Shut-off devices on gas pipelines: types of shut-off valves and features of their installation

It's no secret that gas distribution systems in settlements, as well as apartment and private buildings, are a source of constant danger. The slightest leak of blue fuel can lead to serious problems, even an explosion. And you must agree, to prevent this from happening, it is extremely important to carefully and constantly monitor the condition of gas pipes and fittings on them.

One of the main shut-off elements here is a valve or tap, which, if necessary, turns off the gas in the pipe. And in order for these shut-off devices on gas pipelines to work properly, their selection and installation should be approached with great care. Next, we will analyze all types of such equipment and the rules for its installation.

The content of the article:

Types of gas shut-off devices
Placing shut-off valves on the pipe
Conclusions and useful video on the topic

Types of gas shut-off devices

Valves for gas pipelines can be: shut-off, safety, emergency and reverse action. To turn off the gas manually, the first version of the devices under consideration is used.

They are installed on pipes so that, if necessary, they can quickly shut it off and stop the supply of methane or propane to a particular section of the gas main.

It is prohibited to use water taps, valves and gate valves to shut off natural gas. The switching devices under consideration must be designed to work with gases and liquefied hydrocarbons

Shut-off valves on gas pipelines are installed in the form:

gate valve;
cranes;
water seals;
valves.

Each of these options is designed for its own section and type of gas pipeline.For example, valves, taps or water seals are installed on low-pressure gas pipelines, and on highways high pressure – mainly only valves. And valves are generally used extremely rarely.

Shut-off valves are also divided into devices:

manual;
automatic fast acting.

The former are usually used where the speed of closing the pipe is not very relevant. And the latter, with a magnetic or pneumatic drive, are designed to quickly shut off the gas in case of accidents and detect leaks.

Option #1 – wedge valves

The most common shut-off devices in the case of gas pipelines are valves with a gate that moves inside them parallel to the flow of the working medium. They consist of a body, a cover with a valve, a spindle and an internal wedge-shaped valve.

Wedge valves are used on internal and external gas pipelines, therefore they are produced with DN 25, 50, 150, 350 and 600

Wedge valves are divided into two subtypes:

With non-retractable spindle.
With retractable spindle.

The first version of these disconnecting devices is intended for installation on underground gas pipelines in special wells. It is smaller in size and is usually equipped with an electric drive to remotely control the gas flow in the pipeline.

The second option is more durable and easier to use. The retractable spindle is not exposed to the working environment and lasts longer. Plus, the entire screw mechanism in this device is visible and accessible for repair.

Among the advantages of valves:

extreme simplicity of the locking device;
low hydraulic resistance;
small dimensions in height and length.

Their main disadvantage is a decrease in the tightness of the valve when the seals become clogged and/or worn out.

The retractable spindle is more practical and durable, but when the valve is fully open, it rises high above it and takes up a lot of space.

If the gas pipeline has a working pressure of up to 6 kgf/cm², then the wedge valves on it are installed from gray cast iron. And if the pressure inside is more than 6 kgf/cm², then analogues made of steel or ductile iron are used.

Option #2 – plug taps

The taps have a metal plug inside that rotates around its axis, which is tightly ground to the socket. When opening the disconnecting device with the handle 90⁰ Regarding the gas flow, the plug does not prevent its passage through the fittings, but when closed, it completely blocks the pipe.

Plug taps are made from:

brass;
bronze;
gray cast iron;
become.

For internal gas pipelines and for turning off/on gas appliances, it is recommended to use brass or bronze taps. Due to their high resistance to mechanical stress and increased anti-corrosion characteristics, they will last much longer than other options.

If the gas pipeline has a diameter of more than 25 mm, then cast iron taps are usually installed on it, since they are cheaper. And in high-pressure systems, steel devices are already used.

The highest quality taps for gas pipelines are made of bronze or brass. They are expensive, but very durable and practically eliminate the occurrence of sparks when a metal object hits the reinforcement

Among the advantages of shut-off valves:

low hydraulic resistance;
small overall dimensions;
possibility of connecting an electric drive for automation;
speed of opening/closing (just turn 90⁰ handle);
simplicity of the device.

Moreover, these valves are characterized by low tightness when closed at high gas pressure in the pipes. Plus, if lubrication is poor, the plug often “sticks” to the body. And in order to tear it off, serious efforts have to be made, which negatively affects the service life of the fittings.

Based on the connection method, the valves are divided into flanged, pin-type and threaded (coupled). Moreover, the latter are prohibited by GOSTs from being installed on underground gas pipelines, as they can provoke a gas leak.

There are also ball valves. They are produced in D_U from 50 to 1400 and are intended for main pipelines. They are rarely used in intra-house networks due to their high cost and more complex design.

Option #3 – water seals

Hydraulic seals use ordinary water as a closing element. This fittings are intended for installation on low-pressure underground gas pipelines and exclusively below the soil freezing level. It is highly reliable, but quite difficult to maintain.

Unlike valves, hydraulic valves can be installed directly on the pipeline without installing a well

Water seals are usually installed on branches from the central highway to any facility and on inputs to the building. They are durable and very reliable. However, such fittings only allow you to completely shut off the gas, and not regulate its flow.

Placing shut-off valves on the pipe

Before installation in the gas pipeline system, taps and valves undergo external inspection, lubrication, gasket checks and leak testing. In this case, the location for installing the shut-off device on the gas pipeline is selected in accordance with the recommendations SP 42-101-2003.

Installation of shut-off devices on a gas pipeline is carried out underground - in a well or directly in the ground, or above ground - in fireproof cabinets, on walls or pipes.

Installation of shut-off valves is carried out so that they can be inspected, serviced and, if necessary, dismantled.

The location for inserting the shut-off device into the gas pipeline is selected:

on branches from the main line - outside the consumer’s territory and no further than 100 m from the distribution pipeline;
if there are parallel pipes - at a distance convenient for servicing both devices;
at the outputs and inputs of hydraulic fracturing stations - at a distance of 5–100 meters from the point;
when a gas pipeline crosses an overhead power line - outside its security zone;
on the walls of private houses - at least half a meter from door and window openings;
near the gas stove - on the side of the pipe at the level of the connecting fitting at a distance of 20 cm or more from the tile;
for a gas stove or water heater with top wiring - at a height of 1.5 above the floor.

If the fittings are installed at a height of more than 2.2 m, then a metal ladder and/or platform must be provided at this level.

If wells are being installed, they should be made from fireproof building materials. Stone, brick, concrete, etc. will do. But no wood or plastic.

For internal and above-ground external gas pipelines with steel and polyethylene pipes used for natural gas and LPG in the vapor phase with pressure up to 0.005 MPa, conventional ball valves are recommended

Flange connections should be sealed with the following gaskets:

paronitis – at pressure up to 1.6 MPa;
oil and petrol resistant rubber – at pressures up to 0.6 MPa;
aluminum - at any pressure;
copper - at any pressure (except for gas pipelines with sulfur dioxide);
high and low density polyethylene, fluoroplastic - at pressures up to 0.6 MPa.

It is worth noting that rectangular and square flange connections are quite difficult to process and it is difficult to ensure reliable tightness of the connection, so it is better to give preference to round flange connections.

Disconnecting devices must be installed:

at the entrance to the building;
in front of an external installation consuming gas;
at the inlet and outlet of hydraulic fracturing;
on long dead-end branches;
on branches from the general highway to a village, quarter or enterprise;
when the pipeline crosses railways and highways, as well as water barriers.

All installed rotary taps must have a handle rotation limiter of 90⁰, and the valves are an indicator of the degree of opening.

And all devices with a diameter of up to 80 mm are required to have a mark on the body indicating the direction of gas flow.

Conclusions and useful video on the topic

Technology of operation of control and shut-off valves:

Film about shut-off devices for gas pipelines:

Gas shut-off valves vary in design, material of manufacture and type of connection. It is recommended to install regular plug valves on internal gas pipelines, and for large-diameter main pipes, hydraulic seals and valves are more suitable. The location for installing such devices is selected in accordance with the general rules for the design and construction of gas distribution systems.

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