Pressure testing, drops from 6 to 5.8 bar...

[endecotp]

Dear Experts,

I thought I ought to "do it properly" and test my new CH pipework before I hide it forever under a floor. Speedy Hire didn't have the manual pressure pump I wanted but let me have an electric one for the same price (this one: https://cdn2.ridgid.com/resources/m...&languageCode=en&countryCode=GB&type=document ). I connected it up to the first of my new pipes, filled with water and then closed the temporary valve at the far end. The pressure was pretty much immediately up to 6 bar so I closed the valve on the pump and left it for an hour.

An hour later there were no visible leaks and the pressure gauge on the pump had not noticably moved (it goes up to 60 bar, so a small drop would be hard to see). Good so far, but I had also connected another pressure gauge that only reads up to 11 bar, and on this one I could see that the pressure had dropped from 6 to 5.8.

Same results with second new pipe.

I can think of various harmless reasons for this, including temperature changes, expansion (including a couple of temporary push-fit fittings at either end), or tiny leaks from the pump attachment fittings. Should I worry about a small pressure drop when there are no visible leaks?

Thanks, Phil.

 

[AngelesPlumbing]

its fine, if it hold till tomorrow its ok

 

[John D v2.0]

agreed with the above, it's long term you care about. you can let the water settle down to room temperature and then see. water expands a lot based on the temperature but is incompressible. Also it has a lot of thermal mass. Not like gas where it's all up to temp in a minute, and it's so compressible the pressure hardly changes with a small leak.

 

[endecotp]

Thanks both. I left one pipe pressurised to 5 bar overnight and it was 4.5 this morning.... No visible leaks.

 

[oldbuffer]

If its plastic pipework it "gives" a bit when pressurised, and the testing procedure is different from that for copper piping. I wouldn't be happy losing 0.5 bar overnight, the water has to be going somewhere. Are you sure there is no air in the system?

 

[endecotp]

If its plastic pipework

It's not plastic, it's copper - except that I used a couple of temporary plastic pushfit fittings at either end.

Are you sure there is no air in the system?

If there is any, it's not very much. It's just a horizontal length of pipe with a few joints and elbows, and a short vertical bit at the end for a radiator connection; I ran the pump until water was flowing out of that far end and then closed the valve. I guess there could have been a few small bubbles but nothing more.

I wouldn't be happy losing 0.5 bar overnight

Hmm, that's not what I was hoping to hear. I'm supposed to return the pump on monday morning....
Who has actually used this sort of pump? What normally happens? Note as I said in my first post, these drops would be difficult to measure (certainly over the standard 1 hour) on the pump's built-in gauge.

 

[dilalio]

You need some LDF over each and every joint/connection.

 

[John D v2.0]

With however many litres of water in an incompressible system, no expansion possible, when the water temperature changes it will really affect the pressure. If you have air in the system will actually make the pressure more stable.

 

[endecotp]

You need some LDF over each and every joint/connection.

Ah-ha, "leak detection fluid"! ( https://en.m.wikipedia.org/wiki/LDF )

I know there is "special" LDF for gas, but can I use a substitute (kid's bubble solution etc) in this case?
And hang on, will it do anything useful during a hydraulic test? Surely it needs escaping air to make bubbles...

Still hoping to hear from someone who has used this type of pump and knows what normally happens. Was hoping to glue down floor tomorrow....

 

[AGAS]

and what pressure would the system water be in normal situation

 

[dilalio]

I know there is "special" LDF for gas, but can I use a substitute (kid's bubble solution etc) in this case?
And hang on, will it do anything useful during a hydraulic test? Surely it needs escaping air to make bubbles...

Remove the water and pressurise with just air to 3 bar, then use LDF.
First places to check are at each end (at pushfit cap and connection to pump) as these are temporary fixings and may be at fault. Then it’s test each of your soldered joints.

You can use a concoction (although not supposed to as detergent can damage some fittings) but a tin of LDF is much better and shows pinholes very clearly.

 

[oilboffin]

For gods sake if you are bothered mix some dye in the water and fill it with that we've done it when we've had an inspection to show no leaks.Bob

 

[AlanE]

Remove the water and pressurise with just air to 3 bar, then use LDF.
First places to check are at each end (at pushfit cap and connection to pump) as these are temporary fixings and may be at fault. Then it’s test each of your soldered joints.

You can use a concoction (although not supposed to as detergent can damage some fittings) but a tin of LDF is much better and shows pinholes very clearly.

To use air rather than water is dangerous!!

Water is virtually in-compressible so if a fitting fails you will end up with a pool of water.

Air is highly compressible and therefore stores a large amount of energy. A fitting failing at 3bar can be likened to a shot gun being fired it will become a lethal weapon.

 

[Wildcat1961]

Remove the water and pressurise with just air to 3 bar, then use LDF..

As above.
Pneumatic testing then exclusion zones should be put in place.
Hydrostatic testing is the preferred method.
Pneumatic testing = stray bullet.

 

[dilalio]

Guns don’t kill... people do