Difference In Gas Pressure Drop Readings Mystery

[WSB]

Just a quick question, without going in to the long boring story behind it.

I have had two gas safe registered engineers measure the gas pressure drop after a gas cooker is installed.

1: Engineer 1 came round and measured a 2 mbar drop when the cooker was installed, so disconnected the cooker on safety grounds saying the cooker was leaking.

2: Engineer 2 came round and did the same, using the exact same type of measuring equipment and measured a 0.5 mbar drop and said that although this was within the safety limits because Engineer 1 had deemed it unsafe, then he said he couldn't reconnect until there was 0 mbar drop. He suggested renewing the piping up to the cooker.

3: Engineer 1 came round and replaced the bayonet brass fitting and rubber house with new, did the measurements again and got exactly the same 2 mbar drop, so disconnected the cooker again.

4: Engineer 2 came back and measured 0.5 mbar again as he did before and yet again disconnected cooker again.

Both are slagging each other off but I'm left in the middle of who to believe and in the meantime I have a cooker disconnected.....

The kit they were both using looked like an old fashioned blood pressure kit with liquid in.

Can anyone shed any light on possible causes of this mystery?

Many Thanks

 

[martygturner]

The scale of the pressure drop is not the issue that a drop exists is. The variance in readings could depend on what meter is being used, calibration is everything.

The question would be what was the reading with the cooker disconnected ? if there was no pressure drop then the pipe work is sound and the cooker is at fault.

 

[WSB]

The scale of the pressure drop is not the issue that a drop exists is. The variance in readings could depend on what meter is being used, calibration is everything.

The question would be what was the reading with the cooker disconnected ? if there was no pressure drop then the pipe work is sound and the cooker is at fault.

Thanks

Yeah, basically the cooker was at fault.

Engineer 1 measured 20 prior to cooker connection and 18 afterwards.

Engineer 2 doing exactly the same got 20 prior to cooker connects and 19.5 afterwards.

I was thinking about measurement kit being out of cal but when chatting to one of the engineers, he said that there's nothing to calibrate on these pressure measurement devices as essentially they are just tubes full of liquid.

Cooker is being replaced as still under warranty but I just wanted to get to the bottom of this and get an idea of which engineer was the more reliable for future work.

 

[ianmcd]

calibration is everything.

How do you calibrate a water U guage ?

 

[WSB]

How do you calibrate a water U guage ?

Basically what one of my engineers said

 

[ianmcd]

Basically what one of my engineers said

Sorry just seen your last post we were typing at the same time, many engineers these days use electronic manometers, I do and they need to be calibrated, but a water guage can not be calibrated, did they both take the same amount of time to do the tighness test, should be tested over a 4 minute period

 

[WSB]

Sorry just seen your last post we were typing at the same time, many engineers these days use electronic manometers, I do and they need to be calibrated, but a water guage can not be calibrated, did they both take the same amount of time to do the tighness test, should be tested over a 4 minute period

I've no idea as unfortunately wasn't present at the time.

I'm guessing one of these blokes has messed up. Would be interested to know which, so I can make a point of not using him in future.

Problem is, both just slag each other off which is not helpful for me.

 

[martygturner]

How do you calibrate a water U guage ?

U gauge as are susceptible to their operation being calibrated eg..making sure that the pipe is not kinked and all the air bubbles are out...making sure that the time taken for the readings are consistent... making sure that the number one calibration tool..ie the operator knows how to read it and operate it, ie not moving it whilst testing. Then there is approximation and eye level at reading, that's why in an industrial setting its the reflected measurement that is taken from a fixed gauge...then there is the height at which the meter is placed, then there is the tightness of their connection to the gas test port, if you want to get pedantic the mineral content of water can affect very low readings as can the ph, that's why distilled water is use for scientific u gauges...these are all calibration issues, not just the scale on the back of the tube.

The problem with u gauges is that they show one thing...a leak exsists.

The difference between 0.5 and 2mb between two independent operators would point to a difference in the use of the tool or its design or function or how it was read and is therefore likely to be a calibration issue....why did you assume that its the gauge that needs calibration?

I've no idea as unfortunately wasn't present at the time.

I'm guessing one of these blokes has messed up. Would be interested to know which, so I can make a point of not using him in future.

Problem is, both just slag each other off which is not helpful for me.

They could both be right and they have both showed a pressure drop which is all they can show with their kit...your cooker is not gas tight....all you are arguing about is which is correct which they both could be from their point of view they are looking for a leak, the magnitude of the leak is a moot point, it exists.

If you want an accurate measurement get somebody in with a proper electronic calibrated unit and they know how to use it, ie somebody that is prepared to invest in their business.

Neither of them messed up they found your cooker was leaking....which was their job...

 

[oldbuffer]

There are two main types of liquid manometers:
1. The ordinary water tube type. Essentially a U marked in millibars. Pressure one side and the pressure will push the water down on that side and up on the other. If you start with the level on each side equal, the displacement gives a pretty accurate reading of pressure. Difficult to read as the water and tube get discoloured.
2. The "Regin Premier" type. These use a similar principle, but MUST be filled with special blue fluid, which is quite expensive. If someone uses water, perhaps with blue dye added, in the Regin type, they will not get a true pressure reading.

 

[ianmcd]

U gauge as are susceptible to their operation being calibrated eg..making sure that the pipe is not kinked and all the air bubbles are out...making sure that the time taken for the readings are consistent... making sure that the number one calibration tool..ie the operator knows how to read it and operate it, ie not moving it whilst testing. Then there is approximation and eye level at reading, that's why in an industrial setting its the reflected measurement that is taken from a fixed gauge...then there is the height at which the meter is placed, then there is the tightness of their connection to the gas test port, if you want to get pedantic the mineral content of water can affect very low readings as can the ph, that's why distilled water is use for scientific u gauges...these are all calibration issues, not just the scale on the back of the tube.

The problem with u gauges is that they show one thing...a leak exsists.

The difference between 0.5 and 2mb between two independent operators would point to a difference in the use of the tool or its design or function or how it was read and is therefore likely to be a calibration issue....why did you assume that its the gauge that needs calibration?


They could both be right and they have both showed a pressure drop which is all they can show with their kit...your cooker is not gas tight....all you are arguing about is which is correct which they both could be from their point of view they are looking for a leak, the magnitude of the leak is a moot point, it exists.

If you want an accurate measurement get somebody in with a proper electronic calibrated unit and they know how to use it, ie somebody that is prepared to invest in their business.

Neither of them messed up they found your cooker was leaking....which was their job...

I have never heard so much crap in my life and if you want to be pedantic you are not supposed to use water in a U guage, we all do though

 

[gas112]

I have never heard so much crap in my life and if you want to be pedantic you are not supposed to use water in a U guage, we all do though

who would have thought sticking a bit of water into a u gauge could be made to sound like rocket science