Blow-off pipe in the steam area

The following criteria must be observed when installing the safety valve blow-off pipe for steam:

• The blow-off pipe must be dimensioned so that an inherent back-pressure amounting to 10% of the excess pressure is not exceeded when discharging.
  • Up to a pipework length of 10m and a maximum of 5 elbows: 2 DN larger than the nominal outlet diameter of the safety valve.
  • If the pipework is longer or a greater number of elbows are used, a detailed calculation of the pressure loss in the pipework is recommended.
• A sloping section of pipe (≥0.5%) must initially be mounted at the valve outlet to create a low point in the blow-off pipe from which liquid can drain off via a device which cannot be shut off.
• If there is a drainage hole in the seat of the safety valve, additional drainage should be provided.
• The blow-off pipe must be isolated from other pipework (e.g. air vent lines, expansion lines, safety valve blow-off pipes) and protected against freezing.
• Blocking of the drainage by dirt or foreign matter must be avoided.
• Harmless discharge of condensate must be ensured.
• The blow-off pipe must be installed and fastened so that the safety valve is not exposed to shear, bending or torsional forces (e.g. by using supports, spring-loaded pipe hangers). The reaction forces when discharging must be taken into consideration.
• The blow-off pipe must terminate harmlessly.

The functional capability of the safety valve and blow-off pipe is verified on site by the approved notified body during acceptance testing of the steam boiler, and normally at full combustion output during real operation.

Technical information: requirements for the boiler installation room

Drainage of blow-off pipe and safety valve

Blow-off pipe in the liquid area

The following criteria must be observed when installing the safety valve blow-off pipe for liquids:

• The blow-off pipe of a safety valve which is connected to a water chamber must be equipped with an expansion and water separation chamber.
• The system on the discharge side of the safety valve must be dimensioned so that an inherent back-pressure amounting to 10% of the excess pressure is not exceeded when discharging.
• The section of pipe between the safety blow-off valve and the expansion and water separation chamber must be installed with a slope (≥0.5%).
• If there is a drainage hole in the seat of the safety valve, additional drainage should be provided.
• In doing so, the drain line must be installed with a slope and without constriction.
• Blocking of the drainage by dirt or foreign matter must be avoided.
• The condensate that accumulates in the expansion and water separation chamber must be safely removed and cooled.
• The section of pipe between the safety blow-off valve and expansion and water separation chamber must be installed and fastened so it is not exposed to shear, bending or torsional forces (e.g. by using supports, spring-loaded pipe hangers). The reaction forces when discharging must be taken into consideration.
• High temperatures, flow speeds and flow noise occur when discharging. The blow-off pipe at the expansion and water separation chamber must therefore discharge to the atmosphere in such a way that it cannot pose any danger.
• The blow-off pipe at the expansion and water separation chamber must be isolated from other pipework (e.g. air vent lines, expansion lines, safety valve blow-off pipes) and protected against freezing.

Safety valve with expansion and water separation chamber