Farmer's Pump

"Cameron's Hydaulic Data" shows 10.0 fps for 3,500 gpm for a new 12-inch sch. 40 steel pipe.

The velocity head is 1.55 feet and the head loss per 100 ft is 2.26 feet.

These tables are based on the Darcy Formula.

Cameron recommends a safety factor of 15 to 20 percent be added to the values from their Tables.

Looks reasonable.

The flows seem ok in terms of pressure drop and velocity and sizing etc (having runa quick check on the program we use at work) BUT i have a few issues with the system - you need a suction hose of at least 16" for 4000usgpm

It sounds like the pump is going to be above the water in the canal. Is the 15' a suction lift (ie is the pump 15ft above the canal water level) because this seems a pretty high lift - not impossible of course but if ti is that high you want to minimise the suction friction losses (ie make the suction hose bigger)

On the discharge if I get the calc right the discharge point is 5' below the pump.

based on 242 ft equivalent length I think the friction loss in the pump is about 3 psi (ie 7ft) so there is only a net loss in the discharge circuit of 2ft - unless there are all sorts of restrictions at the discharge point (in which case ignore the worries). The worry I have is that with very low discharge losses the pump will run out to the end of its curve. But if you are feeding some device this will impose a back pressure and provide a sensible operating point

Good morning simonsd. You are correct, the pump inlet will be ~12' vertically above the bottom of the canal, which is where the hose inlet will be, and ~6' above the surface of the h2o. His local pump retailer told him a hose would work. The hose would have a foot valve (check valve) at the bottom of the canal, which would aid in priming the pump. His objective is to avoid a drive shaft to the bottom of the canal. Under this scenario, are you suggesting the hose may have to be larger than 16"?

Yes, the outlet of the discharge pipe will be ~5' below the pump. Other than about 5 each 45º elbows, there are no other restrictions in the pipe. It will discharge into a concrete ditch.

This is an area in which I am a long way from being expert but

The pump is 6ft above the water line - atmospheric pressure is 33ft (approx) so you need to pull <20% vacuum in the suction. In this case I dont think there is too much issue with the pressure drops so a 16in line should be ok. I get about 0.4 psi/100ft line loss in the suctionso call it 0.1 psi line loss or 0.2 ft so the impact is not that significant

Interestingly overall you are lifting the water by 1ft and overcoming some line loss so the power required by the pump once you have established flow is quite low compared to the lift required to get flow established. Obviously the foot valve ensures you dont have to overcome this problem after the first start!

Move to an electric mixed flow pump. the killer is power because the velocity is too high. Move to at least a 14" pipe and preferably 16". Submerge the impeller. If you already have the pipe use 3000GPM. Power for this can be expensive lower the head/friction to save money in the long run.

Call Al @ Shoemakers Welding in North Liberty Indiana. He produces more pumps then anyone I know for draining fields and alike. This guy has forgot more about pumps then most people know. Especially drainage pumps.

Mind you, this is not an ad for this company. Just the best person for this type of issue I know. Good Luck

Wouldn't one of the engineers at actually pump manufacturers, like flygt, peerless, etc. be a better resource for discussing pump performance curves and simple system performance criteria. Because a big portion of the decision process has to do with the peak efficiency of the pumps/system to supply demands relative to electrical or fuel usage. Large water and irrigation districts will spend $100k+ to analyze pump station systems for perfomance and efficiency to determine design parameters for efficient deliveries at minimal electrical cost.

If the final discharge is below the pump, won't the pipe empty when the pump is turned off? Then you will have to figure out how to prime the pump. If the pump is horizontal, how are you going to prime it? The prime water will just run out the discharge, won't it?

If the pump is vertical, it may maintain prime, but only until you get something in the check, and then you are in a lot of trouble. Clearing the check won't be easy.

I would use a submersible. Always primed, no check necessary. The motor can be above, what's wrong with a shaft? I've run shaft pumps in a lift station that ran fine for years, and that was rough service!