Little Centrifugal Water pump questions?

[Lawnmowerboy]

Hi all, I've recently acquired a little centrifugal water pump that I'm setting up on a little 3HP briggs Which i stripped and reassembled yesterday.

I tried running the pump off an electric drill yesterday and filled it with water and stuck an inlet pipe in a watering can and jubilee clipped it to the pump bit it would'nt pump, it was spinning the correct way at about the right RPM (drill is rated 2200 and the engine red lines at 3200)

I still can't get it to pump any idea's?
will

 

[langy]

Probably unable to lift, like a central heating pump

 

[pedrobedro]

If it's not self priming it will need the head of water higher than the pump.

 

[gordon stephenson]

Unless you can fit a non return foot valve to the bottom of your suction pipe to keep the pump full of water prior to starting.

 

[Seano]

Sounds like not enough guts to hold its head....so just like gordon said....

 

[brightspark]

Unless you can fit a non return foot valve to the bottom of your suction pipe to keep the pump full of water prior to starting.

and then prime it with water manualy like one i have

 

[Lawnmowerboy]

It already has a little metal flap that closes over the inlet that i have faced off with wet and dry and a block ive tried a watering can in the end of the pipe pouring water in and i actually managed to get it pumping for a while until the watering can was empty
though when i put my hand over the outlet it had hardly any pressure?
any ideas?

cheers for all the replies guys, i'll sort it eventually =)

 

[Lawnmowerboy]

Also I think the drill maybe wasnt spinning it quick enough maybe? maybe it has sort of a power band where it produces the most power at a certian revs?

 

[brightspark]

Also I think the drill maybe wasnt spinning it quick enough maybe? maybe it has sort of a power band where it produces the most power at a certian revs?

what u need is a positive displacement pump to force water through . its probably just an impeller pump which moves water but not under pressure the same as a central heating pump

 

[Lawnmowerboy]

It's from a little 2 stroke 1950's rotavator, It's definately a proper pump and it isnt that little, The body is about 12 inches tall 4 inches deep and 8 inches across


will

 

[FranV8]

Ah, centrifugal pumps!

You get these in all sorts of flavours, but basically they will be characterised by a pump curve, that shows head (pressure) against flow, normally reduce the flow and the pressure goes up and vice versa, within the limits of the pump.

This might help to understand:

http://www.mcnallyinstitute.com/02-html/2-03.html

If you've got a pump curve for your particular pump it would help, but given it's age I doubt there's one easily available.

As for priming and what you're pumping out of, a centrifugal pump is not normally self priming without add on gubbins, so it needs to have the arrangment you've spoken about (foot valve) and then the pump topped up with water before starting. Some have a vacuum pump to aid starting.

Best is to have a flooded suction (pump inlet is below outlet/liquid level of what you're pumping out of), but a pump also has (by design) something called npsh (Net Positive Suction Head) - this is the maximum height of water it can 'lift' to its inlet, some pumps really do have zero suction lift. You'll find pump performance drops off very quickly above a certain lift value.

On speed variation:

http://www.mcnallyinstitute.com/02-html/2-01.html

Basically your pressure developed varies by the square of the speed, so at 2200 rpm vs 3500, you'll be at less than half the pumps design pressure (head) capability.

The site of linked to is full of great pump info and reference, Mcnally Institute, great that there are some people in the world who put this info up for free.

As for centrifugal pumps vs pressure - I've bought 60 Bar 120 tph centrifugal pumps before (okay, fair enough, multi-stage) - they can be deisgned to do it. Biggest I've seen in single stage is probably 8 bar, and these are classed as relatively high head.

 

[KemppiFrog]

Centrifugal pumps pressure and flow are a square of the RPM. Might be that the original 2T was running at 4/5,000. RPM (dunno about 1950s 2T, might be less) So if you are are using a 4T Briggs and Scrap'em, they tend to run at lower revs and might not produce much with a mismatched pump. Also very unlikely to run unless well primed. The foot-valve is important.
KF

Thanks Fran. slow typing again.... Duh

 

[Lawnmowerboy]

Thanks very much for the replys guys

here is a kind of picture of a graph i just did of how from what i can gather this or most other centrifugal pump works?

will