A pressure relief valve is a safety appliance which is capable of instantaneously evacuating a high flow rate. It protects networks against overpressure due to sudden changes in flow rates (water hammer effects) for example when closing a valve too quickly or in case of sudden moving of air pockets inside the pipes. The range goes from DN60 to DN200, PFA10, 16 or 25 bars. The valve pressure set point has to be indicated by the customer at the order time.

Material and coating

Hydraulic characteristics

The pressure values to be considered are:

• PMS : network maximum service Pressure,

• Valve pressure set point : Pressure at beginning of opening,
• Overpressure: Pressure increase, compared with the pressure set point, to reach the maximum drained flow rate.

The valve pressure set point has to be indicated by the customer at the order time.

The valve pressure set point is given by the network maximum service Pressure (PMS) increased by 5 to 10 %.

Maximum drained flow rate

Choice of DN

DN of the appliance is determined as a function of the flow rate to be evacuated. As a general rule we should choose the flow rate of the pipe on which the relied valve is located.

Installation

The pressure relief valve is to be installed in a vertical position as close as possible to the source of the water hammer effects.

If it is installed in a manhole, an evacuation pipe must be provided. An isolating valve is recommended to enable work to be carried out on the relief valve (regulating, maintenance…) without interrupting the operation of the network.