GB2261277A - Duel purpose sliding-plate valve - Google Patents

Abstract

A sliding-plate valve, that will function in the normal manner, but which when used in conjunction with towed equipment such as cameras or magnetic or nuclear type inspection tools will allow the passage of the tow-line and/or signal cables, has a closure plate, the leading edge of which is recessed to accommodate such a tow-line or cable. When a line or cable is present, flow through the valve is prevented by movement of the closure plate to an intermediate closed position in which the line or cable is held between the base of the recess and annular seals which cooperate with the closure plate. Typically the valve is used for isolating gas mains at pressures up to 2 bar. <IMAGE>

Description

DUAL PURPOSE SLIDING PLATE VALVE This invention relates to improvements to valves of the sliding plate type as used in the gas industry.

Sliding plate valves are used extensively on gas (and water) mains to provide a low profile means of isolating the main when carrying out various routine maintenance operations, such as internal pipe spraying and flow-stopping.

Recently a great deal of emphasis has been placed on mains inspection in order to improve flow characteristics and also to examine for possible areas of failure such as cracks and corrosion in cast iron mains.

Inspection surveys include traversing sections of main using cameras and magnetic and nuclear sensing devices.

These items of equipment can be towed, rodded or motorised along the inside of the main using sliding plate valves as a means of entry and exit.

One major difficulty when operating in mains at pressure (in gas mains typically up to 2 bar) is preventing leakage to atmosphere.

This becomes even more difficult when the tow line or electrical/electronic signal cables must pass through the valves and then be connected to the various inspection tools.

According to the present invention, a slide plate valve is provided with a special sealing plate and seals, and the introduction of a pressure/purge connection which will allow tow-lines and cables to be effectively sealed during connecting to equipment and while traversing through the main. At the end of the inspection run the valve allows the equipment to be safely disconnected.

The embodiment of the present invention into a typical plate valve arrangement is described with the aid of drawings as follows.

Figure 1. Shows a diagrammatic arrangement of a typical inspection tool run with special valve at entry and exit positions.

Figure 2. Shows a section through the plate valve in fully closed position as required for normal isolation of the gas main.

Figure 3. Shows a section through the plate valve in the partially closed position necessary when the winch wire or electronic signal line/cable prevents complete closure but demands effective sealing. This is generally necessary when connecting and disconnecting the towing lines and electronic signal lines.

Figure 4. Shows how the 'V' shaped valve-plate collects the wire or cable into the notch.

Figure 5. Shows how the notch closes around the wire (or cable) and lightly compresses it into the top and bottom seals.

The vent point shown in Figures 2, 3, 4 and 5 allows the safe venting of any leakage gas which may pass the bottom seal, or alternatively allows the introduction of Nitrogen under pressure as a means of surpressing leakage of gas to atmosphere.

Figure 6 Shows an enlarged view of the method of trapping the wire/cable between plate and seals.

Claims (1)

1. Claims:

   A valve of the sliding plate type which will (i) Function in the normal manner.

   ii) When used in conjunction with towed equipment such as for camera surveys, inspection tool surveys etc, will allow passage of towing line or electrical/electronic signal cables but will seal effectively around such lines so as to allow safe connections and disconnections to be effected.

   iii) Where gas leakage cannot be prevented due to minor leakage paths due to the nature of manufacture of the lines a purge/pressure point is introduced to either bleed off gas leakage for safe venting or alternatively to introduce nitrogen (N2) at a slightly higher pressure than the mains pressure so that gas cannot escape to atmosphere.