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ibr piping picture

but i thought, via dan's books, that pumping to was dated, and pumping away is now the ticket. so, are you saying that it's all been reversed back to the old school of pumping to?

and i'll ask again; what is the effect of the placement of the piping for pumping to when it enters the discharge vs the suction side of the pump?


  • [Deleted User]
    ibr piping picture

    i took the liberty to post this pic in order to pose a question; what would be the effect if the tank piping came in on the discharge side vs the suction side of the pump?

    and since 'high' is a relative word when there's no specific number attached to the drawing, for the sake of discussion, the pump is a 1-1/2hp, 30' head; is that pump considered to be a high head pump?
  • hot_rod
    hot_rod Member Posts: 22,476
    A bit dated info

    most, if not all the mod con boilers prefer the circ on the return piping, pumping into the boiler. This causes the boiler HX to see the increase in pressure that the circ provides. And some brands do now require a high head circ. They are often included with the boiler.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • scrook_2
    scrook_2 Member Posts: 610
    pumping away...

    is pumping from the point of no [well actually minimal] pressure change [away from the Expansion Tank], not necessarily (though often) also away from the boiler!

    If the circ is on the return, the X-tank still wants to be on the circ's inlet though.

    If your 30 ft head circ is operating at the 23 ft point on its curve, for example, its outlet pressure will be 10 psi higher then the inlet, so if your static boiler pressure is 12 psi, when the pump starts the boiler will rise to 22 psi immediately, and, if your X-tank isn't infinitely large, it will rise a little more as the water heats, so the relief is now seeing pressures in the low to mid 20's.

    If it's a tall building so you start at 18 psi (~41 ft head) say... you have trouble right here in River City! [pun intended]

    OTOH, if you move the X-tank to the outlet of the circ (at the return to the boiler), the boiler's pressure stays near 12 psi (or 18), but the inlet pressure FALLS 10 psi to +2 psi (or 8) in the direction of cavitation (w/ noise and impeller destruction) and/or air ingress at the seal, not good, though higher static fill pressures help a little.

    The attraction to the circ on the outlet (and X-tank on the circ inlet) is the lowest (and nearly constant by the way) pressure point is also the hottest point in the system and it is here that dissolved air most easily comes out of solution, (thay's why you put the air eliminator there) while the circulator sees nearly constant, reasonably high inlet pressure. The highest pressures are seen just after the circulator's outlet and by the time the return is reached, the pressure has dropped, due to the system tubing's friction.

    Now if the system is low pressure drop, say converted gravity w/ CI rads, then the system & circ head, is low so if the x-tank and circ are on the return side the boiler pressure changes are small -- even if the circ is on the return and the x-tank is on the supply, there still is only a small difference in pressures from lowest (circ inlet) to highest (circ outlet/boiler return) and things can still work.
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