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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.
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