circulator location question

newtoboilers

Can the circulator be located on the return side of the boiler?(while still pumping away from the expansion tank). There seem to be SO MANY acceptable piping arrangements,-from the standpoint of performance which is the "BEST" method?

Uni R

circulator location

It depends. Just as soon as everyone starts to finally catch on to "pumping away", we get some high efficiency units requiring them to be "pumping in". What's old can be new but often for different reasons. For any given boiler there is a best way and that is as per the manufacturer's specification since that is how they tested it and that is what they would prefer to warranty.

Kal Row

By definition “pumping away”

is from the point of zero pressure change, ie just past where the expansion tanks is connected, so if it’s connected on the return, you put it there, however the best place to connect the exp tank, is to the air scoop because you get the most efficient air separation, where the water temp is highest, and the pressure is greatest, ie just past the boiler where the feed and the exp tank is connected, so the preferred method is to put the pump just past that

Justin Gavin

What Type of boiler?

I know on the Munchkin they make you pump into the return because of the water pressure switch. If you have a long run in your primary loop you may run into problems so they reccomend that you pump into the return.

Good Luck

Steve_35

Munchkin & circs

Justin, I may be misunderstanding you but the install literature on Munckin's site is showing the circ in the "pumping away" location on the supply manifold.

Justin Gavin

Misunderstanding

I am talking about the boiler circ pump not the secondary loop piping. From the Munchkins we installed the O & M manuals stated you need 10 psi or you get a fault code.

Sorry I guess I was misunderstanding what he was asking.

Justin

scrook_2

pumping \"away\"

refers to pumping away from the point of no pressure change (PONPC), i.e. pumping *away* from the expantion tank. The boiler location is not specified.

HOWEVER, if you want to get as much air out as possible you want the point of *lowest* pressure to also be the point at the *highest* temperature, since raising the temperature of water and lowering the pressure of water *both* cause disolved gas (air in this case) to come out of solution, forming tiny gas bubbles.

The hottest place it turns out is at/near the outlet tapping of the boiler and the lowest pressure is at the inlet of the circulator, so putting the circulator inlet, the x-tank connection and the air eliminator at the outlet of the boiler and the inlet of the circulator gets you the hottest, lowest pressure water possible at the air seperator. Meanwhile because the PONPC is at the *inlet* of the circulator instead of lowering the pressure at the pump inlet (which if lowered too much will cause cavitation (violent localized boiling -- which will destroy a pump impeller in no time, and make some impressive noises while doing it), you raise the outlet pressure.

Now on a lot of systems, converted gravity particularly, but even some baseboard systems, the pressure drop through the boiler and system isn't too large, so a pump pumping toward the x-tank with a boiler between it and the tank will see enough pressure on its inlet, and the air seperator see's the hottest water in the system at pressures only somewhat lower than max due to the pressure drop through the boiler (especially a big, old, converted coal boiler w/ big, open water passages), so enough air removal still occurs. In addition to the big passages of the old boilers of old, elastomer science wasn't what it was today, so the shaft seals of the old, three piece motor and pump assy's such as the B&G's (read: BiG!) and Red Barons, etc. were not as capable of taking *really* hot water as they are today (for the few jobs not using sealed, wet rotor cartridge pumps anyway), so mounting them in the return side got them 15° to 40°F cooler water. Today the seal (if any) temp. matters much less & the boiler's water passages are much smaller & tighter (as are the fireside passages), but the traditions handed down change slowly, and often the old way seems to work fine anyway.

Some of the new high efficiency units want to be pumped in, but you could put th ex-tank at the inlet of the circ, pump away [from the x-tank] and pump into the boiler at the same time, alas the nomenclature gets confusing.