Suction Pipe Smaller Than Suction Nozzle on PD Pump
Suction Pipe Smaller Than Suction Nozzle on PD Pump
(OP)
All,
I have a positive displacement pump I am considering to unload rail cars with. The area is tight and we have an 8" pipeline that we can utilize for our rail track. The 8" pump we first considered will only give us approximately 1150 GPM, we are looking for more. The 10"x10" positive displacement Viking RS4324A that we were quoted can get approximately 1550 GPM @ 105 psi with an NPSHR of 22 ft. This pump would be side suction/side discharge.
We will have a VFD on the pump that will slow the pump down when the rail cars get low on product (lower NPSHA). We would also be able to install about 10 ft of 10" suction piping before reducing down to the rest of the 8" suction pipe. I ran some calculations on this and the velocity entering the pump is approximately 6.5 ft/s, the worst case NPSHA (when the rail car is near-empty) is 22.65 ft'.
From the numbers ran in AFT Fathom, it seems like this pump will work in this scenario, but I have never used a suction pipe smaller than the suction on the pump. The pump vendor said this would not be a problem, but I'd like to double check where I can. Are there any concerns I should take into consideration that I may have overlooked?
I am in the USA with an liquid storage facility, the product is vegetable oil @ ambient temperature.
Any additional information would be great. Thanks,
EDIT: we are unloading from the bottom of the rail car with 4" hoses going into the 8" suction line.
I have a positive displacement pump I am considering to unload rail cars with. The area is tight and we have an 8" pipeline that we can utilize for our rail track. The 8" pump we first considered will only give us approximately 1150 GPM, we are looking for more. The 10"x10" positive displacement Viking RS4324A that we were quoted can get approximately 1550 GPM @ 105 psi with an NPSHR of 22 ft. This pump would be side suction/side discharge.
We will have a VFD on the pump that will slow the pump down when the rail cars get low on product (lower NPSHA). We would also be able to install about 10 ft of 10" suction piping before reducing down to the rest of the 8" suction pipe. I ran some calculations on this and the velocity entering the pump is approximately 6.5 ft/s, the worst case NPSHA (when the rail car is near-empty) is 22.65 ft'.
From the numbers ran in AFT Fathom, it seems like this pump will work in this scenario, but I have never used a suction pipe smaller than the suction on the pump. The pump vendor said this would not be a problem, but I'd like to double check where I can. Are there any concerns I should take into consideration that I may have overlooked?
I am in the USA with an liquid storage facility, the product is vegetable oil @ ambient temperature.
Any additional information would be great. Thanks,
EDIT: we are unloading from the bottom of the rail car with 4" hoses going into the 8" suction line.





RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
The length would vary with relation to where the rail cars are spotted, the closes railcar would be within 40 feet, but each additional railcar it pulls from would be approximately 75 feet away.
I am unsure if acceleration head is calculated in AFT Fathom, which is the software I used to model this scenario. If it becomes an issue, we would be able to slow the pump down with the VFD automatically if is loses pressure on the suction of the pump.
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
Maybe I did not clarify, but if we are unloading only from one hose, then we would not try to achieve 1550 GPM. That would only be if we have, say, 4 railcars or more unloading simultaneously.
I believe we would be closer to 350-400 GPM through a 4" hose at any given time (9-11 ft/s). This is much more realistic than 30-40 ft/s.
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
I had a quick look and from what I can see the NPSHR of the pump at max rpm is only 13.5 ft ( see page 15 of linked doc ). 22ft for a PD pump looked high
http://vp.salesmrc.com/pdfs/Sec_430.pdf
Just try and maximise the length of the larger size of your inlet pipe (can you make that 10" length 12"?) but if you've calculated the NPSHA and you're ok then just monitor the pump for strange noises and pulsation of flow which is indicating cavitation and vacuum / vapours forming.
At higher rates you may well find that the railcars offload at different rates.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
You need a pressure sensor at near the pump inlet tied to the VFD, to slow down or shut down when the suction is starved.
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P.E. Metallurgy, Plymouth Tube
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
Yes the VFD will have a pressure sensor on the inlet of the pump, which we have a company come out and set up for us. They have done the other pumps on other railcar applications. I do not know what the setpoints are for the pressure at the inlet. I do not know if they have an option of inputting how many 4" lines are in use, but it is a good idea that I will explore.
LittleInch,
Yes it is a gear pump, and I had received that NPSHr from the vendor, maybe they accounted for a safety factor or a recommended NPSHr and not the actual NPSHr from the data you linked.
We are also considering the HXL10E Sliding Vane pump from Blackmer, which we have used in other applications for rail unloading. The NPSHr from the vendor on this is approximately 8.7 ft.
We could also increase the suction side to 12" if needed to slow down the velocity more. The scenario I ran in AFT Fathom shows that the closest railcar would actually unload up to 525 GPM (13.2 ft/s through the 4" hose). Does anyone foresee this becoming an issue?
Thanks for the confirmations in this thread, all. I hope this is helpful to anyone else who may run into a similar problem.
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
Just to update you. Viking updated their document recently, and the pump quoted is the RS in Table 5, pg. 12 of the attached file.
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
Maybe time to choose a different pump....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
Thanks for all the responses.
RE: Suction Pipe Smaller Than Suction Nozzle on PD Pump
Best regards, Morten