Plunger pump vibrations

[Murec]

We have a plunger pump operating at 335 rpm.
Some time ago a backup was added. The backup pump is smaller and operates at 786 rpm. None of the pumps has a pulsation dampener.
The flowmeter on the common discharge works OK with the larger pump, but shows erratic readings with the smaller pump.
Adding a pulsation dampener was suggested, however I suppose that it is the larger and slower pump that would cause harder flow pulsations and not the smaller pump.
There could also be a matter of mechanical vibrations transmitted through the piping, as the backup pump is installed on a steel construction.
Any ideas are welcome
M

 

[btrueblood]

Triplex plunger pumps, both?

What kind of flow meter?

I'd think the higher frequency pulsations from the smaller, higher speed pump could cause more problems, but it's just a guess.

 

[Murec]

Yes, both are triplex plunger pumps.
The flow meter is an orifice plate.

 

[btrueblood]

Ah! Then yes, you may be exciting a vibration mode of the plate at the higher frequency, or (more likely) exciting a longitudinal vibration mode in the pressure tap lines, if they have significant length. Both frequency modes should be easy to determine from reference texts, and see if they fall within 10 or 15% of the 3x rotational speed frequency of the pumps' outputs.

 

[Murec]

Thank you for the advice.
I am considering installing a different kind of flowmeter. An electromagnetic meter, with no parts intruding in the flow might be a better fit.

 

[btrueblood]

We've been very happy with our mag meters. We have several over 15 years old, still accurate to better than 1%.