pumping water using the suction side of pump?

[wildi81]

I was asked about the following project, I would appreciate any comments on it.

The project consist of conveying 7.8cfs of irrigation water 1.5 miles in pvc pipe. Very little drop, approximatly 2"/0.5 mile.

The question presented me was, Is there a way to place the pump at the down stream end of the pipe vs installing it on the up stream end.

The reason for this request is convienance. The pump would be easier to monitor at the downstream end vs the upstream end.

The water is currently conveyed by an open ditch, originating at a resevior. They are wanting to install a pipeline to conserve water and are looking at the cost of using a pump vs gravity so a smaller pipe diameter can be used to save some money.

My first reaction was "IT WAS ASKING FOR TROUBLE".

But I sure do like the idea. Isure would appreciate some input.

Thank

Tom

 

[dtn6770]

So the proposal is to basically have a 1.5 mile long, gravity fed suction line. Are you going to be able to keep that entire line liquid full and not allow any air to enter it? You'll probably need to.

It'll come down to finding the right pump for your hydraulics.

 

[wildi81]

Thanks dtn

Correct it will be a gravity fed suction line. Air will be a problem. Air release valves will probably be needed.

I am worried about sucking the pipe down.

Thanks for your input

Tom

 

[rzrbk]

Making this long pipe a suction line will severly limit the pressure you have to drive the water thru the pipe. Although 10-15'of head (depending on pump NPSHr) is a lot more than 6", the drastic reduction inpipe diameter reduction you are looking for may not be there.

If you end up doing this, I would recommend turning down the outlet of the pipe into a pit (water seal) to get a little extra head, and pumping from the pit with a sump pump.

 

[katmar]

This is way beyond "asking for trouble". It will of course depend on the NPSH requirements of your pump, but because you have such a small slope you will probably not be able to allocate more than about 8 to 10 psi to your line friction drop. If by 7.8cfs you mean 7.8 cubic feet per second then you will need an 18" or 20" line.

If you locate the pump at the source you could allocate around 60 to 90 psi to the friction drop and your line would be only 12". The cost differential of the pipe alone should make it better to place the pump at the source.

How high is the reservoir? It may be feasible to forget the pump and just use gravity.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[dtn6770]

Describe the proposed transition from the reservoir to the pipe. Will it be via a sluice (flume or weir) near the top of the reservoir or are you going to pull from some where below the water surface similar to gates in a dam?

 

[rconner]

Pumping cost might have to get pretty cheap to get cheaper than gravity!

 

[dtn6770]

Has covering the ditch by some means been considered?

7.8cfs (3,500 gpm) would travel through an NPS 12 (sch. 40) pipe at 10 fps. You're talking pretty healthy PVC pipe and rconner is right, a pump for that volume won't come cheap.

 

[RWF7437]

Sounds like you're wanting to pump water downhill ? Why do you want to do this? Achieving a smaller pipe size will save you some construction cost but will require you to pay for pumping power over the life of this system. Gravity is free and is never turned off for non-payment.

 

[BigInch]

If you can do it at all, you probably don't need the pump.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[wildi81]

Thanks everyone

The reason for pumping vs gravity is the cost of 18"pipe for gravity feed.

The water will exit the dam from an existing gate. the pump will e placed in the reservior.

Thanks

Tom

 

[scastillo]

How much water do you need for your application, and is it a constant draw from the supply? Would a resevoir at the downstream end work for you?

 

[wildi81]

Thanks scastillo

This is an appropriation so all 7.8cfs has to be used or it will be taken away.

The draw currently varies due to the level in the reservior and actually the reservior is small and silted in. there are other appropriators up stream causing the leel to change.

This is another reason for using the pump instead of the just gravity, to make sure the full appropriation is taken.

moving the reservior down stream is not an option since the reservior is actually owned by an irrigation district.

Thanks

Tom