Category Archives for Pressure Relief

Relief Header Design

The relief header is a system of piping connecting the outlets of all the relief valves into a common pipe or header that goes to the relief scrubber and then out the vent as shown in Figure 13-11. There are … Continue reading

25. September 2009 by and
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Relief Valve Vent or Flare Tip

A pipe that releases gas to disperse into the atmosphere is called a vent. If the gas is burned at the tip, it is called a flare. In its simplest form, a vent or flare tip is a pipe. Sometimes … Continue reading

25. September 2009 by and
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Relief Valve Vent Scrubber

A vent scrubber is a two-phase separator designed to remove the liquid from the relieving fluids before the gas is flared or vented. The liquid is returned to the process. Design of vent scrubbers is covered in two-phase separators. A … Continue reading

25. September 2009 by and
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Relief Valve Installation

Each relief valve should be equipped with inlet piping no smaller than the valve inlet flange size, and inlet piping should be as short as practical. Inlet piping should be designed so that the pressure drop from the source to … Continue reading

25. September 2009 by and
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Two-Phase Flow Standard Sizes

Two-Phase Flow There are no precise formulas for calculating orifice area for twophase flow. The common convention is to calculate the area required for the gas flow as if there were no liquid present and the area required for the … Continue reading

25. September 2009 by and
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Liquids Flow Rate

Conventional Valve, Balanced-Bellows Valve, or Pilot-Operated Valve The corresponding equations for liquid flow are the following: Note that a preliminary orifice size must be determined in order to calculate Reynolds number. If the viscosity correction is significant, it may be … Continue reading

25. September 2009 by and
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Orifice Gas Flow Rate

The flow rate for gas through a given orifice area or the area required  for a given flow rate is obtained by:

25. September 2009 by and
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Effects of Back Pressure

Back-pressure can affect either the set pressure or the capacity of a relief valve. The set pressure is the pressure at which the relief valve begins to open. Capacity is the maximum flow rate that the relief valve will relieve. … Continue reading

25. September 2009 by and
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Critical Flow

The flow of a compressible fluid through an orifice is limited by critical flow. Critical flow is also referred to as choked flow, sonic flow, or Mach 1. It can occur at a restriction in a line such as a … Continue reading

25. September 2009 by and
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Rupture Discs

These are thin diaphragms held between flanges and calibrated to burst at a specified static inlet pressure. Unlike relief valves, rapture discs cannot reseal when the pressure declines. Once the disc ruptures, any flow into the vessel will exit through … Continue reading

25. September 2009 by and
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