PRESSURE REDUCING & REGULATING SYSTEM
Pressure regulating stations (PRS) /Gas trains are required to supply certain quantity of gas at specific operating pressure. The PRS/ Gas trains essentially performs a safety function i.e. limit the downstream pressure up to predetermined set point though inlet pressure varies between maximum to minimum.
Incidentally the limitation of pressure in the downstream end is supported by safety devices like Slam shut off valve, safety relief valve, creep relief valve etc.
The pressure regulators and safety devices are powered by gas itself, so that this function does not require any external power source i.e. comp. air or electrical supply.
Ball valves: to isolate the system from main supply or to isolate the either side of PRS.
Filtration unit: A filter protects rest of the system from any debris or dust that may carry with gas stream. Debris may for example consist of parts accidently left in the pipe during construction. It could also result from swarf from drilling holes & taps or welding & sand from construction or fine iron oxide dust.
Slam shut off Valve: Slam shut off valves is installed after Filter & before pressure regulator. Slam shut off valve close the supply of gas when a downstream pressure exceeds a pre-determined limit.
Pressure regulator: Pressure regulator maintain downstream pressure at certain quantity of gas , irrespective of variation in upstream pressure from maximum to minimum limit. Spring loaded or Pilot operated pressure regulators are used.
Relief valves: Creep relief Valve: A slight weeping of pressure regulator/ increase in downstream due to rise in downstream surrounding temperature result in increasing the downstream pressure to dangerous level, such creep pressure is blown off through creep relief valve.
Safety Relief Valve: The safety relief valve set at higher pressure than slam shut off valve so that the safety relief valve will operate when slam shut off valve fails to operate.
Pressure gauges: To monitor upstream and downstream pressure, the pressure gauges are installed. Isolation valve is provided with each pressure gauge for easy replacement of pressure gauges in case of failure.