Trying to ID a valve so I can figure it out

[frank1492]

Don't know if this has been mentioned earlier, but get yourself a Spirovent. Purge the air as best you can by the methods noted earlier, the Spirovent will keep you trouble-free after that. (Works much better than a simple float vent IMHO.)

[Paul Franklin]

No idea. It's one of the great mysteries of life, right up there with where do all the missing socks go....

I mean, all such systems have backflow preventer, so even if the boiler pressure were higher than the feed pressure the water could not go out that way. And even if it did, how does air get in to take its place? And leaks usually make themselves known, unless you've got underground piping. There is dissolved air in the water that probably separates out over time, but I find it hard to imagine that it is enough to explain the quantity of air that seems to be in there each fall.

Now if the expansion tank is the type that doesn't have a bladder (most older ones don't), the air in there can dissolve slowly into the water, but with no circulation going on, I don't see how it would end up migrating elsewhere in the system.

So, I got nothin...maybe someone smarter than me knows the answer.

Paul

[keith]

Crap! We know where they go; into the washer zone. ;-)

.... and why does it stay there? This year I did considerable work on the plumbing (a leak and rotted subflooring in the upstairs bathroom convinced me to take a goo look), but amazingly the air wasn't as bad as it has been in the past. ...search me! ;-\\

Exactly. My house usually sounds like Niagra Falls the first time I request heat. I replaced a bleeder underneath this desk last year because it was noisy here (and I stripped the damned thing trying to open it). Hmm, I wonder where I put the key?

The house/furnace is ~20YO, and the expansion tank, perhaps 10 (I replaced it since I moved here in '93).

Yeah, I'm stumped too. ...although I did turn the heat on tonight (it's been in the 30s-50s for several days) and it doesn't seem so bad. I'll let it gurgle a while and then bleed the upstairs, if I can find the silly key. ;-)

Thanks again!

[HeatMan]

WRONG! You should have said "All such systems should have a backflow preventer..."

[Edwin Pawlowski]

It is not full of air, but it does have some air in it. There is an expansion tank that will allow air to get into the system.

Actually, very few systems have backflow preventors. It is becoming more popular as towns enact regulations requiring them. My house, built in 1978, does not have one.

Hard to imagine, but true. One third of the formula H2O is oxygen.

[krw]

Not full of air sure, but it sounds like a waterfall and there is considerable air in there. Why would the expansion tank allow air in? The water that's there would have to be displaced. Where?

I'm not sure there is a back-flow preventer, but there is a pressure reduction fill valve. Since the municipal pressure is above 60psi and the furnace at

14psi, I can't imagine water flowing up that "hill".

Were is the energy coming from to separate the oxygen from the hydrogen. It would truly be scarry if there was free hydrogen and oxygen in the furnace! ;-)

[Roy Starrin]

I believe that getting all the air out requires some sort of black magic. One good source of information is here:

has a forum for posting. Dan is a proponent of the "pumping away" design, which you can probably find among the many books he has for sale. In essence, this design says that most older systems are installed wrong with the circ pump in the wrong place (i.e. pushing water into the boiler, vice pulling it out). Bladder-lined tanks are a must, and perhaps a Spirotherm vent an estimate to converrt my very old, cast iron ("it will be there when the house falls down") Brunham boiler to this design of about $1500, including the tank, rerouting the piping and plus the vents/pump. My major concern is when you start wrenching on the major arteries of a system that old that something is likely to let go in the innards. We are going to start with the vent and the tank to see what happens.

[Cram]

exactly the type of info I needed. Thanks zero.

cram