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Suction diffuser without strainer

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RPK
RPK Member Posts: 99
edited December 2019 in THE MAIN WALL
I’m looking at an installation where y-strainers have been installed upstream of suction diffusers (on base-mounted centrifugal pumps). The mechanical contractor has removed the strainers from the suction diffusers (Armstrong SG) entirely, not just the fine mesh startup strainers. I’m wondering whether the suction diffusers will still perform as intended without the permanent strainers installed. They still have the flow straightening vanes, but I always assumed the permanent strainer helped even things out as well. Of course I’ll check with Armstrong for their opinion, but curious to hear what the Wallies have to say. The IOM for the diffusers makes no mention of ever operating without the permanent strainers.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,287
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    They should be there. I don't think it will harm the pump or the pump's performance to operate without them, but they are the last line of defence for something odd getting in there and really damaging the pump. See what Armstrong says, though.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pecmsg
    pecmsg Member Posts: 4,847
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    > @Jamie Hall said:
    > They should be there. I don't think it will harm the pump or the pump's performance to operate without them, but they are the last line of defence for something odd getting in there and really damaging the pump. See what Armstrong says, though.

    Now what could possibly get in there?
    Budweiser tall boys
    Rags
    Nuts
    Bolts
    Hell
    I found a stainless steel strainer in a pump strainer once. The pump strainer was steel. No idea where the 2” stainless cane from!
  • RPK
    RPK Member Posts: 99
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    Apparently they were removed per request of the design engineer. The mechanical contractor questioned removing them and that’s what they were told. I think the y-strainers that are installed just a few feet upstream should provide adequate protection for the pumps, unless they fall apart or something crazy happens when they’re being cleaned. Armstrong says they will not perform as designed without the strainers but couldn’t speak to how large a difference it would make.
  • Jamie Hall
    Jamie Hall Member Posts: 23,287
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    " unless they fall apart or something crazy happens when they’re being cleaned". Both of which have been known to happen, with catastrophic effects on the pumps.

    The only possible reason I can think of why the design engineer might have requested their removal is that they do slightly increase the required NPSH at the pump. But... if the pumps are running that close... I'd be worried.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,143
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    Did the design engineer spec the Y strainers also, seems like a redundant component if the diffusers have them built in?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,525
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    The engineer doesn't know what he is doing. He looked in a book and it showed a y strainer so he put one in.

    The Y strainers never should have been put in, just a waste of money. Yes the suction diffuser will work fine without the strainer. The right fix is to put the strainer in the diffuser and take the Y strainer out. With both strainers in you may have too much restriction.
  • RPK
    RPK Member Posts: 99
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    I agree that the y-strainers are redundant. The mechanical contractor installed suction diffusers only but was then told by the engineer to add the y-strainers.
  • Mike_Sheppard
    Mike_Sheppard Member Posts: 696
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    The Y strainers should be installed before heat exchangers such as your boiler, chiller, cooling tower, plate & frame, etc. Not before the pump.

    Currently working on a project where the engineer has the pumps on the wrong side of the boilers, boilers piped wrong, check valves drawn backwards, and strainers drawn on the outlet of the boilers... It’s a pain.
    Never stop learning.
  • hot_rod
    hot_rod Member Posts: 22,143
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    Mike_Sheppard said:

    The Y strainers should be installed before heat exchangers such as your boiler, chiller, cooling tower, plate & frame, etc. Not before the pump.



    Currently working on a project where the engineer has the pumps on the wrong side of the boilers, boilers piped wrong, check valves drawn backwards, and strainers drawn on the outlet of the boilers... It’s a pain.

    Well put, avoid any flow reducing devices upstream of a circulator. If the Y strainer is doing it's job, by default it is reducing flow to the pump :)

    If you must, a dirt separator is a better choice upstream of the pump, with very low pressure drop it does not restrict flow as it removes particles and drops them down into the bottom.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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