How to increase flow rate? 1

[321sol]

Hi Guys

We have a pump island that is roughly halfway the distance from one of our tanks and a discharge point on the jetty. See last page in the attached document for illustration.

Pump A is typically used to pump to the jetty, however, whenever the big tank is used, the flow rate is about 20 kL/hr less than when a nearby tank is used. This occurs even when the big tank is filled. Turning on pumps A and B at the same time does not increase the flow rate either; in fact, one operator reported that the flow rate was actually reduced. This flow rate is even further reduced when pumping is done at both the gantry and the jetty.

I was proposing a second identical pump to pump A placed closer to the big tank to increase the discharge head for the first pump A in an attempt to increase flow rate at the jetty. In addition, the suction line to the first pump A would be upsized to 6'' before the strainer. The strainer is 4'' and so the line from the strainer to the pump will be 4''(this is the same for the 2nd pump A).

Additional info:
The pumps are roughly about 2m below the big tank and the jetty is roughly about 1m above the pumps.

The outlets of each existing pump are 3'' increased to 4''. The 4'' outlet line connects to a 6'' line that runs to the jetty.

On the suction side of each pump is a 4'' strainer. We cannot source 6'' strainers locally.

Pump A is a 4 x 3 pump with 9.63'' impeller diameter.

Correction to Drawing: The pump labeling on the existing drawing should be that of the proposed. That is, pump B should be the one at the top or closest to the gantry and pump A should be the one at the bottom or closest to the jetty.

Questions:
Will adding a 2nd pump A increase my flow to the jetty if Pump B is not operating and no one is loading at the gantry?

How would my system/flow rate at the jetty be affected if pump B is operating and there is no loading at the gantry?

How will my system/flow rate at the jetty be affected if pump B is operating and there is loading at the gantry?

Given the existing conditions, how can I increase flow rate at the jetty to about 100 kL/hr?

 

[MFJewell]

The system hydraulics will be different between the "far" tank and the "near" tank (not sure what the difference in line length is), so it isn't surprising that you get different flow rates. You may want to check the NPSHR on both your existing pumps and do a calculation of the NPSHA when the "far" tank is in service as well.

Will adding a 2nd pump A increase my flow to the jetty if Pump B is not operating and no one is loading at the gantry? Mostly likely will increase pressure, but flow rate will close to the same.

How would my system/flow rate at the jetty be affected if pump B is operating and there is no loading at the gantry? Unsure, what else would be in operation?

How will my system/flow rate at the jetty be affected if pump B is operating and there is loading at the gantry? Unsure, what else would be in operation?

Given the existing conditions, how can I increase flow rate at the jetty to about 100 kL/hr? Make system curves and get correctly sized pumps.

What is being pumped by the way?

 

[321sol]

I don't have the numbers with me at the moment, but the NPSHA for the existing system is far below the NPSHR for pump A when the far tank has low levels of liquid. If I swap out that 4'' piece on the suction side of pump A to a 6'' piece, I greatly increase the NPSHA to pump A.

In questions 2 and 3, there will be loading at the jetty.

Diesel is being pumped.

 

[MFJewell]

Have you done the calculations to confirm the NPSHA?

For 2 and 3, I meant are you planning to run the new pump A while running B and flowing to jetty? If so, it will have similar results to question 1.

 

[PipesandPumps]

I agree with MFJewell. We use a hydraulic simulating software at my company called Pipe-Flo and I quickly threw what you had from your sketch and a couple points from the pump curve in there. Right off the bat there were a couple concerning things coming up. If it is water you are pumping there could definitely be NPSHa issues, but is also looks like your pump is probably operating outside it's preferred operating range, which can really affect your reliability/efficiency/longevity. If you are pumping something more viscous than water then you definitely could have some issues with NPSHa. This would also be more accurate if you were to include all the fittings and such as well. You can go to the Pipe-Flo website and get a demo version of the program to try yourself which may be handy. It only allows you five pipes in the demo, but that may be all you need in order to help get a better handle on your problem. I put the link for their demo download page below. If turning on the second pump actually reduced flow though, I would lean towards an NPSH problem. Be careful just adding another pump to the system as proposed. I've seen that have unintended consequences as well.

https://eng-software.com/download/business-development-demo

 

[LittleInch]

OK,

Will adding a 2nd pump A increase my flow to the jetty if Pump B is not operating and no one is loading at the gantry?
Yes, but maybe not by as much as you think. You will in effect have two pumps in series so the outlet pressure from existing pump A will increase, but you might start to operate beyond the end of the curve on the RHS and other problems will then occur ( vibration, over current, excess ware etc

How would my system/flow rate at the jetty be affected if pump B is operating and there is no loading at the gantry?
If it's the same pump as pump A then there should be no difference.

How will my system/flow rate at the jetty be affected if pump B is operating and there is loading at the gantry?
No idea. Depends on how it affects the system curve.

Given the existing conditions, how can I increase flow rate at the jetty to about 100 kL/hr?
A pump by the tank will solve you apprarently chronic NPSH issues, but be careful to control flow to 100 m3/hr.

BTW having NPSH much less than min and the fact your flow rate is dropping by 20% or more says to me you have very bad cavitation at the pump. Operation for any length of time will destroy the impellor ( and may already have done so). Before you do anything else, check the condition of the impellor in pump A.

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