Sun. Jun 20th, 2021

City gas distribution

Transporting future fuel

#67 Valves in CGD

5 min read

Several types of valves are used in the City Gas Station & District Regulating Station namely Slam shut valves, Pressure Regulating Valve, Creep Relief Valve, Control valve, Isolation Valves, Non-Return Valves.

Pressure Regulator lower the gas pressure & thus control the flow rate of the gas. Pressure reduction skids are installed for the reduction of gas stream pressure at City Gas Station & District Regulating Station. Apart from that, regulator valves are also installed in domestic, commercial & industrial setups to further reduce the temperature for the end-user. Creep relief valve & Slam shut valve are installed in the skid for safety purpose. The creep relief valve operates when the stream pressure is more than 1% of the desired level pressure. In case of pressure fluctuation, gas is vented out to stabilize the flow. If the pressure is more than 10% of the decided flow pressure, the slam shut valve will immediately shut off & cut the gas supply.

  1. Spring loaded pressure regulator – A spring loaded regulator has three basic components i.e. Loading element, Sensing element & Control element. A pressure reducing regulator reduces a high upstream pressure of a gas to a lower stable pressure for user’s application.
  2. Loading element provides a pre-load force which determines the outlet pressure of the regulator. Loading element provide the force which is transmitted through the sensing element to the control element, to provide the desired outlet pressure.
  3. Sensing element senses the changes in the outlet pressure through a cavity located underneath it, allowing the regulator to react accordingly to these changes. The sensing element links the loading element to the control element.
  4. Control element reduces the inlet pressure, to a lower working pressure. This pressure is maintained by changing the orifice area. The valve moves towards or away from the regulator seat causing the orifice to become larger or smaller. Thus medium pressure gas is passed through the variable orifice to maintain the desired set pressure.
  1. Slam-shut valve – In conjunction to the control relief valve, the SSV also becomes active when the pressure in the active monitor becomes more than 10% of the desired pressure. In the first stage, increasing pressure pushes the diaphragm up, lifting the ball bearing cage with it. The bearing cage lifts, allowing the bearings to move radically outwards, allowing shaft collar clearance to pass by. The spring force pulls shaft downwards past ball bearings. At the end, the main stem moves down releasing valve disc allowing it to close under spring load.
  • Isolation & Control Valve – An isolation valve is a valve in a fluid handling system  that stops the flow of process media to a given location, usually for maintenance or safety purposes. They can also be used to provide flow logic (selecting one flow path versus another), and to connect external equipment to a system. A valve is classified as an isolation valve because of its intended function in a system, not because of the type of the valve itself. Therefore, many different types of valves can be classified as isolation valves. There are many types of isolation & control valves in the industry. In CGS & DRS isolation valves of 1/2″, 3/4″ & 1″ are used. Ball valves can be used as isolation valves in which full open/closed position shall be at 90 degree. A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level.
  1. Non-Return Valves – Non-Return valves are check valves that allow fluid to flow in one direction. Check valves have two openings in the body. Through one opening the fluid enters & leaves from the other side. The external shells of check valves are plastic or metallic in nature.

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