Manometer

[mediy]

Hi,

Just attached a water filled manometer (the Monument type from B&Q) to the test nipple on my gas meter, turned the gas on and it blew the water out!! What am I doing wrong ?

Thanks

[Phil L]

You turned the gas on? - what did you expect to happen considering the gas is at about 30lbs pressure?

It's for checking differences in pressure, IE you attach it to the nipple when the main is switched off and if the pressure drops, you have a leak, you don't switch the mains on while it's connected or you get wet.

[cucumber]

How about starting by saying what you're trying to do? ;-)

Unless you're just looking for a bite... in which case I'm sure you won't be disappointed.

[Andrew Gabriel]

I wonder if you connected it to the high pressure side before the regulator? Sometimes the regulators fail and let higher pressure through. Maybe you didn't have enough water in the manometer?

What, 2 atmospheres? No way. It's at 20mbar pressure, i.e. 1/50th atmosphere pressure, or around 8" of water. It can creep up higher when there's no flow.

That's not really correct.

[Phil L]

A fiftieth of atmospheric pressure?, if this is true then if you knock a hole in a gas pipe, the air pressure (which is fifty times higher) should rush into the pipe, rather than gas come out?

Gas is 2 bar, each bar is 14.5lbs psi, approx, easily enough to blow a few cc's of coloured water out of a plastic straw.

hmmm

[Guy King]

The message from "Phil L" contains these words:

I think it's reasonable to assume he meant 20mBar over atmospheric.

[dennis]

One atmosphere + a few tens of millibars.

My gas boiler works on 28 mBar but it has an internal regulator. AIUI the mains side of the meter is a few atmospheres. The house side is a few tens of millibars.

It is correct. You turn it on and then turn it off and watch the water level. It is very sensitive. I made my manometer out of some aquarium tube.

[mediy]

[Andrew Gabriel]

It's 1/50th atmosphere pressure ABOVE atmosphere pressure. The manometer measures this difference.

Sorry, wrong, unless as I said he connected it to a high pressure main before the regulator rather than the house pipework.

[Ed Sirett]

Either you didn't hold (or better still hang) the gauge upright or you did not have a gauge that reads to 30mbar (I think thee are some short, tool box friendly, ones around for checking burner pressure that only go to

20 mbar?)

[Ed Sirett]

Sounds like you have an LPG installation, not NG.

[tarquinlinbin]

They distribute natural gas to consumers premises at 2 Bar above atmospheric? wow....

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[tarquinlinbin]

Indeed, though its quite possible that if you whap the ECV on too quickly then it'll blow the water out of the guage. Turn it on slowly.

Its also possible you might have a faulty regulator.

Are you competent by the way ?

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[mediy]

Hi Ed,

It is an NG supply and I am us> >

[mediy]

Obviously not otherwise I wouldn't have a fountain coming out the top of my manometer!! However, associating with the wise and the competent in this forum is my defence.......... ;)

[John Rumm]

Are you sure you are not measuring the standing pressure? If you connect to the test point and turn on the supply, you would expect to see something around the mid 20's. However on load (i.e. when gas is being drawn by an appliance) the pressure at the meter should fall to 21mb over atmospheric.

If it is, I have never managed it ;-)

I find it easier to add the gas after the tube is in place. This will take it to the aformentioned standing pressure. I then let a little leak out from the other end of the tube by the manometer since it is much easier to get this on and off the smaller nipple (and you ain't upside down in a cupboard covered in old shoes!)

[John Rumm]

Sounds like there was either not enough water in it (it wants to be filled to the 0 position with no air bubbles[1], it was not standing up straight, or you have a faulty regulator.

[1] note this is much easier to achieve once you realise the scale slides up and down a bit, so you don't have to get the water level spot on! (DAMHIK)

[Andy]

Your manometer should be about 12" or more deep, you should hold it vertically, and you should have it only about half full of water. When you connect the gas up the water in the high pressure leg wants to drop by about

8" ( about 20mBar ( its 1cm height = 1mBar ). You need to measure the difference in levels of the water in the two legs of the tube.

If the gas appliance being tested is not drawing gas the regulator will not regulate to 20mBar, expect something like 36mBar. That will give you a differential height of 36cm between the two manometer legs and may blow out your water. Either block the free end of the manometer with your finger to keep the water in until the gas appliance is taking gas, or connect it up only after the appliance is turned on.

Your gas regulator only works when there is gas flow.

Andy.

[tarquinlinbin]

Its ok, i was only trying to spark the perennial "are you CORGI regustered"debate then run away and hide :)

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[mediy]