Hello all,

I found a nice fellow to help me out with my boiler.  He and the supplier both say the munchkin contender must be pumped on the RETURN side of the boiler.  I know from what y'all have already said that flow is key with these mod-cons.  That's why they want it on the return.  Does that cause air issues since you'd be pumping TOWARD the point of no pressure change?  Should it really MATTER which side the pump is on, since water's not compressible, and the flow RATE can't change from one point in the piping to the other?

The munchkin specifies that it's got about 7 ft. of head through the boiler.  As long as I'm using a pump that supplies that 7 feet with enough additional for the head in the floor (probably pretty low), shouldn't I be covered no matter which side of the boiler the pump is located?

Air issue scare me here, since my radiation is all in the floor with NO provision for bleeding, save the air separator at the expansion tank.  Am I being paranoid here?  Or can I de-couple the expansion tank and the air separator to locate the air separator at the lowest-pressure point - without putting too much pressure on the boiler by pumping away from the 12psi tank and adding the full pump pressure?

I'm confused . . .

Thanks in advance,
Charlie

Dear Charlie;

Expansion tank below the air separater, pump after, then the boiler. Glad you found competent help.

I'm not gonna have issues popping the relief valve? (12psi + 3psi in boiler + whatever pressure's in the floor to overcome + heat)

Why are expansion tanks labeled in psi, anyway, when all the pumps are rated in feet of head?

You pump toward the boiler to raise the pressure a the heat exchanger, decreasing the size and lifespan of the micro-bubbles of water vapor that form on the water-side contact zone, increasing the heat-transfer efficiency. Pumping away from the boiler lowers the pressure at the heat exchanger, increasing the size & longevity of the micro-bubbles, which are insulative, thus decreasing the heat transfer efficiency.

You could make up for that low-pressure point by raising the pressure on the entire system 5-10psi, but doing it "right" from the get-go makes more sense, lowering the overall mechanical stress. You really want the boiler to be the pressure high-point- the radiation works pretty much the same at any pressure, but properly pressurizing the boiler is critical to it's heat transfer. If the pressure is too low it'll audibly sizzle, and the stack temp goes up, efficiency goes down.

I Have found with a proper air scrubber (cast brass with stainless basket or whisker inside), We like the B&G but there are spiro vent and several others, that the micro bubbles will work out of a system and be gone. it does not take long and works well we are talking days of over all operation. bubbles gone. These things work, I saw a display one time, clear plexy glass tubing 2 inch diameter, a pump and air injector. Inject air to the water it turns milky white (micro bubbles) come back 2 hrs later and the water is clear.
Dan

Cool! Thanks guys!

B&G air separator & pressure reducing valve on order! . . . with all the other gubbins, of course.

charlie

Blueridge
Take that same "2 hrs later and the water is clear" and put it in a vacuum chamber and you'll see lots of bubbles.

For my work, I use lots of silicone oil. The stuff looks great until I draw a vacuum on it.

any problem putting air separators on the supply AND return?

Rcevan,
I did not mean to imply that in 2 hours your air in a system is gone.
My process on any system is to ignite the boiler and purge air while running warm water through, balance your incoming water with out going water to maintain pressure, warm breaks down the flux better. Gallons and Gallons per loop. after you pass a hundred gallons or so of water through you your entire system you have put a dent in the remaining air. This is when the B&G type high quality air scrubbers kick in, with days and days of operation.
Air bleeders on supply and return are common and can be useful, as is a boiler drain on the supply/return manifolds, but 1 good air scrubber in the mechanical room is an essential.
I do not know about about the silicone oil you mention.
Dan

thanks dan.

My guy included a caleffi discal, not a B&G. The screens appear to be plastic. Do I need to be worried? I'm visiting grainger tomorrow to get some odds & ends before putting this thing together, so I can grab a B&G and return the caleffi . . .

charlie