Natural Gas (G20 I
2H
) Tubular Heater
The minimum allowable pre-purge time requires calculating [BS EN1020:1998 clause 6.38].
To do this only the Carbon Dioxide CO
2
figure needs to be measured.
E.G. on a model 250 the calculated minimum time is = 286.2/ ((100 / CO2) + 1)
If the measured CO
2
is 6.7%
Then 100 / 6.7 = 14.9
14.9 + 1 = 15.9
Therefore minimum pre-purge time is = 286.2 / 15.9 = 18.0 seconds
The calculation to be conducted is given below for all models:
Model 250 Minimum pre-purge time = 286.2 / ((100 / CO2) + 1)
Model 330 Minimum pre-purge time = 269.7 / ((100 / CO2) + 1)
Model 410 Minimum pre-purge time = 261.4 / ((100 / CO2) + 1)
Model 490 Minimum pre-purge time = 269.2 / ((100 / CO2) + 1)
The pre-purge time must then be measured. If the measured pre-purge time is lower
than the calculated time STOP and contact Benson Heating.
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