I have just installed a new Diesel

[cjoehilton]

I have just installed a new Diesel Fuel Supply System for our Diesel Fuel Generators. I more or lest replicated the old system except for the old gear pumps were 1" and I increased to 2". The reason being the new pumps were 2" suction and discharge. I have about 18" from my strains to the pump on the suction side. On the discharge side I have a gauge check valve and ball valve, in that
order.

The problem is when I first start the pumps they make a loud grinding noise. I have checked pump and motor alignment and its alright. I have had the pump rep on-site and they say that the pumps are fine. The one thing that I was concern with is the distance from the discharge to the check valve. I a have not found in recommendations for this distance, I have about 8". As a test I removed the swing arm inside the valve and the noise went away.

What should this distance be?

Thank you

 

[jari001]

Was it double checked that the check valve was installed in the proper direction?

 

[cjoehilton]

Thank you for your reply. I that was checked and the valves are installed properly. I have redundant pumps so I have two check valves. My first thought was to move the check valve to upstream of where the discharge side of the piping meet. This would eliminate one check valve and create more head pressure on the discharge side of the pumps.

 

[mk3223]

Quote: As a test I removed the swing arm inside the valve and the noise went away.

It seems that something was wrong about the swing arm of the check valve for the grinding noise?
In the pump discharge, the 8" spool with a gauge before the check valve should not cause any problem. And, the check valve should be installed for each pump discharge for the proper protection.

 

[cjoehilton]

Thanks

 

[LittleInch]

The information as provided makes no sense to me.

The pumps make noise on start up only?
How is flow started / stopped?
Does it stop when flow starts?
What is downstream of the check valve?
Can it increase in pressure (thermal) such that the pump can't pump against it?

distance has nothing to do with it.

Can you sketch your entire system from pump discharge to end point?

You need a check valve on each pump otherwise flow might go backwards through the pump

what sort of pressures do you measure with your guage.

Where is the pressure relief system around the pump r do you rely on the internal one (hopefully) in the pump?

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

 

[cjoehilton]

Thank you for your response
Start up only
Manually start and stop the pumps
After about 20 sec the noise goes away
90 elbow about 8" away
I will try and upload a sketch
60 to 65 psi
The relief valve is on the pump internal

 

[LittleInch]

Hmmmm, Not easy to say based on that info or why taking out the flapper made a difference.

I can only think that there is some sort of lack of fluid entering the pump.

Is the pump flooded suction ( below tank liquid level) or above it?

Maybe the previous NRVs didn't work too well and were passing and the new ones are sealing better than before.

what does the new system look like? Or is it just the pump that was replaced?

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

 

[cjoehilton]

Again thank you for your help.
The pump in below the liquid level. When we open the strainers they are full so I have to believe the pumps are full on the suction side.
The old system pumps were 1" line and we up sized to 2". We did take out an elevated 250gal tank on the downstream side. It was manually operated by opening and closing a ball valve.

My thinking is that the close proximity of the check valve is not allowing for enough back pressure on the discharge side of the pump and by moving the CV further downstream it would create more pressure on the pump.

This is really not my expertise so everyone's help has been greatly appreciated.

 

[LittleInch]

You may well be right about the downstream pipe taking time to fill up or create a bit of back pressure on the pump, but the check valve and the distance shouldn't have anything to do with it.

What type of check valve is it?

what pressure do you read on the guage during start-up and when the noise disappears?

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

 

[cjoehilton]

It is a full port swing check valve. I have about 5 psi constant and I go up to 60 to 65. Not sure at what psi the noise goes away. Everyone I have talked to said the distance does not matter. The supplier suggest larger strainer. I took the baskets out and still got the noise. Only thing that has helped was taking out the flapper in the CV.

 

[LittleInch]

It sounds very much like the pump essentially doesn't have enough back pressure to start with and is essentially free wheeling to start with due to the loss of that elevated tank.

The other option is to insert a back pressure control valve which opens at say 35 or 40 psi and hence should open fully in normal operation, but creates an instant back pressure when you start the pump.

I can only think that the flapper is somehow creating a small back pressure at the start which then causes the gears to chatter against each other creating the noise. As the flow increases and back pressure increases this goes away.

To test this try starting against a manual valve close to the pump discharge which is almost closed and then opening gradually over the next 5- 10 seconds.

Your internal pressure relief should prevent damage to the pump while you do this, but just don't do it for too long and only as a test.

Or just accept it makes a noise for 20 seconds or so. how often do you turn it on and off a day?

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

 

[JJPellin]

I would suspect a water hammer interaction between the internal relief valve and the swing check valve. Running at 1200 rpm, that pump should put out 4500 gph. If you are only using 1400 gph, there is a lot of flow passing back through that relief valve. You stated that the pump has 2 inch ports. Your drawing and the OEM documentation shows 3 inch ports. This pump is much too large for the service. I would adjust the internal relief valve to a lower setting to see if that clears up the problem. Then I would consider dropping down to a model AS4195 with 2-1/2 inch ports to better match the capacity of the service. Please explain the item on your drawing that states "70 gph x 4 x 5 = 1400 gph". Pleases confirm the speed of your pumps at 1200 rpm.

Johnny Pellin

 

[cjoehilton]

Thank you. I agree we could have went with a smaller pump. The inlet and outlet pipe is 2" and the pump inlet and out is 3". I never caught this until we started the installation of the pumps. I contacted the supplier and they said we would be okay but don't go smaller than 2". I assumed this was good because the existing pipe was 2".

Our 1000KVA Generators at full load will use 70gph of fuel. With a safety factor of (4) X 5 Generators. So to maintain the day tanks, we need to be able to pump 1400gph.

The pump is a direct drive so what ever the motor is running should be what he pump is running.

Thank you for your response.

 

[LittleInch]

But do you run these pumps continuously or every hour just to fill the day tanks?

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

 

[JJPellin]

You need to be able to pump 1400 gph to feed 5 generators. But, that includes a factor of safety of 4 times. So, the normal flow is only 350 gph with a pump putting out 4500 gph. The internal relief valve should be designed to pass the full capacity of the pump. That pump is suitable at discharge pressures up to 250 psi. If it is a water hammer, you can probably de-tune it by adjusting the relief valve higher or lower (within the design capability of your piping system). At 350 gph, that 2 inch check valve is just cracked off the seat. I would convert to the smaller pump.

Johnny Pellin

 

[cjoehilton]

Thank you for your help.

 

[cjoehilton]

At this time we don't have the funds in our budget to replace the pump. The de-tuning would be a easy fix. Thank you for your advice.