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Pump Problem

Pump Problem

Pump Problem

Dear Engineers,

The pump that installed to transfer liquid from tank to tanker seems facing a problem. The motor that installed to the pump initially tripped due to high amp. First, the motor that install to the pump is small then I increase the motor size but the suction valve cannot fully open. Even though it cannot fully open, I get the flowrate that required. The pump curve can refer to attachment.

Piping info:
Pipe size : SS304 SCH 10 4 inch
Flow required : 80m3/h
Head : 30 m
Pipe length : 80m horizontal, 6m vertical

Motor : 50Hz 415V 2 poles 2900 RPM 7.5kW
Valve inlet and outlet opening : 1/4

Next trial:
Motor : 50Hz 415V 2 poles 2900 RPM 11kW
Valve inlet and outlet opening : 1/2
**Someone said that cannot open it full as the amp will increase.

I know it is a bit funny to install 7.5kW but I accept that stupidity that I made. I think it is not ok to open at half for the suction valve. I have propose few suggestion to this problem. First to trim the impeller to 160mm diameter. Second, to increase the motor to 15kW. But I don't recommend the second option as it will increase the power consumption and velocity inside the pipe. Hope you guys can share experience and suggestion. If you need another info, I will reply to it. Thank you in advance.


RE: Pump Problem

Never throttle the suction valve of a centrifugal pump!

It is reasonable to throttle the discharge, but not all valves tolerate throttling.

You have a few choices. You can throttle the discharge (likely requires a gate valve being replaced with compatible type), You can trim the impeller, you can use a VFD to slow the pump, or you can install the correct motor. I think you'll find that each option has similar costs so you'll need to identify which one works best with your application. All except replacing the motor will reduce the performance of the system but that may be tolerable.

RE: Pump Problem

MZEngineer, you DON'T have a pump problem you have an application / wrong pump selection for the application problem.
You need to calculate the total discharge head for the pump. Where did the 30m come from, I'm not going to do the calculation for you but would suggest 30m head is excessive.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Pump Problem

This is poor engineering practice , you should first perform a hydraulic calculation . Error and trial is not an option .
A link is provided to you and others to perform the full calculation , expecting you have the pump curve .

Throttling the suction valve is not acceptable unless you want to damage your pump . You have to throttle the valve at the discharge if needed.
note :Someone is right , check the pump curve Power vs Flow rate . The reason why at start up the discharge valve is closed .

Good luck

RE: Pump Problem

Why start new thread about power consumption.
You should add to this one - ask to have the second one removed and added here.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Pump Problem

To add to my previous reply and reading your second post , I believe there is a long way to go . You need to find someone knowledgeable within your organization or hire a contractor to perform the job .
Check for TDH pump using your favorite search engine and Pump head is not the discharge head , it's the difference between discharge head and suction head . Again you need to perform the entire hydraulic calculation of your system to select the right pump .
I cannot offer more .

RE: Pump Problem

As artisi says, first find out what your system needs to flow at 80m3/hr.

If at the end of your pipe you are going straight into a tanker at atmospheric pressure I reckon you need something approaching 8m head at the outlet of your pump.

The pump adds head to what ever comes into it so if the liquid level in the tank feeding the pump is say 3m above the pump then the pump in this case only needs to add 5m head.

Your pump is adding 30m of head - probably 5 - 6 times what you need. That's why you need to throttle it / it's flowing too much if you open everything up. Even at 160mm, you would go off the end of the curve and flow more and use more power.

Do the design work first then get the pump to match, not the other way around.

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

RE: Pump Problem

As always, information is severely lacking...

If this is a regular tanker loading system, most of them that I have worked with have a flow control valve near the tanker.

Post a P&ID/other schematic, specify the fluid, etc. Then we can probably help without conjecturing what the actual system really is.

Rio de Janeiro - Brazil

RE: Pump Problem


Someone is right , check the pump curve Power vs Flow rate . The reason why at start up the discharge valve is closed .

That may depend upon various factors, among them what type of discharge valve it is, how it is actuated, and how powerful the actuator is; the discharge pressure at zero flow is crucial, viz., at low values it may not matter what the actuator is, as either mechanical drive or human muscle will suffice.

At more moderate pressures, it might only be possible to use a mechanical actuator to open the valve, as opening the valve by muscle power may range anywhere from difficult to almost impossible.

If the pressure is great enough and the actuator sufficiently under-powered, the valve will be impossible to operate from the fully closed position.

This being said: another approach that may work is to crack the valve open just slightly before starting the pump. This accomplishes the dual purposes of limiting the current draw of the motor, as well as slowly priming any empty piping. Once priming has been achieved and the throttling burden has either been transferred to a downstreaam valve or established by intrinsic piping system design, the pump discharge may either be fully opened or opened as required to limit flow and/or motor current draw.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

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