Patent Application
20080023918
Pilot-operated valves, such as those set forth in
For better understanding the context of a sealing system applied with such valves, a brief review of the known valves is incorporated herein as follows:
With reference to
In one mode of operation such as for filling the cylinder 6 with gas, when the backpressure passage 17 is closed and in cases where a high supply pressure at the inlet 11,P1 is greater than a low storage pressure in the cylinder 6,P2, the shuttle valve 13 is opened by the differential pressure across the shuttle valve 13 and fluid can reach the cylinder 6,P2. When the backpressure passage 17 is opened to the main flow passage 16, differential pressure across the shuttle valve 13 equalizes and the shuttle valve 13 is biased closed. Without equalization of pressure acting against the backpressure face 33, the differential pressure across the shuttle valve 13 would not be actuable. Equalization occurs because fluid is metered into or out of the backpressure face 33. Fluid is metered from the backpressure face 33 though a bleed orifice 37 formed through the valve body or through the piston itself. As shown, the prior art shuttle piston 20 uses an O-ring seal 39 and the valve 13 uses a plug 38 incorporating the bleed orifice 37. The piston bore 31 intersects the main flow passage 16 at the flow port 35 so that the first shuttle face 32 are subject to the pressurized gas of the second pressure area P2 or cylinder 6. Differential pressure across the O-ring seal 39 causes differential force across the piston 30, urging the piston to open. In the absence of a differential pressure, or at very low differential pressures, a biasing such as a spring 36 urges the piston 30 to the closed position. The fluid at a backpressure side 17 of the piston 30 is controlled to enable formation of a differential pressure thereacross. The bleed orifice 37 enables fluid communication, albeit measured, between backpressure face 17 and the second pressure area P2. The pressure at the backpressure face 17 can be different than either the pressure at the first pressure area P1 or that at the first shuttle face 32.
The prior art O-ring sealing system has disadvantages including a not-insignificant friction in the piston bore 31 and wear. Further, the prior art use of a metal shuttle piston can creates particles and scratches the bore 31 and use of a nitrile based O-ring 39 can wear out after only about 40,000 cycles, limiting the cycle life of the valve. Wear material from the O-ring 39 and the piston 30 can damage other valve components; and the use of a metal ball to seal on a plastic seat requires additional force to prevent leaking. Therefore, a significant spring-biasing force is required to ensure there is no leaking of the system at low cylinder pressures. Further, for equalization; there is a requirement to machine a bleed orifice (−Φ0.16 mm) either through the shuttle piston 30 or the valve 10, such as through the shuttle plug 38, to provide the differential pressure required to displace the shuttle piston 30. Such a strong spring force, combined with the fixed leak rate from the bleed orifice 37, limits the system opening at cylinder pressures lower than 15 bar (gauge) or 15 bar(g) and results in a higher number and cost of components and a need to do sub-assemblies. Some advantages of the current valves include proven operation over a mid-range number of cycles (about 30,000),the significant mass of the piston and a metal ball to flow port seal assembly, and significant spring force combine to reduce the severity of the oscillation of the shuttle system when the cylinder is being filled.
Generally, a sealing system 100 for a shuttle valve 110 is employed in high-pressure valves to allow a reduced amount of gas-flow by a shuttle piston 130 (leak-by) for adjusting differential pressure thereacross.
As shown in
As shown in
With reference to
The annular seal ring 139 is fit to a circumferentially-extending annular piston ring groove 150 formed in an outer periphery of the piston 130. The sealing ring 139 seals against the piston bore 131 and the piston ring groove 150. As shown in
Axial movement of the piston 130 is dictated by fluid dynamics and, in some operations, by biasing of the spring 136. Therefore axially-oriented components of the piston can be described with terms such as high pressure side and low pressure side may alternate as the pressure regime varies.
A leak-by fluid path L, flowing along the annular interface 119 between the piston 130 and the bore 121, is enabled by providing a split 151 through the sealing ring 139. As expected, fluid flows past the leak-by sealing ring 139 from the higher pressure area or upstream to the lower pressure downstream side.
With reference to
Returning to
As set forth above, during reciprocating motion, the sealing ring 139 seals against the piston bore 131 and is typically shifted under fluid pressure from an area of higher pressure to an area of lower pressure. The sealing ring 139 shifts downstream in the groove 150 wherein a downstream sealing side face 171 or 172 engages and seal against a downstream bounding side wall 161 or 162 of the piston groove 150. Without some other means for fluid transmission, fluid upstream of the seal ring is normally constrained from moving downstream past the outer peripheral face 140 by a seal formed at the piston bore 131, and fluid in the groove 150 is constrained from moving downstream further than the inner peripheral face 141 by a seal formed between the side face 171 or 172 of the sealing ring and the side wall 161 or 162 of the groove 150.
For enabling a controlled leak-by flow of fluid FL past the sealing ring 139, the sealing ring is split 151 entirely through its depth D along a cut surface 152 extending between a starting angular location C1 at one side face to a rotated angular location C2 on the other side face and entirely through its annular width W between the outer peripheral sealing face 140 and the inner peripheral face 141. Normally the sealing ring 139 is a unitary ring-shaped body, however the split 151 renders the ring discontinuous with overlapping beveled ends. While appearing generally helical, the cut surface 152 can be a straight cut which is on a plane perpendicular to a tangent, or a truly helical along a plane which rotates about the ring center C. The path of the cut surface 152 may be a two-dimensional plane, or a three-dimensional surface such a helical cut. Some types and methodologies of cutting rings is set forth in U.S. Pat. No. 5,087,057 to Kurkowski, the entirety of which is incorporated herein by reference. A consistent circumferential outer peripheral face 140 is maintained despite the split 151. Care is taken to minimize distortion of the outer peripheral face 140 and of the first and second side faces 171,172 which can occur during formation of the split 151.
With fluid seals formed between the outer peripheral face 140 and piston bore 131, and between the sealing ring's side faces 171 or 172 and groove bounding side walls 161 or 162, applicant believes that the leak-by fluid path L is forced to flow around the ring's annular width into the groove 150 to access the split at the inner peripheral face 141 of the sealing ring 139 before flowing radially outwards along the cut surface 152. As the sealing ring 139 is substantially sealed at the piston bore 131, the fluid flows along the cut surface towards a downstream angular location C1 or C2. Accordingly, the leak-by path L extends from the inner peripheral face 141 and generally radially outwards and axially downstream along the cut surface 152 to exit at the downstream seal face of the seal ring at the outer peripheral face 140 and the annular interface 119 of piston 130 and piston bore 131 Hydraulic forces on the upstream side face 171 or 172 of the sealing ring 139 can press the cut split together along the cut surface 152 as the downstream side face 172 or 171 bears against the downstream groove side wall 162 or 161 while the outer peripheral face 140 remains substantially unchanged and cylindrical.
One embodiment in which one would desire to deliberately establish a leak path is in metering seal system for metering fluid along the annular interface 119 into and out of a chamber 129 at one end of the piston 130 such as for adjusting a differential pressure between the first and second faces 132, 133. Where the piston 130 is driven in part due to differential pressure, and where the piston 130 has a chamber 129 at one end which may be closed for one reason or another, it is desirable to permit pressure, positive or negative (a vacuum) to equilibrate through an flow of fluid into or out of the chamber.
Returning to
The seal system 100 controls flow of fluid through the flow port 134 in the main flow passage 116 between the first area P1 normally at a first pressure and the second area P2 normally at a second pressure which is higher or lower than the first pressure. The cylindrical piston bore 131 is in fluid communication the flow passage 116, the piston 130 having a first piston face 132 in communication with the passage 116 and having a second backpressure face 133. The first face 132 having a seal face 134 adapted to seal to the flow port 135 and the piston being reciprocable in the bore 131 for alternately closing and opening the flow port 135 with the seal face 134. The leak-by sealing ring 139 is fit to the piston 130 and piston bore 131 for metering a leak-by flow fluid along the annular interface 119 to and away from the backpressure face 133 for adjusting a differential pressure between the first and second faces 132,133. The shuttle piston 130 valve is normally biased by spring 136 for closing the main flow passage 116, engaging the seal face 134 and the flow port 135. The backpressure passage 117 extends between the first area P1 and the backpressure face 133 and has a metering orifice 122 therealong. A bleed path extends between the second area P1 and the backpressure face 133, which is formed by the leak-by path L along the shuttle piston 130. A second valve, such as a high-pressure solenoid (HPS) valve 120, is operable for opening and closing the metering orifice 122 and affecting pressure at the backpressure face 133 for operating the piston 130 under active differential pressure or if the differential pressure is substantially zero, under biasing to close the flow port 135.
An example of operation, such as to withdraw a fluid from a cylinder, includes controlled flow of higher pressure fluid from the second area P2 to the first area P1. Higher pressure from the second area P2 is also initially present in the main flow passage 116, and also at the backpressure face 133 via metered leak-by through the sealing ring 139. Accordingly, there is initially no differential pressure across the piston 130 and the piston is biased closed to seal the seal face 134 against the flow port 135. The lower pressure of the first area P1 against the seal face 134 is insufficient to overcome the biasing. As described, the backpressure face of the shuttle piston 130 is also connected to the first area P1 via the backpressure passage 117 and controlled by the high pressure solenoid (HPS) 120. To commence fluid flow from the second area P2 to the first area P1, the HPS 120 is opened and the backpressure face 133 is placed in communication with the first lower pressure area P1. Any high pressure dissipates from the backpressure face 133, through the metering orifice 122, to the low pressure first area P1. At this point, the sealing ring 139 permits yet minimizes the gas flow or leak-by from the front face 132 of the shuttle piston 130 (at the high pressure of the main flow passage 116 and second area P2) towards the backpressure face 133 (now approaching the lower pressure of the first area P1), maintaining a differential pressure (HP>LP) that forces the piston 130 to displace to the open position.
When the HPS 120 is closed, leak-by across the sealing ring 139, from the higher pressure in the main passage 116 to the now isolated backpressure face 133 equalizes the pressure across the piston 130 (HP=HP), permitting the shuttle piston 130 to close under the force of biasing spring 136. One of skill in the art can see that similar examples can be seen to operate under reverse pressure conditions where the first area P1 is at a high pressure than the second area P2, such as during filling of a pressure cylinder.
For example, for flowing fluid from the first area P1 at high pressure to the second area P2 at a lower pressure, and initial condition can be with the HPS 120 open. High pressure along the backpressure passage 117 forms a high pressure at the backpressure face 133 and a pressure differential across the piston 130 to the lower pressure in the main passage 116 and at the at the piston face 132. The leak-by past the sealing ring 139 from the backpressure face 133 to the main passage 116 is insufficient to relieve the pressure differential (HP+biasing>LP). To commence flow the HPS 120 is closed. Leak-by across the sealing ring 139 dissipates pressure at the backpressure face 133 to the main flow passage 116, eventually equilibrating to the lower pressure of the second area P2. Any pressure differential across the piston 130 diminishes until the only forces on the piston are the biasing and the force generated by the higher pressure on the seal face 134 from the first area P1, resulting in a regulated flow past the seal face 134.
The sealing ring 139 can be made from a plastic with adequate mechanical, elastic, thermal and low wear properties, such as Acetal Copolymer (ACETRON™ GPTM, Quadrant EPP USA, Inc, of Reading, Pa.). As shown in
In the embodiment of the sealing system 100, the flow rate of the migration or leak-by path L across the sealing ring 139 is at about ¼ of the flow rate of the flow through the metering orifice 122 of the HPS. The rate of the leak-by increases as cutting plane angle becomes steeper or greater from the side face the leak rate at 70° to 85° being very small and the leak rate at 45 degrees being quite a bit larger.
Controlled migration or leak-by rates are achieved by one or more of: controlling the surface finishes on the shuttle piston groove bounding side walls 161,162 and sealing ring side faces 171,172; designing the sealing ring 139 so that its nominal uncompressed diameter is slightly larger (by about 0.013 mm) than the piston bore diameter (on a nominal 13 mm diameter); and splitting the ring with a steep angle (between 70° and 85°). By means of these three steps, the leak-by path L on the sealing ring 139 is limited primarily to along the ring split, minimizing the flow along the intersection of the sealing ring outer peripheral face 140 and the bore 131. Using a steep angle on the ring, from the axis A′, aids in maintaining the integrity of the seal along most of the circumferential intersection between the outer peripheral face and the bore 131, as shown in
The main advantages of the new sealing system include: simplified shuttle piston and shuttle seat design; operational between temperatures of −40 C through 85 C, all moving parts of the shuttle system can be plastic, therefore minimizing possibility of damage/contamination of other valve components; the ring and piston have a low coefficient of thermal expansion; minimal wear of the moving pistons and absent wear/scratches in the bore where the piston operates; the system performs well independently of the number of cycles and makes possible 100,000 or more cycles of the solenoid valve; optimized geometry and materials allows the system to seal with minimal additional force, therefore, a small spring force ensures there is no leaking of the system at low tank or cylinder pressures; no requirement to machine bleed holes (−Φ0.16 mm) on the shuttle piston or shuttle plug; the reduced spring force, combined with the low leak rate from the sealing ring, allows the system to open at very low cylinder pressures, as low as 0.5 barg; and lower cost of components with reduced need for sub-assemblies. The lower mass of the plastic shuttle piston 130 combined with the smaller spring force can make the shuttle prone to oscillation in occasional circumstances such as when the fluid fuel system is substantially static at low differential pressures (this oscillation is limited to very low pressures [<20 barg], and when the cylinder pressure (second area P2) approaches the pressure of the fill source (first area P1). The tendency to oscillate can be minimized by selecting an adequate combination of preload and spring rate.
With reference to
With reference to
With reference to
| Number | Date | Country | |
|---|---|---|---|
| 60820766 | Jul 2006 | US |
