How do I size a pressure relief valve?

The valve size must correspond to the size of the inlet and discharge piping. The National Board specifies that the both the inlet piping and the discharge piping connected to the valve must be at least as large as the inlet/discharge opening on the valve itself. The connection types are also important.

How do you calculate relieving capacity of a safety valve?

With a set pressure of 100 psig and an overpressure of 10% of the set pressure, or 10 psig, the upstream relieving pressure, P1, is 110 psig. For a conventional relief valve, no backpressure cor- rection is necessary (Kw = 1.0). The volumetric discharge rate, Q, through the relief valve is given as 300 gpm.

How is the relief pressure of a valve calculated?

The Set Pressure is usually given in terms of gauge pressure, therefore any Back Pressure is added to the set pressure and overpressure to calculate the Relief Pressure in absolute units.

What are the capacities of safety relief valves?

– search is the most efficient way to navigate the Engineering ToolBox! Safety valves and maximum relief free air capacity: For full table – rotate the screen! A safety relief valve must be capable of relieving the capacity of the connected compressor (s) at operating pressure.

What should the operating pressure be on a relief device?

Typically, relief devices are set to open at the MAWP. The expected maximum operating pressure should be low enough to prevent relief device activation during routine operations. The difference between the set pressure and the maximum operating pressure is known as the operating margin.

When do you open a pressure relief valve?

Pressure relief valves must start to open at or below the maximum allowable working pressure of the equipment. When multiple pressure relief valves are used in parallel, one valve should be set at or below the MAWP and the remaining valve(s) may be set up to 5% over the MAWP.