Pump foundation to eliminate pipe vibration

[tholz]

Folks,
I am working with my building management to resolve a recent issue with the building rooftop water tank refill pipe transmitting a very audible humming noise to an apartment in the building. The pump is located in the basement and tank feed pipes run directly under the 1st floor apartment and make a 90deg turn up a riser shaft located adjacent to the apartment. The pump was recently changed out to a higher Kwh pump because of the NYC mandated installation of a backflow preventer. Prior to the new pump, no hum was detected. Between the pump and 2nd pipe hanger, is a Flex-Hose NND double sphere flex connector. The pump is mounted on a steel base which sits on 4 vibration isolator pads and is bolted to a sizable cement foundation, which is part of the basement floor. My question is: Is it appropriate to have the pump sit on vibration isolation padding, if we really don't care about any vibration transmitted to the foundation and ONLY care about minimizing vibrations transmitted to the outflow piping? Seems to me that we would be significantly increasing the effective mass of the pump if it where directly and rigidly affixed to the foundation, and thus reducing the vibration into the piping.

I've attached a pic of the piping and pump mount/foundation

thanks in advance for your time and thoughts on this.
Tom

 

[drawoh]

tholz,

Can you connect your pipes through a section of flexible hose? The hoses will not transmit very much force from your pump.

Your studs probably are attached to the top of your rubber pads. If the studs pass through the rubber pad to the floor, you have a rigid coupling, not an anti-vibration mount. Having said that, I have seen people (try to) shock mount by passing screws and studs through single rubber pads. It appears that your pump is moving, i.e. vibrating.

--
JHG

 

[tholz]

Drawoh:
yes, if you see the original picture, you'll see that the bolts touch the base plate frame and go through the vibration pads. However, an analysis of the noise in the apartment indicates vane pass freqeuncy of the pump (5 vanes * 3500 RPM /60) = 291Hz is most prevelant. We are looking into the possibility of using a different impeller, perhaps one that is a bit smaller in diameter to increase cutwater distance, which should dampen the pulses. I believe that flex pipe connecters will not signifigantly supress vane pass pulses, since the wave tranmission is primarly in the water and not so much in the pipe structure - but I'm only speculating here - perhaps someone can comment.

 

[Tmoose]

Was the original pump 5 vanes?
is the black section of piping a "flex" joint of some type? Is it new?
Is the piping rigidly mounted in 3 dimensions right after the flex joint?

can you feel noticeable vibration on the piping beyond the flex joint, and especially where the piping disappears into the basement ceiling/apartment floor?
Is an analyzer phone app available to determine the frequency content of that perceptible piping vibration?