Can't pump from a lake

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Old 07-07-08, 09:15 AM
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Can't pump from a lake

I have a new 1/2 hp Sears shallow well jet pump, for pumping water from a lake into a captive air tank. The inlet pipe is
1 1/4 dia but the distance from the foot valve, in the lake, to the pump is about 80 ft. The vertical pumping height is approx 8ft. The instructions say the outlet on the pump should not be closed while priming.The pump does not pull water and appears to run out of prime.

What do I need to do to make this work and did I buy the right pump?
 
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Old 07-07-08, 10:12 AM
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Pumps don't actually "pull" water, they can only push water. Atmospheric pressure actually pushes water into the pump. With only 8' of lift the atmosphere should be able to easily push water into the pump. 80' of suction line across the ground leaves several opportunities for a suction leak, which would be my best guess.
 
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Old 07-07-08, 10:20 AM
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can't pump water from lake

Thanks for your reply. The inlet line is brand new 1 1/4" poly in one single section, approx 80ft long and a brand new foot valve. I can garuantee no suction leaks.
 
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Old 07-07-08, 10:22 AM
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This is going to be hard.

You are going to have that 80 feet of pipe gradually slope up the 8 feet. If there is a spot that is higher than the rest, a bubble will develop inside and won't allow water to pass. When you prime, you have to fill all that pipe with water before you start the pump.
 
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Old 07-07-08, 10:31 AM
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Then as Vey said, you have a high spot in the suction line.
 
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Old 07-07-08, 11:44 AM
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How can you guarantee no air leaks. I don't know anyone else who can do that.

bob...
 
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Old 07-07-08, 01:58 PM
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Can't pump from lake

Good thought Speedbump,
When I put the fittings together (all new) I was very thorough so there would be absolutely no chance of leaks anywhere.

Thanks VEY,
There is a slight dip in the inlet pipe where it runs under my summer cottage. Maybe that has created an air bubble.

Could there be the following possibilities:

1. 1/2 hp pump not powerfull enough? Would a 3/4 hp pump
overcome this problem?
2. 80 ft run is just to long a run?
3. With the outlet valve slightly open, enough priming
water is pumped out causing a loss of suction enough to
prevent the inlet water from reaching the pump?
4. Will a jet pump reach a prime with the outlet closed?
 
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Old 07-07-08, 03:06 PM
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Originally Posted by w000dy View Post
Good thought Speedbump,

1. 1/2 hp pump not powerfull enough? Would a 3/4 hp pump
overcome this problem?
Deciding how big a pump to buy depends on how many GPM you need to do what you want to do. How many GPM do you need?

2. 80 ft run is just to long a run?
Maybe yes, maybe no. The proper place for a pump is as near the source as possible. I realize that this may cause you to run the electrical wire a long way. This means you need to worry about voltage drop. The higher the voltage, the smaller the guage of wire you would need. So hopefully, the motor can be converted to 240.

See this calculator:
http://www.elec-toolbox.com/calculators/voltdrop.htm
You are using single phase

3. With the outlet valve slightly open, enough priming
water is pumped out causing a loss of suction enough to
prevent the inlet water from reaching the pump?
4. Will a jet pump reach a prime with the outlet closed?
Why are you closing the valve on the output? This has nothing to do with priming a pump. You may need to prime several times.
 
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Old 07-08-08, 05:58 AM
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can't pump from lake

Under my summer cottage (3ft crawl space) the captive air tank is right next to the pump, which is approx 50ft from the lake. There is no good place to put the pump next to the lake.

The instructions with the Sears pump specifically say NOT to prime the pump with the outlet line closed. My question is, will the pump prime with the outlet closed or will that prevent it from primming?

As far as the GPM question, we have a low demand. One toilet, one shower and two sinks so, I don't need a powerful pump. Also the pump is on a 15 amp circut. I believe a 3/4 hp
pump will draw to much power on start up.

The old pump was a Deming piston pump which pumped in both directions of the piston stroke. This pump was approx
50 years old and pumped perfectly with a 1" inlet line. Can't get parts for it anymore.
 
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Old 07-08-08, 06:51 AM
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Piston Pumps draw on the intake stroke and exhaust on the output stroke. Unless you have a Pump with two pistons, it only pushes water on half of the stroke.

More powerful Pumps only produce more water and pressure, they can't physically draw any harder or further.

Closing the output valve on a Jet Pump won't effect Priming as long as you leave the Priming Plug loose to let out air. If you close both, it will not Prime because the air can't get out of the Pump casting.

bob...
 
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Old 07-08-08, 07:29 AM
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The Sears shallow well jets that I'm familiar with have a built in checkvalve on the front of the pump. Are you sure you're getting the suction line completely full of water?
Ron
 
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Old 07-08-08, 12:53 PM
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can't pump from lake

My brother is on another forum site and from the feed back we've gotten it seems that if we fill the 80ft of inlet pipe first we should be able to get a prime going with the 1/2 hp jet pump. Once it is primed it should supply sufficient GPM.
We'll try it this weekend. Also I was just given a used 3/4 hp
Sears jet pump to try out on our 15 amp circuit.

Speedbump, you've been talking to my brother too.
 
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Old 07-09-08, 07:29 AM
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I thought I recognized the scenario.

Filling the pipe will help immensly. I would still get rid of the Check Valve at the Pump. It will be nothing but problems.

bob...
 
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Old 07-09-08, 07:46 AM
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As I said, in my first post:
"When you prime, you have to fill all that pipe with water before you start the pump."

And I am with speedbump. I took my "built-in" check valve out which made priming much easier.
 
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Old 07-15-08, 06:01 PM
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can't pump from lake

Thanks for all the suggestions. It's working!!! We put a priming tee just before the inlet to the pump. Then a 1 1/4 to 3/4 reducing plug, a 3/4 nipple and a 3/4 npt to 3/4 female hose fitting. We screwed a hose on from a submersible pump that was in a big pail of water. My brother held the foot valve open out in the lake while I filled the inlet line with water then I took the hose fitting off the nipple and screwed on a cap. We were able to get the pump working fine after that. The other thing is the 15 amp fuse is handling the 12.4 amps from the 3/4 HP pump......so far.

What an education!!!!
 
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