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Safety shut off valves

Description

Safety shut off valves or slam shut valves, are designed to close the gas flow through the gas line in the event of gas pressure regulator malfunction if pressure after the regulator gets higher than the safety shut of valve preset pressure value. Further opening of gas line is possible only by manual operation on slam shut valve.

For the installations where sudden closing of slam shut off valve can cause serious problems, common principle is designing and installation of two parallel regulating lines with same full capacity, so in the event of slam shut off valve activation on one line, the other gas pressure regulating line takes control of pressure regulation automatically.

Operation

If the pressure under the diaphragm or seat of the safety slam shut off valve is higher than the force generated by the preset spring, diaphragm is raised, causing the sleeve which is integrated with the diaphragm to move the valve is closed. Opening of gas line is possible only by manual operation on slam shut valve.

Safety slam shut off valve activating pressure is set by adjusting the compression of the spring through an appropriate ring. The set pressure should be higher value than activation pressure of safety relief valve. It is recommended that set pressure for slam shut off valve needs to be 15% higher than safety relief valve activation pressure.

Installation

Safety slam shut off valves are normally installed upstream of the pressure regulators. For keeping the pressure in the installation bellow the set value, pressure is tapped after the regulator, so if the tapped pressure is higher than pressure that is set on slam shut off valve spring, the activation will occur, gas line will be closed preventing further pressure increase.

Technical data

For proper safety valve selection, except flow capacity, several more technical informations are required:

Activation pressure[bar]0.02 ... 200
Operating temperature range[OC]-15 ... +60
Ambient temperature range[OC]-30 ... +60
Nominal diametersDN15 ...... 200
Standard pressure categoriesPN16, 25, 40, 63
ANSI 150,300,600
FlangesRFEN1092, ANSI B 16.5

Materials

Commonly used materials for safety relief valves working with natural gas and LPG, as non corrosive medium, are carbon steel with nitrile rubber for control diaphragm, like one example given bellow:

Valve bodyC22.8, ASTM A105 Steel
Safety valve bodyAlSi
Diaphragm80NBR
Seals 80NBR

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