piping vibrations

[jjr1111]

Have a filtering system that is experiencing vibrations and was posting for into in the vibration forum, but and wondering if it could be related to piping system design so wanted to post up here too.

The setup is a PD pump that pumps fluid from a tank through a filter and returns to the tank. Additional process info is the motor around 1350rpm, and is gear box reduced to around 347rpm. Pump has 4" inlet's / outlets, but the process piping is 2". The pump inlets/outlets are reduced down to 2" directly before and after. The pump is .521gal/rev of displacement, so at 347 rpm we're around 180 gpm of flow at 60 psi at process filters. The process fluid path goes from residing in a tank, exits the bottom of the tank, 90's, goes a few feet, then is expanded to 4", then to the pump, then 180 degree turn, then reduced to 2", then goes around 15 feet, through filter bank, heat exchanger, then returns to the tank top through around 20 ft of piping. Viscosity is similar to water.

At 180gpm pipe velocity at the 2" sanitary fittings of 2.067" ID would be around 17.2 ft/s, which seems fast, I though typical was around 7-10ft/s in piping, but not sure what effects of high velocities are. Perhaps there's a NPSH issue on the inlet where going from 2" ID to 4"ID right before the pump is causing cavitation, but I'm not sure how to calculate that.

 

[1503-44]

What kind of PD pump exactly? Some tend to cause more vibration than others.
Piston PD pumps can be much worse than gear pumps.

347 rpm is low and in the Range that can easily cause resonant vibration in pipe spans and pipe supports. Have you tried to determine the frequency of the vibrations? If they are some multiple of 347 rpm, then the pump may be the cause.

Yes, velocity is high, but may not be affecting vibration, if it is constant. There is such a thing as velocity induced vibration and you might want to investigate that too, but do it after you have eliminated the pump as being the cause. Some pumps, ie especially piston pumps, do not produce constant flow and the fluid must be accelerated each cycle of the piston, so higher velocities can increase the mass flow x velocity effects, resulting in higher forces being transmitted to the piping. That is a common cause of vibration, so you should investigate this first.

Where exactly in the system are the vibrations being observed?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Do you mean this thread?

https://www.eng-tips.com/viewthread.cfm?qid=521142

You have a heap of answers and loads more data which is why, in general, double posting is not allowed.

You say you have no pulsation dampers and the pump is too big. you can check NPSH but it needs an acceleration factor specific to the pump type and this is a bit of a strange pump. you don't mention temperature or vapour pressure?

But stick to one forum please.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jjr1111]

I'll stick to one forum going forward, but to respond to both comments, it's a lobe style pump. A Waukesha Cherry Burrell Universal 2 series pump.

I'm not sure I understand what "it needs an acceleration factor specific to the pump type" means?

The fluid is run through a heat exchanger so would consider it around 60 degrees F, viscosity similar to water.

 

[LittleInch]

This is what I mean or search for acceleration head

https://www.blacoh.com/downloads/literature/Solving_Pump_Inlet_Problems_P21E11_010.pdf

The "C" factor is pump dependant or just choose the closest to what you think this type of pump is which is probably smoother than a piston pump, but more pulse like than a centrifugal pump for sure.

Ok so a fairly high vapour pressure

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.