checking operating presure on gas hob


Postby uk_ducati » Mon Apr 13, 2009 7:38 pm

hi
could anybody give me some help with regards to testing operating and working pressure when installing a gas hob/freestanding cooker.

i am currently training towards my ACS and i am getting mixed answers regarding this subject.

if there are no test points for op or wp at the appliance what do i do. is it ok to rely upon pipe sizing and wp at the meter or do i need to temoporary fit a test point as close to the appliance to check for wp at appliance.

also i have been told to check for op by fixing a manometer to a hob injector and run the other 3 to see if there is any drop. is this a valid way to do this

any advice on this would be much appreciated

cheers

paul
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Postby htg engineer » Tue Apr 14, 2009 8:02 pm

If the pipe size is correct, the working pressure at the meter with 3 rings on is correct, and the flame picture is as it should be - then that's as far as I would go.

If you have problems, I would check the working pressure at the meter and at the boiler (maximum drop across the system of 1 mbar). Anymore than this you have a pipe sizing issue or blockage, the same applies if the hob goes out when the boiler fires up etc - check pipe sizing.


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Postby uk_ducati » Tue Apr 21, 2009 5:57 pm

thanks for the reply

i have contacted the training center and asked one of the assesors. they say that i should fix a temporary test point as clost to the inlet of the appliance as possible and test for OP. No answer for the BP.

cheers for your help

paul
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Joined: Wed Feb 13, 2008 8:11 pm


Postby htg engineer » Wed Apr 22, 2009 6:46 pm

The other option as you suggested is to connect your U gauge to the burner injector on the hob.

What the assessor has told you is probably a text book answer, normally written by people sitting behind a desk that never work on appliances themselves, I've never done or known anyone to fit a temporary test point to check the pressure of a gas hob.


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Postby uk_ducati » Wed Apr 22, 2009 8:30 pm

hi

if i was to fit a manometer to an injector on a hob and turn it on i would get standing pressure. if i was then to turn on another hob and light it would the reading be the op of that hob burning?

also when purging the hob after an install is it acceptable to hold a lit blow torch near to a open gas hob untill it lights. i know i have to allow 0.01m3 (textbook) through the meter but i am unsure as to wether this opractice is ok.

cheers

paul
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Postby Steve the gas » Thu Apr 23, 2009 4:43 am

Me neither 8)
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Postby htg engineer » Thu Apr 23, 2009 11:11 am

It would give you the working pressure if you put the gauge on one injector and light the remaining 3 rings.

No, as the gas/air mixture could be explosive, you have to purge 5x badged capacity of the meter, then attempt to light using the spark generator/ignition.

It's LPG where you purge whilst continually trying to ignite as LPG is heavier than air, meaning the LPG would be low lying (gathering at ground level) and could be dangerous when it does finally ignite.


htg
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Postby uk_ducati » Thu Apr 23, 2009 11:36 am

thanks for that htg engineer

i understand all of that apart from the purging 5x badged capacity of the meter.

i thought that with pipes under 28mm dia the purge volume would be 0.01m3 which would be for eg 1 third of a dial on a U6 meter.

or am i totally off the point here

paul
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Postby Steve the gas » Fri Apr 24, 2009 4:37 am

0.01m3 = 5 x badge capacity.

With NG you can now light the burner at a cooker whilst purging- most rgis do anyway- this changed Oct 08 iirc
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Postby uk_ducati » Tue Apr 28, 2009 8:53 pm

ok cheers for that

makes sense now

paul
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