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

 

[maytag]

op9,

Entrained air will generate the noise often associated with cavitation. Look for a leak on suction side of the pump- air can be drawn in-leak does not necessarily have to leak diesel.

Tom

 

[op9]

Hi Tom,
I can't imagine any issues there. Having the diesel head on the pump, would expect a significant leak out of the suspected point of air ingress, especially when the pump is off, as it often is for extended periods. Also the pressure gauge readings on both inlet and outlet are dead steady.
Rod.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[maytag]

This is common in hydraulic systems-not far removed from your application.

Tom

 

[itsmoked]

op9; A star for your excellent question - clearly stated.

Hopefully we can get to the bottom of this.

Standing wave/resonance? Any way to change the motor speed?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[op9]

Hello Keith,
No at present there is no way to change the speed. Lowering it would affect our required pump capacity.

Actually it is interesting that you ask, because when I have used these particular pumps in the past I have always opted for 6 pole motors (950rpm)to provide longevity due to lower sliding speeds. This time the capacity required meant I really had to choose a much larger pump to run at 950rpm or up the speed on a smaller one. However I have not used these convoluted SS flex for pump attachment before.

Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[itsmoked]

It would seem to me that the cyclical pulsing waveform would effectively drive resonances in a system with long straight sections.

I'm more experienced with refrigeration where those flexible coupling are very common and often required to prevent rapid fatigue failures. The compressors are mostly piston based positive displacement and cause even more pulsation than a gear pump could ever manifest. The flex connections tend to reduce noise not increase it. Of course I'm talking a compressible medium unlike your case, so...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[op9]

Actually Keith there is a fairly long straight length of inlet pipework before the flex about 9ft. Maybe another advantage of using rubber hose instead of the SS flex would be to better "insulate" it from any pump induced pulsations??
Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[maytag]

Rod,

For whatever reason I could not get your attachment to open yesterday at work. The SS hose you show is the same type we use for water evacuation on electric arc furnaces and ladle furnace applications(vacuum). They are bad about cracking and sucking air-when this happens we lose vacuum-no water is evacuated and the water cooled roof or sidewalls over-flow.
There is also a pipe union in your piping-NPT fittings should be avoided-especially the use of unions. Replacing this with a reinforced hose suitable for suction service hopefully will take care of your problem.

Tom

 

[hydromech]

Have you exceeded the pumps maximum speed or flow rate?

If the pump is running too fast or the fluid viscosity is too high then the pump will not be able fill properly and will go into cavitation which will be very loud.

Can you be sure that the hose has not blistered inside, choking the flow to the pump?

Adrian

 

[op9]

Hi Hydromech,
No the pump operating conditions are all per manufacturer/ supplier. This pump has been noisy from day 1 when everything was new and the installatiopn is only a few weeks old now. As I said before, we have a significant suction head on the pump, have measured the inlet pressure during operation and it is above the NPSH required.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[muscovy]

I would assume that there is a strainer on the suction side of the pump. I have experienced a similiar problem on #6 oil pumps. We replaced the pump and motor as you stated you have and the noise continued. We kept the same suction strainer on the new pump and that was the problem. I went around the Duplex strainer with an oil can and oiled all the covers and the packing around the switch over handle and the noise went away. At next available time we repacked the gland on the handle and the noise problem was solved.

 

[op9]

Hi Muscovy,
Well "air" ingress has been mentioned before but as there is a significant head on the suction line I would expect an obvious leak to show up when the pump is off and exposed to this liquid head. In your case was there any show of oil coming out through the gland with the pump off?

Yes we have a strainer further back at the tank outlet. Just a single 3" Y-type fitted with a 80# screen.

I will however go over all possible leakage points again. May have to wait a few days as we have just been hit by heavy rain which is supposed to hang around till next week. This plant is out in the open.
Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[hydtools]

Are you sure the noise is hydraulic? It may be mechanical. Something in the mounting or drive is rattling. A stethescope or good old piece of hose to listen the various mountings may help.

Ted

 

[op9]

Hi Ted,
Well it sure sounds mechanical, but if you read my original post I have pretty much checked everything AND installed another new pump and the noise is the same. Tried the listening tricks and it appears to eminate from the pump. However cavitation too can sound very mechanical and/or air in the pump. I was also discounting those except muscovy's post seems very close.

I was wondering about the convoluted SS flex causing flow irregularities into the pump and hoping that someone may have had a similar experience.
Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[MikeHalloran]

>>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.<<

I don't understand how you're getting 5 psi at the inlet port of the pump when the static head of liquid is ~3psi.

Those convoluted flex connections may have an i.d. a bit smaller than pipe of the same size, and present an additional restriction proportional to the number of convolutions.

In the picture, that sure looks like undisturbed factory paint on the plug in the pressure test port of the pump body.

Have you got a compound gage you can trust to put in there to re-run the test yourself? Or a 2-meter stick and some transparent tubing from which to make a standpipe for checking the suction head at the pump inlet?




Mike Halloran
Pembroke Pines, FL, USA

 

[op9]

Well spotted Mike!!

Actually the tank static head on the pump can vary from 5ft to nearly 30ft of diesel, depending on how much they have in it. The highest I have seen is about 12ft. It makes no difference to the noise. The Required NPSH for this pump is 9.5Ft wg. The max flowrate is 15gpm (US). I have about 12ft equivalent length of 1-1/2" suction pipe. My estimation tells me I can suck a lot below the pump before I have a problem.

Why the paint is undisturbed is that this is the just fitted new pump which I haven't measured any suction pressures on. I measured it on the "old" new pump, but replacing it with the current pump produced no difference to the noise.

Spoke to the SS flex manufacturer today and he reckons he has never heard of a problem using these flexes on pump suctions.

Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[hydtools]

Are all the screws put back in to fasten the coupler shield?

Ted

 

[op9]

Ted,
Do you mean the guard over the couplng? If so there are only a couple holding it down at present just to keep it safe. I have had it off and on regularly making sure the pump in not mechanically seizing up. The noise is the same whether it is in position or not!!
I will be back on site again next week but still not satisfied a rubber hose will fix the problem, unless it is some sort of pulse induced resonance with the inlet pipework. Will try wedging or propping the pipework to try and change its natural frequency.

Also will run the pump very briefly empty to see if it is an internal mechanical noise.
Rod.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[Zapster]

I would look at the external pressure regulator. Are you certain that someone did not install a PSV for the external pressure regulator or a pressure regulator that is not suitable for the system? PSVs will chatter when used as pressure control devices. Is there a way you can test your pump without the external pressure regulator using a manually controlled valve to maintain the pressure for the test?