Discuss Gas pressure drop with flow to a larger pipe from a smaller one? in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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Hi,

Non-professional / knowledgeable person here.

I'm a Brit in Romania who volunteers for a charity building an old peoples home for needy old people. Out here competence and integrity is harder to come by in a worker, in fact it's hard to find workers at all where we are in the countryside.

At the moment, if a lot of demand is put on the condenser for a period of time, the unit starts to make a very loud rhythmic banging sound. The volume of the bang is quite unnerving and makes you want to cut the gas supply immediately. It sounds like un-ignited gas is being allowed to built up until it gets to a certain concentration (and larger quantity) when it is able to ignite again.

We have a gas burner / condensing boiler unit that requires a minimum of 27 millibars of gas pressure when the fuel is LPG / propane (the ideal pressure being 37 millibars) . The pipe coming out of the tank outside is 1 inch with a 30 mbar regulator, the pipe then soon transitions to a 1.5 inch pipe which goes all the way to the unit in the house (about 10 metres let's say). I'm guessing that whilst the static pressure might also be 30 mbar in the bigger pipe, when the gas is flowing the pressure would become lower than if it was being provided by the one inch pipe as there is more volume to pressurise when the small pipe goes to the bigger one.

Am I guessing right?
If so, would you think the pressure servicing the unit when it is burning gas would fall below the minimum required pressure?

Before the unit was fully connected to the supply, the pipe used to be 1 inch all the way, but the people who came to do the final connection from this pipe to the unit said the pipe needs to be 1.5 inches in diametre, so they replaced it. The inlet to the unit is 1.5 inches (though confusingly in the manual it labels it as 1 inch). They didn't replace the last bit of 1 inch pipe going into the tank as this was impossible without emptying the tank. In consideration of this and my guess being right that there is a pressure drop when the gas flows into the larger pipe, is the large pipe providing any benefit at all? I guess again that there might be less resistance to the flow in the larger pipe.

Thanks for reading.
 
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what size is the boiler ?
 
what size is the boiler ?

The boiler is a Buderus Logamax plus GB162-70 V2, with the '70' in the model number referring to the boiler's maximum nominal thermal potential as 70 kW. I'm not sure how prevalent Buderus is in the UK, if there are Brits reading this. Buderus seems to have a presence in the U.S. but I can't find our model number for the U.S market.

I managed to find a pdf manual online to share, but only in Italian (attached). We have a hard copy in Romanian. Specs begin on page 9.

It says the 'maximum condensing quantity' is 7.6 litres per hour

I noticed that there is an extra chart in the Italian manual which isn't in our Romanian manual that says that the minimum gas connection pressure should be 42.5 millibars for propane. The Italian manual also has the table that is the only table that exists in our Romanian manual referring to gas pressure which says the minimum nominal gas pressure is 37 millibars.
 

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The boiler is a Buderus Logamax plus GB162-70 V2, with the '70' in the model number referring to the boiler's maximum nominal thermal potential as 70 kW. I'm not sure how prevalent Buderus is in the UK, if there are Brits reading this. Buderus seems to have a presence in the U.S. but I can't find our model number for the U.S market.

I managed to find a pdf manual online to share, but only in Italian (attached). We have a hard copy in Romanian. Specs begin on page 9.

It says the 'maximum condensing quantity' is 7.6 litres per hour

I noticed that there is an extra chart in the Italian manual which isn't in our Romanian manual that says that the minimum gas connection pressure should be 42.5 millibars for propane. The Italian manual also has the table that is the only table that exists in our Romanian manual referring to gas pressure which says the minimum nominal gas pressure is 37 millibars.

More than fine then in 11/5 tube should be around .7 drop from reg to boiler
 

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