Gas fittings and equipment are intended for use on pipelines of transportation and supply systems, as well as the distribution of blue fuel. With the help of these devices and mechanisms, the supply is switched on and off, the amount, direction, or pressure of the gas flow is changed. All fittings are characterized by the following main parameters:
- nominal (conditional) pressure;
- nominal diameter (nominal bore).
The first characteristic is understood as the maximum pressure at a temperature of 20 ° C, which ensures long-term service of various connections of fittings (equipment) and the pipeline. The nominal size (DN or DN) is understood as a characteristic used in pipeline systems, networks as a parameter of the parts to be connected.
According to their purpose, fittings for gas systems are divided into the following types:
- Shut-off valves – for periodic shutdowns of equipment and instruments, as well as individual sections of the gas pipeline from its other parts. In this capacity, valves, taps, and latches are used.
- Regulating – to change and maintain pressure within the specified limits. It includes dampers, gate valves, and the like.
- Safety – used to prevent the gas pressure from rising above the permissible value. This is a relief safety valve.
- Shut-off and emergency – for quick automatic shutdown of various gas appliances, devices, as well as pipelines, where the specified mode of their operation is violated. For example, a safety shut-off valve.
- Reverse acting – prevents the gas flow from moving in the opposite direction.
- Condensate drain – automatically removes the condensate that accumulates in condensate traps and lower points of pipelines.
Ways of connecting gas devices and fittings
There are the following connection methods:
- With flanges – used for fittings with a nominal bore of more than 50 mm. Connection to a tank or pipeline is made using flanges. The main advantage is the possibility of multiple installations and dismantling, as well as great strength, reliability, and applicability for a very wide range of passages and pressures. Disadvantages: large weight and dimensions, over time, the possibility of loosening the tightening with a subsequent loss of tightness is not excluded.
- Coupling connection – for equipment with a passage of 65 mm or less. The connection is carried out using couplings with an internal thread, using a hex key.
- Tsapkovoe with external thread. A device (for example, a tap) is screwed directly into the body of another device or device by means of a thread.
- By welding – rarely used non-separable type of connection. Advantages – reliable and complete tightness, minimum maintenance. The disadvantages include the increased complexity of replacement and installation of fittings.
- Nipple – connection to a container or pipeline is made using a nipple.
- Fitting – using a fitting.
- Coupling – the outlet and inlet pipes are connected to the pipeline flanges by means of studs with nuts located along with the equipment or valve body.
Gas shut-off valves – main characteristics
Gas shut-off valves are the most common equipment for gas systems, among which valves are most often used. They are widely used to shut off the gas flow in pipelines with nominal (nominal) bore diameters of 50-2000 mm, where the working pressure is 0.1-20 MPa. In the valve, the passage is closed by moving the locking device in a direction that is perpendicular to the axis of the gas flow. According to the device of constipation, this equipment is divided into:
- Wedge gates – with a wedge gate, which has sealing surfaces at a certain angle relative to each other. They can be with a hinged valve, which consists of 2 discs, and a solid (wedge).
- Parallel – the valve consists of 2 discs or halves, between which there is a spacer wedge.
The advantages of gate valves over the rest of the valves:
- low resistance to flow in the fully open position;
- lack of turns of the gas environment;
- relatively small face-to-face length;
- ease of maintenance;
- the ability to supply gas in any direction.
Taps and valves are fittings used to quickly connect or disconnect an apparatus, device, or pipeline, as well as regulate the flow of blue fuel through a gas pipeline. The shutter shape is distinguished:
Advantages of taps and valves: multi-purpose, low height and length, can provide a full passage of gas.
Damper – this valve is referred to as shut-off and control equipment, with the help of which the gas flow rate is regulated and its supply in the pipeline is stopped. It consists of a body (usually steel or cast iron), a shut-off body, which is a disc, a drive shaft, and sealing elements. Valves are used in a wide range of temperatures and pressures of the working medium (if the requirements for the tightness of the locking body are not high). They are produced in series for pipelines with a nominal bore of 50-2400 mm and more. Dampers advantages:
- simple construction;
- low metal consumption and weight;
- small face-to-face length;
- the number of elements is minimal;
- low cost.
The listed advantages are obviously the more, the higher the nominal diameter.
Criteria for the correct selection of equipment for gas systems
When choosing fittings for gas systems, one should take into account the chemical and physical properties of the materials used in their manufacture. Natural gas does not affect any ferrous metals in any way, due to which equipment for gas systems can be cast iron and steel. Cast iron fittings have lower mechanical properties than steel fittings and, therefore, can be used at gas pressures that do not exceed 1.6 MPa.
Under the existing norms of the limiting level of hydrogen sulfide content (per 100 m3 of gas – 2 g), blue fuel has practically no effect on copper alloys. In this regard, fittings intended for internal household gas equipment and networks can be made of copper alloys. Valves that are particularly robust must be used with stainless steel insert O-rings.