GB2234063A

GB2234063A - Gas sampling device

Info

Publication number: GB2234063A
Application number: GB8915325A
Authority: GB
Inventors: James Edward Bolwell; John Edward Bolwell
Original assignee: British Gas PLC
Current assignee: British Gas PLC
Priority date: 1989-07-04
Filing date: 1989-07-04
Publication date: 1991-01-23
Anticipated expiration: 2009-07-04
Also published as: GB2234063B; GB8915325D0

Abstract

When a leak of fuel gas from a buried gas pipe is suspected a hole is bored in the ground and tip 8 of the tube 6 of the gas detector 2 inserted down the hole. A pump 10 driven by d.c. reversing motor 14 powered by battery 32 via contacts 30 of relay 28 applies suction to the tube 6 drawing gas into it and feeding the gas to gas detection means 12. Should water seeping into the hole be drawn into the tube 6, the tube becomes blocked thereby to gas flow. Thus the working pump lowers the gas pressure in tube 6 to such a value that when a differential gas pressure across switch 18 exceeds a pre-determined value the switch signals electronic control 20 which causes the relay contacts 30 to change over from positions A to positions B to reverse the polarity of the electrical supply to the motor 14. This drives the motor and thus the pump 10 in reverse causing the pump to blow out the water through tube tip 8. The apparatus operates in blow mode for a pre-determined time, and then the control 20 automatically causes the relay contacts 30 to return to positions A so that the pump is driven again to provide suction. <IMAGE>

Description

GAS SAMPLING DEVICE This invention relates to a gas sampling device.

Gas sampling devices in the form of gas detectors are known for detecting when there is a leak in the ground of fuel gas such as from a buried gas pipe. A known gas detector comprises a casing or instrument body from which a sampling tube extends to an open end of the sampling tube. When there is a suspected gas leak in the ground a hole is bored or punched thereinto using a bar, and then the open end of the sampling tube is inserted down the hole. The detector can have manually or electrically operated pump means applying suction force to the tube to draw gas into the open end of the pipe and convey the gas along the tube into the instrument body for detection by gas detection means in the form of one or more pellistors within the body. Because there is always the risk of water seeping into a hole in the ground, there is always the risk of water being drawn into the sampling tube.

Potentially this is serious because the pellistor(s) can be ruined by contact with water. To stop that a 0.5 micron filter (sometimes called a hydrophobic filter) is mounted in the instrument body at the end of the tube just before the gas path reaches the pellistor(s) so that the passage of water to the pellistor(s) is blocked. Near its open end the tube is provided with a removable and replaceable second filter in the form of a pad of cotton wool or close packed fibres. When the pad becomes soaked with water it expands and so clogs the tube that water cannot pass along the tube and into the instrument body. This also stops gas entering the body, sometimes to the annoyance of the person operating the gas detector, who may remove the pack and not fit a fresh one with the result that further operation of the gas detector draws water along the tube.

Notwithstanding that the water cannot reach the pellistor(s) it may still leak from the tube and fill up the instrument body and interfere with electrical or electronic parts and thus stop the detector working. It is also possible that the pad forming the second filter can be a rather loose fit so that before it has a chance to expand and block the tube, water has by-passed the pack and entered the instrument body.

An object of the invention is to provide a gas sampling device which can avoid the aforesaid difficulties.

According to the invention a gas sampling device comprises a tube, means which applies suction force to said tube interior to draw gas into an open end of the tube and convey said gas along the tube from said end, and liquid detection means, and the device being so arranged that when said liquid detection means detects when liquid is drawn into the tube end and substantially blocks off the tube to gas flow past the liquid the application of said suction force is automatically stopped and blowing force is automatically applied to the tube interior towards said end to discharge the detected liquid from the tube out through said end.

The invention will now be further described, by way of example with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic representation of one embodiment of a gas sampling device formed according to the invention.

Fig. 2 is a diagrammatic represenatation of a modification which can be applied to the device in Fig.

1, and Fig. 3 is a diagrammatic repesentation of another embodiment of a gas sampling device formed according to the invention.

In the drawings like or comparable parts are identified by the same reference numerals.

In Fig. 1 a gas sampling device in the form of a gas detector is shown at 2. The gas detector comprises a casing or body 4 from which a sampling tube 6 emerges to extend to an open end or tip 8. For at least part of its length the tube can be flexible.

Included in tube 6 is a pump 10. Another section 6' of tube leads from the pump 10 to gas detection means 12 of any suitable kind known per se capable of responding to and identifying the gas to be detected, for example a fuel gas or some other gas which may be explosive and/or poisonous. A final section 6" of tube connects the interior of the gas detection means 12 with the surrounding atmosphere.The pump 10 can be driven in either forward or reverse directions by a d.c. electric, reversing motor 14. When the motor 14 is driven in the forward direction the pump 10 is also driven in the forward direction and applies suction force to the interior of the tube 6 thus drawing gas into the pipe through the tip 8 and conveying the gas to the detection means 12.When the motor 14 is driven in the reverse direction so is the pump 10 which then applies blowing force along the interior of the tube 6 after drawing in air via the tube sections 6' and 6" and gas detection means 12 towards the tip 8. The pump 10 may be a vane pump.

Another tube 16 branches from the tube 6 at a position intermediate the pump 10 and the tip 8. The tube 16 is connected to a pressure switch 18. The switch 18 is a differential pressure switch arranged to observe when the pressure difference between the pressure inside the tube 6 and a reference pressure, for example that of the ambient atmosphere surrounding the switch 18, exceeds a predetermined value, for example substantially 150mm of H20, when there is a pressure drop in the tube. Also provided within the body 9 is an electronic control 20 including an electronic timer 22.

Control 20 is connected by signal path 24 to a driver 26 of relay 28 comprising a pair of contacts 30 movable by the driver from positions A to positions B when the driver receives a change-over signal on the path 24 from the control 20.

In the absence of a change-over signal the relay 28 automatically returns and maintains the contacts 30 in positions A. When the relay contacts 30 are in the postions A a battery 32 drives the motor 14 and thus the pump 10 is the forward direction. But when C the contacts 30 are in the positions B, the electrical connections between the battery 32 and the motor 14 are reversed and thus the battery drives motor and thus the pump in the reverse direction.

The pressure switch 18 is connected to the control 20 by a signal path 34. to convey electrical or other signals from the switch to the control. Should the switch 18 observe the attainment of said pre-determined pressure difference between the interior of the tube 6 and the surrounding atmosphere, the switch provides a control input signal to the control 20 for the duration that the said pre-determined pressure difference is exceeded.

When the apparatus is initially switched on, the relay contacts 30 are in positions A and thus the pump 10 is driven forwards to suck in gas from the tube tip 8 and deliver it to the gas detection means 12.

Should the tip 8 be inserted into a hole in the ground to detect, for example, a leak of fuel gas and water becomes drawn into the tube 6; then if the water is in such quantity as to occupy the cross section of the tube, this causes a gas-tight blockage situated between the tip 8 and junction 36 of the tube 6 with the tube 16. Consequently the operation of the pump 10 causes a pressure drop in tubes 6 and 16, and when the pre-determined pressure difference is observed by the switch 18 the control signal appears on path 34. This causes the control 20 to give a change-over output signal on path 24 causing the relay contacts 30 to move to positions B. Because the polarity of the electrical supply to the motor 10 is now reversed, the motor 14 goes into reverse and drives the pump 10 in reverse causing it to blow down the tube 6 towards the tip 8 to automatically eject the water.

At the same time as the control 20 commences to give the change-over signal, the timer 22 starts to count out a pre-determined time interval, for example a few seconds, for example four or five seconds. When the pre-determined time interval is counted out, the control 22 automatically cancells the change-over signal and relay contacts 30 automatically return to positions A.

Thus the motor 10 drives the pump 10 forwards again and suction is applied to the tube 6. This may be only momentary if water is again drawn into the tube 6 causing a differential pressure at the switch 18 to again exceed the pre-determined value.

Tube sections 6' and 6" include filters 38 and 39, for example hydrophobic filters, as a safety measure to prevent water reaching the gas detection means 12.

If desired filters 40, for example dust filters, may be provided in the tube 6 at either side of the junction 36.

Visual and/or audible alarm means 42 can be provided and operated by the control 20 to indicate that the pump 10 is blowing along the tube 6 towards its tip 8.

In a modification a valve arrangement 42 may be included in the tube section 6'. This valve arrangement shown in more detail in Fig. 2 comprises two non-return valves 44 and 46. The non-return valve 44 comprises a displaceable valve member or pivotted flap 48 to co-operate with a valve seat 50. The non-return valve 46 comprises a displaceable valve member or pivotted flap 52 to co-operate with a valve seat 54 at the exit of an air inlet tube 56 open at its other end to atmosphere. When the pump 10 is driven in the forward direction gas sucked into the tube 6 through its tip 8 (Fig.1) is blown along the tube section 6' to the gas detection means 12 (Fig. 1) through the open valve 44, whereas the valve 46 is held closed by the gas pressure in the valve arrangement 42.But when the pump 10 is driven in reverse it applies suction to the tube section 6' causing the valve 44 to close, thereby isolating the gas detection means 12 from the pump 10 and tube 6. At the same time the suction applied to the tube section 6' opens the valve 46 allowing the pump to draw in air through the inlet 56 and blow that air along the tube 6 towards it tip 8.

In Fig. 3, gas detector 102 comprises a pump 110 which is driven in the forward direction by electric motor 114 via a sprag or one-way free wheeling clutch 150 when contacts 30 of relay 128 are in positions A, so that the pump applies suction to the tube 6. The pump 110 is driven in the reverse direction (to blow along the tube 6 towards the tip 8) by an electric motor 114' via a sprag or one-way free wheeling clutch 152 when the contacts of relay 128 are in ppsitions B when a change-over signal exists on signal path 24. As for relay 28, the contacts 30 in relay 128 are automatically returned to positions A and maintained there when there is no change-over signal on path 24.

Claims

1. A gas sampling device comprising a tube, means which applies suction force to said tube interior to draw gas into an open end of the tube and convey said gas along the tube from said end, and liquid detection means, and the device being so arranged that when said liquid detection means detects when liquid is drawn into the tube end and substantially blocks off the tube to gas flow past the liquid the application of said suction force is automatically stopped and blowing force is automatically applied to the tube interior towards said end to discharge the detected liquid from the tube out through said end.

2. A gas sampling device as claimed in Claim 1, in which the liquid detection means comprises pressure difference observing means operable to cause said blowing force when gas pressure in the tube falls so that a pressure difference between the tube interior and a reference pressure exceeds a pre-determined value.

3. A gas sampling device as claimed in Claim 1 or Claim 2, in which a reversible electric motor drives pump means included in said tube, said motor being rotatable forwardly to drive the pump means to apply said suction force, said motor being rotatable in reverse to drive the pump means to apply said blowing force to the tube, and the motor being driven forwardly or in reverse according to an output signal from control means responsive to a signal from the liquid detecting means.

4. A gas sampling device as claimed in Claim 1 or Claim 2, in which the tube includes pump means arranged to be driven by first and second motor means, the pump means when driven by the first motor means applying said suction force and the pump means when driven by the second motor means applying said blowing force, and the first or second motor means apply drive to the pump means according to an output signal from control means responsive to a signal from the liquid detecting means.

5. A gas sampling device as claimed in Claim 2, in which the liquid detection means comprises a differential pressure electrical switch.

6. A gas sampling device as claimed in any one preceding claim, wherein timer means controls a pre-determined time duration for which said blowing force is applied before said suction force is re-applied to the tube.

7. A gas detector comprising a gas sampling device as claimed in any one preceding claim, and gas detection means for the supply of gas thereto from said tube

8. A gas detector as claimed in Claim 7, in which a non-return valve arranement is included in a gas path between the gas sampling device and the gas detection means.

9. A gas detector substantially as hereinbefore described with reference to Fig. 1, or Figs. 1 and 2, or Fig. 3, or Figs. 2 and 3, of the accompanying drawings.