FR2596171A1 - Device for maintaining the pressure in a piping downstream from a gas pressure reducing valve supplying an all-or-nothing utilisation - Google Patents

Abstract

The device for compensation for the variations in pressure of the gaseous fluid flowing in a portion of main conduit is characterised in that it comprises a short additional piping 21 linking the said conduit portion 14 to a variable-volume capacity 205 delimited by a flexible membrane 203 and by a rigid shell 201 mounted on the said short additional piping 21 and supporting the flexible membrane 203 and in that it further comprises an elastic means 206, 210 acting on the said flexible membrane 203 in order to establish a predetermined datum pressure on the flexible membrane. Application to the compensation for pressure variations in a portion of conduit situated between a regulator - pressure reducer and a shut-off valve operating in all-or-nothing placed downstream from the regulator.

Description

DEVICE FOR MAINTAINING PRESSURE IN A CANALIZATION
DOWNSTREAM OF A GAS RELAXATION STATION FEEDING ANY USE OR NOTHING.

 The present invention relates to a device for maintaining the pressure in a pipe downstream of a gas expansion station supplying an all-or-nothing use.

 The gas supply of appliances such as burners of gas boilers or industrial furnaces, carried out in all or nothing, is cyclically controlled by shutters constituted by electro-valves with a very short response time.

 The gas pressure flowing in the supply line on which the shutter is operated in all or nothing is itself regulated by a regulator-regulator located upstream of the shutter. However, the regulator regulators generally used are pneumatic operating members whose response time is much longer than that of the electro-valves operating in all or nothing to control the supply of the device of use such as a boiler burner .

 Because of the difference between the response time of the regulator-expander and that of the solenoid-valve acting shutter, there occurs in the pipe section between the regulator-regulator and the solenoid valve an overpressure at each closing of these control members and a depression at each opening of these control members.

 These pressure variations are all the more annoying as the set pressure is low and lead to trips of safety devices which then imply manual reclosures.

 Thus, during a sudden interruption of flow downstream by the control valve of the operating device, it occurs because of the delay inherent in the pressure regulator overpressure which can cause triggering of maximum pressure safety devices associated with either the regulator-regulator or the apparatus of use.

 Conversely, during a sudden call flow downstream by the control valve of the operating device, the longer reaction time required for the regulator-regulator to move into an open position causes in the supply line downstream of the regulator-regulator a pressure drop which can cause trips of safety devices at minimum pressure when they are not equipped with a time delay.

 Moreover, even in the absence of flow in the supply line, there may be an increase in pressure due to the effect of the temperature on the volume of gas included in the pipe between the pressure regulator and the Electro-valve control of the power supply of the device of use and this increase of pressure can also cause triggers of safety organs.

 To overcome the above drawbacks, there is generally an oversizing of the pipe between regulator and solenoid valve, but this leads to increase the size and cost of installation, without really solving the problem posed.

 It has also been proposed to solve the problem of overpressures at closure by using a venting valve. This solution, however, causes an increase in gas consumption and creates a potential risk of explosion or fire.

 According to yet another possible solution, described in French Patent No. 73 17815, an auxiliary circuit is mounted in shunt with respect to the gas supply line, on either side of the pressure regulator, and the auxiliary circuit comprises a vacuum pump, an auxiliary valve located upstream of the vacuum pump and a fixed volume capacity connected to the vacuum pump. During the operation of the regulator, the vacuum pump creates a vacuum in the auxiliary capacity and when closing the solenoid valve supply of the user device, the auxiliary valve is also closed thus stopping the operation of the vacuum pump. The excess gas introduced into the main line between the regulator and the main solenoid valve can then be sucked by the auxiliary capacity.

 Such a system makes it possible to reduce the overpressure created when closing the main solenoid valve and generally avoids the triggering of the safety devices associated with the regulator or the apparatus of use. However, this known system does not make it possible to reliably remedy the problem of depressions at the opening of the valve or of pressure variations as a function of temperature variations. Moreover, the known system which involves the putting into service of an auxiliary circuit in connection with the regulator is relatively expensive and bulky, involves the use of connections with a pressure tap upstream of the regulator and must be adjusted in situ. Moreover, the response time of the aforementioned device is not negligible and the accuracy in the maintenance of the pressure is insufficient for certain applications.

 The present invention aims to overcome the aforementioned drawbacks and to ensure effective and accurate maintenance of the gas pressure in the pipeline between a regulator-expander and a shutter operating on all or nothing in all operating conditions , without risk for users and in general, reducing the size and cost of installation.

 The invention also aims, more particularly, to ensure a pressure maintenance using a cheap auxiliary device, small footprint, fast response, pre-adjustable at the factory, operating statically and connectable in a manner simple on the pipe section between a regulator-regulator and a solenoid valve control of a device of use.

 These objects are achieved by means of a device for compensating the pressure variations of a gaseous fluid in a portion of a supply line situated between a regulator-expander and an obturator operating on all or nothing placed downstream of said regulator-regulator characterized in that it comprises a short additional pipe connecting said pipe portion to a variable volume capacity delimited a flexible membrane and a rigid shell mounted on said short additional pipe and supporting the flexible membrane and in that it further comprises a elastic means acting on said flexible membrane to set a predetermined set pressure on the flexible membrane.

 Said elastic means is constituted by a mechanism having a low stiffness.

 According to an advantageous embodiment, said low-stiffness mechanism comprises, on the one hand, a helical spring of predetermined stiffness K exerting a force on the face of the flexible membrane outside said variable-volume capacity, and, on the other hand, a predetermined stiffness spring system K 'close to the stiffness K of the coil spring and exerting a force on the face of the inner flexible membrane to the variable volume capacity.

 More particularly, said spring system is disposed in the cavity forming a variable volume capacity and comprises a spring whose ends are connected on the one hand by two links and a joint common to the flexible membrane, on the other hand, by a fixed link and an articulated connection to the rigid shell supporting the flexible membrane.

 The helical spring is disposed inside a second rigid shell contributing with the first rigid shell to the support of the flexible membrane.

 The resilient means may be adjusted to allow an increase in the variable volume capacity to limit overpressure in the feed pipe portion or, conversely, be adjusted to allow a decrease in the variable volume capacity to limiting pressure drops in said feed pipe portion.

 Several devices according to the invention adapted to the overpressure compensation or depressions can be used in the same installation and can each be equipped with a solenoid valve to be selectively put into service depending in particular on the position of the electro- main control valve of a device of use.

 In general, thanks to the implementation of a variable capacity of relatively low volume, but whose volume variations can be rapid, the device according to the invention makes it possible to accurately carry out a pressure maintenance in a main pipeline, and in addition to considering the realization of facilities with less overall capacity.

Other characteristics and advantages of the invention will emerge from the following description of a particular embodiment, given by way of example, with reference to the appended drawings, in which:
FIG. 1 is a schematic view of a gas supply installation to which a pressure-maintaining device according to the invention is added,
FIG. 2 is a schematic view of a conventional gas supply installation according to the prior art, and
- Figure 3 is a schematic sectional view of a particular embodiment of the pressure holding device according to the invention.

 FIG. 2 represents the diagram of a traditional natural gas supply installation of utilization apparatuses 19 such as boiler burners or industrial ovens intended to operate in all or nothing.

 A regulator-expander 11 is mounted on a pipe 10 for supplying pressurized gas to supply gas in the main line 17 located downstream of the regulator-expander 11 of gas under a predetermined effective set pressure which can be for example of the order of 20 mbar.

 A safety member 12 is associated with the expander 11 to react when the pressure exceeds a predetermined value. A counter 13 may be mounted on the pipe 17 downstream of the regulator regulator 11. A solenoid valve 15 for controlling the on-off supply of the burner of the apparatus of use 19 is mounted on the pipe 17 downstream. of the regulator-expander 11 and the counter 13. A safety member 16 of the user apparatus 19 is also mounted on the line 17 in the vicinity of the solenoid valve 15 and the user apparatus 19 to react at a maximum pressure, or a minimum pressure in the pipe 17 and cause a stop of use if the pressure in the pipe 17 exceeds the maximum pressure or falls below the minimum pressure.

After each triggering of the safety member 16, or the safety member 12, a manual reset is necessary to put back into service the gas supply system.

 In the traditional installation of FIG. 2, the pipe 17 located between the regulator 11 and the solenoid valve 15 has a relatively large cross section in order to constitute a large capacity so that the overpressures or depressions created in the pipe 17 during the closures or openings of the solenoid valve 15 and, with a longer response time, the regulator-expander 11, are slightly attenuated given the large volume of gas present in the pipe section between the regulator 11 and the electro 15. In order to reduce the overpressures in the pipe 17, a venting valve 18 is mounted on a pipe connected to the pipe section 17 between the meter 13 and the solenoid valve 15, to evacuate the pipe. excess gas in the pipe 17 when the solenoid valve 15, whose response time is of the order of a few hundredths of a second, was closed, while the pressure regulator-pressure regulator of g az 11 whose response time is of the order of the second or the half-second, still allows a flow of gas entering the pipe 17. The reaction time of the valve 18 is however itself not negligible and it is unsatisfactory to evacuate gas into the atmosphere.

 The installation of FIG. 1, which is in accordance with the invention, does not require modification of the elements 11 to 13 and 15, 16 of FIG. 2, but avoids the use of the valve 18 for setting the atmosphere. With the measurements according to the invention it is furthermore possible to use a pipe 14 of reduced cross section between the regulator 11 and the solenoid valve 15, the capacity between the regulator 11 and the solenoid valve 15 being relatively limited. However, the invention naturally also applies to existing installations comprising an oversize pipe 17 like that of FIG. 2.

 According to the invention, it is not necessary to make a connection upstream of the regulator 11 on the gas supply pipe 10 of relatively high pressure, but it is sufficient to connect a static device 2 for maintaining pressure, which can be pre-set at the factory, by a tap on the pipe section 14 located between the regulator 11 and the solenoid valve 15.

 The pressure maintaining device 2 essentially comprises an assembly 20 constituting a variable volume capacity connected directly or by a valve 22 to an auxiliary pipe 21 of short length opening into the main supply line 14, and pre-adjusted in such a way that to automatically modify its capacity according to the pressure variations in the pipe 14.

 The device 2 connected to the pipe 14 thus varies more or less rapidly the total capacity between the expander 11 and the use 19 depending on the pressure so as to oppose the pressure variations. The device 2 may be adapted to have a capacity which increases in the event of an increase in pressure in the pipe 14 in order to reduce this pressure increase to zero or on the contrary can be adapted to have a capacity which decreases in the event of pressure decrease. in line 14 in order to limit and cancel this pressure decrease.

 Several devices 2 adapted to compensate for increases or decreases in pressure can be used simultaneously in the same installation such as that of FIG. 2. A first device 2 can thus be pre-set to compensate for sudden overpressures at closing of the device. solenoid valve 15. A second device 2 may be pre-set to compensate for sudden depressions at the opening of the solenoid valve 15 and a third device 2 "may be pre-set to compensate for slow increases in pressure in the line 14. due to a heating of the gas present in this pipe 14 between the regulator 11 and the solenoid valve 15 when the latter is closed.

According to a possible implementation of the invention, the valves 22, 22 ', 22 "making it possible to place the variable capacitors 20, 20', 20" of the devices 2.2 ', 2 "in communication with the pipe 14 are electro-valves actuated synchronously with the solenoid valve 15 of the main pipe 14. Thus, the valves 22 and 22 "can be opened to close the solenoid valve 15 while the valve 22 'is closed to the opening of the solenoid valve 15. Such a mode of implementation is however not absolutely necessary and a device 2 provided to react to a variation of pressure with respect to an absolute pressure of reference can be used without having solenoid valve synchronized with the solenoid valve 15 which makes its installation particularly convenient.

 The theoretical determination of the minimum volume VD of a compensating device 2 as a function of the volume of the pipe 14 between the expander 11 and the shutter 15 will be indicated below. The formula is established for the case of the. overpressure compensation but can naturally be established in the same way for the compensation of pressure drops.

Let VD be the minimum volume of the variable capacity device 20,
Let VC be the volume of line 14,
Let DP be the pressure increase observed during a shutdown of the installation without the device 2,
Let P be the set absolute pressure in line 14,
We have the relationship
VD = VC x DP / P (1)
VD and VC on the one hand, DP and P on the other hand being expressed respectively in the same units.

For example, for =
VC = 70 liters
DP = 25 mbar
P = 1020 mbar
The minimum volume VD is thus 1.715 liter.

 An exemplary embodiment of a device 2 for maintaining the pressure according to the invention will now be described with reference to FIG.

 According to this example, the device 20 with variable capacity comprises a rigid housing 201, 202 supporting a flexible membrane 203 sealingly mounted between two rigid shells 201,202 constituting the housing. A cavity 205 of variable volume is defined between the rigid shell 201 and the membrane 203 and can be placed in communication through the valve 22 and the pipe 21 with the main pipe 4 of the installation of FIG.

 The membrane 203 is itself integral with a plate 204 to which is attached a helical spring 206 disposed between the membrane 203 and the second shell 202 extended in the axis of the device 20 by a tubular portion 207 forming a housing for the spring 206 which determines a set pressure for the membrane 203. The spring 206 placed between the plate 204 and the bottom 208 of the tubular housing 207 is preferably relatively long and very flexible to allow a large displacement of the membrane 203 even for a small variation pressure in the cavity 205.

 In order to allow the use of a spring 206 of reduced length, it is possible to associate with this main spring 206 of the stiffness K, a mechanism 210, resulting stiffness K 'close to the stiffness K, which exerts on the membrane 203 an antagonistic action with respect to that of the spring 206.

 The mechanism 210, placed in the cavity 205 comprises an auxiliary spring 211 which is arranged parallel to the membrane 203 and whose ends are connected on the one hand, by two rods 213, 214 to a rod 212 connecting to the plate 204 of support of the membrane 203 and secondly, by a fixed connecting element 218, and an articulated connecting element 219 to the rigid shell 201. Each of the two rods 213, 214 is hinged on the one hand at one end 215, 216 auxiliary spring 211, on the other hand at a common point 217 of the rod 212.

The main set spring and the mechanism 210 define a system which is all the more sensitive as the active surface
S of the membrane 203 is large and the stiffnesses K and K 'of the spring 206 and the counter mechanism 210 are similar.

 The device 20 therefore preferably has a flattened shape with for example two rigid shells 201, 202 in the form of spherical caps, the membrane 203 being clamped between the two caps 201, 202.

 Naturally, it is possible to use other mechanisms than the mechanism 210 cooperating with the coil spring 206 to provide a set pressure on the face of the outer membrane 203 to the cavity 205.

Claims (8)

 1. A device for compensating the variations of pressure of a gaseous fluid in a portion of a supply line (14) situated between a regulator-expander (11) and a shutter (15) operating in any manner placed downstream of said regulator pressure reducer (11)  characterized in that it comprises a short additional pipe (21) connecting said pipe portion (14) to a variable volume capacity (205) delimited by a flexible membrane (203) and a rigid shell (201) mounted on said additional short pipe (21) and supporting the flexible membrane (203) and in that it further comprises an elastic means (206,210) acting on said flexible membrane (203) to set a predetermined set pressure on the flexible membrane.  2. Device according to claim 1, characterized in that said elastic means (206,210) is constituted by a mechanism having a low stiffness.  3. Device according to claim 2, characterized in that said low stiffness mechanism (206,210) comprises firstly, a helical spring (206) of predetermined stiffness K exerting a force on the surface of the flexible membrane (203) outside to said variable volume capacity, and on the other hand, a spring system (210) of predetermined stiffness K 'predetermined close to the stiffness K of the coil spring (206) and exerting a force on the face of the flexible membrane ( 203> inner to the variable volume capacity.  4. Device according to claim 3, characterized in that said spring system (210) is disposed in the variable volume capacity cavity (205) and comprises a spring (211) whose ends are connected on the one hand, by two links (213,214) and a joint joint (217) to the flexible membrane (203), on the other hand, by a fixed connection (218) and an articulated connection (219) to the rigid shell (201) supporting the flexible membrane .  5. Device according to claim 3 or 4, characterized in that the coil spring (206) is disposed inside a second rigid shell (202) contributing with the first rigid shell (201) to the support of the flexible membrane (203).  6. Device according to any one of claims 1 to 5, characterized in that said elastic means (206,210) is set to allow an increase in the variable volume capacity (205) to limit overpressure in the portion of supply line (14).  7. Device according to any one of claims 1 to 5, characterized in that said elastic means. (206, 210) is adjusted to permit a decrease in the variable volume capacity (205) to limit pressure drops in said supply line portion (14).  8. Device according to any one of claims 1 to 7, characterized in that it comprises a valve (22) additional mounted on said additional pipe (21) between the supply line (14) and the capacity (205) variable volume to selectively activate the additional capacity (205).