What is a safety valve?
Definition of a safety valve according to DIN EN ISO 4126-1
A safety valve is a valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure beeing exceeded, and which is designed to reclose and prevent further flow of fluid after normal pressure conditions of service have been restored.
The difference between safety valve and pressure relief valve
- Certified valves with TÜV / PED and/or CE Type Test Approval
- Normal lift- Full lift opening / closing characteristic
- Higher blow-off capacities than pressure relief valves
Pressure relief valves
- Valve without certification/approval (without safety function according to PED)
- Proportional opening- / closing characteristic
- Lower blow-off capacities than safety valves
When do you use a pressure relief valve or a safety valve?
Whether a plant operator is allowed to use a pressure relief valve, or if he must usa a certified safety valve depends primarily on the type of application or plant. Both valve types are intended to be the last safety device in a system. In the case of systems or plants requiring official approval or which fall under the European Pressure Equipment Directive (PED), the valve must hold corresponding approvals and certifications.
Functioning of a safety valve
The function of a safety valve is based on a simple balance of forces between the force of the pressure spring and that of the medium.
In the closed position, which is the normal position of the valve when installed on the plant, the spring force is greater than the force of the medium and the valve seals the plant tight. In case the set pressure of the valve is exceeded due to an increase in the plant pressure, the valve opens to relieve the excess pressure by blowing-off the medium.
After excess pressure in the plant has been relieved below the closing pressure, the valve closes completely.
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