How can air enter a hydronic system ?

Plumdog_2

If your expansion tank has become waterlogged, or hard, your expanding liquid will push out thru the PRV, and when it cools off and shrinks, the system will suck air in thru the auto vent, and it will migrate out into your system.

Andy_27

How can air enter a pressureized hydronic system ?

System is a weil_mclain CG. It is hooked up to the household water supply (thru a regulator and backflow prevnter). system pressure varies between 12 and 20 psi.
Somehow it keeps getting air into the loops. Any ideas would be appreceated.

Thanks

bob young

A spirovent should do it .. with water comes air

[Deleted User]

Let me count the ways...

1. In the incoming water (H2-0hhh). Feel the make up connection where it meets the heating pipes. If its cold, you have a leak.

2. If there is an auto vent on the top of the system and a high head pump is pumping towards the expansion tank, AND the system pressure drops so low that the top of the system could see negative pressure generated by the pump (rare, but possible). Try closing the A.V.'s

3. In the form of micro bubbles through the wall of plastic tubing, rubber gaskets, graphite packing glands. These micro bubbles don't typically cause air binding.

That pretty much covers it, I think... Oh yeah, forgot one. Draining the water from a system induces a LOT of air into the system. Just because you see water from the return when purging does not mean you are completely purged. I've started using a clear plastic hose so I can "see" when its purged.

ME

Brad White_185

What Mark Said

Especially regarding point #2, I would point out that even near the bottom of the system, a high head pump could pull in air from any air vent or seal defect at the same level. (I have seen a 26-99 on a radiant manifold that did just that. It would suck in air like a straw and vent only when the circulator was off.)

To see if your system drops to sub-atmospheric, put a compound gauge on your highest radiator in the vent tapping. Just some 1/8" brass pipe, a 1/4" increaser and vent cock to reinstall your vent when done. Record the pressure "at rest" then again with the circulator and system on.

If you get a drop, I suspect an incorrectly located expansion tank.

If you leak is small, the "cold pipe test" is not too definitive though. The pipe may warm up ahead of the heat lost from cold water. To verify this, I would shut off the CW fill valve and watch the pressure to see if it drops. Do not leave this unattended though unless you have a working low water cut-off (LWCO).

My $0.02

Brad

Andy_27

As it turns out I have a leak in one of my loops. The really bad news is that it is under the slab. I guess I have only three solutions - Drill into the slab and repair -- expensive and not easy. Intstall aftermarket radient above the slab -- expensive. Bypass the bad section by plumbing above the slab -- cheaper and quick -- will require some trim work later. Any other suggeations ?

Thanks

Weezbo

there is a very cool pinner jack hammer set...

that uses a small air hammer tool...i found it in an automotive shop one day

i have used it to correct a variety of problems set in concrete. it runs off a small compressor and a lot less troublesome than a jack hammer.

with a known point of the leak ,like cement sharks pulling the wire mesh up too high and then the expansion cutter slicing the pipe ...it is easy enough to repair..