Abstract:
A three-way two-position poppet valve ( 10 ) comprising a housing ( 12 ) with a generally cylindrical valve chamber ( 14 ), a first ( 20 ) and a second ( 16 ) port with coaxial  1  valve seats ( 26, 28 ) at the ends of the chamber, and a third lateral working port ( 18 ). A poppet body ( 36 ) is disposed reciprocably in the valve chamber so that in a first position of the poppet body the first valve seat ( 26 ) is sealed and the second port communicates with the working port, and in a second position the second valve seat ( 28 ) is sealed and the first port communicates with the working port. The valve is characterized in that the housing has two coaxial cylindrical passages ( 24, 30 ) adjacent the respective valve seats, while the poppet body has two coaxial cylinder parts ( 44, 48 ) slidingly and sealingly fitting the cylindrical passages, so that the poppet body is always supported in at least one of the cylindrical passages and fluid communication between the first and the second port is always prevented.

Description:
FIELD OF THE INVENTION 
   This invention relates to three-way poppet valves, more particularly to valves specially designed for use in work exchanger systems. 
   BACKGROUND OF THE INVENTION 
   A work exchanger is a device that obtains energy from one stream of fluid and transfers that energy to another stream. It can be also described as a pump driven by fluid flow, most often of opposed piston/diaphragm type. Work exchangers are vital for energy recovery in reverse osmosis processes such as desalination, since by itself the RO separation is power-consuming process which becomes economically feasible if only a substantial part of the energy resident in the reject or/and permeate streams is returned back into the process. 
   A work exchanger system typically comprises two (or more) pressure cylinder vessels with a brine port at one end, a feed water port at the other end, and a plunger freely sliding between the ports. A system of valves connects and disconnects these ports to high-pressure brine line coming from RO modules, brine discharge line, low-pressure feed water line, and high-pressure feed water line going to the RO modules. Each pressure cylinder performs a two-stroke cycle whereby the energy of the high-pressure brine is transferred to the stream of feed water. The resulting low-pressure brine is discharged. 
   At the first stroke, the brine port is connected to the brine discharge line while the feed water port is connected to the low-pressure feed water line. The vessel is filled with low-pressure feed water which displaces the plunger towards the brine port and brine is discharged through the non-pressurized discharge line. 
   At the second stroke, the brine port is connected to the high-pressure brine line, while the feed port is connected to the high-pressure feed water line. The vessel is filled with high-pressure brine which displaces the plunger back towards the feed port so as to squeeze feed water into the high-pressure feed water line. 
   The operation of the work exchanger requires special timing, reliable synchronization and sealing of the valves in order to perform efficiently the above two-stroke cycle. 
   A report on experimental work “A Flow Work Exchanger for Desalination Processes”, Kansas state Univ., Manhattan, August 1968, discloses usage of pilot-operated Hunt double plunger hydraulic valve with a work exchanger. This valve has a housing with two parallel cylinder bores and four lateral ports opening into the bores. Two rigidly connected parallel plungers are movable in the bores, providing communication between the ports through specially formed channels and cavities in plunger bodies. The plungers are always in hydrostatic balance. 
   U.S. Pat. No. 5,306,428 to Tonner discloses a rotary valve used to direct brine to/from different work exchanger ports. The feed water stream is regulated by two check valves at each feed water port. The rotary valve of Tonner is not hydraulically balanced, which causes excessive wear on the sealing surfaces due to side loads exerted on the central rotating assembly. There are also internal and external leakage problems between the high pressure inlet and outlet ports and the low pressure drain ports. This, in turn, reduces the efficiency of the Tonner valve and imposes size limits on any such device that can be manufactured in practice. 
   U.S. Pat. No. 5,797,429 to Shumway suggests the usage of a five-way or four-way linear spool valve in a work exchanger system. The Shumway valve comprises two pistons connected by a rod (spool) located inside a cylinder. The cylinder has five ports: a high pressure brine inlet, a first work exchanger vessel port, a second work exchanger vessel port, and two low-pressure brine discharge outlets which may be connected. By moving the spool back and forth within the cylinder, the work exchanger ports are alternately opened and closed, and this directs flow in the proper sequence to the proper port. The feed water stream in the Shumway work-exchanger system is regulated by two check valves at the feed water port of each exchanger vessel. 
   The linear spool valve of Shumway is hydraulically balanced axially. As a result, the force required to move the linear spool is only that force needed to overcome the friction of the sealing surfaces associated with the pistons, which permits the driving device of the valve to be of low power. However, the Shumway valve has also leakage problems. The attempts to reduce leakage by tighter fitting of the pistons to the cylinder lead to excessive wear which seems to be an inherent problem in every spool valve device because the sealing in spool valves is not provided by positive displacement. This problem is even more aggravated in work exchangers of large capacity and power that are employed in modern desalination plants using RO technology. 
   Poppet valves have relatively simple design and provide very reliable sealing achieved by positive displacement. A typical three-way poppet valve comprises a valve chamber with a central port and two coaxial valve seats leading to two end ports, and a poppet body disposed in the valve chamber. The poppet body is adapted for reciprocation between two positions so that in a first position it seals the first valve seat and fluid communication is provided between one end port and the central port, and in a second position the poppet body seals the second valve seat and fluid communication is provided between the other end port and the central port. However, during the travel between the valve seats, the poppet body allows fluid communication between all three ports. The poppet valve also shuts-off and opens abruptly which may cause water hammer, and is not hydraulically balanced. 
   SUMMARY OF THE INVENTION 
   According to the present invention, there is provided a three-way two-position poppet valve comprising a housing with a first port, a second port, a third working port and a generally cylindrical valve chamber with an axis. The valve chamber is defined between a first coaxial annular valve seat associated with the first port, and a second coaxial annular valve seat associated with the second port. The working port is connected laterally to the valve chamber. The poppet valve further comprises a poppet body disposed in the valve chamber and adapted for reciprocation between two positions so that in a first position the poppet body seals the first valve seat and fluid communication is provided between the second port and the working port, and in a second position the poppet body seals the second valve seat and fluid communication is provided between the first port and the working port. 
   The valve is characterized in that the housing has a first coaxial cylindrical passage adjacent the first valve seat and a second coaxial cylindrical passage adjacent the second valve seat, while the poppet body has a first coaxial cylinder part slidingly and sealingly fitting the first passage, and a second coaxial cylinder part slidingly and sealingly fitting the second passage, so that the poppet body is always supported in at least one of the cylindrical passages and fluid communication between the first and the second ports is always prevented. The cylindrical passages and the cylinder parts of the poppet body preferably have the same diameter D. 
   In one embodiment of the three-way valve, the first valve seat is at a distal end of the first cylindrical passage, adjacent the first port, and a distal end of the first cylinder part of the poppet is equipped with a first sealing rim matching the first valve seat. Preferably, the first cylindrical passage has a proximal part flaring towards the poppet body so that the first cylinder part of the poppet body would smoothly change the flow through the first port and the pressure in the valve chamber when entering or exiting the first cylinder passage. 
   The second valve seat is at a proximal end of the second cylindrical passage, adjacent the valve chamber, and a proximal end of the second cylinder part of the poppet is equipped with a second sealing rim matching the second valve seat. Preferably, said poppet body further comprises a profiled part adjacent to the distal end of the second cylinder part, so that the profiled part would smoothly change the flow through the second port and the pressure in the valve chamber when entering or exiting the second cylinder passage. 
   The profiled part has a shape adapted to change flow section area of the second valve seat as a predetermined function of time for a given velocity of the poppet body axial movement. Preferably, the profiled part comprises a shallow straight cylinder step adjacent to the distal end of the second cylinder part, the cylinder step having radial depth and axial length such that, after the second cylinder part leaves the second cylinder passage, pressures in the second port and in the working port are equalized in a predetermined finite time for a given velocity of the poppet body axial movement. 
   In another embodiment of the three-way poppet valve, the second port is disposed laterally to the axis and the housing further comprises an auxiliary coaxial cylinder chamber of diameter D communicating at a proximal end thereof with the second port and the second cylindrical passage, and closed at a distal end thereof by a lid. An auxiliary piston is mounted for sliding in the auxiliary chamber and is firmly connected to the poppet body by an axial rod. The auxiliary piston, the axial rod and the poppet body form a poppet assembly which is axially balanced with respect to flow pressure in the second port. 
   The auxiliary piston sealingly fits the auxiliary cylinder chamber, thereby defining a sealed volume between the lid and the auxiliary piston. Preferably, the sealed volume is provided with fluid communication to the first port, so that pressures acting on the poppet assembly from the sealed volume and from the first port are equalized. The fluid communication may be provided by an external pipe connecting the sealed volume to the first port or by a channel made in the rod. 
   According to another aspect of the present invention, there is provided a work exchanger module adapted to utilize the energy of high-pressure working fluid for pumping feed fluid, comprising an exchanger cylinder with a first working fluid end and a second feed fluid end, and a piston freely sliding therebetween. A first three-way poppet valve as above is connected by its working port to the first end of the exchanger cylinder, by its second port to a source of high-pressure working fluid and by its firs port to a non-pressurized discharge outlet. A second three-way poppet valve is connected by its working port to the second end, by its first port to a source of low-pressure feed fluid and by its second port to a high-pressure feed fluid consumer. 
   According to yet another aspect of the present invention, the two poppet valves of the above work exchanger module are equipped with a first and a second hydraulic cylinder, each having a “push” and a “pull” port, such that connecting the “push” port to a pressure source would drive the associated poppet valve to the first position thereof and vice-versa, wherein the “push” port of the first hydraulic cylinder is connected directly to the “pull” port of the second hydraulic cylinder. Thereby, the reciprocating motions of the two poppet valves are fully synchronized. 
   Preferably, for such synchronized motion, the flaring part of the first cylindrical passage in the first three-way poppet valve is axially longer than the corresponding flaring part in the second three-way poppet valve, so that when the two poppet bodies move towards opening the first port in both three-way valves, the first port in the first valve is connected to the exchanger cylinder before the first port of the second valve. 
   The poppet valve of the present invention provides combined advantages of poppet and spool valves: reliable sealing of the ports, avoiding mixing of flows and leakages, controlled shut-off and opening of the flow passages and preventing water-hammer, axially balanced poppet assembly allowing low-power drives, reduced use of expensive materials, robust construction and low production costs. 
   The three-way poppet valve of the present invention is advantageously used in energy recovery plants of RO installations of large capacity. It allows constructing of large work exchanger units where a number of exchanger cylinders are connected in parallel to one poppet valve. Opposite-phase operation of two work exchangers, which is necessary in such energy recovery plant, can be effectively synchronized by designing the profile of the poppets such that while one valve opens its high-pressure brine port and the other valve closes its high-pressure brine port, the total sectional area of the high-pressure brine flow remains constant. 
   The three-way poppet valve of the present invention, with the hydraulic drive, can be advantageously used also at the feed water end of the work exchangers, instead of two check valves. Thus, with no springs or other elastic elements used in valve motion, arbitrary closing/opening or “hesitation” of the valves is avoided, as well as noise and “water hammer”. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic cross-sectional elevation of a three-way balanced poppet valve of the present invention, in a first extreme position of the poppet. 
       FIG. 2  is a schematic cross-sectional elevation of the three-way balanced poppet valve of  FIG. 1  in a second extreme position of the poppet. 
       FIG. 3  is a schematic cross-sectional elevation of a work-exchanger module equipped with two three-way poppet valves of the present invention. 
       FIG. 4  is a scheme of a RO desalination plant with energy recovery plant comprising the work exchanger of  FIG. 3 . 
       FIGS. 5A and 5B  show alternative embodiments of the three-way poppet valve of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIGS. 1 and 2 , there is shown a three-way, two-position poppet valve  10  comprising a housing  12  with a generally cylindrical valve chamber  14 , a first (outlet) port  20 , a second (inlet) port  16 , a third (working) port  18 , and a poppet assembly  22 . The valve chamber  14  has a coaxial cylinder passage  24  of diameter D towards the inlet port  16 . The cylindrical passage  24  comprises a first valve seat  26  of diameter D disposed at the distal end thereof, in communication with the axial outlet port  20 , and a flaring annular part  27  at the proximal end. A second annular valve seat  28  is at the opposite side of the valve chamber  14 , communicating with the inlet port  16 . The working port  18 , which is disposed laterally between the valve seats  26  and  28 , is directly communicating with the valve chamber  14 . A coaxial cylinder passage  30  of diameter D is provided between the valve seat  28  and the inlet port  16 . The housing  12  further has an auxiliary coaxial cylinder chamber  32  of diameter D adjacent to and communicating with the inlet port  16 , the auxiliary chamber being closed by a lid  34 . It should be noted that the first port  20  and the second port  16  are named here“outlet” and “inlet” just for convenience while either of them can be inlet or outlet. 
   The poppet assembly  22  comprises a poppet body  36  with an axial stem  38  and an auxiliary piston  40 . The poppet body  36  comprises a metal dish  42  fixed to the stem  38  and having a sealing rim with an annular seal  44 , a first cylinder body  46  with a metal sealing ring  52 , and a second cylinder body  48  with a profiled, generally tapering, extremity  50 . Both the flaring part  27  and the extremity  50  profile are designed for obtaining smooth flow at opening and closing the first and the second port, respectively. Their particular form depends on the application of the valve as will be explained below. The cylinder bodies  46  and  48  fit slidingly and sealingly into the cylindrical passages  24  and  30 , respectively. The auxiliary piston  40  fits sealingly into the auxiliary chamber  32 , thereby defining a balancing pressure chamber  54  between the piston  40  and the lid  34 . The pressure chamber  54  is in fluid communication with the outlet port  20  via a pipe  56  (shown in  FIG. 1 ) or, alternatively, via a channel  58  obtained through the stem  38  (shown in  FIG. 2 ). The axial stem  38  extends, with a sealing sliding fit, through an opening in the lid  34  and is connected to an external hydraulic cylinder  60 . 
   In operation, the hydraulic cylinder  60  reciprocates the poppet assembly  22  between two extreme positions: in a first position (shown in  FIG. 2 ), the first valve seat  26  is sealed by the sealing ring  52  and fluid communication is provided between the second (inlet) port  16  and the working port  18  under pressure P 2 ; and in a second position (shown in  FIG. 1 ), the second valve seat  28  is sealed by the sealing rim  44  and fluid communication is provided between the working port  18  and the first (outlet) port  20  under pressure P 1 . 
   During the reciprocating motion, the poppet assembly  22  is supported by the cylinder bodies  46  and  48  sliding in the cylinder passages  24  and  30 . The axial lengths of the cylinder bodies and the cylinder passages are selected so that cylinder passages  24  and  30  are never opened simultaneously and thus flows via the first port  20  and the second port  16  are not mixed. These axial lengths may be further varied if necessary for adjusting the valve operation cycle (timing) to the working cycle of a machine where the valve is used. 
   The profiled extremity  50  of the poppet body has a shape adapted to change flow section area of the second valve seat  28  as a predetermined function of time for a given velocity of the poppet body axial movement. For example, if two valves  10  are used with two work exchange cylinders operating in opposite phase (see  FIG. 4 , valves  80  and  80 ′), the extremities of their respective poppet bodies may be shaped so that when one valve opens its second port and the other valve closes its second port, the total sectional area of the flow through these second ports remains constant. 
   The profile of the extremity  50  has a shallow straight cylinder step  51  adjacent to the second cylinder body  48 , with depth d and axial length l. These dimensions are selected such that, when the second cylinder body  48  leaves the second cylinder passage  30  opening it, pressures in the second port  16  and in the working port  18  are equalized to P 2  in a predetermined finite time for a given velocity of the poppet body axial movement. This timing is necessary in order to avoid occurring of “water hammer”. It will be appreciated that particular dimensions of the step  51  depend also on the pressure differential between ports  16  and  18  before opening of the valve seat  28 , on the volume of a fluid container filled through the working port  18 , and on the elastic properties of this container, the associated piping, and of the fluid. For example (see  FIG. 3 ), a work exchanger vessel  72  of volume V connected to a poppet valve  80  may operate under high pressure P 2 =70-80 ata and expand its volume by ΔV when exposed to such pressure. The vessel  72 , the water therein, and the connecting piping therearound constitute an elastic oscillating system characterized by basic natural frequency f or period T. Thus, it is desirable to feed the volume of water ΔV into the vessel, under the pressure P 2 , after the valve seat  28  is opened, for a time equal or longer than half the period T. This time can be attained by selecting the depth d and the axial length l of the step  51 . 
   With reference to  FIG. 2 , in the first extreme position of the poppet, axial forces applied to the poppet assembly  22  from the pressure P 2  within the assembly are mutually balanced, since the chamber  32  and the passage  24  have the same diameter D. These forces are balanced during the whole travel of the poppet assembly towards the second extreme position and in the second position ( FIG. 1 ). 
   The axial pressures acting from the balancing pressure chamber  54  onto the piston  40  and from the outlet port  20  onto the cylinder body  46  are both equal to P 1  due to the fluid communication  56  (or  58 ) that transmits the pressure of the outlet port  20  to the chamber  54 . However in the first position ( FIG. 2 ), the area of the poppet body exposed to the axial pressure P 1  in the valve seat  26  is slightly less than πD 2 /4 because the annular seal contact surface has finite width extending inside of the diameter D. (This width can be minimized by the channel  53  in the sealing ring  52 ). Conversely, in the second position ( FIG. 1 ), the area of the poppet body exposed to pressure P 1  in the valve seat  28  is slightly more than πD 2 /4 because the annular contact surface of the seal  44  has finite width extending outside of the diameter D. Between the extreme positions, the area of the poppet body exposed to the axial pressure P 1  from the outlet port  20  is equal to πD 2 /4. The area of the piston  40  exposed to pressure P 1  is also less than πD 2 /4 by the area of the rod  38  cross-section. 
   The above balancing scheme is especially advantageous for use with the pressure in the second port much higher than the pressure in the first port (P 2 &gt;&gt;P 1 ) since all unbalance due to differences of areas is associated with the lower pressure. Thus, the construction of the three-way poppet valve of the present invention allows the poppet assembly to be reciprocated without overcoming pressure differentials of the inlet and outlet flows, while the constant diameter D facilitates working and finishing of the bores  24 ,  30  and  32  in the housing  12 . 
   With reference to  FIGS. 3 and 4 , there are shown two identical work exchanger modules  70  and  70 ′ used in a power recovery system  62  connected to a reverse osmosis desalination plant  64  (RO plant). The power recovery system  62  utilizes the energy of high-pressure brine for pumping feed water to the RO plant. 
   The module  70  comprises an exchanger cylinder  72  with a brine port  74  at one end, a feed water port  76  at the second end, and a plunger  78  freely sliding between the ports. The module  70  is equipped with two three-way poppet valves, as described in relation to  FIGS. 1 and 2 . The first three-way poppet valve  80  is connected by its working port  82  to the brine port  74 , by its second (inlet) port  84  to a high-pressure brine line  86  of the RO plant, and by its first (outlet) port  88  to a non-pressurized brine discharge line  89 . The second three-way poppet valve  90  is connected by its working port  92  to the feed water port  76 , by its second (outlet) port  94  to a high-pressure feed line  96  of the RO plant, and by its first (inlet) port  98  to a low-pressure feed line  99 . In the position of the poppet valves  80  and  90  shown in  FIG. 3 , the work exchanger module  70  receives low-pressure feed water and discharges brine. The work exchanger module  70 ′ has its valves  80 ′ and  90 ′ in reverse position where high-pressure brine is fed into the cylinder and pumps high-pressure feed water into the RO plant. 
   With reference only to  FIG. 3 , the first poppet valve  80  has a hydraulic cylinder  100  with ports “pull”  102  and “push”  104 , the second poppet valve  90  has a hydraulic cylinder  110  with ports “pull”  112  and “push”  114 , and the hydraulic cylinders are powered by a hydraulic station  120  with inlet port  122  and outlet port  124 . The “pull” port  102  of the cylinder  100  is connected directly to the “push” port  114  of the other hydraulic cylinder  110 , while the “push” port  104  of the cylinder  100  is connected to the hydraulic station outlet  124  and the “pull” port of the cylinder  110  is connected to the hydraulic station inlet  122 . The line  102 - 114 , which is not connected to the hydraulic station, has means for compensation of leakage  126 . 
   It would be appreciated that in this way the reciprocation of the two poppet valves is synchronized: When high pressure is fed to the hydraulic station outlet  122 , the piston of the cylinder  110  and the poppet valve  90  are pulled to the position of  FIG. 3  while simultaneously the cylinder  100  and the poppet valve  80  are pulled to the same position due to the connection  114 - 102 . The reverse motion is also synchronized. This method of synchronization is suitable for use with sensors (not shown) for measuring position and speed of the plunger  78 . 
   The first three-way poppet valve  80  may have a flaring annular part  87  of the cylindrical passage  24  which is axially longer than the corresponding flaring part  97  in the second poppet valve  90 , so that during synchronized motion of the two poppet bodies towards opening the first ports  88 ,  98  in both three-way valves, the first port  88  in the first valve  80  is connected to the exchanger cylinder  72  before the first port  98  of the second valve  90 . This is done in order to relief the high pressure in the exchanger cylinder  72  from the previous (second) stroke into the brine discharge line  89  (see also  FIG. 4 ) and not into the low-pressure feed line  99 . 
   Although a description of specific embodiments has been presented, it is contemplated that various changes could be made without deviating from the scope of the present invention. For example, the poppet valve of  FIG. 1  could be modified as shown in  FIGS. 5A and 5B . In  FIG. 5A , a three-way poppet valve  130  has a cylinder passage  24 ′ at the axial outlet  20  designed symmetrically to the cylinder passage  30 , with a valve seat  26 ′ similar to the valve seat  28  (see  FIG. 1 ). The poppet body  36 ′ in this case has symmetrical form with a cylindrical body  46 ′ complemented by a profiled extremity  50 ′, and a sealing rim  52 ′ similar to the rim  44 . Alternatively, as shown in  FIG. 5B , a three-way poppet valve  140  may have a cylinder passage  30 ′ designed symmetrically to the cylinder passage  24 , with valve seat  28 ′ at the distal end of the passage  30 ′, and a flaring annular part  27 ′ at the proximal end. The poppet body  36 ″ in this case is a symmetrical cylinder without profiled extremities. The second sealing rim  44 ′ is similar to the sealing rim  52 . These valve variations, however, can not be balanced completely with respect to either pressure P 2  or P 1 .