of 1 square inch, then the output to input pressure ratio of the pump in this mode would be 10:1. With the total stroke of the piston rod again being 3 inches, the discharge through the discharge port 56 would be approximately 3 cubic inches on both the "push" and "pull" strokes.

Figure 3 shows the performance curves of the pump during both of its modes of operation, assuming an input pressure of 100 psi. In the graph, the performance curve for each mode of operation is superimposed upon the other. The point at which the two curves intersect is the predetermined set or trip point of the sequence valve 80. It will be seen that the pump of this embodiment is particularly well suited to applications such as filling vessels, where liquid first flows at a high rate under low pressure (e.g. R=5:l) and then, when filling is nearly complete, under a high pressure (e.g. R=10:l) at a low flow rate.

Anotker embodiment of tke present invention is illustrated in Figure 4. In tkis embodiment, tke pump operates again in two modes, tkat is, a medium pressure-kigk flow rate mode and a kigk pressure-low flow rate mode. Tke pump employs basically tke same arrangement of parts as tkat used in tke pump illustrated in Figures 1 and 2 except tkat in this case a smaller surface area hydraulic piston 88 is employed. In addition, the ckeck valve 60 skown in Figure 1 is omitted. As indicated before, the ratio of output to input pressure is inversely proportional to the ratio of air to hydraulic piston surface areas. Thus, for any air piston of a given surface area, it is possible with a conventional pump to produce high pressure ratios by simply making the surface area of the hydraulic piston as small as possible. At the same time, kowever, tke displacement of tke pump may be significantly reduced. Witk tke pump of tke present invention, kowever, tke total volume of liquid displaced tkrougk the discharge port of the pump can be maintained at a relatively high level since the hydraulic piston is "double acting" and discharges liquid during both the "push" and "pull" strokes. In addition, the volume of liquid discharged from the first hydraulic chamber 34 is optimized in this embodiment by employing a smaller cross-sectional area piston rod 90. Assuming the air and hydraulic pistons to have surface areas of 10 and 1 square inches, respectively, and the piston rod to have a cross-sectional area of 0.2 square inches, then in the first mode of operation (i.e. sequence valve 80 is closed) the output to input pressure ratio of this pump would be approximately 10:1 during the "push" stroke of the piston rod. During the "pull¹' stroke, the pressure ratio would be (10-0.2)/(l-0.2) or 12.25:1 (i.e. nearly equal pressure ratios). If the total stroke of the piston rod is again 3 inches, the volume of liquid discharged through the discharge port would be approximately 3 cubic inches on the "push" stroke of the piston rod and slightly less than 3 cubic inches on the "pull" stroke. Figures 5 and 6 graphically represent the performance of a pump according to the specifications given in the above example when operated in the low pressure-high flow rate mode, assuming an input pressure of 100 psi. Comparing the performance of this pump against that of the pump illustrated in Figures 1 and 2, it will be seen that the output pressure ratio for this pump is twice that of tke pump of Figure 5 in tke first mode of operation, altkougk tke total displacement of tke latter is considerably larger tkan tke pump illustrated in Figure 4.

As soon as tke pilot pressure (i.e. pressure in tke outlet conduit 52) reackes tke predetermined set or trip point, tke sequence valve 80 opens and tke pump begins to operate in its second mode. However, tke operation of tke pump in tkis mode is somewkat different tkan tke second mode of operation for tke pump skown in Figure 1. ' In tkis case, tke majority of tke oil disckarged from tke second hydraulic chamber 36 during the "push" stroke by-passes the discharge port 56 and flows under pressure into the first hydraulic chamber 34 via the cross-over conduit 82 and the open sequence valve 80, the balance of the oil discharging directly through the discharge port 56. In the "pull" stroke of the piston rod 90, the oil discharges from the first hydraulic chamber 34 via the cross-over conduit 82 to the second hydraulic chamber 36 while at the same time oil is also drawn into the second hydraulic chamber 36 from the oil reservoir 72 via the inlet port 46. Since the majority of the oil discharged from the second hydraulic chamber 36 flows into the first hydraulic chamber 34 via the cross-over conduit 82 during- the "push", stroke, the hydraulic piston is essentially "single acting" in this mode of operation. Moreover, as described hereinabove, when the pump is operated in this second mode, the output pressure is determined by the ratio of the air piston surface area to the cross-sectional area of the piston rod (rather than the surface area of the kydraulic piston). Tke pressure in tke two kydraulic ckambers 34, 36 is tke same and the effective surface area on the "push" stroke is the difference between the areas on each side of tke piston 88, i.e., the difference being the cross-sectional area of the piston rod 90. Accordingly, with the same surface area values given above, the output to input pressure ratio of the pump in this second mode of operation is 10/0.2 or 50:1.

Figure 7 shows tke performance curves for tke pump during its two modes of operation, assuming an input pressure of 100 psi. Tke curve representing tke low pressure-kigk flow rate mode (R=10/12.25:1) is identical to tkat illustrated in Figure 5. Tke performance curve representing tke high pressure-low flow rate mode (R=50:l) is superimposed on tke former curve, tke point at which the two curves intersect being the predetermined set or trip point of the sequence valve 80. Comparing the performance curves for the pump of this embodiment with the curves illustrated in Figure 3, it will be seen that the present pump is capable of performing at significantly higher output pressures, e.g. 5,000 psi, and at lower but satisfactory flow rates.

Another embodiment of the present invention is illustrated in Figure 8. Here, in this embodiment, the pump operates in three different modes, i.e., a low, medium and high pressure mode. The pump employs basically the same arrangement of parts as used in the pump illustrated in Figure 1. In addition, the pump employs a "break-down" relief valve 92 and a by-pass conduit 94 which communicates between the second hydraulic chamber 36 and an auxiliary discharge port.96 when the relief valve- 92. is open.

The "break-down" relief valve 92 is an internally pressure operated valve that can be adjusted to open at a predetermined pressure.- The dotted line shown in Figure 8 represents an internal pilot pressure required to operate the valve. The valve is normally closed at zero pressure across its inlet 98. As the hydraulic pressure is increased, the valve remains closed up to its present trip point. With pressure at or above tkis point, tke valve opens fully and allows oil to flow tkrougk tke valve and out tkrougk the auxiliary discharge port 96 to the oil reservoir 72. The valve will reset or close itself when the hydraulic inlet pressure is reduced to or near zero. A suitable "break-down" relief valve for use in this embodiment is Model No. 8500281 manufactured by Delta Power Hydraulic Co. of Rockford, 111.

During the period when the hydraulic pressure at the inlet 98 of the "break-down" relief valve 92 is closed, the pump operates in either one of its low or medium pressure modes. The operation of the pump in either mode is exactly tke same as tkat previously described in connection with the pump of Figure 1. In the first or low pressure-kigk flow rate mode, tke pilot operated sequence valve 80 is closed and oil is disckarg-ed from the first and second hydraulic chambers 34, 36 via the outlet conduits 52, 54 during the "pull" and "push" strokes of the piston rod 90. The total output flow per cycle is the sum of the outputs from the first and second hydraulic chambers 34, 36. As soon as the output pressure reaches the preset trip point of the sequence valve 80 (hereinafter trip point "A"), the valve 80 opens and the pump begins to operate in its second mode, i.e. medium pressure-medium flow rate mode. During this mode of operation, the total output of the pump per cycle is the sum of the output from the second hydraulic chamber 36 less the displacement of the first hydraulic chamber 34 during the "push" stroke and the output from the first hydraulic chamber 34 during the "pull" stroke of the piston rod.

Upon further increase of the outlet pressure up to or above the preset trip point of the "break-down" relief valve 92 (hereinafter trip point "B"), the relief valve 92 opens and the pump begins to operate in its third mode, i.e. very high pressure - very low flow rate mode. During the "push" stroke of the piston rod 90, hydraulic oil from the second chamber 36 is forced under pressure into the first hydraulic chamber 34 via the cross-over conduit 82 (sequence valve 80 remains open during this mode of operation). However, the majority of the oil from the chamber 36 flows through the relief valve 92 which is fully open. Conversely, during the "pull" stroke of the piston rod 90, oil is discharged from the first chamber 34 to the discharge port 56 via the outlet conduit 52.

A fixed restrictor 100 may also be employed in the by-pass conduit 94 below the outlet of the valve 92. This restrictor is employed to control the speed of the piston and rod assembly during the push portion of the cycle while in the high mode. It also provides a desired amount of back pressure to adequately "supercharge" the small volume in the first hydraulic chamber 34, thereby precluding cavitation of this ckamber.

It will be seen that in this mode of operation the pump is "single acting" and discharges oil only during the "pull" stroke of the piston rod. The total volume of liquid discharged from the pump is equal to the displacement of the first hydraulic chamber 34. The output pressure, on the other hand, is proportional to the ratio between the air piston surface area and effective surface area of the hydraulic piston in the first chamber 34, i.e., surface area of the hydraulic piston less the cross-sectional area of the piston rod 90. Assuming the air and hydraulic pistons to have surface areas of 10 and 1.0 square inch, respectively, and the piston rod to have a cross-sectional area of 0.6 square inch, then the output to input pressure ratio of the pump would be (10-0.6)/(l .0-0.6) or 23.5:1. If the total stroke of- the piston rod is assumed to be 3 inches, the displacement would be approximately 1.2 cubic inches during the "pull" stroke of the piston rod. This same pump when operated in the medium pressure-medium flow rate mode would have an output to input pressure ratio of 16.7:1 and the total displacement of the pump would be 3 cubic inches. Conversely, the pump when operated in the low pressure-high flow rate mode would have an output to input pressure ratio of 10:1 and the total displacement of the pump would be 4.2 cubic inches.

Figure 9 graphically represents the performance of a "triplex" pump made to the specifications given in the above example when operated in all three of its modes, assuming an input pressure of 100 psi. In the graph, the performance curves for each of the three modes of operation are shown superimposed upon each other, the two points "A" and "B" at which the three curves intersect being the predetermined set or trip points of the sequence valve 80 and the "break-down" relief valve 92. It will be seen that the pump of this embodiment is able to automatically adjust its output ratio to a fixed input pressure in order to accommodate the particular requirements of the working load. For example, in most kydraulic cylinder applications, tkere are tkree distinct phases for one given work cycle. In the first phase, a mechanism is usually moved through air (clearance) at very low resistance (load) and utilizes a large stroke. In the second phase, contact is made with the workpiece and energy is spent in the form of driving friction, spring-action or plastic deformation, for example, requiring a moderately increasing load and small stroke. In a third phase, a final clamping, crimping or breaking action occurs at high load and virtually no displacement. The "triplex" pump monitors the working pressure and automatically initiates the transition from one phase to the other, adjusting its output to input pressure ratio in order to accommodate the load requirements in each phase of the operation.

It will of course be understood that the present invention is by no means limited to the exact embodiments disclosed hereinabove and that various modifications and adaptations can be made in the fluid intensifier pump. For example, it is possible to pump a gaseous medium, suck as nitrogen or carbon dioxide, instead of a liquid. In suck case, kowever, gas-sealed components must be employed instead of liquid-sealed components. Various otker modifications and adaptations can of course be made in tke pump as will readily occur to tkose skilled in tke art.

Claims

What is claimed is:

1. In a fluid intensifier pump including a cylinder having slidably mounted therein a piston which divides said cylinder into two chambers, a piston rod extending through the first of said chambers and having one end connected to said piston and means for reciprocating said piston inside said cylinder, a first and second inlet conduit communicating respectively between the first and second chambers and a fluid reservoir, a first and second outlet conduit communicating respectively between the first and second chambers and a pump outlet, valve means in said first inlet conduit and said second outlet conduit which allow fluid to flow in one direction only from the fluid reservoir to the first chamber and from the second chamber to the pump outlet during the push stroke of said piston rod, valve means in said second inlet conduit and said first outlet conduit which allow fluid to flow in one direction only from the fluid reservoir to- the second chamber and from the first chamber to the pump outlet during the pull stroke of said piston rod; the improvement comprising, in combination:

(a) a cross-over conduit communicating between said first and second chambers; and

(b) valve means in said cross-over conduit which when open allows fluid to flow from said second chamber to said first chamber during the push stroke of said piston rod.

2. A fluid intensifier pump according to claim 1 wherein the means for reciprocating said piston inside^'said cylinder is a gas pump.

3. A fluid intensifier pump according to claim 1 wherein tke valve means in said cross-over conduit is an externally pressure operated sequence valve.

4. A fluid intensifier pump according to claim 1 wkerein a by-pass conduit communicates between said second ckamber and said fluid reservoir and wkerein valve means are provided in said by-pass conduit which when open allows fluid to flow from said second chamber to said fluid reservoir, by-passing said valve means in said first inlet conduit, during the push stroke of said piston rod.

5. A fluid intensifier pump according to claim 4 wherein the valve means in said by-pass conduit is a break-down relief valve.

6. A liquid intensifier pump comprising, in combination:

(a) a hydraulic cylinder having a hydraulic piston slidably mounted therein, said piston dividing said cylinder into a first and a second chamber;

(b) a piston rod extending through said first chamber and being affixed at one end to said hydraulic piston;

(c) a gas pump including a gas piston connected to the opposite end of said piston rod for reciprocating said hydraulic piston inside said cylinder;

(d) a liquid reservoir;

(e) a discharge port;

(f) a first and second inlet conduit communicating between said first and second chambers and said liquid reservoir;

(g) a first and second outlet conduit communicating between said first and second ckambers and said disckarge port;

(k) valve means in said first inlet conduit and said second outlet conduit wkick allow liquid to flow in one direction only from tke said liquid reservoir to tke first ckamber and from tke second ckamber to tke disckarge port during the push stroke of said piston rod;

(i) valve means- in said second inlet conduit and said first outlet conduit which allow liquid to flow in one direction only from said liquid reservoir to said second chamber and from said first, chamber to said discharge port during the pull stroke of said piston rod;

(j) a cross-over conduit communicating between said first and second chambers; and

(k) valve means in said cross-over conduit which when open allows liquid to flow from said second chamber to said first chamber during the push stroke of said piston rod.

7. A liquid intensifier pump according to claim 6 wherein the valve means in said cross-over conduit is an externally pressure operated sequence valve.

8. A fluid intensifier pump according to claim 6 wherein a by-pass conduit communicates between said second chamber and said liquid reservoir and wherein valve means are provided in said by-pass conduit which when open allows liquid to flow from said second chamber to said liquid reservoir, by-passing said valve means in said first inlet conduit, during the push stroke of said piston rod.

9. A liquid intensifier pump according to claim 8 wherein the valve means in said by-pass conduit is a break-down relief valve.

10. A liquid intensifier pump according to claim 9 wherein a restrictor valve is provided between said relief valve and said liquid reservoir.

11. A liquid intensifier pump according to claim 6 wherein the gas piston has a relatively large surface area.

12. A liquid intensifier pump according to claim 11 wherein tke kydraulic piston kas a relatively small surface area.

13. A liquid intensifier pump according to claim 6 wkerein tke piston rod kas- a relatively small cross-sectional area in order to optimize tke displacement of liquid from said first ckamber during tke pull stroke of said piston rod.

14. A liquid intensifier pump according to claim 6 wkerein tke piston rod kas a relatively large cross-sectional area in order to optimize tke output pressure from said first ckamber during tke pull stroke of said piston rod.

15. A liquid intensifier pump comprising, in combination:

(d) a liquid reservoir;

(e) a discharge port;

(f) a first- and second inlet conduit communicating between said first and second chambers and said liquid reservoir;

(g) a first and second outlet conduit communicating between said first and second chambers and said discharge port;

(h) valve means in said first inlet conduit and said second outlet conduit which allows liquid to flow in one direction only from the liquid reservoir to the first chamber and from the second chamber to the discharge port during the push stroke of said piston rod;

(i) valve means in said second inlet conduit and said first outlet conduit which allow liquid to flow in one direction only from said liquid reservoir to said second chamber and from said first chamber to said discharge port during the pull stroke of said piston rod;

(j) a cross-over conduit communicating between said first and second chambers;

(k) a pilot operated, sequence valve in said cross-over conduit which when open allows liquid to flow from said second ckamber to said first ckamber during tke pusk stroke of said piston rod; and

(1) means communicating witk said sequence valve for applying tkereto a pilot pressure corresponding to tke outlet pressure from said pump.

16. A liquid intensifier pump according to claim 15 wherein a by-pass conduit communicates between said second chamber and said liquid reservoir and wherein a break-down relief valve is provided in said by-pass conduit which when open allows liquid to flow from said second chamber to said liquid reservoir, by-passing said valve means in said first inlet conduit, during the push stroke of said piston rod.