Gas testing manometer

[nb Stockton]

Hi there,

 

I have recently modified the gas installation on my boat, fairly simple, now it only has a gas cooker. Before I use it I need to check for leaks, so I have brought 3m of clear hose with which to make my own manometer. I am quite happy with the theory etc, but does anyone know how long the manometer needs to be? I am not sure what the pressure involved is and therefore what the maximum displacement will be.

 

Can anybody help?

 

Thanks

 

Richard

[David Schweizer]

Hi there,

 

I have recently modified the gas installation on my boat, fairly simple, now it only has a gas cooker. Before I use it I need to check for leaks, so I have brought 3m of clear hose with which to make my own manometer. I am quite happy with the theory etc, but does anyone know how long the manometer needs to be? I am not sure what the pressure involved is and therefore what the maximum displacement will be.

 

Can anybody help?

 

Thanks

 

Richard

Hi Richard, Make a U shape of about 2ft deep (I fixed mine to an old plank with a few cable clips) and fill the bottom 9inches with some coloured liquid (I used food dye). The lose end is connected to the test point, and the gas turned on until the liquid finds a new level. make a mark by the new level, then turn the gas off. Wait a few minutes and check whether there has been a change in the level, if there has you have a leak (but make sure it is not a bad joint with the clear tube) If there is no change in the level everything should be OK, but repeat the test again just to make sure.

 

The pressure is measured in inches, but you don't need to worry about this, it is just any drop in pressure that you need to know about. If you really want to know the pressure measurement, pin a piece of paper behind the short tube and mark it off in 1/2 inches. Each half inch mark denotes an inch of pressure, number these starting with 0 at the liquid level. But as I have already said you don't need to know the presure to measure gas soundness.

Edited February 26, 2007 by David Schweizer

[John Orentas]

Just to add a little to Davids comments, the output pressure from your Propane regulator should be 14.8 inches of water, but the important bit as he says is that the pressure must hold a static indication, zero leakage is allowed, my bloke always wants see it to hold without change for 30 minutes.

[ChrisPy]

just for the record - propane regulators are set to 37millibar.

1 bar (1000millibar) reresents a column of water 10m high (near enough). So 37mbar is 37cm. That means a difference in level of 37cm.

Metric is easy, innit ?

[Keeping Up]

Just to add a little to Davids comments, the output pressure from your Propane regulator should be 14.8 inches of water, but the important bit as he says is that the pressure must hold a static indication, zero leakage is allowed, my bloke always wants see it to hold without change for 30 minutes.

And just to add a little bit more, my inspector reminded me that there may be a fair bit of gas in the high-pressure pigtail between the gas cylinder and the regulator, which could maintain the pressure on the low pressure side for quite a long time even if there is a small leak. To get around this he always turns the gas off at the cylinders, then runs one of the gas hobs (alight of course) until the manometer drops by an inch or so. Then he truns off the hob and observes the manometer for 30 minutes. If it holds this level without change for 30 minutes you can be certain there is no leak.

[chris w]

just for the record - propane regulators are set to 37millibar.

1 bar (1000millibar) reresents a column of water 10m high (near enough). So 37mbar is 37cm. That means a difference in level of 37cm.

Metric is easy, innit ?

 

Well half of this actually (18.5cm), as measured against a starting mark, as one end of the water goes up and the other end goes down. If the "up" end moves 18.5cm that's equivalent to a 37cm total movement.

 

Chris

[ChrisPy]

Well half of this actually (18.5cm), as measured against a starting mark, as one end of the water goes up and the other end goes down. If the "up" end moves 18.5cm that's equivalent to a 37cm total movement.

 

Chris

that's why the DIFFERENCE is 37cm, Chris

[chris w]

that's why the DIFFERENCE is 37cm, Chris

 

 

IMHO, your post was ambiguous to anyone not au fait with manometers. One doesn't see a difference of 37cm against a starting mark, one sees 18.5cm. Just to avoid confusing anyone.

 

Chris

[David Schweizer]

IMHO, your post was ambiguous to anyone not au fait with manometers. One doesn't see a difference of 37cm against a starting mark, one sees 18.5cm. Just to avoid confusing anyone.

 

Chris

I thought that I had already implied that, except that being old I still use inches rather than centimetres.

[chris w]

I thought that I had already implied that, except that being old I still use inches rather than centimetres.

 

 

Yes David you did. It wasn't your post to which I was referring.

 

Chris

[nb Stockton]

Thanks everyone. I will make the manometer about 2ft (60cm) deep and that should be fine. I just did not want to make it so that all the water shot out the end if you know what I mean.

 

Happy testing this weekend then.

 

All the best

 

Richard

[Theo]

Thanks everyone. I will make the manometer about 2ft (60cm) deep and that should be fine. I just did not want to make it so that all the water shot out the end if you know what I mean.

 

Happy testing this weekend then.

 

All the best

 

Richard

 

I have to add my two pennorth.

 

My CORGI told me that you need to run the gas out of the pigtails then leave it for 5 minutes to stabilise before running the test. the reason is that the gas expands and cools a lot as it goes through the pressure reducer. The five minutes may well see the manometer increasing as the temperature of the gas reaches ambient. Once it has done this the monitoring for leaks can start.

 

Nick

Edited February 27, 2007 by Theo

[salmiron]

just for the record - propane regulators are set to 37millibar.

1 bar (1000millibar) reresents a column of water 10m high (near enough). So 37mbar is 37cm. That means a difference in level of 37cm.

Metric is easy, innit ?

 

No it isn't. How long is 37cm? I cannot visualise it.

[bottle]

No it isn't. How long is 37cm? I cannot visualise it.

 

30 cms equals about 1ft

 

Therefore 37cms = about 1ft 3 ins

 

This only approximate