expansion tank pressure

jonny88

how important is it that your expansion tank matches the system presssure,our heating expert in the company says it doesnt but dan says it does,,,who do i go with here,by the way system 30lbs and expansion tank was set for 12,which was waterlogged,think im going with dan on this one

Mark Eatherton

He's wrong, you're right....

The bladder should be aired up to the static fill pressure of the system.



The static fill pressure of the system is dictated by the height of the system. Roughly 1/2 PSI per vertical foot of system elevation, plus 5 PSI to keep the top of the system under positive pressure. (assumes boiler is in basement)



In your co-workers case, if the tank is left at 12 PSI on the bladder, and the system is filled to 30 PSI, then the tank has given up a lot of its fluid acceptance capacity due to diaphragm being compressed with the fill pressure, instead of the expanding fluid pressure .



All of the above assumes you are using a diaphragmatic or bladder type of tank. If you are using the old, ceiling hung cushion tank, then the tank MUST be completely empty before filling the system, and it will take care of itself. Just make sure that with the old style tank that there are NO automatic air vents in the system or your compressible cushion will be expelled.



ME

jonny88

thanks mark,also another ?

on the return side of the system we usually put a spring check,we have been getting a lot of call backs about them rattling,today for example we had a spring check placed right above the hot water circulating pump and it was tattling like crazy,is there a better place to put them are is it possible thatmaybe 20% of them are defective.it is a pain in the **** call back.im coming here because the more i learn here the more i realise our expert isnt what he claims to be.thankyou again for your time.

Mark Eatherton

Swing versus Spring check...

Swing checks do have a tendency to rattle, unless slightly undersized (1 pipes size smaller than piping to which its connected,)



Spring checks, for the most part, are usually fairly quiet, but have heard some rattle under low flow conditions. I have heard that they too can be undersized, one pipe size, to keep the check completely unseated and avoid rattling. Personally, I've never had a bad check (written or otherwise) in my possession.



I usually also put the checks on the discharge of the pumps. Seems to keep them quieter.



Keep coming here and I guarantee you will be the sharpest tool in your companies box of hydronic technicians, and NEVER be afraid to ask a question.



ME