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(OP)
Hi,

May I know what are the other consequences if our Pump Head design larger than System Head? From my understanding, the pump will required excessive power.

For example, system head only required 30 m/98 ft but we use a pump that can delivered 50 m/164 ft at required flowrate.

#They design like this to give some margin for future expansion but after 10 years, no future expansion and no action to lower down the pump head

The system flow will usually increase. Flow will increase until system pressure drop equals pump total discharge head.

Your pump design head is significantly higher than what is needed. You can investigate if a control valve on the pump discharge will work. Control valves can be a good solution when you need 75 to 100% of pump rated head. That is still too high for your short term head prediction.
A possibly better option may be to install a VSD. VSD may work quite well, as you must lower the discharge head now by 40% or so. You could run the pump at about 75% of rated speed now and increase it using the VSD to higher speeds as more head is needed later on.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

So these look like theoretical numbers. What flowrate are you actually flowing at?

My guess is that if you have no pressure or flow control on the system then you're flowing at probably about 20-25% more than you think the basis of your 30m requirment, but every system is different dependoing on how much of that 30m is a static head and how much is friction losses.

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

You need to look at your pump curve to see how much more power you are using, but if its higher flow then it's less time so total energy might be less....

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

Hi,
Probably good to review the basics. Consider the document attached to support your query.
Your Operating point is at the intersection between your pump curve and system curve.
You may want to share those curves with us.
Several options to consider:
a) Install a VFD
b) Trim the impeller.
note: Drop an email to the pump's vendor and request his/her support.
Good luck
Pierre

Great comments on the system. The system you have from your description sounds like it does not have and VFD (mentioned already) or any flow control devices like a triple-duty valve. If your system's primary loop is allowed to flow freely, do you have flow control on your terminal devices? Also, what is your pump speed (1800 rpm vs. 3600 rpm)? It might help if you have a high-speed pump with a low-speed TDH.

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