problem pumping from a lake with 12 V Shureflo pump

System · July 2009

Hi,

We are having a problem getting water up to our sink.
We installed a solar system at my mothers cabin on a island in Canada last year. We used to have a hand pump to get water up from the lake to a sink in the cottage and wanted to replace this with a 12 v pump system. This will only supply one sink and nothing else. The solar company reviewed the setup and sold us a Shurflo 2088 3.6 GPM 45 psi 12 V DC pump. We initially installed the pump about 12 feet up the hill from the lake and had a 16 foot pipe into the lake and the pump could not prime. We moved the pump down to the lake and the pump then was able to prime. The outlet pipe converts from 1/2 inch to 3/4 inch and then goes up a hill for about 25 feet at a 35 to 40 degree angle and then a fairly flat run of about 60 feet. and then up into the cabin to the faucet. We turn on the pump and it fills the lines and we get water at the faucet. We shut the faucet and then wait, but the pump continues to run and doesn't shut off, but we can't find any leaks. We then open the faucet and do not get any water and the pump still runs. If we drain the pipe and start over, we will get water out of the faucet again but once we close it and then open it, no water and the pump still runs.
1) one suggestion is that we are getting air into the pump on the intake side somehow
2) another suggestion is that we should install a pressure tank and bypass the pressure switch on the pump or put a switch over at the sink to turn the pump on when needed.
3) another suggestion is to use 1/2 inch pipe for everything, but the 3/4 inch pipe should have less friction loss.

I am going up again late July and will be tackling this project and would like to get it resolved this year (we installed it last year) so I would really appreciate any input or help with this problem.

Thanks,

JJ

icarus · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

I agree that you might look for air leakage on the suction side. Second,, I think a Pressure tank is a good idea. It cuts down on pump cycling and help pump life.
It also would allow you to pump water while there is good sun, increasing total efficiency. I also think that the larger (3/4") pipe should be fine. I would also install a check valve below the pump so that it doesn't lose it's prime.

Remember,, it is easier to push water up the hill rather than pull it from the lake.

Tony

dwh · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

Shurflo has a troubleshooting guide for those pumps:

http://www.shurflo.com/pdf/industry/general/911/911-2088-514-145.pdf
Page 3

From what you described, it could be an incorrectly adjusted pressure switch, improper voltage or air in the system.

I think that the 3/4 providing "less resistance" doesn't sound right. The pump manual specifies a 1/2 line - moving to a larger line might change the pressure. With a smaller line, the pump probably won't have to work as hard to achieve 45 psi. The pump is factory calibrated to create 45 psi with either 3/8 or 1/2 line.

Also, the bigger line holds more water, which puts more weight trying to push back down against the check valve.

My WAG is that the water is pushing back down (maybe a weak check valve), sucking air into the top of the line, which the pump then keeps trying and trying to compress to 45psi.

icarus · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

The pressure is the same, regardless of the size of the pipe, (not including pipe friction).

I have had trouble with the P-switches on shurflos before. I usually just by pass the on board switch and use the tank switch..

Tony

Cariboocoot · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

Increasing the pipe size will have no effect on the pressure, as a sealed system has essentially the same pressure throughout (until you open a tap). It will decrease the velocity, but that shouldn't be a problem either as it will be restricted to 3/8 when it gets to the sink anyway. There is no real advantage to going up to 3/4, and 1/2 pipe would have been cheaper. But it's installed so that's irrelevant now.

Tony's recommendations for a pressure tank, remote switch, and intake check valve are spot on. Providing nothing is actually wrong. But it does sound like a classic case of losing prime due to air infiltration.

Another possibility: what have you got for an intake? Lakes have a lot of current in them, and it's actually possible for that to suck water back out of the intake line, creating a partial vacuum between the pump and foot valve which the pump can't overcome. My recommendation for lake intakes: TWO check valves. One at the actual intake (foot valve - make sure it's as secure and immovable as possible) and one in-line near the shore line, but still several feet before the pump. This will prevent the aforementioned vacuum condition, and it makes it easy to check the prime: open up the intake at the pump, wiggle the line back and forth. The two valves will act like a pump in these conditions and allow you to force water up to the pump just by wiggling the line. If that works and the pump still won't provide for the house, there's something wrong with the pump.

Any possibility the pump froze? There could be an internal crack between the intake and outlet which will reduce it's pumping ability considerably.

BB. · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

Possible limitations of "over piping" your plumbing... The larger the diameter the pipe, the slower the water flow...

1. Slow water flow could allow sedimentation to build up in pipe and angles.

2. Large pipes with slow moving water can also collect air/gasses in high spots instead of flushing them out every time the pump cycles... These large(r) air pockets could also cause loss of prime too.

3. Too large of diameter on the inlet may actually reduce inlet efficiency... I am wondering if the momentum of higher speed water actually helps flow into the pump inlet ("RAM" effect through the valves and into the pump chamber)... I have seen (I think I remember correctly) that somebody here experienced reduced flow with a very large diameter inlet pipe (just guessing here).

-Bill

icarus · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

Good point on the freezing Marc. The wobble casting is very likely to crack if left with even a wee bit of water in it.

Also,, I suggest that you look at your intake screen. It is possible that depending on how your lake works,, algae/slime may have partially plugged the screen. I know that our lake grows its bottom algae in the spring,, and so items left in the water will be fine all summer and fall,, but if they are left in the water after break up in the spring,, they get covered with green algae pretty quickly.

I don't think the system has had enough use for any appreciable sediment to plug the line,,, unless it is sucking sand.

Tony

Cariboocoot · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

Just a couple of further notes:

We don't know what type of piping is being used here. Generally sediment build-up is only a problem at fittings, but if the intake and/or outlet are galvanized or (shudder) black iron there could already be resistance in the line somewhere.

Air on the pressure side would not effect prime on a pump of this type (positive displacement). It might not even show up as a leak. If it's that minor, it wouldn't be a big problem and certainly wouldn't stop the pump from working.

Too large an intake can lead to low pressure on the intake side, making the pump work too hard. Similar to the partial vacuum trouble I mentioned before.

RCinFLA · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

On rough calculation from your info it will take about 20 psi just to get up the hill. This still leaves you with a reasonable pump pressure margin. Even with a small leak, the pump pressure switch should shut off the pump if pressure switch activates at anything greater then 20 psi. If you have a leak, the pump will come on again after leaking to its low pressure activation point. Sounds like a bad pressure switch or too low setting adjustment on the pressure switch.

Install a pressure gauge at the output of the pump and see what pressure the pump shuts off at.

Check valve should be on input side of pump and a something like a filter screen at lake feed to keep anything from getting sucked in and stuck under check valve seat.

RCinFLA · July 2009

Re: problem pumping from a lake with 12 V Shureflo pump

You usually would like to have a minimum of 18-20 psi at faucet so with 20 psi up hill loss it does not give you too much margin to put in a bladder storage tank.

For an air bladder storage tank at the pump would like to see a 35-40 psi turn-on (20 psi for faucet pressure plus 20 psi uphill loss) and 55-60 psi turn-off points. Bladder air charge should be about 5 psi less then pump turn-on pressure with empty tank (30-35 psi) to achieve good volume use of tank.

Not sure how long the pump is going to run trying to build up 55-60 psi. Setting turn-off and turn-on closer then 10 psi delta starts to get unreliable. May chatter off and on or at least a short cycle off-on.

System2 · August 2009

Re: problem pumping from a lake with 12 V Shureflo pump

Hi everyone,

I just wanted to say thanks for all your input. I know it has been a while since I originally posted my question, but I did look at all the replies and they were very helpful. I apologize for not responding sooner, but I was laid off mid June and things have been a bit crazy lately. I did go up to the cottage and here is what we did. First we put the bladder/pressure tank in halfway up the hill. This got us water up to the cottage once and no more. The pump would continue to run and would only get the gauge at the tank up to about 18 psi. It would then loose pressure down to about 12 psi and we would not get water at the tap unless we drained the entire system and started over. My brother and I determined that indeed we were getting air into the system on the intake side and that we were loosing pressure on the output side somewhere as well. We decided that we had too many connections with the 3/4 pipe and got a new 100 foot piece of 1/2 inch pipe and started over. With a new 1/2 pipe coming from the water to the pump and then from the pump up to the tap we consistently got water although it was pulsing with the pump running whenever we turned the water on. We then added the pressure tank down at the pump, got just over 30 psi and smooth water at the faucet. We also replaced the single valve faucet which leaked and replaced it with a faucet that had a valve for hot and a valve for cold - no leaks and smooth running water every time. The pump would only turn on when the pressure in the tank dropped to a certain point which easily allows us to run the water for a minute or two without it turning on. So the problem is solved - next we need to build a pump house to keep the pump and tank in over the winter. On to the next project.

Thanks again for all your help.

JJ

icarus · August 2009

Re: problem pumping from a lake with 12 V Shureflo pump

Good job, glad we could help,

No such thing as too big a p-tank!. Make sure you drain the pump for the winter. Consider fitting it with cam lock fittings so that you can just uncouple it easily, unplug it from the wiring, and take it inside to assure it is completely drained.

T.

Sawman · March 2021

I have given this a lot of thought and am going to try using two pumps one to push and one to pull. Leave the tap open in the cottage till the water comes then see if the line retain pressure its a 150 ft run with about a 20 ft. Rise . Iuse one for doing maple syrup and think this will work

BB. · March 2021

Sawman I would ask that you start a new thread/discussion for your Q&A. This is a dozen year old thread and the orginal poster is probably long gone.

Regarding putting pumps in series... In general, pumps are more efficient and reliable if they have positive pressure on the inlet. At best, a perfect vacuum can lift water around 30 feet (no water flow). And anything over a 20 foot lift (for those pumps designed for suction lift), is not really going to work.

For a 20' lift, that is something like 8.7 lbs of pressure (vs lift suction). For a pump with 40-60 PSI of output, that is not much.

https://www.convertunits.com/from/foot+of+water/to/psi

And running a negative pressure on the inlet... If you have any screens/filters on the inlet, that is even more pressure loss. And running a "vacuum" on the pump inlet can run into cavitation issues (basically the ground temperature water "boils"/creates small bubbles inside the pump--And the creation/collapse of those "bubbles" can quickly erode the inside of the pump's components.

https://www.csidesigns.com/blog/articles/what-is-pump-cavitation-and-how-to-prevent-it

What tends to be a larger issue is friction from pipe length, any joints/fittings/angle turns which can quickly add up to more pressure loss at higher flow rates. Using a (via quick search) pipe loss calculator:

https://goodcalculators.com/friction-loss-calculator/

A 1/2 PVC pipe @ 200 feet @ 4 gallons per minute:

Results

Pipe Material: Polyvinyl Chloride, PVC

Friction Head Loss: 32.206 psi

Fluid Velocity: 6.541 ft/s

So, in this made up example, the above system has 8.7psi+32.2psi=40.9psi "pumping losses".

And note that you generally want some pretty good ft/s flow rate to prevent silt build up in the pipe (if you have silt/debris in the water). A very large pipe with low flow rate will settle out/collect sediment in the line.

There are times when two pumps are needed and work out well.. One common method is to "slow pump" from a source (low flow well, etc.) with a relatively small motor ("solar friendly" motor/pumping system). In general, pumps that are designed for positive inlet pressure are more efficient than pumps designed to lift with a negative pressure inlet.

Pump to a holding tank somewhere... Elevated tanks above use can save money on 2nd pump. Pressurized tanks can hold water for use (under pressure). Or to a cistern with a second pump sized for pressure/volume and other needs (such as DC 12/24 volt RV water pump for pressurizing a cabin or small home). The small second pump can be very solar friendly too (and have its own small surge tank).

There are folks here that know much more about water pumping than I--But talking more about your exact needs and limitations (site, power, water usage) will get you better answers.

-Bill

problem pumping from a lake with 12 V Shureflo pump

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