EP2616728A1

EP2616728A1 - Pressure compensated valve

Info

Publication number: EP2616728A1
Application number: EP11754423.9A
Authority: EP
Inventors: Roger Studer; Sebastian Gelfert
Original assignee: Norgren GmbH
Current assignee: Norgren GmbH
Priority date: 2010-09-13
Filing date: 2011-09-10
Publication date: 2013-07-24
Also published as: CN103201548B; WO2012034953A1; CN103201548A

Abstract

A valve (200) including a housing (201) and a process fluid supply port (112) formed in the housing (201) to receive a process fluid is provided. The valve (200) includes a piston (202) movable within the housing (201) between an open position and a closed position. The piston (202) includes a first pressure-compensating surface (315) in fluid communication with the process fluid supply port (112) when the piston (202) is in the open position. The piston (202) further includes a second pressure-compensating surface (316) with a first portion (210) in fluid communication with the process fluid supply port (112) when the piston (202) is in the open and the closed position and a second portion (208, 317) in fluid communication with the process fluid supply port (112) when the piston (202) is in the open position.

Description

PRESSURE COMPENSATED VALVE

TECHNICAL FIELD

The present invention relates to, valves, and more particularly, to an improved pressure compensated valve.

BACKGROUND OF THE INVENTION

Blow molding is a generally known process for molding a preform part into a desired product. The preform is in the general shape of a tube with an opening at one end for the introduction of pressurized gas, typically air; however, other fluids may be used. One specific type of blow molding is stretch blow molding (SBM). In SBM applications, a valve block provides both low and high-pressure gas to expand the preform into a mold cavity. The mold cavity comprises the outer shape of the desired product. SBM can be used in a wide variety of applications; however, one of the most widely used applications is in the production of Polyethylene terephthalate (PET) products, such as drinking bottles. Typically, the SBM process uses a low-pressure supply along with a stretch rod that is inserted into the preform to stretch the preform in a longitudinal direction and radially outward and then uses a high-pressure supply to expand the preform into the mold cavity. The low-pressure and high-pressure supply can be controlled using one or more blow-molding valves. The resulting product is generally hollow with an exterior shape conforming to the shape of the mold cavity. The gas in the preform is then exhausted through one or more exhaust valves. This process is repeated during each blow molding cycle.

As can be appreciated, with the high speed of the molding cycle that is currently achievable, even small increases in energy during each molding cycle can result in substantial increases in operating costs. One of the major costs associated with SBM systems and blow molding in general, is the compressed gas used to expand the preform. The amount of gas required and the amount of energy required to pressurize the gas can be significant. Further, due to the high pressures required during both the low-pressure and the high-pressure blowing phases, a significant amount of energy is currently required to operate the blow-molding valves due to the high pilot pressure requirements. Prior art blow-molding valves may be either pilot actuated or electrically actuated, for example. If the blow molding valves are pilot actuated, the valve typically requires a large cross-section for the pilot fluid to act upon or alternatively, a high pilot pressure is required. If the cross-section of the valve is large, the valve's "foot print", i.e. , the area occupied by the valve can significantly increase the overall size of the valve block. Alternatively, if the cross-sectional area of the valve that is acted upon by the pilot pressure is small, a significantly higher pilot pressure is required, resulting in increases in operating costs.

If on the other hand, the blow-molding valve is electrically actuated, such as a solenoid- actuated valve, a strong biasing member, such as a strong spring is required to overcome the blowing process fluid pressure acting on the valve' s sealing surface. As the strength of the spring increases, the energy required by the solenoid to overcome the spring force likewise increases. This increase in energy can significantly increase the operating costs of the valve block.

FIG. 1 shows a cross-sectional view of a portion of a prior art blow molding valve block assembly 100. The valve block assembly 100 includes a valve block housing 101, a valve 102 located within the housing 101, and a stretch rod 103. While only one valve 102 is shown, it should be appreciated that the valve block assembly 100 typically includes more than one valve. Generally, three or more valves similar to the valve 102 are provided in a valve block assembly with a first valve providing the low- pressure supply to the preform, a second valve providing the high-pressure supply to the preform, and a third valve provided to exhaust the preform. In some prior art valve block assemblies, a fourth valve is also provided that recycles a portion of the gas in the molded product during the exhausting phase.

The stretch rod 103 comprises an elongated rod that extends through a stretch rod bore 104 and contacts the preform (not shown) when extended, as is generally known in the art. The position of the stretch rod 103 may be controlled by a separate device (not shown), which is generally known in the SBM industry and is not important for an understanding of the present invention.

Each valve 102 is configured to control the flow of pressurized gas into and/or out of the preform in order to mold the preform and exhaust gas out of the preform at the end of the molding cycle. In order to control the flow of pressurized gas, each valve 102 includes a movable piston 105. The movable piston 105 is located within a control chamber 106. The control chamber 106 is adapted to receive a pilot pressure through a pilot pressure port 107. The pilot pressure acts on the piston 105 to move the piston 105 up as shown in the figure. The control chamber 106 further includes a vent 108 that prevents a vacuum from forming when the piston 105 moves within the control chamber 106.

As shown, the piston 105 further includes a piston rod 109 extending from the piston 105. The piston rod 109 includes a sealing surface 110 adapted to seal against a valve seat 111 formed in the body 101 when the pilot pressure is acting on the piston 105.

With the valve 102 in the open position, as shown in FIG. 1, a process air is supplied through a process air supply port 112. The process air can travel towards an opening 113 formed in the stretch rod 103 in order to communicate with the preform. In other prior art valve block assemblies, the opening 113 may be formed between the stretch rod 103 and the stretch rod channel 104.

In many prior art systems, the process air is supplied to the valve block assembly 100 at pressures of approximately 40 bar (580 psi). With the valve 102 open, the 40 bar pressure acts on substantially the entire sealing surface 110. In one example of a prior art valve, the sealing surface 110 comprises a diameter, d_l5 of approximately 30 mm (1.2 inches) while the piston 105 comprises a diameter, d₂, of approximately 50 mm (2.0 inches). With the 40 bar process fluid acting on the sealing surface 110 a force of greater than 2,827.44 N (635.63 lb_f) is required to close the valve. If the valve is pilot actuated, such as shown, a pilot pressure supplied through the pilot pressure port 107 of approximately 15 bar (218 psi) acting on the piston 105 across the diameter, d₂, is required to close the valve 102. Therefore, not only does the prior art valve 102 occupy a significant amount of space, thus requiring a larger valve block assembly 100, but the prior art valve 102 also requires a relatively high pilot pressure to operate the valve 102. The high pilot pressure is, in part, because the pilot pressure is required to overcome substantially the entire force created by the process air acting on the valve 102. This increased pilot pressure results in a significant increase in the operating costs of the valve block assembly 100. Therefore, there is a need in the art for a valve that can reduce the operating costs associated with the valve block assembly. Further, there is a need in the art for a valve that can reduce the size of a valve block assembly while accommodating the high pressures (40 bar) often associated with blow molding applications. The present invention overcomes these and other problems and an advance in the art is achieved. The present invention provides a pressure-compensated valve that can reduce the area occupied by the valve while simultaneously lowering the required pilot pressure delivered to the control chamber of the valve. SUMMARY OF THE INVENTION

A valve is provided according to an embodiment of the invention. The valve comprises a housing and a process fluid supply port formed in the housing to receive a process fluid. According to an embodiment of the invention, the valve further comprises a piston movable within the housing between an open position and a closed position. According to an embodiment of the invention, the piston includes a first pressure-compensating surface in fluid communication with the process fluid supply port when the piston is in the open position. According to an embodiment of the invention, the piston further includes a second pressure-compensating surface with a first portion in fluid communication with the process fluid supply port when the piston is in the open and the closed position and a second portion in fluid communication with the process fluid supply port when the piston is in the open position.

A method for operating a valve including a piston with first and second pressure- compensating surfaces and movable within a housing between an open position and a closed position is provided according to an embodiment of the invention. According to an embodiment of the invention, the method comprises a step of supplying a pressurized process fluid to a first portion of the second pressure-compensating surface to actuate the piston from the closed position towards the open position. According to an embodiment of the invention, the method further comprises a step of supplying the pressurized process fluid to the first pressure-compensating surface to provide a biasing force on the piston towards the closed position. According to an embodiment of the invention, the method further comprises a step of supplying the pressurized fluid to the first portion and to a second portion of the second pressure-compensating surface of the piston to provide a biasing force on the piston towards the open position, wherein the biasing force on the second pressure-compensating surface is greater than the biasing force on the first pressure-compensating surface to retain the piston in the open position. ASPECTS

According to an aspect of the invention, a valve comprises:

a housing;

a process fluid supply port formed in the housing to receive a process fluid;

a piston movable within the housing between an open position and a closed position and including:

a first pressure-compensating surface in fluid communication with the process fluid supply port when the piston is in the open position; and

a second pressure-compensating surface with a first portion in fluid communication with the process fluid supply port when the piston is in the open and the closed position and a second portion in fluid communication with the process fluid supply port when the piston is in the open position.

Preferably, the first portion of the second pressure-compensating surface comprises a pressure-actuating lip.

Preferably, the second portion of the second pressure-compensating surface comprises a valve sealing surface and a sloped surface.

Preferably, the valve further comprises a valve seal base coupled to the housing and including a portion surrounded by the piston.

Preferably, the valve seal base comprises a valve seat configured to form a substantially fluid tight seal with a piston sealing surface formed on the piston when the piston is in the closed position.

Preferably, the valve further comprises a control chamber defined by the housing and the piston.

Preferably, the valve further comprises a pilot pressure port formed in the housing and in fluid communication with the control chamber. Preferably, the valve further comprises a pressure-compensating chamber in fluid communication with a process fluid outlet and in fluid communication with the process fluid port when the piston is in the open position.

Preferably, process fluid pressure within the pressure-compensating chamber provides a biasing force on the first pressure-compensating surface in a first direction and provides a biasing force on the second pressure-compensating surface in a second direction substantially opposite the first direction.

Preferably, the housing comprises a portion of a housing for a blow molding valve block assembly.

According to another aspect of the invention, a method for operating a valve including a piston with first and second pressure-compensating surfaces and movable within a housing between an open position and a closed position comprises steps of: supplying a pressurized process fluid to a first portion of the second pressure- compensating surface to actuate the piston from the closed position towards the open position;

supplying the pressurized process fluid to the first pressure-compensating surface to provide a biasing force on the piston towards the closed position; and supplying the pressurized fluid to the first portion and to a second portion of the second pressure-compensating surface of the piston to provide a biasing force on the piston towards the open position, wherein the biasing force on the second pressure-compensating surface is greater than the biasing force on the first pressure-compensating surface to retain the piston in the open position.

Preferably, the method further comprises a step of pressurizing a control chamber to a threshold pressure to actuate the piston to the closed position.

Preferably, the method further comprises a step of supplying the process fluid to a preform when the piston is in the open position. Preferably, the method further comprises a step of forming a substantially fluid tight seal between a valve sealing surface of the piston and a valve seat when the piston is in the closed position. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a portion of a prior art blow molding valve block.

FIG. 2 shows a cross-sectional view of a valve according to an embodiment of the invention.

FIG. 3 shows a cross-sectional view of the valve according to another embodiment of the invention.

FIG. 4 shows a cross-sectional view of a portion of a blow molding valve block with the valve according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 - 4 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 2 shows a cross-sectional view of a valve 200 according to an embodiment of the invention. According to the discussion below, the valve 200 may be adapted to operate with a valve block assembly for a blow molding system, such as the valve block assembly 400 shown in FIG. 4 incorporated into a SBM system. Therefore, the valve 200 may be provided to improve upon the valve 102 provided in FIG. 1. Consequently, some reference numbers from FIG. 1 are used throughout the remainder of the description to illustrate how the valve 200 may be incorporated into the valve block assembly 400. However, while the valve 200 is discussed as being incorporated into a valve block assembly for a SBM system, such as the valve block assembly 400 shown in FIG. 4, it should be appreciated that the valve 200 may be incorporated in other systems. Therefore, the present invention should not be limited to SBM applications or blow molding applications in general.

According to an embodiment of the invention, the valve 200 comprises a housing 201. It should be appreciated that the housing 201 may comprise a portion of a valve block housing such as shown in FIG. 4 or comprise a separate housing that may be located within the prior art housing 101, for example. Alternatively, the housing 201 may comprise a stand-alone assembly. According to an embodiment of the invention, the valve 200 further includes a piston 202 movable within the housing 201 and a valve seal base 203 coupled to the housing 201 and at least partially surrounded by the piston 202. According to an embodiment of the invention, the piston 202 is movable between a closed position (FIG. 2) and an open position (FIG. 3).

According to the embodiment shown, at least a portion of the valve seal base 203 is also positioned within the housing 201. While the entire valve seal base 203 is shown positioned within the housing 201, it should be appreciated that in other embodiments, a portion of the valve seal base 203 may be located outside of the housing 201. In the embodiment shown, two sealing members 203a, 203b form a substantially fluid tight seal between the valve seal base 203 and the housing 201. It should be appreciated that in other embodiments, one sealing member or more than two sealing members may be provided. As shown in FIG. 2, a portion 250 of the valve seal base 203 extends into the piston 202 and is surrounded by the piston 202. Therefore, the piston 202 can include a generally hollow portion 251 that is adapted to receive the portion 250 of the valve seal base 203.

According to an embodiment of the invention, the valve 200 comprises a control chamber 204. The control chamber 204 may be defined at least in part by the housing 201 and the piston 202. More specifically, the control chamber 204 may be defined at least in part by the housing 201 and a piston face 205 exposed to the control chamber 204. The control chamber 204 can include the pilot pressure port 107, such as seen in FIG. 1. The pilot pressure port 107 is in fluid communication with the piston face 205 of the valve piston 202. Advantageously, when a pilot pressure is supplied from a pilot pressure supply (not shown) to the pilot pressure port 206, the pilot pressure acts on the piston 202 to bias the piston 202 in a first direction, which is up as shown in FIG. 2 towards the closed position. According to an embodiment of the invention, the piston 202 includes a sealing member 215 that forms a substantially fluid tight seal with the housing 201 in order to retain the pilot pressure within the control chamber 204.

It should be appreciated that while the present invention is shown according to one embodiment comprising a pilot-actuated valve, in other embodiments, the valve 200 may be electrically actuated. For example, the piston 202 may be actuated using a solenoid rather than a pilot pressure. Therefore, the present invention should not be limited to pilot- actuated valves.

According to an embodiment of the invention, the housing 201 further comprises a process fluid supply port 112. The process fluid supply port 112 can receive a pressurized process fluid from a process fluid supply (not shown) as explained above for FIG. 1. As discussed above, in some embodiments where the valve 200 is used for a blow molding application, the process fluid may be supplied at pressures up to and exceeding approximately 40 bar. The process fluid is typically air, but may comprise other fluids.

According to an embodiment of the invention, the valve 200 further comprises a pressure-compensating chamber 206, which is in fluid communication with a process fluid outlet 207 and is selectively in fluid communication with the process fluid supply port 112. The process fluid outlet 207 may be in fluid communication with the opening 113 formed in the stretch rod 103, for example (See FIG. 4). Alternatively, the process fluid outlet 207 may lead to another component (not shown) that is selectively provided with the pressurized process fluid by the valve 200.

According to an embodiment of the invention, the piston 202 may be actuated using less force than required to actuate the prior art piston 105. This may result in a lower pilot pressure or less power used if the valve is electrically actuated. In the embodiment shown in FIG. 2, the piston 202 is in a closed position. According to an embodiment of the invention, the piston 202 can be moved to the closed position when the pilot pressure in the control chamber 204 reaches a threshold pressure. In the closed position, a valve sealing surface 208 of the piston 202 forms a fluid tight seal with a valve seat 209 of the valve seal base 203. In the closed position, the process fluid supplied to the process fluid supply port 112 is substantially prevented from reaching the pressure-compensating chamber 206 and the process fluid outlet 207. In some embodiments, the valve sealing surface 208, the valve seat 209, or both may include a suitable sealing material, such as rubber or some other partially compressible material, which may increase the sealing capabilities between the valve sealing surface 208 and the valve seat 209, for example.

According to an embodiment of the invention, the piston 202 further includes a pressure-actuating lip 210. In the embodiment shown in FIG. 2, when the piston 202 is closed, process fluid from the process fluid supply port 112 flows through fluid passageways 211, 212 and acts on the pressure-actuating lip 210. As shown, the pressure-actuating lip 210 extends substantially perpendicular to the movement of the piston 202, which is along a longitudinal axis, L. In other embodiments, the pressure- actuating lip 210 may be formed at an angle with respect to the longitudinal axis, L. With the pressure-actuating lip 210 in fluid communication with the pressurized process fluid even when the piston 202 is closed, the process fluid acts on the pressure-actuating lip 210 thereby providing a biasing force the piston 202 in a second direction, which is substantially opposite the first direction the piston 202 is biased in by the pilot pressure.

As can be appreciated, because the pressure-actuating lip 210 is exposed to the process fluid supply 112 when the piston 202 is in the open and the closed position, the process fluid provides a biasing force on the pressure-actuating lip 210 whenever process fluid is supplied to the port 112. According to an embodiment of the invention, the piston 202 further includes one or more high-pressure sealing members 213 that substantially prevent the high-pressure process fluid from escaping to a vent port 214 formed in the piston 202 and in fluid communication with the vent port 108 formed in the housing 201. The sealing member 213 may comprise an O-ring, a k-ring, etc. The particular sealing member used should not limit the scope of the present invention.

According to an embodiment of the invention, the pressure-actuating lip 210 is sized such that with a piston face 205 having a diameter, D_l5 of approximately 25 mm (0.98 inches), a pilot pressure of less than 10 bar (145 psi) and more preferably, approximately 8 bar (116 psi) can close the valve 200 when the process fluid is at a pressure of approximately 40 bar (580 psi), which is typical in SBM applications. As can be appreciated, the piston face 205 in the present example embodiment comprises a diameter that is half the diameter, d₂, of the piston 105 of the prior art valve 102. Assuming a circular cross-section, this results in a reduction in area occupied by the piston face 205 by a factor of four (4). According to an embodiment of the invention, this reduction in the cross-sectional area of the piston face 205 is possible where the outer diameter of the portion 250 of the valve seal base 203 extending into the piston 202 comprises a diameter, D₂, of approximately 24 mm (0.94 inches) and the pressure- actuating lip 210 comprises an outer diameter, D₃, of approximately 25.5 mm (1.00 inches). As can be appreciated, the space between the diameter D and D₂ results in pressure acting on both the pressure-actuating lip 210 and the sealing member 213. These dimensions result in an effective area of approximately 58.32 mm (0.09 in²) for the 40 bar process fluid pressure to act on when the piston 202 is sealed against the valve seat 209. This results in a force of 233.26 N (52.44 lb_f) in the second direction. Therefore, with the biasing force provided by the process fluid acting on the pressure- actuating lip 210, the valve 200 can operate without the need for a spring or other biasing member to open the valve. Those skilled in the art will readily appreciate that the above-mentioned dimensions and pressures are merely examples and should in no way limit the scope of the present invention.

As can be appreciated, the piston 202 may remain in the closed position until the force on the piston 202 in the first direction drops below a threshold force, i.e., 233.26 N in the present example.

FIG. 3 shows a cross-sectional view of a portion of the valve 200 according to another embodiment of the invention. In the embodiment shown in FIG. 3, the pilot pressure in the control chamber 204 has dropped below the threshold level required to keep the piston 202 in the closed position. Consequently, the piston 202 has moved in the second direction to an open position due to the biasing force provided by the process fluid acting on the pressure-actuating lip 210 and the sealing member 213. In the open position, the piston 202 is unseated from the valve seat 209. The piston 202 may fully open and a protrusion 330 extending from the piston face 205 is resting against a portion of the housing 201 that forms the control chamber 204. In embodiments including the protrusion, the protrusion 330 can prevent the entire piston face 205 from contacting the housing 201, which would decrease the area of the piston face 205 exposed to the pilot pressure to the area of the pilot pressure port 107 when the piston 202 is in the open position. Such a configuration would require a higher pilot pressure to initially move the piston 202 and expose the remainder of the piston face 205 to the pilot pressure. In other embodiments, the piston face 205 may be flat and the protrusion 330 may extend from the housing 201.

According to an embodiment of the invention, when the piston 202 is in the open position, the process fluid outlet 207 and the pressure-compensating chamber 206 are in fluid communication with the process fluid supply port 112. With the process fluid supplied to the pressure-compensating chamber 206, the process fluid acts on first and second pressure-compensating surfaces 315, 316 of the piston 202. As shown, the second pressure-compensating surface 316 includes a first portion comprising the pressure-actuating lip 210. As explained above, the first portion is in fluid communication with the process fluid supply 112 when the piston 202 is in the closed position as well as in the open position.

According to an embodiment of the invention, the first portion of the second pressure-compensating surface 316 may further include the portion of the sealing members 213, 313 exposed to the process fluid. As shown in the figures, when the piston 202 is in the open position, the process fluid will also act on the sealing members 213, 313 to bias the piston 202 in the second direction. In some embodiments, the pressure acting on the sealing members 213, 313 may be neglected due to the relatively small area compared to the remaining area of the second pressure-compensating surface 316. However, with a 40 bar process fluid pressure, it may be desirable to account for the force created by the pressure acting on the sealing members 213, 313.

The second pressure-compensating surface 316 also includes a second portion that is in fluid communication with the process fluid supply 112 when the piston 202 is in the open position. According to an embodiment of the invention, the second portion is substantially sealed off from the process fluid supply 112 when the piston 202 is in the closed position. According to an embodiment of the invention, the second portion of the second pressure-compensating surface 316 comprises the piston sealing surface 208 and a sloped surface 317. It should be appreciated, that in some embodiments, the sloped surface 317 may be omitted and rather, the sealing surface 208 can extend to the end of the piston 202. However, the sloped surface 317 may be provided to help direct the fluid through the pressure-compensating chamber 206 and out of the valve 200 when the piston 202 is in the open position. According to one example embodiment of the invention, the sloped surface 317 is at an angle of approximately 30° with respect to the longitudinal axis, L, of the piston 202. This angle is merely an example and should in no way limit the scope of the present invention.

As can be appreciated, the pressure acting on the first pressure-compensating surface 315 provides a biasing force on the piston 202 in the first direction, which is up (closed) as shown in the figures. Conversely, the process fluid acting on the second pressure-compensating surface 316 provides a biasing force on the piston 202 in the second direction, which is down (open) as shown in the figures. With the pressure acting on the two pressure-compensating surfaces 315, 316 acting in substantially opposite directions, a portion of the biasing forces acting on the piston 202 cancel, i.e., balance resulting in an at least partially pressure-compensated valve. Consequently, with the piston 202 unseated from the valve seat 209, the process fluid pressure provides a relatively small net force acting on the piston 202 compared to the force acting on either of the pressure-compensating surfaces 315, 316. The net force acting on the piston 202 can be determined based on the difference between the surface area of the first and second pressure-compensating surfaces 315, 316.

According to the embodiment shown in the figures, the outer diameter of the first and second pressure-compensating surfaces 315, 316 are substantially equal. However, the area of the pressure-compensating surfaces 315, 316 are different due to the differences between the first diameter, D_l5 of the piston face 205, which is substantially equal to the inner diameter of the first pressure-compensating surface 315 and the second diameter, D₂, of the portion 250 of the valve seal base 203 located within the piston 202, which defines the inner diameter of the second pressure-compensating surface 316. Using the same dimensions in the example illustrated above, in one embodiment, the first diameter, D_l5 is approximately 25 mm (0.98 inches), while the second diameter, D₂, is approximately 24 mm (0.94 inches). Based on this difference, the effective net surface area for the second pressure-compensating surface (area of second pressure-compensating surface 316 minus the area of the first pressure- compensating surface 315) is 38.48 mm² (0.06 in²). The effective net surface area essentially amounts to the area provided by the outer diameter of the piston face 205 (25 mm) minus the area provided by the outer diameter of the portion 250 of the valve seal base 203 extending into the piston 202 (24 mm). The is because the pressure acting on the areas of the first and second pressure-compensating surfaces 315, 316 beyond the diameter of the piston face 205 cancel out.

The effective net surface area assumes that the piston 202 and the portion 250 of the valve seal base 203 extending into the piston 202 comprise circular cross-sections. It should be appreciated that the valve 200 may comprise other cross- sectional shapes. Based on a 40 bar process fluid, the net force acting on the piston 202 provided by the process fluid when the piston 202 is unseated from the valve seat 209 is 153.94 N (34.61 lb_f). According to an embodiment of the invention, with a net force of 153.94 N acting on the piston 202 to bias the piston 202 open, the 8 bar pilot pressure can easily close the valve 200, when desired. As mentioned above, the dimensions and pressures provided are merely examples and should in no way limit the scope of the present invention. Rather, the particular values provided are to aid in the understanding and appreciation of the invention.

FIG. 4 shows a cross-sectional view of a portion of a blow molding valve block 400 according to an embodiment of the invention. The blow molding valve block 400 is similar to the prior art blow molding valve block shown in FIG. 1. Therefore, similar components share the same reference numerals with FIG. 1. The difference between the prior art blow molding valve block 100 and the blow molding valve block 400 of the present invention is the valve 200 that has replaced the prior art valve 102. As shown, the valve 200 receives a process fluid supply from the process fluid supply port 112 formed in the housing 201, which comprises the housing of the valve block 400 in FIG. 4. Further, the process fluid outlet 207 is shown in fluid communication with the opening 113 formed in the stretch rod 103. Therefore, those skilled in the art can readily appreciate that the valve 200 can substantially decrease the energy requirements of operating the valve block 400 compared to the prior art valve block 100. Further, it should be appreciated that while one valve 200 is shown in FIG. 4, in actuality, the valve block 400 may include more than one valve 200. For example, the valve block 400 may include three or four valves as explained above.

In use, the valve 200 may be used to control a pressurized process fluid supply. The process fluid supply may be for a SBM system or some other system requiring a pressurized fluid supply. According to an embodiment of the invention, the valve 200 may be actuated to a closed position by supplying a pilot pressure to the control chamber 204 to pressurize the control chamber 204 to a threshold pressure. With the valve 200 actuated to the closed position, the valve sealing surface 208 forms a substantially fluid tight seal with the valve seat 209. Consequently, the process fluid acts on the first portion of the pressure-compensating surface 316, comprising the pressure-actuating lip 210 and the sealing member 213 and not the entire second pressure-compensating surface 316 to provide a biasing force on the piston 202 in the second direction. Therefore, based on a pilot pressure of 8 bar (116 psi) and a process fluid pressure of 40 bar (580 psi), the piston 202 is biased in the first direction by the pilot pressure with a force of approximately 392.70 N (88.28 lb_f) and in the second direction by the process fluid pressure with a force of approximately 233.26 N (52.44 lb_f). Therefore, the piston sealing surface 208 remains sealed against the valve seat 209 with a net force of 159.44 N (35.84 lb_f).

Once, the pilot pressure is removed or falls below a threshold level, which is approximately 4.75 bar (68.90 psi) based on the above-mentioned dimensions and the 40 bar process fluid pressure, the process fluid acting on the first portion of the second pressure-compensating surface 316 provides sufficient force to move the piston in the second direction (down as shown in the figures) to an open position. As discussed above, in the open position, the protrusion 330 extending from the piston face 205 rests against the housing 201. Advantageously, the pressure-actuating lip 210 substantially eliminates the need for a return spring or the like to move the piston sealing surface 208 away from the valve seat 209.

According to an embodiment of the invention, with the piston 202 moved to the open position, the process fluid can act on the first pressure-compensating surface 315 to provide a biasing force on the piston 202 in the first direction, towards the closed position. The process fluid can also provide a biasing force on the second pressure- compensating surface 316 in the second direction, substantially opposite the first direction. With the biasing force acting on the piston 202 partially compensated, the net force acting on the piston 202 to bias the piston 202 to the open position is approximately 153.94 N (34.61 lb_f) due to the larger surface area of the second pressure- compensating surface 316, as discussed above. To close the valve 200 once again, the control chamber 204 can be pressurized to above the threshold pressure to overcome the net biasing force on the piston 202. The present invention as described above can substantially reduce the size and/or the pilot pressure required to operate the valve 200. The process pressure acting on the piston 202 is advantageously partially compensated by first and second pressure- compensating surfaces that cancel a portion of the force generated by the process fluid. Advantageously, the net force acting on the piston 202 is substantially reduced even when operating in high-pressure environments, such as 40 bar. The present invention further provides a pressure-actuating lip 210 that is in fluid communication with the process fluid when the piston 202 is open as well as closed in order to eliminate the need for a return spring or the like.

The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors to be within the scope of the invention. Indeed, persons skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create further embodiments, and such further embodiments fall within the scope and teachings of the invention. It will also be apparent to those of ordinary skill in the art that the above-described embodiments may be combined in whole or in part to create additional embodiments within the scope and teachings of the invention.

Thus, although specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other valves, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the invention should be determined from the following claims.

Claims

CLAIMS We claim:

1. A valve (200), comprising:

a housing (201);

a process fluid supply port (112) formed in the housing (201) to receive a process fluid;

a piston (202) movable within the housing (201) between an open position and a closed position and including:

a first pressure-compensating surface (315) in fluid communication with the process fluid supply port (112) when the piston (202) is in the open position; and

a second pressure-compensating surface (316) with a first portion (210) in fluid communication with the process fluid supply port (112) when the piston (202) is in the open and the closed position and a second portion (208, 317) in fluid communication with the process fluid supply port (112) when the piston (202) is in the open position.

2. The valve (200) of claim 1, wherein the first portion of the second pressure- compensating surface (315) comprises a pressure-actuating lip (210).

3. The valve (200) of claim 1, wherein the second portion of the second pressure- compensating surface (315) comprises a valve sealing surface (208) and a sloped surface (317).

4. The valve (200) of claim 1, further comprising a valve seal base (203) coupled to the housing (201) and including a portion (250) surrounded by the piston (202).

5. The valve (200) of claim 4, wherein the valve seal base (203) comprises a valve seat (209) configured to form a substantially fluid tight seal with a piston sealing surface (208) formed on the piston (202) when the piston (202) is in the closed position.

6. The valve (200) of claim 1, further comprising a control chamber (204) defined by the housing (201) and the piston (202).

7. The valve (200) of claim 6, further comprising a pilot pressure port (107) formed in the housing (201) and in fluid communication with the control chamber (204).

8. The valve (200) of claim 1, further comprising a pressure-compensating chamber (206) in fluid communication with a process fluid outlet (207) and in fluid communication with the process fluid port (112) when the piston (202) is in the open position.

9. The valve (200) of claim 8, wherein process fluid pressure within the pressure- compensating chamber (206) provides a biasing force on the first pressure- compensating surface (315) in a first direction and provides a biasing force on the second pressure-compensating surface (316) in a second direction substantially opposite the first direction.

10. The valve (200) of claim 1, wherein the housing (201) comprises a portion of a housing for a blow molding valve block assembly (400).

11. A method for operating a valve including a piston with first and second pressure- compensating surfaces and movable within a housing between an open position and a closed position, the method comprising steps of:

supplying a pressurized process fluid to a first portion of the second pressure- compensating surface to actuate the piston from the closed position towards the open position;

12. The method of claim 11, wherein the first portion of the second pressure- compensating surface comprises a pressure-actuating lip.

13. The method of claim 11, wherein the second portion of the second pressure- compensating surface comprises a valve sealing surface and a sloped surface.

14. The method of claim 11, further comprising a step of pressurizing a control chamber to a threshold pressure to actuate the piston to the closed position.

15. The method of claim 11, further comprising a step of supplying the process fluid to a preform when the piston is in the open position.

16. The method of claim 11, further comprising a step of forming a substantially fluid tight seal between a valve sealing surface of the piston and a valve seat when the piston is in the closed position.