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Question re: Taco 007e and expansion tank position.

George_BGeorge_B Posts: 3Member
I have a newly installed boiler with a new Taco 007e pump. The installers put the expansion tank connection near the pump but on the downstream side. After the installation was complete, I saw in the boiler manual (and the info regarding the 007e I found online) that the expansion tank should be installed upstream (suction side) of the pump and if installed otherwise it would affect pump performance. My questions are (1) how does this affect pump performance, (2) given that the pump is a variable speed that senses changes in hydrostatic pressure, does the expansion tank’s position in the loop negate pressure changes and cause the pump to stay on a slower speed always, and (3) could this cause the boiler to short-cycle because return water is entering the boiler is at too low of a flow. Currently I’ve got the high limit set at 180, the return temp is about 115 to 120 and the boiler runs a minute and a half before shutting off on limit. Outside temp is minus 22. Thanks in advance for any help or suggestions.

Comments

  • hot_rodhot_rod Posts: 12,584Member
    The expansion tank really should be upstream of the circ, that’s not really debatable 😉 Plenty of books in the bookstore here to confirm that requirement. Gift him a copy of Pumping Away

    That wide delta indicates another concern

    What type of heat emitters?

    Multiple zones controlled by zone valves?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,884Member
    What type of boiler as well?
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • George_BGeorge_B Posts: 3Member
    Boiler is a Weil-McLain CGa series 2. One pump w/ 4 zone valves.
    Emitters are baseboard. House is 3200 sq ft.
  • Jamie HallJamie Hall Posts: 12,137Member
    To answer your first question specifically -- the pressure tank location is important for two reasons: one, it ensures that the pressure at the inlet to the pump is always adequate for the pump to operate correctly and second, that the pressure in the rest of the system is always high enough for proper function. It really isn't an option.

    Questions 2 and 3 the answer is no.

    As @hot_rod said, though, that wide a delta T means that you have nowhere near enough flow, regardless of where the expansion tank is. Something else is amiss.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,557Member
    @George_B

    Years ago pumps were installed on the return pumping toward the expansion tank for various reasons. As time went on it was found that pumping away from the expansion tank worked better.

    Pumping away from the expansion tank will work on every job so it is the preferred method.

    That being said, pumping toward the expansion tank on a residential system with a cast iron boiler with low pressure drop will likely cause no issues. So it's up to you.

    If you not having any issues I would leave it as is
  • hot_rodhot_rod Posts: 12,584Member
    > @EBEBRATT-Ed said:
    > @George_B
    >
    > Years ago pumps were installed on the return pumping toward the expansion tank for various reasons. As time went on it was found that pumping away from the expansion tank worked better.
    >
    > Pumping away from the expansion tank will work on every job so it is the preferred method.
    >
    > That being said, pumping toward the expansion tank on a residential system with a cast iron boiler with low pressure drop will likely cause no issues. So it's up to you.
    >
    > If you not having any issues I would leave it as is


    Really depends on the circulator and system piping, I would not try that with a high, or even medium head circ
    The delta P developed could pull parts of the system into subatmospheric conditions. Same with a low fill pressure 10 psi fill with a circ developing 16 psi differential, not going to be acceptable
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,557Member
    @hot_rod
    I agree, with a high head system you must pump away. But I can't see the expansion tank location causing a flow issue, unless he has air in the system and is tying to pump bubbles

    He is also at -22 OA, obviously some problem in the system
  • hot_rodhot_rod Posts: 12,584Member
    It frightens me when “Newly installed” boilers are piped like that🙄
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • George_BGeorge_B Posts: 3Member
    Thank you all for the input.

    I found this from a contributor to a different thread on variable speed pumps:

    "A delta P pump has the ability to see "holes" in the system and it increases its speed to fill those holes in with flow. If there are no "holes" open, then it idles back to a minimum position while maintaining a pressure differential between its inlet and outlet, but continues watching for changes in demand. As soon as a hole pops up, the pump increases its RPM's to maintain the calculated, required pressure differential."

    My theory remains that the position of the expansion tank (1.5 feet downstream of the circ) will negate any "holes", resulting in the speed of the pump remaining constant.

    I'll update once I have the installer move the tank to the suction side.


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