Issue with inlet gas pressure on multifunction valve giving false reading

[standard8]

Interested to know if anyone else has had experiance of this. First time I noticed it was on a 60Kw floor standing air heater. We did the entire installation including the gas line from the meter to the unit. On commision gas reading showed a drop accross the gas line of about 4mBar. Then the sweating started. Cheacked my gas pipe sizing calc's about a dozen times, got another enginner to check, all appeared correct. in the end put a test point into the purge point and checked the inlet pressure there. Had a difference of 3.5mBar. i.e. the pressure drop through the gas valve was 3.5Mbar. The pipework was fine about .5Mbar drop.
I have kept my eye out for this ever since and several times been caught with commertial and on occation domestic boilers. ANyone else had this happen to them.

 

[migoplumber]

ive had a 5mb drop over an skp twin valve set before.
spoke to manufacturers and was informed that so long as the supply pressure to the valve inlet (working) was in the range they asked for it did not matter.

 

[stevetheplumber]

ive had a few like this where ive done inlet preasures from the gas valve and its under when you ring manufacturers they will often give you a figure that is satisfactory at the gas valve point some as low as 16mb so there must a 4 mb drop across the valve