expansion tank on residential boiler?

stevo_2

How do you figure out what to pressurize the expansion tank to on a new system. I know they are suppose to come from the factory at about 12 PSI.

Kal Row

mesure the height from the

highest point to the lowest point in ft and divide 2.33 -
then, if your expansion tank tee's in before the circulator, – add 1 pound and you are done, if it tees in after the circulator – then you also need to add the pump's differential pressure to the total – usually about 5 pounds extra

note the highest point may be an air vent in the attic,
also, this base pressure setting is with the system at 60 degrees - it will rise when hot – be sure to keep the total, when hot, at the boiler’s gauge, 5 pounds below the relief valve rating – cause it the relief seeps, fresh oxygenated water will enter, and ruin your system

Kal Row

note my correction - \"divide by 2.33\"

they come set for 12 since the avg system height for 2 story + basement home is 18ft and the avg sytem has the pump on the return and the exp tank on the supply so they add 5 to get apx 12 -

again as long as you are 5psi lower then the relief at max temp, the extra pressure wont hurt - on the contrary - it keeps the air out with hurts your system

stevo_2

WHAT IF THE HOUSE IS ON A SLAB AND THE BOILER IS ON THE SAME FLOOR? wHAT WOULD THE EXPANSION TANK BE PREEURIZED TOO?

Robert O'Connor_7

EX-Trol Q??

What's wrong with the factory set pressure? In your aplication, set it @ 12#'s (or leave it) It's probably already there....Robert O'Connor/NJ

Kal Row

you want at least the default 12lbs

so that, when on those real cold days, your boiler runs the temp up to 180+, it wont flash into steam inside the suction eye of the pump and cause cavitation - which kills pumps,
(you know it’s happening if the pump sounds like it has gravel inside)

in our wethead tecno speak - this is called keeping the pump at a Net Positive Suction Head (NPSH) - this is why we place the pump after the expansion tank - because the point were the exp tanks tees in, is the point of zero pressure change, ie that pump's suction, can’t reduce the pressure at that point, so it's developed pressure differential, is forced to increase it instead on the outlet side, - this so-called "pump-away" system is the only way to go, especially today, with the compact wet rotor pumps

stevo_2

your suppose to set the psi on the tank before installing on the boiler am I correct? For this you need the fill pressure of the system. If you ever saw the extrol factory its in denver colorado By the time I get it to long island the pressure changes due to atmoshperic pressure.

Kal Row

i think the xtrol people set it -correction-

by hooking up air to both sides and setting it to 12 on the air side and 29.92hg mecury at 59f (SAE std atmosphear) on the water side, then when they release the air pressure on the water side, the diaphragm stretches toward that end, so it reads less over there, but reads close to it at lower altitudes, once it's in a system in, with the weight of the water on it, then with 12psi on boiler's gauge, the diaphragm should be neutral, (at least that's the way i would do it - for all i know - they just pump it to 12psi and ship - since their design is very forgiving)

i wish they made these out of lexan plastic - so you could see what’s going on, cause if the diaphragm is already stretched toward the air side - the system pressure will rise rapidly because the diaphragm is already stretched out

they could at least make a clear plastic tube about half the travel on the air side and put the shrader valve at the end of it, and inside of it have an indicator stick glued to the middle of the diaphragm – so it would add 4 inches to the total length – big deal –
at least this way – you could fill the system and set the stick end to the center of the glass by adding or releasing air – or adjusting the water pressure cold

Dale

Watch the fill trol ones

Some new systems use a fill-trol tank from the same company as the exrol, on that one the air fill pressure determines the water fill pressure.

Kal Row

i sent this request to info@amtrol.com

this is a new expanstion tank feature i would like to see implemented, would also tell you if your diaphragm failed and the tank is waterlogged

Weezbo

Extrol has a sheet of specs you can entertain your self with.

) experience tells me though that you are overly concerned with some aspect What? loop lengths? return temps? limit range on boiler?type of boiler?stand alone fill system?High fired burner? under sea level? way up in the mountains? type of zone valve, What?
Basically the thing is pre set at 12 lbs the fill devise same thing ... dont fix them they aint broke:)