Title of Invention

"A DEVICE TO LIMIT THE FORCE ON A LPG VALVE DURING A VALVE CHANGE OPERATION"

Abstract

The present invention relates to a device to limit the force on a LPG valve during a valve changing operation on a pressurized cylinder. It comprises a sensing rod connected to said socket and extending upwards through an axial hole in the shaft. An intermediate portion of said sensing rod contains radial pins extending outwards through slots in said shaft The outward ends of said radial pins are fixed to a feedback ring such that any axial motion of the socket is transferred to said feedback ring. A feedback lever is connected to said slide by a pivot at its one end and the other end resting on said feedback ring such that any axial motion of the feedback ring causes the feedback lever to rotate about said pivot. A roller lever is mounted on said slide to actuate a hydraulic spool valve with the roller resting on top of said feedback lever such that the movement of said feedback lever causes the roller lever to move the spool of the hydraulic valve. The hydraulic output ports are connected to rod and cap end of the hydraulic cylinder, such that when the roller lever is raised up from neutral position, it causes the rod of the hydraulic cylinder to extend and when the roller lever is lowered from neutral position, it causes the rod of the hydraulic cylinder to retract for lirmting the force impressed on the LPG valve.

Full Text

The present invention relates to a device to limit the force on a LPG valve during a valve change operation, particularly for incorporation in a machine which can change the valve while the cylinder is pressurized. Background of the invention LPG Cylinders contain a valve that can be used for filling the LPG cylinder and to withdraw gas from it. This valve is screwed into a threaded bung welded to the cylinder. These valves are regularly checked for leakage in the cylinder filling plant. Any valve found leaking must be replaced before the cylinder is safe for use by the customer. Modern techniques of valve replacement require replacing the valve while the cylinder is pressurized. In order to clarify the need for the present invention it is necessary to describe how this operation is performed. The valve change Machine has a sealing bell enclosure that is lowered and clamped firmly onto the top of the cylinder. Affecting a gas tight seal around the bung and valve. A shaft with a socket adapted to the valve is then lowered through the bell and onto the valve and rotated via hydraulic means to unscrew the valve. The shaft is then raised out the bell carrying the socket and valve with it. The purpose of the sealing bell is to prevent the gas in the now open cylinder from escaping to the atmosphere. The old valve in the socket is then replaced by a new one and the shaft, socket and valve are lowered back into the sealing bell until they reach the bung. The shaft is then rotated to screw the new valve into the cylinder. Once the new valve is screwed in the sealing bell can be lifted and the cylinder removed from the machine. The shaft carrying the socket must be driven down with sufficient force to overcome the gas pressure inside the sealing bell, this requires designing the shaft drive to provide more than enough force to overcome the highest gas pressure likely to be encountered. In practice this requires shaft forces of hundreds of kilograms. After the valve contacts the bung, this entire force is impressed onto the valve. The valve is constructed of brass and attempting to engage it to the bung under such high axial force greatly increases the chance of misthreading and damage to both the valve and bung. The described device greatly reduces these forces and also provides an automatic and sensitive way for the shaft to follow the valve up or down as it is unscrewed from or screwed into the bung. This ensures that the axial force on the valve and bung remain low throughout the valve change operation. Object and summary of the invention The object of this invention is to overcome the above drawbacks by providing a device which greatly reduces the aforementioned forces and also provides a sensitive way for the shaft of a valve changing machine to follow the valve up or down as it is unscrewed from or screwed into the bung for ensuring that the axial force on the valve and the bung remains low throughout the valve change operation. To achieve the said objectives the present invention provides a device to limit the force on a LPG valve during a valve changing operation on a pressurized cylinder using a valve changing machine comprising a shaft mounted on u slide which moves up or down by a hydraulic cylinder and containing a socket mounted slidably within a cavity at the lower end of the shaft, characterized in that a sensing rod connected to said socket and extending upwards through an axial hole in the shaft, an intermediate portion of said sensing rod containing pins radially extending outwards through slots in said shaft, outward ends of said radial pins are fixed to a feedback ring such that any axial motion of the socket is transferred to said feedback ring, a feedback lever connected to said slide by a pivot at its one end and the other end resting on said feedback ring such that any axial motion of the feedback ring causes the feedback lever to rotate about said pivot, a roller lever mounted on said slide to actuate a hydraulic spool valve with the roller resting on top of said feedback lever such that the movement of said feedback lever causes the roller lever to move the spool of the hydraulic valve, and - the hydraulic output ports being connected to rod end and cap end of the hydraulic cylinder, such that when the roller lever is raised up from neutral position, it causes the rod of the hydraulic cylinder to extend and when the roller lever is lowered from neutral position, it causes the rod of the hydraulic cylinder to retract for limiting the force impressed on the LPG valve. The uppermost end of said sensing rod is mounted slidably into a balancing chamber in the upper end of the shaft, an axial hole provided within the sensing rod connects the inside of said sealing bell to said balancing chamber for equalizing the pressures on the lower and upper ends of the sensing rod. Brief description of the accompanying drawings The invention will now be described with reference to the accompanying drawings. Figure 1 shows a sectional view of the valve and bung of a known LPG cylinder. Figure 2 shows a sectional view of the shaft of a valve change machine having the device according to the present invention lowering onto a cylinder to screw in a valve. Figure 3 shows a sectional view of the condition when the LPG valve has touched the bung, causing the device according to the present invention to halt the motion before the valve is overloaded. Figure 4 shows a sectional view of the condition if the downward motion of the slides overshoots causing the device according to the present invention to raise the shaft. Detailed description of the accompanying drawings Figure 1 shows an LPG valve screwed into the bung of the cylinder. The valve has a hexagonal portion of the valve (20) which is used to apply torque to engage and tighten the valve into the bung (420). Figure 2 shows a valve change machine containing a shaft (500) mounted on a slide (210) that is moved up or down through a sealing bell (300) by a hydraulic cylinder (200) and contains a socket (100) mounted slidably within a cavity (501) at the lower end of the shaft. The upper end of the shaft (560) is mounted on bearing (212) within the slide 210 The present invention relates to a device which limits the force on a LPG valve during a valve change operation. It consists of a sensing rod (110) connected to the socket and extending upwards through an axial hole (502) in the shaft. The the upper portion of said sensing rod contains pins (121) which extend radially outward through slots (550) in the shaft (500). The outward ends of the radial pins are fixed to a feedback ring (120). The arrangement being such that any axial motion of the socket (100) is transferred to the feedback ring (120). Further, a feedback lever (150) is connected pivotably to the slide (200) at one end and rests on the feedback ring (120) at the other end. The arrangement of the lever being such that any axial motion of the feedback ring causes the feedback lever to pivot about pin (152). A roller lever actuated hydraulic spool valve (160) is mounted on the slide (210) with the roller lever (161) resting on the top of the feedback lever (150). The arrangement being such that movements of the lever (150) cause movements in the roller lever (161) and thus move the spool of the hydraulic valve. The output ports (163) and (164) are connected to the rod and cap ends of the hydraulic cylinder (200) respectively. Rising of roller lever (161) from the neutral position causes oil to be supplied to port (164) and lowering of roller lever causes oil to be supplied to port (163). The ports (163) & (164) are connected to the rod and cap ends of the hydraulic cylinder (200) respectively. Supplying oil to the cap end causes the cylinder (200) to extend and supplying oil to the rod end causes it to retract. The hydraulic valve is supplied with a supply of pressurized hydraulic oil at port (P). returning oil is directed to a tank via port (T). Figure 2 shows the shaft (500) lowering onto the cylinder to screw in a new valve. The lowering is accomplished by the hydraulic cylinder (200) acting on the slide (210). The shaft (500) is mounted on the slide (210) and moves vertically with it. In the condition shown in figure 2, the sealing bell (300) has already been lowered onto the cylinder (400) and the seal (310) has made contact with the top (410) of the cylinder. This produces a gas tight seal around the bung (420) of the cylinder. The shaft slides in through the aperture (320) on top of the bell. The seal 320 prevents the leakage of gas from the sealing bell 300 As the shaft lowers, the valve (20) contacts the bung (420) of the cylinder, continued downward motion of the shaft after this contact causes the wrench socket (100) to be forced upwards relative to the shaft (500). This causes the sensing rod (110) connected to the socket to similarly move upwards. This motion causes the feedback ring (120) rigidly connected to the sensing rod (110) to move upward. Upward movement of the feed back ring is transferred to the feedback lever (150) and forces it up around the pivot (152) This motion is transferred to the lever (161) that actuates the hydraulic spool valve (160) which is fixed to slide (210). This shifts the spool of the hydraulic valve spool (162) such that the flow of oil to the hydraulic cylinder via port (163) is interrupted, arresting the motion of the cylinder and shaft. This condition is shown in Figure 3. Note that if the slide motion over shoots then the servo valve spool is shifted even further Causing the valve to supply oil to the port (164) this condition is shown in Figure 4. This port is connected to the opposing end of the hydraulic cylinder. And flow to this port causes the cylinder to move the slide & shaft upward until the hydraulic spool valve (160) is again in the neutral position. From the preceding description, it can be seen that the action of the device is like a servo system to maintain the socket (100) at such a position within the cavity (501) that the hydraulic valve (160) is in the neutral condition. In this neutral condition, the axial load impressed on the LPG valve (20) is limited to the sum of the weights of the socket (100), sensing rod (110), radial pins (121), feedback ring (120), feedback lever (150) and the roller lever (161). This load substantially lower than the hundreds of kilograms of hydraulic force acting on the shaft (500) to force in inot the sealing bell (300). The device also maintains the load limiting action while the LPG valve is screwed from the bung (420). For example, unscrewing the LPG Valve (20) makes it rise out of the bung forcing the socket upwards. The sensing rod, feedback nng and lever transfer this upward movement to the roller lever (161) causing the hydraulic valve (160) to shift from the neutral position and supply oil to port (164). This action raises the slide (210) until the hydraulic valve is again in the neutral position. Due to the action of the above device the full hydraulic force is prevented from ever impressing itself on the valve. In addition, a balancing chamber (170) is provided for preventing the sensing rod from being forced upwards by the pressure of the gas in the bell. The hole (111) within the sensing rod directs the gas pressure to the chamber (170). This pressure then acts downwards on the top of the sensing rod to balance the pressure acting on the lower end of the rod inside the pressurized sealing bell. 1 claim: 1. A device to limit the force on a LPG valve during a valve changing operation on a pressurized cylinder using a valve changing machine comprising a shaft mounted on a slide which moves up or down by a hydraulic cylinder and containing a socket mounted shdably within a cavity at the lower end of the shaft, characterized in that a sensing rod connected to said socket and extending upwards through an axial hole in the shaft, an intermediate portion of said sensing rod containing radial pins extending outwards through slots in said shaft, outward ends of said radial pins are fixed to a feedback ring such that any axial motion of the socket is transferred to said feedback ring, a feedback lever connected to said slide by a pivot at its one end and the other end resting on said feedback ring such that any axial motion of the feedback ring causes the feedback lever to rotate about said pivot, a roller lever mounted on said slide to actuate a hydraulic spool valve with the roller resting on top of said feedback lever such that the movement of said feedback lever causes the roller lever to move the spool of the hydraulic valve, and the hydraulic output ports being connected to rod end and cap end of the hydraulic cylinder, such that when the roller lever is raised up from neutral position, it causes the rod of the hydraulic cylinder to extend and when the roller lever is lowered from neutral position, it causes the rod of the hydraulic cylinder to retract for limiting the force impressed on the LPG valve. 2. The device as claimed in claim 1 wherein the uppermost end of said sensing rod is mounted shdably into a balancing chamber in the upper end of the shaft, an axial hole provided within the sensing rod connects the inside of said sealing bell to said balancing chamber for equalizing the pressures on the lower and upper ends of the sensing rod. 3. The device to limit the force on a LPG valve during a valve changing operation on a pressurized cylinder using a valve-changing machine substantially as herein described with reference to and as illustrated in the accompanying drawings.

Documents:

1155-del-2003-abstract.pdf

1155-del-2003-claims.pdf

1155-del-2003-complete specification (granted).pdf

1155-del-2003-correspondence-others.pdf

1155-del-2003-correspondence-po.pdf

1155-del-2003-description (complete).pdf

1155-del-2003-drawings.pdf

1155-del-2003-form-1.pdf

1155-del-2003-form-19.pdf

1155-del-2003-form-2.pdf

1155-del-2003-form-3.pdf

1155-del-2003-pa.pdf