The gas supply to each burner or group of burners shall be under the control of two class A automatic shut-off valves of EN 161 in series in the gas pipework.

For natural draught burner with a controlled capacities below 70 kW there shall be at least two class B valves of EN 161.

A thermo-electric flame supervision device complying with EN 125 is acceptable for natural draught burners operating in open air with controlled capacities below 70 kW and for natural draft burners operating in combustion chamber with controlled capacities below 2,5 kW.

For multiple burner installations, the individual burner shut-off valve shall be considered as one of the automatic shut-off valves specified above provided it is at least of the same class. For typical examples of piping see informative Annex C.

The automatic shut-off valve(s) shall not open or shall shut off the fuel to the entire IThE or independent zone when the limit of any safety condition is reached. The following condition shall be taken into account:

• minimum and maximum gas flow;¹⁾
• minimum and maximum gas pressure;¹⁾
• minimum and maximum air flow;¹⁾
• minimum and maximum air pressure;¹⁾
• failure of power supply and/or other utilities (e.g. compressed air, steam);
• failure of heat transfer fluid;
• fume extraction malfunction;²⁾
• maximum operation temperature of IThE;
• minimum and maximum combustion chamber pressure;²⁾
• flame failure;
• failure of system tightness check and/or valve proving system;
• incorrect air/gas ratio as referred in 5.2.3.3.

In these cases the relevant automatic shut-off valves shall be de-energised by a protective system.

This function shall meet the requirements of the protective system according to 5.7.2 and 5.7.3.

NOTE     In addition there may be processes and/or machine conditions that cause a risk if the burner continues to fire. However these conditions are not covered by this standard.

It shall only be possible to manually reset the lock-out (see 3.48) of a closed automatic shut-off valve.³⁾

Flame failure⁴⁾ or process control shut-down⁵⁾ shall cause the closing of two automatic shut-off valves piped in series except in the following cases where single individual burner shut-off valve is sufficient:

• in case of high temperature equipment;
• in case of low temperature equipment providing the following conditions complied with:
  • a system leak tightness test to ensure that the individual burner automatic shut-off valves are closed is conducted at each start up of the IThE or other specific test period of the burner group and this shall not be less than once per week; and
  • dilution of gas leakage (at full burner capacity) of one valve is under 25 % of LFL, achieved by fresh air or flue gas considering all modes of operation (maximum power and part load of the heating system as well as variation of the LFL with furnace temperature).

For typical examples of piping and components see informative Annex C.