GB2359891A

GB2359891A - A fluid pressure proving system with a shut-off valve and pressure sensing means

Info

Publication number: GB2359891A
Application number: GB0023992A
Authority: GB
Inventors: Nigel Thornley
Original assignee: MEDEM
Current assignee: MEDEM
Priority date: 2000-03-02
Filing date: 2000-10-02
Publication date: 2001-09-05
Anticipated expiration: 2020-10-02
Also published as: GB0023992D0; DE60131794D1; GB0004951D0; DE60131794T2; GB2359891B

Description

-I- - P09805 - A FLUID PRESSURE PRO VING S YS TEM 2359891

THIS INVENTION concerns a system for determining the integrity of, for example, a gas supply system including pipework leading to a number of gas outlets such as rnight be found in a school laboratory. The system is intended to ensure the safety of the installation by checking for any leaks or valves left open, prior to admitting, in this example, gas to the system. While the following description will relate to installations connected to a gas supply, it is also applicable to any other form of fluid supply such as liquids and vapours.

According to the present invention, there is provided a fluid pressure proving system comprising a flow control valve adapted to be introduced into a fluid supply duct, actuating means adapted selectively to open and close the flow control valve, a fluid pressure sensing device connected to the flow control valve to sense a pressure difference between inlet and outlet sides of the flow control valve and having transducers to produce signals representative of the pressures at the inlet and outlet sides, and control means responsive to signals from the transducers and adapted to determine a pressure differential and to operate the actuating means to close the flow control valve when the fluid pressure at the outlet side has a value less than a predetermined proportion of that at the inlet side.

The flow control valve may be a solenoid operated valve.

The fluid pressure sensing device may be a pair of pressure transducers communicating with the inlet and outlet respectively of the flow control valve.

The control means may include a key-operated switch, an emergency stop switch, a plurality of indicators and a microprocessor.

A bypass duct may be connected between the inlet and outlet sides of the flow control valve and having a cut-off valve thus, when required, to bypass the flow control valve.

A fluid pressure proving system in accordance with the invention, may be provided as part of a fluid distribution means in combination with a fluid supply duct and a distribution duct including a plurality of user outlets each of which 'Includes a cut-off valve.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 schematically illustrates a fluid pressure proving system according to a first embodiment; and Fig. 2 similarly illustrates a second embodiment.

Referring now to Fig. 1, a gas distribution system incorporating a gas pressure proving system in accordance with the invention comprises an inlet pipe 10 for the supply of gas and an outlet pipe 11 connected to a manifold 12 for the supply of gas selectively to a plurality of valved outlets 13 for example, the gas taps in a laboratory.

The proving system consists of a gas control or cut-off valve 14 disposed between the inlet pipe 10 and the outlet pipe 11, a pair of pressure transducers 15 and 16 connected and preferably, though not necessarily, physically attached to the cut-off valve 14 in order to sense and measure the gas pressures on the inlet and outlet sides respectively of the valve 14, and a control unit 20 adapted to receive electrical signals produced by the transducers 15 and 16. The control unit may be positioned remote from the valve 14 and transducers 15 and 16.

An output from the control unit 20 is connected via line 21 to a solenoid 22 being the actuator for the flow control or cut-off valve 14.

A bypass duct 23 is connected between inlet and outlet pipes 10 and 11 such as to bypass cut-off valve 14, and itself contains a cut-off valve 24. Electrical connections are provided between the control unit 20, the solenoid 22 and the cut-off valves 14 and 24.

The control unit 20 may include a pair of pressure indicators 25 and 26 which, according to signals fed from the transducers 15 and 16 provide an indication of the instantaneous gas pressures in the inlet and outlet pipes 10 and 11.

A number, preferably six, of LED indicators 27 to 32 are provided on the control unit 20 to provide operational indications as will be described, and a key operated ON/OFF switch 33 and stop button 34 are also provided.

Within the control unit 20 but not shown in detail herein is a microprocessor and a plurality of timers adjustable to provide pre-set time delays of between 1 and 99 seconds.

Operation of the gas proving system is as follows. With the key switch 33 in the OFF position only LED 27 is illuminated, in green, to indicate that electrical power is supplied to the system.

When the key is inserted and switch 33 is turned to the ON position the inlet gas pressure detected by transducer 15 is read and will appear on pressure indicator 25. If the inlet pressure is less than e.g. 12 millibars then a timer within the control unit 20 will wait for e.g. 10 seconds to confirm a continuous low-pressure situation. At the end of the 10-second period LED 31 will show yellow to indicate the low pressure supply and the main and bypass valves 14 and 24 will remain closed. Further testing will not continue.

If the inlet gas pressure is greater than the predetermined minimum of 12 millibars, then the instantaneous gas pressure in the outlet pipe 11 and manifold 12 read by transducer 16 will be compared to that in the inlet pipe 10 i.e. the signals produced by the pressure transducers 15 and 16 and fed to, and differentiated in, the control unit 20. During a period of 2 seconds LED 28 will show red to indicate that an initial test is being carried out. If the control unit determines that the pressure on the outlet side of closed valve 14 is at least a predetermined proportion, say 80% of the value of the pressure on the inlet side, then no further testing is required since it has thus been determined that the installation at and downstream of the outlet pipe 11 is sound. Th is bei rig so, LED 28 w i 11 be extinguished and the main gas control or cut-off valve 14 is opened whereupon LED 29 will show red to indicate that the gas supply is connected. The instantaneous pressure in pipe 11 is displayed on pressure indicator 26.

If, during the aforementioned test, the pressure in outlet pipe 11 were less than 80% of that in the inlet pipe 10 then a second phase of testing is automatically commenced whereupon a signal from control unit 20 causes bypass valve 24 to open for a pre-set time to charge or fill the system at and downstream of outlet pipe 11. Once the bypass valve 24 is closed the outlet pressure is monitored for a preset time and again during this period LED 28 will show red to indicate that a test is being conducted.

At the end of this period if the outlet pressure is at or above the predetermined proportion of the value of the inlet pressure then LED 28 is extinguished -6and the main cut-off valve 14 is opened whereupon LED 29 is illuminated to indicate that the gas supply is connected.

If, at any time, during the second test phase the outlet pressure falls below 80% of that of the inlet pressure then LED 30 will show yellow to indicate that the system has failed the test and the main cut-off valve 14 will not be opened. The system cannot be activated until the key switch 33 has been turned to the OFF and then the ON position.

It will be seen that under all test conditions, the control unit, via the separate pressure transducers 15 and 16 is evaluating the pressure difference between the inlet and outlet sides of valve 14 and is not simply measuring and monitoring the outlet pressure. By comparing inlet and outlet pressures in this way the system compensates for pressure variations in the supply due to seasonal or other fluctuations.

During normal operation of the system the gas supply can be shut off in a number of ways. These include simply turning off the key switch 33 or, alternatively, pressing the emergency stop button 34 which also causes the main cut-off valve 14 to close. If this occurs LED 29 is extinguished and LED 32 will show yellow to indicate that the emergency stop button 34 has been pressed. The system must then be re-set by turning the key switch 33 to the OFF and then the ON position.

The main gas cut-off valve 14 will be closed also in the event that the gas inlet pressure should fall below the pre-determined minimum of say 12 millibars for at least 10 seconds. In these circumstances LED 31 will be illuminated and once again the system can be re-set only by turning the key switch 33 to the OFF and then the ON position. A time delay before the system responds to low gas pressure is provided to ensure that the pressure has not fallen momentarily due to valves in the system being opened.

The control unit is designed also to ensure that should the electrical power supply fail then the valve 14 will he closed automatically and the system cannot be restarted until the key switch 33 is turned first to the OFF and then the ON position.

The microprocessor within the control unit 20 is programmed such as to be capable of doing a checksum to verify that it has not become corrupted during normal running. In the event of a fault the system will perform an internal reset and will close off the main valve 14 such that it must be reset once again by turning the key switch 33.

If preferred, bypass 23 and valve 24 may be omitted, and the main cutoff valve 14 used to charge the system.

Referring now to Fig. 2, where like parts are denoted by like reference numerals, in a gas burner system operating above a certain power output, legislation requires that there shall be two cut-off valves disposed in series in the gas supply duct thus -8to ensure continuing safety in the event of one of the valves failing. It Is a requirement that when the burner is first operated the valve system must be proved to check for any leaks or non-operation of the valves. This can be determined once again by monitoring the pressure differential across the first valve by use of the transducers 15 and 16 and the control unit 20.

In this case therefore, a second cut-off valve 40 is provided between the valve 14 and the outlet pipe 11. The valve 40 is actuated by a solenoid 41 and thus there is a short length of pipe 42 between valves 14 and 40.

The double valve system as illustrated herein operates as follows.

Initially, both valves 14 and 40 are in the closed position. When the control unit 20 receives a signal from the main burner control, valve 40 is opened thus allowing any gas trapped in the pipe 42 to be vented to atmos phere through the bu rner f 1 ue. Valve 40 is then closed and the pressure in the pipe 42 between the two valves is monitored for a pre-set time. If no significant pressure increase is detected at the end of this period it can be assumed that valve 14 is gas tight. Thus, valve 14 can be opened for a preset time sufficient to pressurise the connecting pipe 42, and then closed.

Control system 20 then receives pressure differential signals from transducers 15 and 16 for a pre-set time whereupon if the pressure in the connecting pipe 42 has not decreased to a level less than the predetermined proportion of that in the inlet -9pipe 10, it can be assumed that the valve 40 is gas tight. Thus the control unit may transmit a signal to the main burner control whereby both valves 14 and 40 can be opened and normal operation can commence.

In relation to both embodiments of figures 1 and 2 it will be seen that inlet and outlet pressures can be continuously monitored and shown on indicators 25 and 26 thus providing a read-out for commissioning and maintenance purposes.

A further device illustrated at 42 in Fig. 1 and connected to control unit 20 serves to shut off the gas supply to the system 12 after a predetermined time.

In the event that the system is inadvertently left switched on then after the predetermined time which may be preset as required at any time interval, between two and five hours, the valve 14 will be closed automatically, and a further LED 43 labelled, for example, AUTO STOP will illuminate to indicate an automatic shut down. This mode can be reset in the normal manner by turning the key switch 33 to the OFF position and then to the ON position. The automatic cut-off is designed to prevent the gas supply being left on over night or over a weekend, for example. The period during which the system may stay active before automatic cut-off may be preset during manufacture or by the user, and if required the automatic cut-off may be disabled within the system for example when installed in a restaurant or hotel. Preferably, the LED 43 is designed to flash for one second in every five seconds during the half hour period before shut off thus to warn the operator that the system is about to shut down. Thus, an automatic failsafe system is -10 provided whereby the gas supply cannot remain on inadvertently during periods of nonuse.

Some conventional systems include a 24-hour or 7-day timer which may be set to turn off the supply of gas at night and during the weekends but such timers need to be reset twice a year at the change over between GMT and BST. The present system incorporating an automatic shut off after a predetermined time avoids this problem.

Since the valves 14 and 40 and transducers 15 and 16 could be mounted at some distance from the control unit 20, an appropriate electrical connection e.g. RS 485 is used to transmit the signals such that no data corruption will occur.

While the component parts and operation of the system have been described in relation to a gas proving device, nevertheless the device is equally applicable to other ducted fluids such as liquids and vapours and the device may be readily applied to any existing fluid distribution system connected to one or more pipework systems downstream of the cut-off valve.

Claims

A fluid pressure proving system comprising a flow control valve adapted to be introduced into a fluid supply duct, actuating means adapted selectively to open and close the flow control valve, a fluid pressure sensing device connected to the flow control valve to sense a pressure difference between inlet and outlet sides of the flow control valve and having transducers to produce signals representative of the pressures at the inlet and outlet sides, and control means responsive to signals from the transducers and adapted to determine a pressure differential and to operate the actuating means to close the flow control valve when the fluid pressure at the outlet side has a value less than a predetermined proportion of that at the inlet side.
A fluid pressure proving system according to Claim 1, wherein the flow control valve is a solenoid operated valve.
3.

A fluid pressure proving system according to Claim 1 or Claim 2, wherein the fluid pressure sensing device is a pair of pressure transducers communicating with the inlet and outlet respectively of the flow control valve.
4. A fluid pressure proving system according to any preceding claim, wherein the control means includes a key-operated switch, an emergency stop switch, and a plurality of indicators and a micro-processor.
5.

A fluid pressure proving system according to any preceding claim, including a bypass duct connected between the inlet and outlet sides of the flow control valve and having a separate cut-off valve thus, when required, to bypass the flow control valve.
6.

A fluid pressure proving system according to any preceding claim, including, an automatic timed shut-off device adapted to close the flow control valve after a predetermined period.
A fluid pressure proving system according to any preceding claim, including at least one adjustable timer thus to provide a pre-set time delay in one or more phases of operation of the system.
8.

A fluid pressure proving system according to any preceding claim, wherein the control unit includes means to cause closure of the flow control valve automatically upon failure of an electrical power supply to the system.
9 A fluid pressure proving system according to any preceding claim, including pressure indicators providing visual indications respectively of the pressures at the inlet and outlet sides of the flow control valve.
10. A fluid pressure proving system according to any preceding claim, including a further flow control valve connected to the outlet side of the first flow control valve and having a separate actuator connected to the control unit, and means in the control unit for selectively opening and closing the two flow control valves thus to enable the integrity of each valve to be tested.
11.

A fluid pressure proving system according to any preceding claim, when included within a fluid distribution means in combination with a fluid supply duct and a distribution duct including a plurality of user outlets each of which includes a cutoff valve.
12. A fluid pressure proving system substantially as hereinbefore described, with reference to, and as illustrated in, the accompanying drawings.