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Centrifugal Pump Head

05/26/2009 2:06 AM

How can i increase head of a centrifugal pump? Is it good idea to increase pump head by increasing its RPM?

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#1

Re: Centrifugal Pump Head

05/26/2009 2:43 AM

Upto a certain extent only. Go for multistage pumping.

The pumps have there balancing as well has the fundamental frequencies of the systems designed for the RPM, going too far away may lead to vibrations, which can only be catastrophic.

Check up with the manufacturer for the data or use some experts, who will check the frequencies at new parameters and tell you the condition.

Don't forget the bearings and the sealings- whether gland, mechanical or elastomeric (that limits the rollong speed in bearings or the surface speed in seals- for proper operation and life), and the coupling too.

In short, I do not propose except a few 10s of % and definitely that's not what you are looking for.

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#2

Re: Centrifugal Pump Head

05/26/2009 6:00 AM

Not sure to what extend and conditions you need to increase the head.

In addition to the GA by SB you may also consider reducing losses (bigger piping) or by adding a booster or a further parallel pump.

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#3
In reply to #2

Re: Centrifugal Pump Head

05/26/2009 9:45 AM

oHHHHH Hendrric

I think you mean series not parallel , Am'i right

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#9
In reply to #3

Re: Centrifugal Pump Head

05/28/2009 10:38 AM

No I did mean parallel.

If one introduce a second pump (or use the standby) in parallel without increasing the flow the duty point will move to the left of the pump curve and will deliver some more head. (not a very efficient method but it can be useful in emergency situations)

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#4

Re: Centrifugal Pump Head

05/26/2009 11:18 PM

Two suggestions to add ...

1) Check with manufacturer - you may be able to increase the head by upgrading the pump impeller to a larger diameter. This may or may not be possible with the current pump/impeller combination you have.

2) If the pump's motor is run using a variable speed drive (VSD/VFD), then you may be able to over-clock the RPM to increase the pressure for a given flowrate. Check with pump/motor manufacturer if this is possible/reconmended. Get permission in writing, as doing this without the OK from manufacturer will certainly void any warranty claims.

I've recently over-clocked a 260 kW motor using VSD - worked well (increased rpm by 20%). But do this in consulation with Technical help from the manufacturer of both the pump/motor, and VSD.

Good luck

Anthony

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#5

Re: Centrifugal Pump Head

05/26/2009 11:27 PM

Most pumps are shipped with less than the maximum diameter impeller, so ask the supplier what is the maximum diameter impeller you can install. This will increase the head capacity. Speed also, as pointed out, but 5%-10% is suggested as flow will also increase and you may have a suction pressure issue (low) by increasing the flow capacity also. Cavitation may occur. Power will increase by a ratio of the cube of the speed and head by square of the speed so you can't just blindly add more head capacity and / or flow without considering what this will do to the driver and coupling. You should have minimum 10% extra driver by design so you might be OK. Careful of increasing head capacity by significant amounts or piping and pump case may not take the extra pressure capacity if you have a zero flow condition while running (blocked flow by closed discharge valve or closed check valve or other 'shutoff' condition).

Wild ideas include pressuring the suction system by a gas blanket (air or nitrogen ?) if the suction is from a pressure vessel. The idea is pointed out already by a 'booster' pump, or any other way to increase suction pressure by X amount. X amount increase passes through the pump and is added to discharge head (pressure).

Lastly you can have my ex-wife just stand near the pump. Pressure will increase .... I promise. Not the least expensive though... might cost you $500,000 or so from what I figure.

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#6

Re: Centrifugal Pump Head

05/27/2009 1:29 AM

Yes, head can be increased by increasing RPM but it will have a limit. For higher heads, you should go for multistaging. Decreasing flow can also increase head.

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#7

Re: Centrifugal Pump Head

05/27/2009 10:58 AM

zeeshan, did you receive a pump curve sheet with the pump? If not, you should be able to go to the manufacturer's site and obtain one for your pump. Review of the pump curve will reveal the "break-over" point where the maximum output of the pump can be acheived verses RPM. If you notice in the curve plot there will be a point wherein the pump output will reach a maximum value then for a short period of time an increase in RPM will cause the pump output to "flatline" (depending on pump casing and impeller design) and then the pump will reach a point wherein any RPM increase thereafter will result in cavitation and loss of output.

Also; many pump manufacturers use the same pump casing for different applications and sometimes there are casing liner and/or impeller kits available to change the dynamics of the pump output. A call to the pump manufacturer should yield the answers you need.

Good luck,

Shockhiscan

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#8

Re: Centrifugal Pump Head

05/27/2009 12:12 PM

First step, remove any artificial head losses from main loop balancing "circuit setters" or other valves.

Next, look for any system restrictions that are not adjustable valves but can be economically replaced with a lower pressure drop type of device or option.

Then get the largest available impeller for that pump body.

VFD control of the pump motor is how we then adjust the flowrate of the system, though specifically for "increasing" pump head you may be asking about is replacing the motor with one that is wound for a higher rpm. Yes, if it is economically feasible for you to do this versus the added benefit, it can be a "good" idea so long as this is within the parameters of the rest of the system.

I would suggest modelling your hydronic loop first - you can get a free download of the TACO version of HVAC Solution here: Hydronic System Solution - HSS

It is a simple drag-and-drop graphic calculation program that will help you diagram and identify potential issues or possible improvement points in your circuits by immediately calculating the resulting head/flow savings from various improvements. The more detailed you get with the components present in your system, diameters, pipe materials, fittings, etc, the more accurate your diagrammatic design loop will be. You will immediately see the results of any tweaking you choose to do.
The pump selection will also give you an idea of the operating efficiency of your pumping package at the system resistance curve of your existing installation, so you can best analyze what new pump type/size/horsepower/rpm will be the best to upgrade to when it is time for that investment.

download the free version directly here:
http://www.taco-hvac.com/en/embargo_form.html?soft=HVACSolutionTacoHSS.exe

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ajwinemaker (1); Anonymous Poster (1); Hendrik (2); IRSHAD (1); PetroPower (1); Sandman (1); sb (1); SHOCKISCAN (1)

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