Noisy gear pump 2

[op9]

I have a gear pump installed pumping diesel oil. Specifically it is a Viking HJ4195 running at 1450rpm (4pole 50Hz supply) at 66psi delivery pressure. The suction is supplied wth a head of about 6ft plus and we have checked the pressure at the inlet port during operation and it is 5psi or higher depending on liquid level in the fuel tank.
The pump is a new installation and has been noisy (sounds like a bag of old bolts...grinding raspy sound)from the start. I have had the supplier look at it and they are at a loss. A new pump was supplied last week and after installation and alignment it was just the same.
Just a few more notes:
1) Pump alignment is OK
2) Current draw is fine and pump is free and its own bearigs OK.
3) Motor is new, bearings fine and runs separately smoothly.
4) Going on inlet pressure measurement does not appear to be a cavitation or NPSH problem
5) Internal relief valve is not operating as pressure is set by external pressure regulator (returning to tank) and internal relief opens at about 85psi (delivery press 66psi).
6) The only thing I am considering is that the pump is installed with two 1-1/2" flexible connections (convoluted SS covered with braid about 12" long) see attached photo, to alleviate any piping stress on the pump. Could these be causing irregularities in the flow as the bore is not smooth as would be the case with rubber hose?

Has anyone had similar instances when using convoluted SS flex to supply pumps?

Any comments would be appreciated.
Thanks in advance,
Rod


Rod Nissen.
Combustion & Engineering Diagnostics

 

[op9]

Hi Zapster,
The external pressure regulator is a Jordan sliding gate back pressure regulator...probably the best type of valve for this application. I have used them exclusevely for years. The regulation is done with the lower edge of the sliding gate against the orifice. So there is no seat and lid as in a conventional valve to chatter if oversized or if just a PRV/PSV etc. I can shut this valve right off and then the internal relief of the pump opens ...basically the noise is still there. I am also confident that the pump internal relief is fully shut during normal operation.
Thanks for the input.
Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[hydtools]

If you have a manual shutoff valve in the suction line air may be entering by way of the valve stem seal. A valve that works in a pressure line may not be good in the suction line. The valve stem seal may be an omnidirectional seal working well with pressure but allow air to enter when working with suction. Drop some light weight oil around the stem and see if the oil disappears when the system is running indicating that suction is pulling air in around the stem.

Ted

 

[op9]

Hi Ted,
Only valves on the suction side are a large 3" tank 1/4 turn ball valve before the strainer and another ball valve 1-1/2" before the pump inlet flex. The suction line is under tank head pressure (positive always). I will however try the light oil next time on site. Have to go work interstate till the weekend so only will be back there next week.
Thanks, Rod.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[arunmrao]

How about temporarily introducing rubber hose to eliminate the doubt?

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
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[rzrbk]

It sounds like air entrainment. I agree that NPSH or mechanical problems would show up in vibration or unsteady pressure readings.

Suspect that air may be trapped in any high points in the line such as the hose corregations. (especially if hose is arched/pocketed) If so, this air could be gradually fed to the pump over time.

It would also serve as a collection point for any entrained air to gather and do the same.

 

[op9]

Just to keep you informed.
Went back and tried the oil over the spindle glands of both ball valves on the suction side. The oil just remained where it was, no sucking or reduction in pump noise. I am having some rubber hoses made up to try.
Thanks to all so far.
Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[ccfowler]

op9,

I would consider using pulsation dampers at the pump suction and discharge ports. This would isolate the inertia of the fluid in the piping from the high frequency flow rate fluctuations that are a characteristc of this type of pump. The greater speed of the pump increases the effects of the inertia at a rate much beyond the speed ratio. Even though you may have enough nominal suction pressure, the instantaneous suction pressure may actually be greatly reduced.