DIFFERENTIAL PRESSURE CONTROL VALVE

Abstract: This invention is directed to a differential control valve. The differential pressure is maintained by differing area surfaces on a piston assembly which will be balanced at a predetermined differential established at the manufacturing operation. There is a spring member operating on two valve balls which provides a delayed pressurization of the controlled chamber. The control valve has a ball valve at the exit port to control the low pressure side of the differential control valve assembly, providing a fail-safe system with no adjustments required after manufacture if there is a pressure increase downstream.

Description: The invention relates to a differential pressure control valve enabling the control of a fluid circuit as to a predetermined pressure difference between the pressure of the entering fluid and the pressure of the exciting fluid, comprising a low pressure chamber connected to house the exciting fluid, a high pressure chamber connected to house the entering fluid, and a control valve to allow a temporary connection between the high pressure chamber and the low pressure chamber for adjusting the pressure difference. The use of a corresponding differential pressure control valve is described in EP-A-75288. In this system there are three different valves for keeping a differential pressure, for regulating the amount of pressure and to release the fluid out of a manifold if necessary. Problems have been experienced by this pressure differential control system in which the user can adjust the pressure differential and defeat the purpose of the system. Further, the known system did not provide a failsafe operation if there was a malfunction causing a pressure increase in the manifold and thus in the lower pressure portion of the differential pressure control valve. It is the object of the present invention to improve the known differential pressure control valve which is fixed as to the predetermined pressure difference and which allows the low pressure side to be initially connected to the atmosphere. For fulfilling this object the invention proposes that a piston assembly in the low and high pressure chambers carries a diaphragm member which separates the chambers, the piston assembly having a larger surface area on the low pressure side than on the high pressure side, and that a delay pressurizing means is positioned between a port of the entering fluid and the control valve. The present invention covers a differential pressure control valve which has an automatic system to provide a preselected delayed pressurisation of the lower pressure chamber permitting other functions to take place during this period beneficial to this application. The invention also includes a means of automatically close off the exhaust portion of the differential pressure control valve when operating conditions have been met which can automatically be deactivated if a malfunction in another part of the system increases the pressure in the lower pressure chamber so that the increased pressure can be exhausted to the atmosphere. In the accompanying drawings, a preferred embodiment of the invention is illustrated and a method of its application disclosed. The invention will be further understood from the following, more detailed, description taken with the drawings in which: Figure 1 is a schematic view of a tire retreading system illustrating an application of the present invention; Figure 2 is a cross-section of a tire assembly as mounted in Figure 1 taken along line 2-2 of Figure 1; Figure 3 is a view taken from the circled area of Figure 2 illustrating the envelope's action on the groove and the pressure differential of the system controlled by the differential pressure control valve; Figure 4 is a cross-sectional view illustrating the principles of the present invention in its preferred embodiment. Referring generally to Figure 1, there is illustrated a tire retreading system, including an autoclave or pressure vessel, generally referred to as 10 which is adapted to receive through an enclosure 12 a plurality of tire assemblies 14 for retreading. Interior of the vessel 10 can be pressurized from a fluid pressure 16 by way of a shop pressure line 18 with air, water, steam or a mixture of steam and air. The pressurizing medium is heated either before introduction into the vessel or after introduction by means of a heater as indicated by numeral 19 located in the vessel 10. The shop pressure line 18 may be pressurized at approximately 8 bar (115 PSI), for example. The line 18 is connected to a regulator valve 20 which adds pressure up to 10,6 bar (150 PSI) and is then closed. A line 21 passes fluid to a tire inflation manifold 23 from valve 20. The fluid passes from manifold 23 through the tire inflation line 25, which inflates the curing tube 26 of the tires to a predetermined pressure of 8 bar (115 PSI). A pressure vessel fill line 27 is connected to line 21 between valve 20 and the manifold 23. The line 27 connects to a differential check valve 31, which opens when the pressure in line 27 is 2,15 bar (30 PSI) higher than the downstream pressure past valve 31. A line 32 connects valve 31 to a pressure regulator valve 34, which will close when the pressure in line 32 reaches 6 bar (85 PSI). A line 35 connects the valve 34 to the pressure vessel 10. Each tire assembly 14, best viewed in Figure 2, includes a tire casing 40, a precured tread 42, and a layer of rubber-base bonding material 44, sometimes referred to as cushion gum, between the upper surface of the tread 42 and the crown surface of the tire casing 40. A flexible fluid tight member 46, sometimes referred to as an envelope, is made of rubber, for example, overlies the tread 42. The embodiment in Figure 2 illustrates the member 46 being held in sealing contact to the sidewalls of the tire casing 40 at location 47 and that the tire casing is inflated as disclosed, for example, in U.S. patent number 4,434,018. The tire casing 40 is mounted on a rim 49 with the flange member 51 positioned on the rim. The envelope member 46 is positioned between the flange and the tire casing 40. Pressure in the curing tube 26 forces the envelope 46 into sealing contact with the tire casing 40 along the area designated as 47. The flexible member 46 is provided with a fitting 54 which connects the space 56 between the envelope 46 and the tread 42 with the conduit 58. Conduit 58 passes through the pressure chamber 10 and connects with an envelope manifold 60 as shown in Figure 1. Along the path of conduit 58 is provided a valve member 62. Valve member 62 has three positions. It can be closed, it can be open to the envelope manifold, or it can be opened to the atmosphere. The overall function of the illustrated system is, of course, to pressurize the tread 42 against the tire casing 40 by means of fluid in the chamber 10 and simultaneously to heat the bonding material or cushion gum 44 to a temperature at which it can be vulcanized, securing the tread to the tire casing. A line 64 connects the chamber to a pressure differential control valve 100. The full function of the pressure differential control valve will be explained in detail below. Fluid under high pressure coming into the differential pressure control valve 100 from the pressure line 64 will pass through the differential pressure control valve into the pressure line 71, which is connected to the envelope manifold 60. The fluid under pressure in the envelope manifold 60 will pass through the valve members 62 into conduit 58 and into the envelope 46. The purpose of the control valve is to apply pressure in the space 56 between the envelope member 46 and the precured tread 42 during the curing operation. The differential pressure control valve 100 has two major portions. These are top cap 102 and bottom cap 104. These two members are secured together in a conventional manner by cap screws not shown. A piston assembly 106 is positioned between top cap 102 and bottom cap 104. The piston assembly has a piston plate 108 and a piston member 110 held together by connecting screws 111. Positioned between the piston plate and the piston member is diaphragm 112. The diaphragm extends out and is positioned as the sealing element between the top cap 102 and the bottom cap 104. The top cap 102 has a control chamber 114 that extends through its central portion. An inlet nut 116 is screwed into the upper end of the control chamber 114 and has an inlet seat 117 at its bottom portion. The inlet nut is connected to pressure line 64 and receives fluid from that line under its pressure. There is an inlet port 118 that extends from the inlet nut 116 to the bottom of the top cap 102 and exits into a high pressure chamber 120. The control chamber 114 has a control seat 122 at its lower end. A ball spring assembly is positioned between the inlet seat 117 and the control seat 122. The ball spring assembly includes a force spring member 123, an inlet ball 124, and a control ball 125. The spring 123 urges the inlet ball 124 into sealing contact with the inlet seat 117 and the control ball 125 into sealing contact with the control seat 122. The piston assembly 106 has an opening 127 which receives a ball activator shaft 129 that extends through the opening 127 into the bottom end of the control chamber 114. The ball activator shaft 129 has a shaped surface on part of its circumference which permits a passage port 131 to connect the control chamber 114 to a lower pressure chamber 133, which is part of the top cap 102. The lower pressure chamber 133 connects to an exit port 135 which passes from the top cap 102 through the bottom cap 104 into the bottom cap chamber 137. The bottom cap 104 has a fitting plug 138 screwed into the bottom cap chamber, which provides an initial seat 139 for envelope valve ball 140. The bottom cap chamber 137 connects with an exhaust chamber 142 and an envelope outlet 144. The exhaust chamber 142 has an opening at its upper end to receive the piston member 110 of the piston assembly 106. A sealing ring 145 is provided in the piston member 110 to seal the high pressure chamber from the exhaust chamber 142. Exhaust ports 146 are provided from the exhaust chamber to the atmosphere outside the differential pressure control valve 100. The envelope outlet 144 connects to the line 71 which is connected to the envelope manifold 60. The exhaust chamber 142 has an exhaust seat 147 at the upper end of the bottom cap chamber. When the pressure vessel 10 is being activated to retread tires, it is desirable to have the chamber 10 under pressure that acts on envelope member 46 of the tire assembly 14. This will assist in expelling any undesirable air between the precured tread 42 and the tire casing 40. After the pressure in chamber 10 has had time to initially act on the envelope 46, expelling any residue, the system is then prepared to receive pressure in the space 56. This is the function of the spring assembly and the envelope valve ball 140, as will be explained in detail below. As the pressure in the chamber 10 is starting to rise, the fluid under pressure will pass to line 64 into the outlet nut 116. This pressure will be transferred to the high pressure chamber 120 through the inlet port 118. As the pressurized fluid initially acts on the lower surface area of the piston plate 108, the piston assembly 106 will be moved to an up position. The ball activator shaft 129 will contact the control ball 125. As soon as there is enough pressure in the high pressure chamber 120 to overcome the forces of spring 123, the control ball 125 will be removed from the control seat 122. At this time, the inlet ball 124 will be in sealing contact with the inlet seat 117. When the pressure from the inlet nut 116, acting on inlet ball 124, reaches approximately 0,7 to 0,85 bar (10-12 PSI), the inlet ball 124 will be removed from the inlet seat 117, permitting air to pass into the control chamber 114 and pass the control ball 125 into the lower pressure chamber 133 through the passage port 131. The upper surface area of the piston plate 108 will be acted on by this pressure. The lower and upper surface areas of the piston plate can be made in various ratios to predetermine the pressure differential between the entering and exit pressures of differential pressure control valve 100. In our present illustration, the differential pressure requires 1 (15) to 1,2 bar (17 PSI) more pressure on the high pressure chamber side of piston plate 108 than the low pressure chamber side of piston plate 108 for the control valve 100 to be in balance. As the fluid enters the low pressure chamber 133, it will pass to the exit port 135 and pass over the envelope valve ball 140, which is in its initial position shown in phantom. In the initial position, the envelope valve ball is in contact with initial seat 139. There is a space between the exit port 135 and the envelope valve ball 140 permitting the air to pass over the valve ball and into the exhaust chamber 142 and out through the exhaust ports 146 to atmosphere. The fluid which was squeezed out of the tire assembly 14 would pass through line 71 to the envelope outlet 144, then into the exhaust chamber 142 and out through the exhaust ports 146. This condition will remain until the pressure in the exit line 135 reaches approximately 1,8 to 2,1 bar (25-30 PSI). The velocity of the air passing over the envelope valve ball 140 will draw the valve ball to its up position to be seated in sealing contact with the exhaust seat 147, thus sealing off the exhaust chamber 142 and the exhaust ports 146 from any pressure source. The fluid from the exit port 135 will then pass through the bottom cap chamber 137 through the envelope outlet 144 into the envelope manifold 60. When the pressure vessel 10 is pressurized to 6 bar (85 PSI), the pressure regulator valve 34 will be closed and the pressure in the pressure vessel will be stabilized at 6 bar (85 PSI). At this time, the pressure in the high pressure chamber 120 will be 6 bar (85 PSI) and when the pressure in the low pressure chamber reaches 5 bar (70 PSI), the piston assembly 106 will be equalized. At this time, the spring 123 will move the control ball 125 back into sealing contact with the control seat 122 and no further pressure can be transferred into the low pressure chamber from line 64. The fluid under pressure in the low pressure chamber 133 will pass through the exit port 135 into the bottom cap chamber 137 and will hold the envelope valve ball 140 in sealing position at the exhaust seat 147, and the system is now stabilized. If, for some reason, one of the envelope members 46 would experience a small leak, the additional pressure would be effective in the envelope manifold 60 and also via line 71 in the envelope outlet 144 and would raise the pressure in the bottom cap chamber 137, thus increasing the pressure in the exit port 135 and in the low pressure chamber 133. At this time, the piston assembly 106 would be moved down because of the imbalance between the pressures in the high pressure chamber 120 and the low pressure chamber 133. A ball actuator 148 will contact the envelope valve ball 140, moving it off exhaust seat 147 so excess air under the increased pressure would be discharged through the exhaust chamber 142 and the exhaust ports 146 until the predetermined pressure differential is reached. If there is a small leak, this arrangement can handle the overflow of pressure. If there is a large leak, the operator will hear the whistle sound from the volume of air discharging through the exhaust ports 146. The operator can determine the tire assembly 14 causing the problem by checking the individual valves 62. When the correct tire assembly 14 is determined, that valve 62 can be vented to the atmosphere so as not to jeopardize the other tire assemblies. While the preferred embodiment of the differential pressure control valve has been shown and described herein in detail, those skilled in the art will recognize various alternative design embodiments for practicing the present invention as defined by the following claims.

Claims: A differential pressure control valve (100) enabling the control of a fluid circuit as to a predetermined pressure difference between the pressure of the entering fluid and the pressure of the exciting fluid, comprising a low pressure chamber (133) connected to house the exciting fluid, a high pressure chamber (120) connected to house the entering fluid, and a control valve (122, 125) to allow a temporary connection between the high pressure chamber (120) and the low pressure chamber (133) for adjusting the pressure difference, characterized in that a piston assembly (106) in the low and high pressure chambers (133, 120) carries a diaphragm member (112) which separates the chambers (120, 133), the piston assembly (106) having a larger surface area on the low pressure side than on the high side, and that a delay pressurizing means (117, 123, 124) is positioned between a port of the entering fluid and the control valve (122, 125). A differential pressure control valve (100) as in claim 1, characterized in that the delay pressurizing means is positioned in a control chamber (114) and that said means includes an inlet ball (124) adjacent an inlet seat (117) and a force spring (123) acting on the inlet ball (124) which urges it towards its seat (117). A differential pressure control valve (100) as in claim 2, characterized in that the control valve comprises a control ball (125) and a control seat (122), that the piston assembly (106) has a ball activator shaft (129) to act on the control ball (125) to move it off the control seat (122) when the low pressure chamber (133) has a pressure below the predetermined pressure difference, that the control valve (122, 125) is positioned in the control chamber (114) and that the force spring (123) acts also on the control ball (125). A differential pressure control valve (100) as in one of claims 1 to 3, characterized in that the diaphragm member (112) is in sealing contact between a top cap member (102) containing the low pressure chamber (133) and a bottom cap member (104) containing the high pressure chamber at its outer edge and connected to the piston assembly (106) at its inner edge. A differential pressure control valve (100) as in one of claims 1 to 4, characterized in that the low pressure chamber (133) is connected to a bottom cap chamber (137) having an outlet (144) for use of the lower pressure, an exhaust seat (147) separating the bottom cap chamber (137) and an exhaust chamber (142) with exhaust ports (146) connecting it to the atmosphere, and an envelope valve ball (140) which is initially positioned on an initial seat (139) and which makes sealing contact with the exhaust seat (147) when the piston assembly (106) is in balance. A differential pressure control valve (100) as in claim 5, characterized in that the piston assembly (106) has a ball activator member (148) to act on the envelope valve ball (140) and move it off the exhaust seat (147) when the low pressure chamber (133) has a pressure above the predetermined pressure difference.

Inventors: BREWER, DONALDEE
Applicants: BANDAG LICENSING CORPORATION
Application year: 1986
Main classification: G05D16
IPC codes: G05D16, F16K17