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Noise from Grundfos UP 26-96 F/VS

Harold Member Posts: 249
I have a Grundfos UP 26-96 F/VS pump in my new heating system. This is a 205 W unit. I have several smaller units around 85 W. The small units are virtually noiseless. The large unit is, in my mind, unacceptably noisy. The wall it is mounted on (with all the piping) is drywalled on the equipment side and has 7/16 OSB on the ohter side (a hallway). The noise reverberates in the hall which is open (no covering yet) on the other side. The piping is attached with clamps that have some isolating rubber.

It is a large house at 2 floors of about 3200 sft each. With no drywall I can here that pump in every room of the house. If you hold the pipes in the boiler room or even just rest your hand on the buffer tank shell you can feel clear vibration when that pump is running.

The pump has been just been filled/flushed and the pump has been bled twice and there was no soldering anywhere in the system so debrie should be minimal.

I have no objective standard to determine if the this noise is normal. The contractor does not have an installation with a similar pump for comparison. He is contacting Grundfos. Subjectively, I used to have a system with two quite large motors and coupled pumps. One I believe was a 1HP motor. Until the bearings started to go I beleive these were quieter than this much smaller pump. The Grundfos is about 2.5 times larger than the other pumps in the system but seems way more than 2.5 times noiser.

Doea anyone have any comments or suggestions about how to resolve this. One obvious one is, of course. to swap out the pump.


  • Paul Pollets
    Paul Pollets Member Posts: 3,658
    Pump noise

    The pump may be way oversized for the load, and without calcs, schematics or pics, it's just an educated guess. I'd install a Pressure Bypass Differential valve (PBD) around the pump ASAP, and consider trying either the 26-64 pump or even the 15-58 on high speed. The correct flow rates and "head" requirements should be known by the installing contractor...

    A PBD should be used on circ pumps, regardless, but sizing the pump correctly requires expertise. The 26-99 is just as quiet as any of Grundfos' small pumps. Something's wrong here.

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  • Harold
    Harold Member Posts: 249
    System flow was designed

    I am sorry I should have made this more clear. The system was designed and installed by a professional in whom I have the highest degree of confidence. The pump and pipes are well matched to required flow.

    The system is specifically designed not to use a bypass valve. The pump is variable speed and a differential pressure controller serves the same purpose as the bypass valve.
  • hr
    hr Member Posts: 6,106
    A variable speed circ as

    a system pump? What type of control is modulating the speed?

    Describe the noise. A crackling type of noise could be air or cavitation. A loud hum or vibration could be a balance issue.

    It doesn't take much at all to throw one out of balance and start the whole wall, or house, a rocking.

    I'd remove the motor from the volute, with the iso valves shut off of course, and look for a solder ball, wood chip, even a small shard of copper from reaming a tube will upset the balance and cause noise.

    Also look for a broken vane on the impeller. This will also get them shaking.

    If it was run dry, even for a very short period, they will sometimes develop a bearing noise that won't quit. Even when wet.

    Too bad we can't post sounds on the Wall. Maybe Dan could work on that. In his spare time :)

    hot rod

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  • RoosterBoy
    RoosterBoy Member Posts: 459
    The Noise and Vibration isnt Normal.

    there is always an underlying cause...an educated guess from the pro would be interesting...my guess might be that there is air still in the system,i have no idea how the pump may be piped however, say it was bolted to some unistrut,and it had a bit of air still entrained ...i think not only could you hear it, you would likely feel the harmonic rippling thru the wall it was bolted to. if i installed one it would lkely have a nokink or some means of purging air from the line and returning from the field,and as there isnt aheck of alot of variables why not try turn off the pump,hook a wyane transfer pump to one no kink and one to another in the direction of flow thru the pump and crank it up for a few mins...opening and closing valves in the field as you do so...valve off the buffer /supply to the pump...and the valve from the return to the buffer from the fields...first...

    once you have done that open the return and the supply and turn off the wyane pump...power the recirc back up....if you hear bunch of gurgling sounds in the tank i think maybe that you have discovered a bunch of cure for alot of possible problems...one thing though ,if you still hear noise and "heavy vibration" id shut the thing down and pull the pump motor and replace it...because as Hot Rod says if it has already run dry .... the impeller could be heat warpped,or a wood chip could be stuck in it or like me...a few days ago found the stainless steel had a casting defect clear as a bell....brand New outta the box....when i went back the parts person my friend said "oh wow thats the third one !we dont have any more of them...' that too is something most of us seldom consider as a possibility..that band new outta the box some hidden hassel is waiting to happen.
  • Harold
    Harold Member Posts: 249

    Hotrod - thanks for the ideas. I will talk to the contractor about opening the unit if a replacement unit is not supplied.

    The control system is a differential pressure sensor and a PLC (Programmable Logic Controller) that will take the output of the sensor and generate the control voltage for the pump. It will maintain a generally constant pressure across the manifold as loops open and close. It will shut down the pump when no heat demand is present.
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