Sealed system pressure loss

[SMG]

I have a pressure gauge on my sealed cylinder at the top, together with an isolation valve, Just recently I have been replacing some pipework from the cylinder. Together with a new alkathene cold feed into the house. I have isolation valves fitted which stop the mains flow into the cylinder, & another isolation valve at the top stopping the DHW. I shut both valves to replace pipes. Effectively sealing the cylinder.

I isolated the cyl with 3 bar pressure showing. Over a few days it has lost about 5 psi. There are no leaks, not loosing water through the heating coils.
No leaks at the immersion heater seal, the cyl is sealed from the expansion tank too.

Any ideas why its loosing pressure? It works fine in service.

 

[SMG]

Anyone help please??

 

[Dan Robinson]

Dude , with that random spattering of old an new terminology applied to things it probably shouldn't be applied to; coupled with the fact that despite your best efforts we have no idea what you are really talking about...


Perhaps a couple of photos identifying the various bits?

 

[SMG]

Right, thanks, basicly, I am testing my cylinder. The top dhw outlet pipe has a pressure gauge & bleed nipple. Mains cold is fed into the cyl mains inlet, through a stop tap, & the cylinder filled. The cyl heating coil pipe connectors are disconnected & open. I pressurise the cyl up to 3 bar. Over a week it has lost about half a bar pressure. No leaks anywhere. Does that make better sense?

Thanks

 

[bolshy]

It's cooled down a bit.

 

[SMG]

Logical, except I drained the cyl to replace the mains inlet. It was filled with cold water & the pressure is still dropping, but still no leaks??

 

[petertheplumber12]

If it lost 5psi that is a 1/3bar and over a week on 3 bar that isn't a lot to see. I could be inside the coil and not visible.

 

[gigz]

Could be due to temperature difference, you would have to make sure you compared pressure at the same temp (in and out the cylinder) but as said i think you are worrying for nothing especially as you say there's no leaks.

 

[petertheplumber12]

If no leaks and if it was sealed JUST to test it then no PRV to leak so stop worrying.

 

[SMG]

Thank you, I was concerned at the loss of pressure, but haven't found a drop of water anywhere. I just don't understand why the pressures dropped.

 

[bolshy]

I told you, it's cooled down a tad
Unless you're certain it's temperature is within a degree or two of when you began your test. If it's solid with water then a change in temp of 1 ° C can cause a change in pressure.

 

[SMG]

The temp is constant, cold, there is no heat or drafts in this room, just checked & its half a bar in 6 days.

 

[bolshy]

So you are categorically stating the room temperature hasn't varied by as much as a single degree in 6 days? I give up

 

[SMG]

No m8, the temperature of the small room has been pretty much the same all week, I haven't had a temp gauge in there. If you guys say its fine then i`m cool with that, it just seemed a lot to me.

 

[andytw]

I have isolation valves fitted which stop the mains flow into the cylinder, & another isolation valve at the top stopping the DHW. I shut both valves to replace pipes. Effectively sealing the cylinder.

But do they seal the cylinder or are just presuming they do ?
The mains flow one must be working or the pressure would be going up.
Is there an expansion vessel involved or is this just a solid tank of water ?


andytw