Abstract:
A valve is formed to resist snap-action closure forces and provides a smooth closing action to minimize or eliminate water hammer. The valve is opened and closed by modulating the relative air pressures above and below a piston in the valve. Because the air pressures above and below the piston produce partially offsetting forces on the piston, the net closure force on the valve plunger is limited, and the rate of valve closure is reduced enough to achieve the effect of minimizing water hammer. A separate vent port volume may vent to atmosphere to further limit valve closure speed, and to further reduce water hammer. The valve can provide the capability to control the flow of fluids over a wide temperature range over a long service life while reducing or eliminating water hammer. The valve is well suited for use in injection mold temperature control systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of application Ser. No. 10/235,283, filed Sep. 5, 2002, the disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to plastics injection mold temperature control systems and to valves capable of controlling the flow of coolant in an injection mold temperature control system.  
       BACKGROUND OF THE INVENTION  
       [0003]     The flow of coolant (typically water) through the mold of plastics injection molding systems requires valves capable of rapidly controlling fluid flow over a wide temperature range. Injection molding is a well-known process which may be used for the fabrication of complexly-shaped plastic (or metal) parts. In the injection molding process, a molten plastic material is introduced into a mold and allowed to set or cure by cooling. Once the plastic is set or cured, the mold is opened, and the molded part is released. The temperature of the injection mold is preferably controlled so that the mold is at the proper temperature when the mold material is injected into the mold such that the object formed in the mold is set or cured at a rate that maintains the quality of the molded object while minimizing the setting or curing time to maximize production rates. Initially, an injection mold should be brought up to a steady-state operating temperature that is ideal for the particular molding operation. This can be achieved at start-up by, for example, forming a few scrap parts using heat from the liquid plastic to warm the mold or introducing heated water into channels within the mold. As hot molten material is injected into a mold, the mold absorbs heat from the molten material which must be removed from the mold to maintain the mold temperature within the ideal operating range. If heat is not removed at a sufficient rate, the mold temperature will tend to increase as a series of objects are successively molded. Mold temperature regulation is therefore generally desirable to maintain the temperature of an injection mold, both to minimize shrinkage and distortion during the setting or curing process and to ensure uniformity among a series of molded objects in a production run. Temperature control of an injection mold is typically accomplished by circulating cooling fluid through channels fashioned in the walls of the mold. The temperature of the mold initially increases upon the introduction of the hot molten material, but is restored to the desired operating temperature by the circulation of the cooling fluid through the channels in the mold. More precise control may be achieved through the use of multiple channels to circulate coolant through multiple zones in the mold.  
         [0004]     Methods and devices for controlling the temperature of a fluid-cooled injection mold without the need for a continuous flow of cooling fluid are described in U.S. Pat. Nos. 4,354,812 and 4,420,446 to Horst K. Wieder. These patents describe methods by which an injection mold can be maintained at a desired operating temperature using a cooling fluid. Accurate control of the temperature of an injection mold can be achieved by mounting a temperature sensor onto or within the mold and using valves to control the flow of coolant based on the sensed mold temperature.  
         [0005]     Water or petroleum based cooling fluids are commonly used for heat transfer in injection molding systems. A high-temperature injection molding process may involve normal mold temperatures in excess of 300° F., with molten material injected into the mold typically at a much higher temperature, e.g., 700° F., or higher. It is therefore necessary that the elements that carry the heat transfer fluids be capable of reliable service when exposed to fluids within these temperature ranges.  
         [0006]     Controlling the flow of pressurized high-temperature fluids such as, for example, water, demands rugged valve construction. This is particularly true where long valve service life is required. Such valve design can be made even more demanding in applications in which the valve must also control large flow rates of fluids having wide temperature ranges. Such high-capacity valves may also be subject to the effects of water hammer when they close rapidly.  
         [0007]     The operation of valves controlling the flow of pressurized heat transfer fluids will often lead to water hammer effects. Water hammer is a phenomenon related to the back pressure wave that results from an abrupt change in the flow rate of a fluid. The back pressure wave travels from the point where the flow was interrupted back towards the source of the flow. This can stress and damage hoses, pipes, joints, pumps and seals throughout the fluid system. Since the fluid is often pressurized within the system, leaks can result and lead to damage to equipment, controls, materials, and people in the area, in addition to causing costly down-time.  
         [0008]     Water hammer is often dealt with by suppression measures that include such things as adding check valves or risers to limit or attenuate the back pressure wave, or to confine it to a particular area of the fluid system. However, these suppression devices, in addition to increasing cost, size, and weight, often introduce additional seals that must be maintained. Furthermore, over time, the gas in a riser dissolves into the fluid; consequently, the use of risers requires that the system be drained on a routine basis to maintain its water hammer suppression capability. Other mitigation techniques include increasing the pipe diameter to reduce the fluid flow velocity; however, such mitigation suppression techniques can add significant cost and require extra space.  
         [0009]     Rapid valve closure can directly cause water hammer. Within a typical valve controlling a pressurized fluid flow, the plunger naturally tends to snap shut. As the plunger closes, fluid flow becomes restricted; but, before flow is entirely shut off, the velocity of the fluid around the plunger increases, causing a corresponding decrease in pressure that naturally leads to an accelerating closure force on the plunger. The resulting snap action tends to decrease the time it takes to interrupt the fluid flow, and it tends to produce a sharp step-like reflected pressure wave, i.e., water hammer.  
       SUMMARY OF THE INVENTION  
       [0010]     In accordance with the present invention, a valve for control of coolant provides the capability of controlling the flow of cooling fluids over a wide temperature range and exhibits long service life while reducing or eliminating the production of water hammer. Furthermore, a distribution system including a plurality of valves in accordance with the present invention can be advantageously used in a plastics injection mold temperature control system which is capable of controlling heat transfer fluids to regulate the temperature of a plurality of channels in a mold. A controller can be used to operate such valves by using high and low pressurization states.  
         [0011]     Use of the fluid control valve of the invention with reduced water hammer is particularly advantageous in complex pressurized hydraulic systems such as injection molding systems. By reducing water hammer, the mean time between failure of components in the pressurized fluid supply lines, including valves, seals, and pumps, can be increased. The valves themselves will have increased service life because of the elimination or reduction of water hammer. The benefits include cost recovery accruing from reduced maintenance, extended service life, and increased operational production throughput time. Further, the suppression methods typically employed for reducing water hammer, as discussed above, can be minimized or eliminated. In addition to avoiding the creation of water hammer, the valve of the present invention can be ruggedly designed for high capacity and long service life while controlling pressurized fluids, such as water, at high-temperatures and high flow rates.  
         [0012]     The valve of the invention is constructed to resist snap-action closure force, and provides a smooth closing action that can minimize or eliminate water hammer. The valve is opened and closed by modulating the relative air pressures above and below a control piston that is connected to operate a plunger. By providing nearly offsetting forces above and below the control piston to transition from open to closed, the net closure force on the plunger is limited such that the velocity and acceleration of the plunger are small enough to achieve the desired effect of minimizing water hammer.  
         [0013]     In a preferred embodiment of the valve of the invention, the control piston and two slideable seals define three independent volumes of air in a piston chamber: an upper piston volume, connectable via an upper pressure port to a first air pressure line; a lower piston volume, connectable via a lower pressure port to a second air pressure line; and a vent port volume having a vent port. The vent port can be open to ambient air during the steady-state time between transitions so that the vent port volume reaches ambient pressure. In a preferred embodiment of the invention, the vent port volume pressure experiences transient increases due to the use of a flow restrictor that may be attached to the vent port. When the vent port restrictor is used, the vent port volume pressure acts to resist piston movement, thereby resulting in reduced acceleration and velocity of valve plunger transitions. During the steady-state time between transitions, the vent port restrictor permits pressure in the vent port volume to equalize to ambient air pressure.  
         [0014]     In addition, having a vent port in the valve body which can be open to the ambient atmosphere provides the ability to detect leaks within the valve, such as from worn out shaft seals around the valve stem. Leaks in such seals may be detected by observing liquid leaking from the vent port and accumulating, for example, in a drip pan. In a further preferred embodiment, a hose can be attached to the vent port such that the leaking fluid can be directed to a convenient collection point. This capability is valuable because it enables simple and low-cost monitoring of valve shaft seal integrity without unnecessary preventative maintenance and without the need to open the pressure control lines to look for evidence of leaks.  
         [0015]     In one preferred embodiment, the upper pressure port and the lower pressure port may be supplied from two separate air pressure sources. Alternatively, these two ports may be supplied from the same air pressure source, with one of the pressure ports disconnectable from the pressure source by use of a modulating device such as, for example, a three-way valve. Where such a valve is used, the pressure may be reduced to one port to cause a valve transition from open to closed or vice versa. When activated, such a valve may, for example, release the pressure on one of the pressure ports to ambient air pressure.  
         [0016]     In a preferred embodiment, the valve is normally closed when no pressure is applied. When the valve is closed, the plunger engages a valve seat and seals a hydraulic inlet port from a hydraulic outlet port such that fluid from the inlet port cannot reach the outlet port. The valve is preferably normally closed when no pressure is applied to either of the two pressure ports or to the hydraulic inlet port because of a piston spring that provides a closing force. The valve will remain closed until pressurized fluid from the hydraulic inlet port overcomes the pressure exerted by the piston spring. When pressure is applied to the two pressure ports, an additional closing force is applied because the area of the top of the piston exposed to the upper piston volume is preferably greater than the area of the bottom of the piston exposed to the lower piston volume, thereby producing a net downward force on the piston and on the plunger connected thereto. The valve carries out a transition from closed to open, for example, when the relative pressure in the upper piston chamber is reduced, such as by releasing the pressure in the upper piston volume to ambient pressure level. Resupplying pressure to the upper pressure port will cause the valve to smoothly close since the pressure in the lower piston volume will reduce the closure rate. This gradual closure will help prevent the rapid increase in back pressure in the hydraulic line connected to the hydraulic inlet port that could otherwise produce a water hammer effect.  
         [0017]     A cooling fluid distribution system in accordance with the present invention includes a manifold connecting a plurality of the valves. Such a system may have a selected number of such valves. Four valves may be advantageously used in a system such as in an injection mold temperature control system. Preferably, a pair of valves may be operated in coordination such that one of the two valves controls the supply fluid flow to a mold and the second valve controls the return fluid flow from the mold. Furthermore, a plurality of valve pairs may be operated in coordination such that each pair of valves controls fluid flow to a different channel in the mold. Such a plurality of valves in a fluid distribution system simplifies routing and connection of valves to both the air pressure lines and the hydraulic supply and return lines.  
         [0018]     The distribution system may include multiple connected sets of valves, with each set of valves connected to a distribution manifold. Each manifold preferably distributes fluid flow to at least one channel in a mold for the purpose of regulating the temperature of that channel and the adjacent material in the mold. A controller may be utilized to control the state of the valves. Preferably, the controller controls two valves in coordination, such as, for example, by simultaneous actuation of a supply valve and a return valve that together control the flow of a heat transfer fluid to a channel in a mold.  
         [0019]     Water is a preferred hydraulic fluid for controlled mold cooling in accordance with the present invention. The present invention may also be used advantageously to control flow of other fluids, such as petroleum-based oils or synthetic heat transfer fluids.  
         [0020]     Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     In the drawings:  
         [0022]      FIG. 1  is a cross-sectional view of a valve in accordance with the present invention, shown in the closed position.  
         [0023]      FIG. 2  is an illustration of the valve of  FIG. 1  shown connected to a portion of a schematically illustrated hydraulic system and pneumatic control system.  
         [0024]      FIG. 3  is a side cross-sectional view of a section of a dual valve and manifold distribution system for controlling the flow of pressurized fluid from two different sources to a hydraulic mid-point connection. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Referring to the drawings, a valve in accordance with the present invention is shown generally at  10  in cross-section in  FIG. 1 . The valve  10  includes a top housing  12  that is connected to a valve body housing  14 . The valve body housing  14  is further connected to a valve mount  16 , preferably attached using mounting hardware such as, for example, at least one mounting screw  18 . The top housing  12  has internal surfaces defining a piston chamber  20 . In fluid communication with the piston chamber  20  are an upper pressure port  22 , a lower pressure port  24 , and a vent port  26 . The valve body housing  14  and the valve mount  16  have internal surfaces that together define a plunger chamber  28 . The valve mount  16  has a hydraulic inlet port  30  and a hydraulic outlet port  32 .  
         [0026]     A valve plunger  34  is slideably disposed within the plunger chamber  28 . When the valve plunger  34  is in the closed position engaged against a valve seat  35 , pressurized fluid is blocked from flowing from the hydraulic inlet port  30  to the hydraulic outlet port  32  through the central opening  37  of the valve seat  35 . The valve plunger  34  is fixed to one end of a valve stem  36  by a plunger pin  38 . The valve plunger  34 , when actuated from the closed position to the open position, moves upwardly within the plunger chamber  28  in response to net upward force on the valve stem  36 . Opposite the valve plunger  34 , the other end of the valve stem  36  is rigidly attached to a piston  40  that is slideably disposed in the piston chamber  20 . The valve stem  36  is slideably disposed between the plunger chamber  28  and the piston chamber  20  through a valve stem channel  42  defined by the valve body housing  14 . An extended portion of the valve stem channel  44  extends above the bottom surface of the piston chamber  20 , forming a hollow cylindrical member. The piston  40  has internal surfaces defining a corresponding cylindrical walled cup shape, adapted for slideably encompassing the extended portion of the valve stem channel  44  when the piston  40  is downwardly disposed. The valve stem channel  42  is sealed from fluid in the plunger chamber  28  by a spring washer  46  around the opening of the valve stem channel  42  in the plunger chamber  28 , the spring washer  46  being held in place by a piston spring  48  that is preferably under compression and biases the plunger  34  toward its closed position. In addition, the valve stem channel  42  is also guided by shaft bearings  50  disposed around the valve stem  36  substantially along the length of the valve stem channel  42 . These bearings permit the valve stem  36  to slide axially within the valve stem channel  42 . In addition, the valve stem channel  42  is also sealed by at least one, but preferably two, shaft seals  51  disposed around the valve stem  36  at intervals along the length of the valve stem channel  42 . These shaft seals  51  permit the valve stem  36  to slide axially within the valve stem channel  42 , but they prevent fluid in the plunger chamber  28  from passing through the valve stem channel  42  up into vent port volume  56 .  
         [0027]     Within the piston chamber  20 , two slideable seals define with the piston  40  three independently sealed volumes: an upper piston volume  52  above the top surface of the piston  40 ; a lower piston volume  54  below the bottom surface of the piston  40 ; and, a vent port volume  56  below the piston  40  around the valve stem  36  that is separate from the lower piston volume  54 . A piston OD (outer diameter) seal  58  attaches to an inner sidewall of the piston chamber  20  and forms a slideable seal with the outer cup surface of the piston  40 . The OD seal  58  thus separates the upper piston volume  52  from the lower piston volume  54 . A rod quad ring seal  60  attaches to an extended portion of the valve stem channel  44  and forms a slideable seal with the inner cup surface of the piston  40 . The rod quad ring seal  60  thus separates the lower piston volume  54  from the vent port volume  56 .  
         [0028]     The piston  40  actuates the valve stem  36  in response to changes in pressure existing above and below the piston  40 . The upper piston volume  52  is capable of being pressurized through the upper pressure port  22 . The lower piston volume  54  is capable of being pressurized through the lower pressure port  24 . The vent port volume  56  is in fluid communication with the vent port  26 . Each of these ports may have appropriate means for connecting to a pressurized air line. In the case of the vent port  26 , a pressure restriction element may be connected between the vent port volume  56  and ambient air pressure.  
         [0029]     The valve stem  36  is preferably secured to the piston  40  by a stem cap nut  62  that is threaded to the end of the valve stem  36  above the piston  40 , compressing a stem O-ring  64  around the valve stem  36  to the top surface of the piston  40 . Furthermore, two bellow washers  66  mounted around the valve stem  36  may be secured to the top and bottom surfaces of the piston  40 . In a preferred embodiment, a top housing O-ring  68  also seals the threaded interface between the top housing  12  and the valve body housing  14 . In a similar manner, a valve mount O-ring  70  seals the interface between the valve body housing  14  and the valve mount  16 . A plunger seal  72  provides preferably an O-ring type seal when the plunger  34  is in the closed position and the O-ring is engaged against valve seat  35  to form a hydraulic seal.  
         [0030]     With reference to  FIG. 2 , the valve  10  of the present invention resists snap-action closure force and provides smooth closing action that can minimize or eliminate water hammer production. The valve  10  is opened and closed by modulating the relative pressures in the upper piston volume  52  and the lower piston volume  54 . By offsetting the pressures above and below the piston  40 , the net closure force on the valve stem  36  is reduced such that the velocity and acceleration of the valve stem  36  and plunger  34  are small enough to achieve the desired effect of minimizing water hammer. In one embodiment, the upper pressure port  22  and the lower pressure port  24  are supplied from two separate air pressure sources. The separate air pressure sources can consist of, for example, a single pressure source  100 , illustrated schematically in  FIG. 2 , connected to two shut-off valves  102  through separate air pressure lines  106 , each shut-off valve  102  being connected to one of the two pressure ports  22  and  24 . In a preferred embodiment, the two pressure ports may be supplied from the same air pressure source  100 , wherein one of the pressure ports is disconnectable from the pressure source by use of some pressure modulating device, such as, for example, a shut-off valve  102 . Where such shut-off valve is used to alter the pressure applied to one of the pressure ports in order to cause a valve transition, activating the shut-off valve preferably releases the pressure applied to one of the pressure ports to ambient air pressure. Subsequent de-activation of the shut-off valve  102  results in repressurization of the connected pressure port and the return of the valve  10  to its original state.  
         [0031]     Valve transitions occur when a non-zero net force on the valve stem  36  causes the valve stem  36  and connected plunger  34  to displace in an axial direction defined by the major dimension of the valve stem  36 . Pressure in the upper piston volume  52  exerts a force on the top surface of the piston  40  in the downward axial direction (i.e., toward plunger chamber  28 ); similarly, pressure in the lower piston volume  54  and the vent port volume  56  can exert an axial upward (i.e., toward piston chamber  20 ) force on the bottom surface of the piston  40 . The resultant net force on the piston  40  is transmitted to the plunger  34  via the valve stem  36 . If the piston spring  48  is biased under compression, it will exert a downward axial force on the plunger  34 . If a pressurized fluid exerts itself against the bottom surface of the plunger  34  when it is in its closed position, this will provide an axial upward force on the plunger  34 . Axial displacement of the plunger  34  will result from an imbalance in the net axial force exerted on the plunger, including any other forces such as friction, gravity, etc.  
         [0032]     In the preferred embodiment, the valve  10  is normally closed when no pressure is applied to either of the two pressure ports  22  and  24 . However, the present invention may be embodied in a normally open valve design, such as by biasing the piston spring  48  under tension instead of under compression. Nevertheless, with reference to the preferred embodiment, which is a normally closed configuration, the plunger  34  is closed in the absence of pressure on the two pressure ports  22  and  24  or pressure at the hydraulic inlet port  30  because the piston spring  48  is under compression to provide a closing force. The plunger  34  will remain in the closed position until, for example, pressurized fluid from the hydraulic inlet port  30  overcomes the closure force from piston spring  48 . As described above, pressurizing the upper  22  and lower  24  pressure ports equally results in a net downward force on the valve stem  36  because the top surface area of the piston  40  exposed to the upper piston volume  52  is greater than the bottom surface area of the piston  40  exposed to the lower piston volume  54 , the pressure in the vent port volume  56  being preferably at ambient pressure in the steady-state. The bottom surface area of the piston  40  exposed to the unpressurized vent port volume  56  accounts substantially for the difference in surface areas between the pressurized top surface area of the piston  40  and the pressurized bottom surface area of the piston  40 . The top surface area of the piston exposed to the upper piston volume  52  may be several times greater than the bottom surface area of the piston exposed to the lower piston volume  54 , such as four times, for example. The valve  10  may transition from closed to open, for example, when the pressure in the upper piston volume  52  is reduced relative to the pressure in the lower piston volume  54 , such as when pressure in the upper piston volume  52  is vented to ambient pressure level. Reapplying pressure to the upper pressure port  22  will cause the valve  10  to transition back from open to closed.  
         [0033]     The closure transition is smooth when the net closure force on the valve stem  36  is small. The valve  10  in accordance with the invention will close smoothly because the pressure in the lower piston volume  54  provides a counteracting force to resist the closure force. A small closure force produces a more gradual displacement of plunger  34 . Because the plunger  34  only gradually restricts the flow rate from the hydraulic inlet port  30 , snap-action closure does not occur. By resisting a snap-action closure, the valve  10  may reduce or eliminate the generation of water hammer.  
         [0034]     A valve  10  in accordance with the present invention may also include a vent port restriction element  104  (not shown) connected to the vent port  26 . This restriction element  104  may be, for example, a small aperture (flow restrictor) vent or an adjustable restricted flow valve. Without an attached restriction element, the aperture of the vent port  26  may be any suitable diameter for the intended application, such as approximately 0.044 inches, for example. One purpose of the vent port restriction element  104  is to provide ambient pressure in the vent port volume  56  during steady-state, and to provide resistance to the closure force during transitions. This resistance to a closure force during transitions results from restricting air flow out of the vent port volume  56  during a closure transition. As the increasing pressure in the upper piston volume  52  causes the piston  40  to move downwardly, the effective volume of the vent port volume  56  decreases, causing a corresponding air pressure increase. This increased air pressure will equalize with ambient air pressure rapidly unless the vent port  26  includes a pressure restriction element. If a vent port restriction element  104  is provided, then the vent port volume  56  will experience a transient increase in air pressure during the closure transition until the pressure is able to equalize with ambient air pressure through the restriction element  104 . During this transient period, the increased pressure in the vent port volume  56  will exert an upward force on the bottom surface of the piston  40  that opposes its downward movement. This transient upward force opposes the closure force and therefore promotes the desired result of smooth plunger  34  closure.  
         [0035]     In one embodiment of the present invention, the valve  10  may not include a vent port  26  such as may be typically formed by machining or drilling holes into the valve body housing  14 , as shown in  FIG. 1 . Instead, other valve constructions in accordance with the present invention may expose a larger portion of the bottom surface of piston  40  to ambient pressure by having more material removed from the valve body housing  14 . Removing more material may result in less air flow restriction during valve transitions, and thus provide a decreased resistance to valve closure. Under conditions in which the additional upward resistance provided by restricting air flow out of vent port  26  is not necessary to prevent water hammer, at least the vent port  26 , vent port volume  56 , and vent port restriction element  104  may not be necessary to practice the present invention.  
         [0036]     As an alternative to a restriction element on the vent port, an air flow restriction element may be advantageously incorporated into at least one of the air pressure lines  106  connected to the pressure ports  22  and  24 . In a manner similar to the foregoing description, such an airflow restriction element may be arranged to produce a transient reduction in the net closure force on the valve stem  36  and thereby to achieve smooth valve closure. Preferably, such an airflow restriction element permits rapid depressurization of the upper piston volume  52  while preferentially restricting pressurization of the upper piston volume  52 : such asymmetric pressurization can provide for rapid opening transitions while ensuring smooth closure transitions to obtain the desired effect of reduced water hammer. Alternatively, an airflow restriction device that preferentially restricts airflow out of the lower piston volume  54  may obtain similar results.  
         [0037]     In a further embodiment, either with or without the vent port restriction element  104 , the vent port  26  may accept a drain line  108 , e.g., a hose, capable of directing any moisture that accumulates in the vent port volume  56  into a desirable location, such as a drip pan. One advantage of the drain line  108  being connected to the vent port  26  is that it allows the detection of failure of the shaft seals  51  in the valve stem channel  42 . By monitoring the accumulation of fluid in a drip pan placed in a convenient location, imminent failure of the valve  10  may be detected.  
         [0038]     One advantage of the valve of the present invention is the capability to gang a plurality of valves together to control the distribution of fluid flow to or from a channel in a mold, for example. With reference to  FIG. 3 , a plurality of valves  10  in accordance with the present invention may be connected to a manifold  110 . Such a configuration may form a portion of a fluid distribution system. Specifically with reference to the exemplary application of an injection mold temperature control system, it may be appreciated that a manifold  110  connected to a plurality of the valves  10  in accordance with the present invention may be configured to supply, for example, a heat transfer fluid, such as water, to a plurality of channels in a mold (not shown). By way of example,  FIG. 3  illustrates a manifold with two valves  10 . This configuration is capable of controlling the supply of hot and cold water to a channel in a mold. In this example, it may be further appreciated that an additional manifold with two valves may optionally control the return of the hot and cold water after it passes through the mold channel.  
         [0039]     A temperature control system using manifolds  110  with a plurality of pairs of valves  10 , each pair of valves  10  as represented in  FIG. 3  preferably capable of controlling the flow of hot and cold water to or from a mold channel, may be extended to regulate the temperature in a plurality of channels (not shown) in an injection mold control system. It is evident that the system of the present invention is not limited to the particular configuration illustrated, but is adaptable to any number of valves.  
         [0040]     A controller to control a valve in accordance with the present invention may be any suitable commercially available process controller capable of operating shut-off valves to regulate a process temperature. Referring back to  FIG. 2 , a controller (not shown) may actuate the valves  10  either directly or indirectly. Using direct control, the controller may distribute air from a pressurized source  100  directly to the appropriate pressure ports of a valve  10  to be controlled. Preferably, at least one air pressure line  106  output of the controller may supply an upper pressure port  22  of a valve  10  so that when the controller disconnects pressure from the pressurized source  100  to the upper pressure port  22 , the valve  10  transitions from closed to open. The pressurized source  100  may connect directly via a pneumatic control line  106  to the lower pressure port  24  such that when the controller distributes pressurized air to the upper pressure port of valve  10 , the upper pressure port  22  and the lower pressure port  24  experience substantially the same pressure such that the valve  10  will transition from open to closed. When the controller disconnects the pressurized source  100  from the upper pressure port  22  and the pressure in the upper piston volume  52  is allowed to vent to ambient pressure, the pressure in the lower piston volume  54  will overcome the reduced pressure in the upper piston volume  52  and produce a transition of valve  10  from closed to open. In this exemplary configuration, the controller may cause adequate depressurization of the upper piston volume  52  by allowing the pressure applied to the upper pressure port  22  to fall to ambient air pressure. However, the pressure in upper piston volume  52  need not fall to ambient to produce a valve transition from closed to open. Depending upon the net force on the valve stem  36 , a transition may occur at a pressure in upper piston volume  52  either above or below ambient air pressure.  
         [0041]     On the other hand, using indirect control, the controller described above may control the state of at least one valve  102  to control the pressurization of piston volumes  52  and  54 . In one embodiment, a valve  102  may be connected between a pressure source  100  and the upper pressure port  22  by air pressure lines  106 , as shown in  FIG. 2 . This valve  102  may be a three-way valve that, in a first state, may permit pressure source  100  to pressurize upper piston volume  52 , and, in a second state, may vent upper piston chamber  52  to ambient pressure, and, in a third state, may block all airflow. Optionally, a similar valve  102  may also be connected between pressure source  100  and the lower pressure port  24  by air pressure lines  106 .  
         [0042]     In a complex system, such as a multiple channel injection mold, water hammer can affect a large number of components via complex interacting mechanisms, and it can thereby lead to an increased probability of system down time. In such a complex system, the cost of down time is magnified by the proportionally larger investment in equipment. A valve in accordance with the present invention can thus save cost and reduce system downtime because the reduced water hammer improves the mean time between failure of the many connected components, including hoses, valves, seals, and pumps in the pressurized hydraulic supply lines. Indeed, the valves themselves realize increased reliability as a result of the reduction or elimination of water hammer. The benefits of this improved system include cost recovery accruing from reduced maintenance, extended service life, and increased productivity.  
         [0043]     As used herein, supply refers to a pressurized source of fluid, typically either hot or cold water. Return refers generally to a low pressure hydraulic sink, such that fluid flows from the supply to the return. The exemplary cold supply and cold return hydraulic lines may be connected to a chiller system. The hot water referred to in the exemplary application may be provided by a pressurized hot water heating system. Also, the valve of the present invention may be controlled using vacuum pressures (below ambient) supplied from a pressure source instead of the conventionally positive (above ambient) pressures described in the exemplary embodiments. Although the exemplary embodiments of the present invention refer to air as the ambient and pneumatic gas for control and operation, other gasses known to those skilled in the art as having properties suitable to control and operate the valve may be appropriately substituted.  
         [0044]     It is understood that the invention is not limited to the particular embodiments described herein, but embraces all such modified forms thereof as come within the scope of the following claims.