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BS 5990-2006 pdf free download
BS 5990-2006 pdf free download.Specification for direct gas-fired forced convection air heaters with rated heat inputs greater than 330 kW but not exceeding 2 MW for industrial and commercial space heating – Safety and performance requirements (excluding electrical requirements) (2nd family gases).
15.5 Combustion air, pre-purge and post-purge
The l)unwr shall he fitted wit Ii a suitable device for proving adequate air flow during the pre-purge, ignition and operation of the burner. Air flow failure at any time during the pre-purge, ignition or operation of the l)urner shall cause safety shut-down. The air proving (levice shall he proved in the ‘no air’ position prior to start-up. Failure to prove ‘no air’ shall prevent start up or cause lock-oul
Proof of adequate air flow can be achieved as follows.
a) By static or differential pressure sensing, where it can be shown that it, provides satisfactory and reliable proof of air flow during the pre-purge, ignition and operation of the burner.
h) By flow sensing.
c) For on/off burners with a fixed or preset air damper (when fitted) by means of a centrifugal switch connected directly to the fan impeller. This switch shall be direction sensitive when used with three-phase fan motors.
Means shall be provided to prevent large objects from entering the fan, to minimize the risk of blockage an(l to prevent acei(lental injury to personnel. This requirement shall lx’ deemed to be met if entry is prevented of the standard test fingers specified in BS EN 61032.
Immediately before any attempt at ignition or the opening of gas safety shut—off valves, the appliance shall l)e purged. The pre—purge perlo(l shall be a minimum of 30 s at full combustion air rate, or pro rata longer periods at lower air rates.
The pre-purge shall be at the highest flow rate possible, shall not be less than 25% of the full combust ion air rate and shall be such as to give at least five volume changes of the combustion chamber and gas passages up to the flue gas exit from the appliance.
In the case of door curtain heaters, tile total pre-purge period may he redtlce(l below 30 S provl(led that the heater and its outlet ductwork are purged to give at least five volume changes and that the flame safeguard safe start check exists for at least 10 s during the pre-purge period.
The purge air shall be proved to be at the required rate. BS 5990-2006 pdf free download.
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