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Right size engine for a pump


 
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Rance
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PostPosted: Fri Jun 01, 2018 4:10 pm    Post subject: Right size engine for a pump Reply to specific post Reply with quote

I have a Witte L-3 centrifugal pump and am wondering the right size engine to match to it. The pump has a 12" diameter impeller, 3" inlet/outlets bushed down to 2", flat belt drive pulley 4" wide x 3" diameter. When I bought it, it was mounted on an engine cart with a hand pull so the original engine couldn't have been all that big.

I've got a 1939 Lister CS 3/1 diesel (3 HP) I'd love to use with it, but think its probably too weak in the power department for that pump. (sure not going to try to mount that beast on a hand pull cart though!!!) Any ideas? Thanks
 
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Indiana Ken
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PostPosted: Sat Jun 02, 2018 5:52 am    Post subject: Re: Right size engine for a pump Reply to specific post Reply with quote

CVPost-Rance wrote:
(quoted from post at 17:10:39 06/01/1Cool I have a Witte L-3 centrifugal pump and am wondering the right size engine to match to it. The pump has a 12" diameter impeller, 3" inlet/outlets bushed down to 2", flat belt drive pulley 4" wide x 3" diameter. When I bought it, it was mounted on an engine cart with a hand pull so the original engine couldn't have been all that big.

I've got a 1939 Lister CS 3/1 diesel (3 HP) I'd love to use with it, but think its probably too weak in the power department for that pump. (sure not going to try to mount that beast on a hand pull cart though!!!) Any ideas? Thanks


Do you have any specs for the pump as to: RPM level, flow rate versus pressure. This is typically in the form of a chart and called a pump curve? If you can provide some info on the pump and what you want to do - I can estimate the power requirement for you. I suspect the pump is intended for a larger engine however, it also depends on what you wish to do.
 
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Rance
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PostPosted: Sat Jun 02, 2018 7:05 am    Post subject: Re: Right size engine for a pump Reply to specific post Reply with quote

Unfortunately Ken I have zero info about the pump and Googling brings up nothing. Given how it was mounted it was probably powered by something about 5 HP, but who knows if that was original. Given the 12" dia. impeller it was probably designed for relatively low RPM. I want to use it for irrigation, about 8 ft lift on the intake side, 30 ft head on the output. Volume, as much as I can get. Attached is a pic (borrowed from a 2002 posting on SmokStak-thanks Harry!) of a Goulds pump very similar to mine. The engine I want to use is a 600 RPM 3HP Lister, and given the size of this engine I think those are three very big horses...
Many thanks for your response.

 
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Indiana Ken
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PostPosted: Sat Jun 02, 2018 11:17 am    Post subject: Re: Right size engine for a pump Reply to specific post Reply with quote


Yes, a large impeller could be run at low RPM. Is there any info on the Gould's pump: model number etc.? It may be easier to find a pump curve for it.
 
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Indiana Ken
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PostPosted: Sun Jun 03, 2018 7:14 pm    Post subject: Re: Right size engine for a pump Reply to specific post Reply with quote


I didn't hear back from you (I know pump curves are hard to come by) so I decided to go ahead with my comments.

The HP required to pump water is given by:

Pump HP = (GPM x Psi) / (1715 x E) Where E is the pump efficiency. For 100 % efficiency E would = 1.0. Of course this is never possible. Modern pumps can be 80% +/-.

Using your head requirements of 8 Ft lift, 30 Ft output and assuming a flow rate of 100 GPM we have:

Pressure across the pump = (8 Ft + 30 Ft) / 2.31 = 16.5 Psi

Pump HP = (100 x 16.5) / 1715 = 0.96 HP @ 100% efficiency. We don't know what the efficiency of your pump will be however, at an efficiency of 50% you would only need 2 HP engine output. Perhaps the 3 HP Lister could power the pump for your application. Lets look at it some more:

I have a water pump with a 5.5" impeller, operating at 3400 RPM. From the pump curve, again using a 100 GPM flow rate the discharge head is given as 65 Ft. For centrifugal pumps we can use the "Pump Affinity Laws" to estimate the pump output with different impeller diameters and operating at different RPMs.

For a change to a 12" diameter impeller we multiply by the ratio of the diameters:

New flow rate = 100 x (12 / 5.5) = 218 GPM

New discharge head = 65 x (12 / 5.5) Squared = 309 Ft

The above is operating at 3400 RPM with a 12" impeller. Lets reduce the RPM to something more in line with your application. I am going to guess at a speed of 1250 RPM. For a speed change we multiply by the ratio of the RPM:

Final flow rate = 218 x (1250 / 3400) = 80 GPM

Final discharge head = 309 x (1250 / 3400) Squared = 42 Ft

Pressure across the pump = (42 + Cool / 2.31 = 22 Psi

Pump HP = (80 x 22) / 1715 = 1.03 HP @ 100% efficiency.

NOTES:

- You stated that the Lister diesel was 3 HP and operates at 600 RPM. If this means engine produces 3 HP @ 600 RPM, then select your pulley ratio to operate the engine @ 600 RPM and drive the pump @ 1250 or other RPM of your selection. If the 3 HP rating is @ an RPM other than 600 then you will not have 3 HP when operated @ 600.

- You can vary the pump RPM to get the operating point most to your liking. The above numbers are estimates. Also, a valve can be used in the discharge line to reduce the flow rate, increasing the discharge pressure. Typically reducing the flow rate will reduce the HP required. However, this depends on the pump flow curve and is not always the case. Never restrict the inlet flow using a valve or other device.

Good Luck - send pictures and let us know how it turned out.

Ken
 
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Butch(OH)
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PostPosted: Mon Jun 04, 2018 4:44 am    Post subject: Re: Right size engine for a pump Reply to specific post Reply with quote

With all due respect to Ken I am not sure how a person can apply any pump science to this question when nothing at all is known about the pump other than its physical size, we dont even have an actual picture to use for educated guesses?

I can add some practical experience. I have a 3" inlet and outlet Gorman Rupp centrifugal and it is powered by a 30 Hp Duetz and it works it hard when flows are high at low head. Also have a 1 1/2" NT irrigation pump with a 6HP Honda and when running a single gun with a 5/8 jet the govenor has the carburetor held wide open.

I also happen to be into Lister CS diesels. I would say that all effort and time spent attaching that 3HP CS to that pump would be a total waste of time.
 
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Rance
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PostPosted: Mon Jun 04, 2018 6:18 am    Post subject: Re: Right size engine for a pump Reply to specific post Reply with quote

Ken/Butch: Thanks for your comments! Ken: You sure seem to know your stuff when it comes to pumps and thanks for your calculations. I am familiar with pump performance curves in general, having used them with regard to a modern Berkeley pump. I poked around the internet and couldn't find curves from any manufacturer for really old pumps and I have to wonder a bit how applicable modern curves are to a nearly 100 year old pump. Ultimately it all boils down to a matter of physics: X amount of HP mated to a pump of Y efficiency can only pump Z amount of water given a certain amount of head (pipe friction losses, etc. aside). I guess I have two choices, I can grind through a bunch of calculations, or cobble the thing together, probably getting wet, smelling of diesel fuel, mashing fingers, and not to mention a hernia from moving all that iron. Seems to me the latter choice is a lot more fun. After all, that's why we're on the YT site! Butch, you may be right, that Lister is too small, but who knows. I've learned that ancient iron somehow has the ability to do things that modern engineering says it can't. I'll let you know what happens. Thanks again. R.
 
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