Leaking PRV valve on closed system?

KAGY

Hi all,
I was fitting a new sink yesterday and I had to drain the cylinder to do it, I have a closed, pumped system. Since filling the pump has been constantly cycling, on for 10s off for 1 and back again. I noticed a small drip from the safety overflow so it's probably one of two safety valves, I've attached a pic. One is a 3.5bar relief valve, the other is a 4bar / 95deg steam valve.
In your experience which is more likely to be leaking?

Do I have to fully replace the valve can I just replace something inside it like a valve seat/seal?

I've also heard that an unpressurised expansion cylinder can cause cycling, but would this cause a steady drip or occasional blow out?
PS There's no leak in the new work, in fact I've turned off the isolation valves (after the cylinder) for the whole house and it's still doing it.
Thanks in advance

youtheman

I profess to being no expert on the closed system but the following are my observations:

The valve you call the 3.5 bar 'relief' valve appears to be a pressure 'regulating' valve (i.e. relief normally implies that excess pressure is vented to atmoshere). The 4 barg valve appears to be the relief valve. So you have 'belt and braces', the first valve sets and maintaines the pressure and the second one relieves the pressure if the first one fails to do its job. There is a screw top on the regulating valve to adjust the set pressure.

You appear to also have an accumulator on top of the system, this contains a diaphragm, one one side you have fluid and the other side you have gas. A small fluid loss will not cause a drop in pressure as the gas expands thus keeping the pressure on the fluid side.

So I'd say the problem is with your accumulator, see if you have instructions on how to recharge it (the air side that is). See if there is a pressure gauge on the air side, I presume you'll need this.

KAGY

Thanks for your reply, The problem has relieved itself only cycling once every 20 mins or so. So no major panic.

I'm pretty sure I have the valves sussed out, for the sake of others reading this thread this is my reasoning

youtheman wrote: »

The valve you call the 3.5 bar 'relief' valve appears to be a pressure 'regulating' valve (i.e. relief normally implies that excess pressure is vented to atmoshere).

This (3.5bar) valve does vent to the outside, via the line I've drawn in black in the OP. Twisting the blue cap opens up the valve and water runs out. (maybe you didn't see it, it's upside down!

youtheman wrote: »

The 4 barg valve appears to be the relief valve.

This one is rated in kW, a temperature 95degC and the pressure, so it's what I called a steam valve, I think that it just keeps venting (the black line again) to stop the immersion coils boiling the water in the case of a malfunction.

youtheman wrote: »

There is a screw top on the regulating valve to adjust the set pressure.

The black cap on the reg valve is fixed (rated 2.1bar), probably a cheaper option than the adjustable

youtheman wrote: »

You appear to also have an accumulator on top of the system,<snip>
So I'd say the problem is with your accumulator, see if you have instructions on how to recharge it (the air side that is). See if there is a pressure gauge on the air side, I presume you'll need this.

Thanks, I'll try that. Again for others reading the tread with similar problems on the top of the small cylinder there's a large black plastic cap, this can be screwed off to show a schraeder valve (the same as on your car wheels!) I'll try pumping this up when I get a chance

I'm assuming that it should be charged up to 2.1bar, the same as the reg valve?