GB2356432A

GB2356432A - Fluid powered pump with valve control

Info

Publication number: GB2356432A
Application number: GB9927242A
Authority: GB
Inventors: Colin Pearson
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-11-18
Filing date: 1999-11-18
Publication date: 2001-05-23
Also published as: GB9927242D0

Abstract

A pump, such as for waste energy recovery in reverse osmosis systems, has two piston-in cylinder assemblies with the pistons 113 linked by a piston rod. A control valve 104 directs powering fluid between the cylinders to reciprocate the pistons by means of poppet inlet and outlet valves 205,206,216,221 or spool valves (figures 6a-d) which are driven to either extreme of their travel by fluid flow and pressure, and actuated by contact with the pistons 113 at the end of each stroke. To prevent the valves from remaining in a stall position, springs 203,217,219 compressed by piston travel, or other energy storage means, is provided on the valves to ensure continued movement of the valves when the pistons have stopped at the end of each stroke. The poppet valves have pressure balancing secondary valves 204,208,214,215 which reduce the pressure required to open the poppet valves.

Description

2356432 Improvements in Fluid-Powered Pumps The present invention is

particularly applicable to waste energy recovery in reverse osmosis systems, or to other systems where energy lost by releasing a first high-pressure fluid flow to waste can be recovered and used to impel a second fluid flow. It is also applicable as an hydraulic intensifier, where a first fluid flow is used to impel second fluid flow of higher pressure, or as a similar device providing a second fluid flow of higher flow rate and lower pressure than the first.

Reverse osmosis systems are commonly used to separate solvents from the solutes they contain, by pumping the solution, at a significant pressure, through a semi-permeable membrane. This membrane allows the solvent to pass through while preventing the solute from so doing. To prevent the membrane from becoming clogged by the solute, it is necessary to flush away the solute by arranging a flushing flow of solution along the solution side of the membrane that is significantly higher, typically by a factor of four, than the flow of solvent through the membrane. The flushing flow of concentrated solution leaves the membrane at a pressure which is not much less than the solution pressure at the input to the membrane. This flushing flow is commonly released to waste via a pressurereducing valve, wasting typically 80% of the pumping energy. Reciprocating fluid-powered pumps, similar to hydraulic intensifiers, have been proposed and built to recover this wasted energy, and it is to these pumps that the present invention relates.

The novelty in the present invention rests primarily in control valve means supplying fluid to the motor cylinders of a reciprocating fluidpowered pump. These means differ from prior art in that fluid pressure and piston contact are used to move the control valve between states. This results in a simpler arrangement than prior art methods that include multiple valves, mechanical toggle and detent devices, and electrical systems. The present invention also concerns associated flow control means.

Figure I shows an example of a reverse osmosis system with energy recovery, in which the secondary pump works in parallel with the primary pump to augment the latter's flow. An externallydriven primary pump, 1, impels a primary flow of solution to the membrane assembly, 4, from a solution inlet, 9. Extracted solvent passing through the membrane leaves the system at a solvent outlet, 11. The flushing flow of concentrated solution passes to the waste outlet, 10, via a fluid motor, 6. Said fluid motor drives a secondary pump, 5, which impels a secondary flow of solution to the membrane. The pressure rise across the secondary pump must be higher than the pressure drop across the fluid motor, to allow for pressure and friction losses. Consequently, the flow delivered by the secondary pump must be less than the flow through the fluid motor. A flow control valve, 8, restricts the flow through the motor, 6, and thereby the flow from the secondary pump, 5. Said flow control valve serves to regulate the ratio of flushing flow to solvent output flow, which would otherwise vary significantly as a result of slight changes in system pressure and friction losses. Said flow control valve may be a constantflow valve of conventional type, closing as flow through it increases, it may be controlled by membrane solution pressure, opening as said pressure increases, or it may be controlled in any other convenient manner. Items 2, 3 & 7 in figure 1 show alternative positions for the flow control valve, 8. Position 8 has the advantage of being at a point of minimal pressure in the system. Position 3 has the advantage that a commonly available pressure relief valve may be used to control the flow as a function of membrane pressure.

Figure 2 shows an alternative energy recovery scheme for reverse osmosis, in which the secondary pump works in series with the primary pump, to augment the latter's pressure. An externally-driven primary pump, 1, supplies solution from a solution inlet, 9, to the secondary pump, 5, which increases solution pressure and delivers solution to the membrane assembly, 4. Extracted solvent passing through the membrane leaves the system at a solvent outlet, 11. The flushing flow of concentrated solution passes to the waste outlet, 10, via a fluid motor, 6. Said fluid motor drives the secondary pump, 5. The flow delivered by the secondary pump must be greater than the flow through the motor, the difference in flows being equal to the output flow of solvent passing through the membrane. The flow control valve shown in figure 1 is not needed, as the ratio of flushing flow to solvent output flow is controlled by the ratio of secondary pump delivery to fluid motor throughput. Said ratio would commonly be fixed by the dimensions of said pump and motor, but could be made adjustable by use of a variable-displacement pump and/or motor, or by use of a variable speed ratio drive between pump and motor.

Figure 3 shows a sectional view of a fluid-powered pump, applicable to the system shown in figure 1, the secondary pump working in parallel with the primary pump.

A body, 114, defines two cylinders of equal diameter separated by a third bore of smaller diameter, the axes of all three bores being parallel but not necessarily co-linear. A piston assembly, 113, comprises two piston means linked by a rod means, both piston means being free to reciprocate within the larger bores and the rod means being free to reciprocate within the smaller bore. Seal means, 112 & 115, prevent leakage between the pistons and the bores. Seal means, 107, which may be fixed to the rod or to the bore in which it reciprocates, prevents leakage between the rod and the bore. Two enclosed chambers are defined within each of the larger bores by the two faces of each piston. The outer chambers, defined by the piston outer faces, serve as a double-acting motor. The inner chambers, defined by the piston inner faces, serve as a double-acting pump. Since the effective area of the inner face of each piston is less than that of the outer face, the difference in areas being equal to the crosssection area of the rod, the flow rate pumped by the inner chambers will be less than the flow rate through the outer, motor, chambers.

In figure 3, pump inlet flow, 117, and pump outlet flow, 116, are directed to and from the pump chambers by the non-return valves, 108 to 111, in a conventional manner. Flow to and from the motor chambers is directed by a control valve, 104. The control valve has two main states, at the two extremes of its operating travel. The first state, as shown in figure 3, at the rightmost extreme of control valve travel, directs the motor inlet flow, 100, to the right hand motor chamber and directs motor outlet flow, 101, from the left hand motor chamber, causing the piston assembly to move to the left. The second state, at the leftmost extreme of control valve travel, directs the motor inlet flow to the left hand motor chamber and directs motor outlet flow from the right hand motor chamber, causing the piston assembly to move to the right. The control valve is moved between the extremes of its travel by contact with the pistons, via pushrod means 102 & 106, at the end of each stroke of the piston assembly. Seal means, 103 & 105, prevent leakage around said pushrod means Figure 4 shows a sectional view of a fluid-powered pump, applicable to the system shown in figure 2, the secondary pump working in series with the primary pump. It differs from the fluid-powered pump shown in figure 3 in that the inner chambers act as a pump while the outer chambers act as a motor.

A body, 114, defines two cylinders of equal diameter separated by a third bore of smaller diameter, the axes of all three bores being parallel but not necessarily co-linear. A piston assembly, 113, comprises two piston means linked by a rod means, both piston means being free to reciprocate within the larger bores and the rod means being free to reciprocate within the smaller bore. Seal means, 112 & 115, prevent leakage between the pistons and the bores. Seal means, 107, which may be fixed to the rod or to the bore in which it reciprocates, prevents leakage between the rod and the bore. Two enclosed chambers are defined within each of the larger bores by the two faces of each piston. The outer chambers, defined by the piston outer faces, serve as a double-acting pump. The inner chambers, defined by the piston inner faces, serve as a double-acting motor. Since the effective area of the inner face of each piston is less than that of the outer face, the difference in areas being equal to the crosssection area of the rod, the flow rate through the outer, motor, chambers will be less than the flow rate pumped by the inner chambers.

In figure 3, pump inlet flow, 117, and pump outlet flow, 116, are directed to and from the pump chambers by the non-return valves, 108 to 111, in a conventional manner. Flow to and from the motor chambers is directed by a control valve, 104. The control valve has two main states, at the two extremes of its operating travel. The first state, as shown in figure 4, at the rightmost extreme of control valve travel, directs the motor inlet flow, 100, to the left hand motor chamber and directs motor outlet flow, 101, from the right hand motor chamber, causing the piston assembly to move to the left. The second state, at the leftmost extreme of control valve travel, directs the motor inlet flow to the right hand motor chamber and directs motor outlet flow from the left hand motor chamber, causing the piston assembly to move to the right. The control valve is moved between the extremes of its travel by contact with the pistons, via pushrod means 102 & 106, at the end of each stroke of the piston assembly. Seal means, 103 & 105, prevent leakage around said pushrod means In both figure 3 & figure 4, since there must be a stall position in the control valve travel where flow to and from the motor chambers is interrupted or directed in such a way that the piston assembly stops, it is necessary to provide means to ensure that valve travel continues when the piston assembly is 2 stopped, and means to ensure that the valve does not remain at the stall position during system startup. In the present invention, this is achieved by interposing spring means between the piston assembly and the control valve to maintain movement of the valve when the piston assembly is stopped, and by configuring the valve so that fluid pressure within the valve forces it away from the stall position to one or other extreme of its travel.

Figures 5a to 5d show, schematically, a control valve embodying the present invention as applied to the fluid-powered pumps shown in figures 3 & 4.

Figure 5a shows the valve in its state at mid-stroke of the piston assembly, when the piston assembly is moving from right to left. Motor flow enters at the inlet port, 201, and leaves from the outlet port, 218. Flow to and from the motor chambers passes through the motor ports 200 & 220. For the pump shown in figure 3, the left hand motor port would be connected to the right hand outer chamber and the right hand motor port to the left hand outer chamber. For the pump shown in figure 4, the left hand motor port would be connected to the left hand inner chamber and the right hand motor port to the right hand inner chamber.

Flow from the inlet port 201 to the motor ports, 200 & 220, is controlled by primary inlet valves, 205 & 206. Flow from the motor ports, 200 & 220, to the outlet port, 218, is controlled by primary outlet valves, 216 & 221. The primary valves, which are of poppet type, have secondary valves, 204, 208, 214 & 215, serving to relieve the pressure across them, thereby reducing the force required to open the primary valves. Said secondary valves control bleed flow through the clearance between the valve stems, 207, 210 & 213, and the bores of the primary valve poppets. The poppets of primary inlet valves 205 & 206 are connected together by a tube means, 202, which is pierced to permit said bleed flow. Springs, 203, 217 & 219, which are compressed by piston travel during valve operation, provide the energy to complete valve operation once the pistons have stopped. Seal means, 211 & 212, which may be of conventional type, prevent leakage around the valve stems where they enter the pump chambers.

As shown in figure 5a, motor inlet flow is directed to the left hand motor port, and outlet flow is directed from the right hand motor port, causing the piston assembly, 209, to move leftwards. The primary valves, 206 & 216, and their associated secondary valves, 208 & 214, are held closed by the pressure differences across them. Primary valve 205 is held open by its attachment to primary valve 206. Primary valve 221 is held open by a spring 219.

Figure 5b shows the state of the control valve when the piston assembly has reached the end of its leftward stroke. Valve stems 210 & 213 have been moved leftwards by the piston, closing primary valve 221, opening secondary valves 208 & 214, and compressing springs 203 & 217. Flow from the inlet port through secondary valve 208 cannot escape to the outlet port because primary valve 221 is now shut, causes the pressure in the right hand motor port 220 to rise. When said pressure approaches the inlet port pressure, the spring, 203, overcomes the pressure differential across primary valve 206, opening it and closing primary valve 205, as shown in figure 5c.

At the leftward stroke end, the piston assembly is substantially locked by the pressure differentials across it, until such time as the left hand motor chamber pressure is substantially equal to the motor inlet pressure and the right hand motor chamber pressure is substantially equal to the motor outlet pressure.

In figure 5c, the left hand motor port, 200 has been disconnected from the inlet port, 201, by closure of primary valve 205 and secondary valve 204. Flow through secondary valve 214 to the outlet port reduces the pressure in the left hand motor port. When said pressure approaches the outlet pressure, the spring 217 overcomes the pressure differential across primary valve 216 and opens it, as shown in figure 5d.

In figure 5d, the left hand motor port is connected to the inlet port, and the right hand motor port is connected to the outlet port, causing the piston assembly to move from left to right.

Stroke reversal at the end of the rightward stroke is achieved in the same manner as described above for the leftward stroke, the control valve mechanism being symmetrical.

3 The above mentioned bleed flow, controlled by the secondary valves, which relieves the pressure differential across the primary valves, is restricted to prevent significant fluid loss during stroke reversal. Said fluid loss occurs for the brief period when the control valve is in the state shown in figure 5b, when fluid can pass from the inlet port to the outlet port via primary valve 205 and secondary valve 214. Bleed flow need be sufficient only to relieve the pressure across the primary valves quickly enough to achieve an acceptably rapid stroke reversal, and may typically be 5% to 20% of the motor fluid flow rate.

The control valve shown in figures 5a to 5d may be an integral part of the fluid-powered pump. When applied to the fluid-powered pump shown in figure 4, the motor ports and valve stem seals may be omitted so that the valves communicate directly with the inner chambers of the fluid-powered pump.

During start-up of the fluid-powered pump, fluid flow through the control valve causes the inlet valve assembly, 207, 204, 205, 202, 203, 206, 208 & 210, to move to either extreme of its travel, preventing both primary inlet valves, 205 & 206, from remaining open. This happens because any movement of the inlet valve assembly from the central position causes a pressure differential accelerating that movement. For example, a rightward movement from centre will cause the left hand primary inlet valve, 205, to open further than the right hand primary inlet valve, 206, causing a higher pressure in the left hand motor port, 200, than the right hand motor port, 220. This pressure differential causes the inlet valve assembly to accelerate further to the right until it reaches the end of its travel. In a similar manner, the outlet valve assembly, 214, 216, 217, 219, 221, 215 & 213, will also move to one extreme of its travel. Interaction between the inlet and outlet valve assemblies causes them to move to the same extreme of travel. For example, if the inlet valve assembly moves to the right, it will direct more fluid flow to the left hand motor port than to the right hand motor port, causing the pressure in the left hand motor port to be higher than in the right hand motor port. This pressure differential acts on the discharge valve assembly causing it also to move to the right. It would be theoretically possible for both inlet and outlet valve assemblies to stay at dead centre positions in the unlikely event that they had both stopped there, but in practice flow turbulence prevents this from happening.

Figures 6a to 6b show an alternative embodiment, applicable to the fluidpowered pumps shown in figures 3 & 4.

Figure 6a shows the state of the control valve at mid-stroke of the piston assembly, when the piston is moving right to left. A valve body, 300, which may be part of, or enclosed within, the main motor-pump body, contains a valve bore 301. Within said valve bore reciprocates a valve spool assembly, 308, 312, 314 & 316, which may be substantially of conventional type. The clearances between the valve spool assembly and the valve bore are restricted to limit leakage between the separate flow paths in the valve to typically less than 5% of the flow controlled by the valve. The volumes defined by the valve spool assembly within the valve bore are linked by flow passages 311 & 317. As shown, these passages are within the valve spool assembly, but they could equally well be within the valve body.

The stem, 308, of the valve spool assembly is extended at either end to pass through the valve body into the inner chambers of the fluid-powered pump, being sealed by seals 306 & 307. At either end of the spool assembly are spring means, 309 & 310. Inlet flow to the motor enters through inlet port, 303, and outlet flow may pass from either of outlet ports, 302 & 304, depending on the position of the valve spool assembly within the valve bore. Flow to and from the motor chambers within the fluid-powered pump passes through motor ports, 313 & 315. For the fluid- powered pump shown in figure 3, where the outer chambers act as the motor, the right hand outer chamber is connected to the left hand motor port, 313, and the left hand outer chamber is connected to the right hand motor port, 315. For the fluidpowered pump shown in figure 4, where the inner chambers act as the motor, the left hand inner chamber is connected to the left hand motor port, 313, and the right hand outer chamber is connected to the right hand motor port, 315.

As shown in figure 6a, the valve spool assembly is at the rightmost extreme of its travel. Inlet flow is directed to the left hand motor port, 313, and outlet flow is directed from the right hand motor port,315, causing the piston assembly of the fluid-powered pump to move from right to left. The valve spool assembly is held at its rightmost extreme of travel by the pressure difference across the central large diameter portion, 314, which has inlet pressure on its left side and outlet pressure on its right side.

4 Figure 6b shows the control valve when the piston assembly has moved far enough for the right hand piston to contact the spring means, 309, and thereby move the valve spool assembly. The spring rate of spring means 309 is chosen so that the pressure force on the valve spool assembly is insufficient to compress it completely. As the valve spool assembly moves leftward, it restricts flow through the inlet and outlet ports, causing the piston assembly to slow down, and reducing the pressure differential and consequent pressure force on the valve spool assembly. Since the pressure force is reduced, spring means 309 expands, causing the valve spool assembly to move faster than the piston assembly.

Figure 6c shows the control valve when the valve spool assembly has reached the mid point of its travel. In this position the pressures at the two motor ports are substantially equal, since the leakage resistances from the inlet port are equal, as are the leakage resistances to the outlet port. With no pressure differential to drive it, the piston assembly has stopped. With no pressure differential across the valve spool assembly, spring means 309 will continue to expand, driving the valve spool assembly further leftward. This leftward movement will increase the pressure at the right hand motor port and reduce the pressure at the left hand motor port, thus causing the piston assembly to start moving to the right, and the valve spool assembly to continue moving to the left.

Figure 6d shows the control valve at its leftward extreme of travel, when the piston assembly is moving from left to right.

The control valve shown in figures 6a to 6d may be an integral part of the fluid-powered pump. When applied to the fluid-powered pump shown in figure 4, the motor ports and valve stem seals may be omitted so that the ends of the valve bore communicate directly with the inner chambers of the fluidpowered pump.

During start-up the valve spool assembly will be driven to one or other extreme of its travel by fluid pressure, since the pressure force on the valve spool assembly will drive it away from the central position. It would be theoretically possible for the valve spool assembly to stay at its central position in the unlikely event that it had stopped there, but in practice flow turbulence prevents this from happening.

It may be advantageous in some applications to add more ports to the motor control valve shown in figures 6a to 6d, using them to direct flow to and from the pump chambers of the fluid-powered pump in place of all or some of the non-return valves shown in figures 3 & 4.

claims fluid-powered pump having a pump flow rate greater than the motor flow rate, said fluid-powered pump consisting of: Two truncated cylinders having their axes parallel and being joined together by a central body and being closed at their outer ends by end closures. A piston assembly comprising a piston rod having a piston attached at each end, said piston rod passing through a bore in said central body parallel to the axes of said cylinders and one said piston being within each said cylinder, said piston assembly being free to reciprocate parallel to the axes of said cylinders, said pistons dividing each said cylinder. into an inner chamber and an outer chamber. Seal means to prevent or restrict fluid flow between each said piston and said cylinder which contains it. Seal means to prevent or restrict fluid flow between between said piston rod and the bore through which it passes in said central body. Pump inlet valve means and pump inlet fluid passages to direct pump inlet flow to each said outer chambers when the associated said piston is moving towards said central body. Pump outlet valve means and pump outlet fluid passages to direct pump outlet flow from each said outer chamber when the associated said piston is moving away from said central body. Motor control valve means and motor fluid passages to direct motor inlet flow to alternate said inner chambers and to direct motor outlet flow from the opposite said inner chamber. Valve elements directing flow within said motor control valve means, said valve elements being configured to be driven to either extreme of travel by fluid flow and pressure, said valve elements having no stable position between extremes of travel while said fluid-powered pump is operating. A valve mechanism to move said valve elements between extremes of travel, said mechanism being actuated by contact with said piston assembly, and said mechanism including spring or other energy storage means to continue movement of said valve elements when said piston assembly has stopped at the end of its stroke.

fluid-powered pump having a pump flow rate less than the motor flow rate, said fluid-powered pump consisting of: Two truncated cylinders having their axes parallel and being joined together by a central body and being closed at their outer ends by end closures. A piston assembly comprising a piston rod having a piston attached at each end, said piston rod passing through a bore in said central body parallel to the axes of said cylinders and one said piston being within each said cylinder, said piston assembly being free to reciprocate parallel to the axes of said cylinders, said pistons dividing each said cylinder. into an inner chamber and an outer chamber. Seal means to prevent or restrict fluid flow between each said piston and said cylinder which contains it. Seal means to prevent or restrict fluid flow between between said piston rod and the bore through which it passes in said central body. Pump inlet valve means and pump inlet fluid passages to direct pump inlet flow to each said inner chambers when the associated said piston is moving away from said central body. Pump outlet valve means and pump outlet fluid passages to direct pump outlet flow from each said inner chamber when the associated said piston is moving towards from said central body. Motor control valve means and motor fluid passages to direct motor inlet flow to alternate said outer chambers and to direct motor outlet flow from the opposite said outer chamber. Valve elements directing flow within said motor control valve means, said valve elements being configured to be driven to either extreme of travel by fluid flow and pressure, and said valve elements having no stable position between extremes of travel while said fluid-powered pump is operating. A valve mechanism to move said valve elements between extremes of travel, said mechanism being actuated by contact with said piston assembly, and said mechanism including spring or other energy storage means to continue movement of said valve elements when said piston assembly has stopped at the end of its stroke.

6 3 A fluid-powered pump as claimed in claim 1, where said valve elements comprise a plurality of primary valves of poppet type and a plurality of secondary valves serving to relieve the pressure across the primary valves.

4 A fluid-powered pump as claimed in claim 2, where said valve elements comprise a plurality of primary valves of poppet type and a plurality of secondary valves serving to relieve the pressure across the primary valves.

A fluid-powered pump as claimed in claim 1, where said valve elements comprise an unbalanced spool-type valve configured so that the spool is driven away from the middle position by the pressure differentials across said spool.

6 A fluid-powered pump as claimed in claim 2, where said valve elements comprise an unbalanced spool-type valve configured so that the spool is driven away from the middle position by the pressure differentials across said spool.

7 A reverse osmosis or related system including the fluid-powered pump claimed in claim 1 or claim 3 or claim 5, said system using the concentrated solution flow from the membrane to power the motor of the fluid-powered pump and using the pump of the fluid-powered pump to increase the pressure of the input solution flow to the membrane.

8 A reverse osmosis or related system including the fluid-powered pump claimed in claim 2 or claim 4 or claim 6, said system using the concentrated solution flow from the membrane to power the motor of the fluid-powered pump and using the pump of the fluid-powered pump to increase the quantity of the input solution flow to the membrane by providing a secondary flow to supplement a separate primary flow.

9 A reverse osmosis or related system as claimed in claim 8, in which theflow rates through said fluidpowered pump are controlled by a constantflow valve, said valve controlling the flow to or from the motor or to or from the pump of said fluid-powered pump.

A reverse osmosis or related system as claimed in claim 8, in which the flow rates through said fluipowered pump are controlled by a pressurecontrolled valve, said valve controlled by the pressure at the membrane and controlling the flow to or from the motor or to or from the pump of said fluidpowered pump so that flow rate increases with pressure.

8 A reverse osmosis or related system as claimed in claim 8, in which the flow rates through said fluidpowered pump are controlled by a flowcontrol valve, said valve controlled by the flow rate of a primary solution flow to the membrane and controlling the flow to or from the motor or to or from the pump of said fluid-powered pump, so that the secondary flow provided by said fluid-powered pump has a flow rate proportional to that of the primary flow.

9 A Fluid-powered pump or reverse osmosis system as herein described and/or as shown in the accompanying drawings.

7