Pump Suction

[garciaf]

Here´s my issued:
The discharge line that is installed is 4 inches diameter 2000 m in length, from the ship to Tank
The tank maximum level is 12 meters
Sea level to the level of tank 8 meters
The pumping liquid is Gasoline
Data from software:
Flow: 200 gpm
Diameter of suction: 4 Inches
Diameter of Discharge: 4 Inches
Suction Pressure: -5.21 psig
Discharge pressure: 52.43 psig
Pump Head: 56.37 m
Pump NPSHa: 1.452 m
These are the data from the calculation with Pipeflow Expert

When I am going to select the pump.
I find a pump curve that match, but the issue is the following:
The Suction of the pump is 3 inches and the discharge is 2 inches.
the calculations done with the software both the suction and discharge are with 4 inches. See image attached

When I change the suction line for 3 inches in order to match with the suction flange pump, the NPSHa is lower that NPSHr which is not possible due to cavitation.
My question is the following:
Can I keep the same suction line with 4 inches and do a reduction 4X3 in order to match; also the discharge line from 2 to 4 inches because the line installed is 4 inches.
How this can affect the pump, is this Ok.
Please help.
Thanks for you time

 

[mk3223]

The answer is "Yes" as the pump is adequate for your case, and the reducers are needed for connecting to both Suction and Discharge nozzles of the pump.
Or, you may seek a different pump which meets the process design requirements and has the pump nozzle(s) to match the piping size.

 

[LittleInch]

You need the match the pump to the service. If that needs 4" pipe then use 4" pipe.

The key issue though is NPSH. 1.4m is very low

Gasoline is volatile and often suffers from suction issues. Looks to me like you need to lower the pump.

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

 

[HTURKAK]

Additional info. to MR. mk3223 (Mechanical) respond, the ecc. reducer 4X3 (FOT) is O.K. at suction side...apparently the discharge line is horizontal..similar concept shall be used at discharge side also, that is ECC. RED. 2X4 in FOT.

The boiling point of gasoline varies and minimum value is, 38 C. I will suggest to pull down the level of pump to reduce the suction head.

 

[1503-44]

Gasoline has a range of vapor pressures depending on grade and addatives. VP can be much lower than 38C. At 9.5 psia suction pressure, you may be entering the boiling ranges for some at 20C

 

[garciaf]

Thanks for your time
I appreciated so much.
I attached a document, please review.

In the document you could find
The calculations of the pumping system, and some questions that I have.

what I am thinking about is to change the pump, please review the document.
Thanks

 

[1503-44]

Could you please post a pdf. Thanks.

 

[LittleInch]

Well a PD pump is probably better than a centrifugal because you have the ability to self prime and LOWER NPSH, but still not zero. So if you've only got approx 3m NPSHA, you still need to choose carfully and get data from the vendor.

Slding vane looks OK, possibly at 520 rpm you might be looking a 1 to 1.5m NPSHR.

So your gasoline temperature had better not go up or your suction lift becomes more than 3.5m. If it does you won't be able to pump.

also what is the maximum liquid level in your shore tank?

But now you need to keep the differential pressure under control so you need a full flow pressure relief valve. Note also that as the differential pressure rises the power goes up, so you need to be careful where you set the pressure relief and watch the power to not exceed the installed motor capacity.

Gasoline can get very difficult to pump, especially if you have negative head from the liquid level.

The friction in the inlet pipe is low so increasing pipe size won't do very much. Lowering the pump has a much greater impact.

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