Choke or Timer to restrict flow.

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Niccoleman

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Lowara 16GS40/B 3-phase 4kW pump. This is rated at 8 to 22 m3/hr at 83 to 25 m head.
Flexiline riser. 200’ down borehole. Pumping up to 18,000 gallon reservoir where there is a level switch. Pressure at borehole head while pumping is 2bar.
We use 80 to 100 m3/day for a couple of farms and villages on our Estate. Our system was built in 1943 by Italian Prisoners of War, 20 miles of underground pipework dug all in by hand! in 1943 a 15 hour test yielded 7m3/hour to empty, restored level to 130’ in 25 mins.

Problem in drought conditions that we now have every summer is that a Water Company has deep boreholes nearby that lower the static water level in chalk aquifer now that nearby towns have doubled in size. And then charge us £2/3m when we have to switch over to their mains.

We pump 12 m3/hr (3000 US gallons) but only need to draw an average of 4 m3/hour. (1,000 USG)
Pumping at 12 m3/hr is ok in winter but in this drought we are pumping 50% air and 50% water so too fast for the level to recover. Only want 4 or max 6 m3/hr.

Dry running protection provided by Guardian 2E control box, but this does not help the borehole itself.
Counter-intuitive but a lower rate of flow should increase available water, also will save wear on pump, and save damage to borehole.

Questions are will a choke burn more electricity or less?
What pressure will it be safe to have at wellhead without damage to pump or burst riser?

Is it preferable instead of choking the flow to fit a time delay cyclic relay, wired into the float switch line. Say 15 minutes on (which is max time before flow starts to fail) and 30min off, for level recovery. I guess this would save electric which currently is costing us £10,000 a year?
 

LLigetfa

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Questions are will a choke burn more electricity or less?
Generally, the power consumed is somewhat proportional to the gallons moved so slowing the GPM in some cases reduces current draw. This however can vary depending on how the stages and bearings are stacked. This can be observed with an ammeter while choking the flow with a valve.

Cary ( @Valveman ) at cyclestopvlves can probably give a better answer if he knows the characteristics of that particular pump.

See the following animation:
 

Valveman

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It won't hurt anything to choke that pump back to 4 m3/hr. I can't find a HP curve for that pump, but the energy consumption should drop about 40%-50%. However, it will have to run 3 times as long, so the total energy consumption will increase. The amps will drop almost exactly the same when choking the pump back with a valve as if you slowed it down with a VFD. You have a three phase motor so, it would work with a VFD. But like I said choking it back with a simple inexpensive valve will reduce the energy consumption of the pump just as much as reducing the speed with an expensive VFD.

There will be about 130 PSI back pressure when restricting this pump to that flow rate.

To save the most energy you would need to replace the pump with another that is 1/3rd the size.
 

Niccoleman

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Thanks for the advice. Choking back 1/3rd may not lead to it running 3 times as long as at present if it results in pumping water not air. Will try this first. Then may try a cyclic timer relay.
If I can adjust flow to rate of well recovery in one way or another then I can use the reservoir as a balancing tank, rather than as a permanently full holding tank which in effect is all that it is when just using a on/off float switch. Long term will fit smaller size pump when this one fails.
 

Niccoleman

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Have choked back to 5 bar 72psi at wellhead. Result significant reduction in electric and no reduction in volume pumped over 24hrs.
Pumping about 1 hr on 1 hr off to keep reservoir full. Still pumping at a faster rate than well can recover as flow slows after 30 minutes.
When you say choke back to 9bar 130psi is this the pressure at wellhead or down at pump?
Am I right in thinking that 130psi at top of 60m 196' well riser would be 15bar 220psi down at pump? I am guessing here that a flexiline riser should be able to take 25bar 360psi ?
 

Reach4

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I am guessing here that a flexiline riser should be able to take 25bar 360psi ?
Polyethylene pipe that I commonly read of is rated for working pressure values from 100 psi to 250 psi, with 160 being fairly common. 250 is readily available. My point is to not assume they are rated for 350 psi. It is good that you are concerned by the pressure that the pipe will see just above the pump.

Burst strength is much higher than the working pressure rating, but you would like to pretty much stay within the rating.

There are devices that can shut down the pump for a while as the water runs out. They do that by looking at the current. Current is lower when the water runs out. https://cyclestopvalves.com/pages/cycle-sensor-pump-monitor is one such device, but I am pretty sure that will not be available to ship to the UK. Different rules, and high shipping and paperwork, and more. But there are bound to be devices that have a similar function available there. https://www.enviropro.co.uk/entry/42525/Crest-Pumps/PSP1-dry-run-protection-monitor/ could be useful, or they may be able to refer you to a useful device.

https://www.waterpump.co.uk/dry-running-protection-system could maybe be used where its output drives a big relay. However this seems very consumer-grade vs high-reliability. To use that, you would divide the output flow to valve the right % of flow thru a flow meter. When the flow goes below a setpoint, you would turn off the pump for a timed interval. I am not a pro.
 
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Valveman

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Max pressure that pump can build is 141 PSI. That is at the bottom of the well. The pump is only lifting from the surface of the water, not the depth of the well or pump setting.
 
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