DOES THE PRESSURE OF EXPANSION VESSELS VARY?

[damomor]

POTTERTON PUMA 80e. PRESSURE KEEPS RISING AND NEEDS TO BE SHUT DOWN BEFORE THE PRV GOES. I HAVE NOW CHECKED THE EXPANSION VESSEL AND HAVE RE-PRESSURISED IT TO 0.9 bar but this seem to be insufficient.It has made a difference though and the pressure is not rising as fast as it was.It is almost back to normal. Thanks for your help so far guys. You know who you are.

 

[bogstandard]

Perhaps the instrument you are using is not accurate in measuring the pressure (Car tyre pump?) I use a car pump but check the pressure with a somewhat better quality guage. Certainly around 1 bar is the pressure to aim for or slightly less. Try another half a bar - its will have to be try it an see. I find it best to release all pressure before repressurising showed you also what in the chamber Is it only "Air"

 

[croydoncorgi]

You MUST release all pressure in the system before re-pressurising the EV!!! Then, if all that happens when you pump it up is a faint hissing noise, you will know the EV diaphragm has had it!

The WHOLE POINT of pre-loading the EV is to maximise its capacity (by pushing the diaphragm towards the water connection). But the preload MUST NOT be greater than about half the design pressure of the system (ie about 0.5 Bar, typically), otherwise the diaphragm will not be able to move very far in the other direction when the CH system is pressurised.