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Losing Prime?

Posted by weatherboy80 central FL (My Page) on
Wed, Aug 9, 06 at 14:19

Losing Prime?

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I have a 5 yr old sprinkler system (3 zone) that seems to be losing its prime causing the pump to run dry for much longer than it should (i.e. I dont want the pump to burn out). If/once the pump has water in the system the sprinklers will work fine.

This problem really only occurs when the system is off for longer than a few hours (or between days). For example -- when I get it to initially work -- or it has been running on, lets say, zone 1, then shuts off for 15 minutes before zone 2, it works like it should (i.e. zone 2 comes on right within a few seconds ).

To confirm that it was a prime issue, last night I used a garden hose with city water to fill up the pump and the system started right away. Then I waited overnight and turned the system on again and it took quite a while for the system to pump water again. I'm guessing the longer I will wait between "waterings" the harder it will be initially pump water.

To me this sounds like a faulty check valve - which BTW is brass and is inches from the suction side of the pump in my garage. Otherise I really hope this isn't an air leak somehwere in the sunction pipe. Since the syetem is pretty young I would'nt expect this to be the case. Any ideas?

Also, if it is the check valve - how easy is it to replace (i.e. tools, steps etc ...)?

If you need more details let me know.

Thanks

Joe


Follow-Up Postings:

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RE: Losing Prime?

Both the check valve and suction line leaks could be the cause, however I would consider the foot valve the problem, assuming there is a foot valve.

I cannot see how the check valve is installed so I cannot comment on replacing/repairing the valve.

Is this a self priming pump on a shallow well? If yes do you know if a screen and foot valve ( Check valve at the end of the suction line in the well ) were installed. Foot valves are notorious for leaking.

At this point there are some things you can do;
1) You can install a permanent pump fill circuit ( with city pressure ) operated by another control valve ( will likely need backflow prevention ). This would be the first valve in the controller to energize ( assuming your controller has more than 3 station capabilities ) and remain open for the time needed at worse case, your first irrigation valve would be energized immediately after the fill line valve closed. Since you have city pressure available I would recommend this to be done regardless.

2) The check valve at the pump is likely not to "hold water" for prime but rather to protect the pump against flow reversal ( one of the effects of water hammer when the irrigation flow is stopped ). If this is the case it is placed upstream of the pump rather than downstream ( at the discharge ) due to a pressure switch application at the discharge of the pump. The check valve has to be upstream of the pressure switch. If this check valve is a "swing check", ( regardless of its purpose ) often used due to its low pressure drop, REPLACE it with a spring operated check valve ( sound engineering makes this mandatory and not optional, deal with the pressure loss ).

3) If your system does not include a foot valve, then move the existing check further upstream ( all the way to the well head if not to far from the pump ( say 20-25 feet ).

4> If your system does have a foot valve you can try to backflush your suction line to clear the obstrucion. With the city pressure. Now you would have to make a hose connection upstream of the check valve ( between the check valve and the well ).

5) and of course there is the possibility of leaks in the suction side piping, allowing air to be drawn into the piping. This does not sound like the problem to me. This would cause problems when the pump is "working ok".

I hope this provides some help

booster pump tech


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RE: Losing Prime?

Thanks for the detailed analysis of my problem. I'm going to spend some time this weekend to take a look at this thing and will let you know if any of your suggestions is occuring.

I think the easiest thing to do at this point will be to try a new check valve as you suggested.

At the moment not sure about the foot valve; but I'm guessing the system does have one.


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RE: Losing Prime?

  • Posted by mikie z9 St.Pete.FL (My Page) on
    Thu, Aug 10, 06 at 10:47

Most florida lawn pumps dont have a foot valve. Usually multiple shallow well sand points. The check valve holds the collum of water and pump prime, which ideally that check should be after about 9" or so from a straight pipe leading into pump inlet to avoid turbulence.

Probably that check valve is leaking.

Most pumps around here have a pressure tank and are left energized full time so there pressure forcing closed the check and if there is a slow leak the pressure switch will cycle on/off sometimes to keep the prime. At least until you have time to replace a leaky faucet washer or check valve.


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RE: Losing Prime?

Great thanks - I'm sure it is a faulty check valve since it is a few inches upstream of the pump. I'm not sure about the foot valve though.


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RE: Losing Prime?

I have the same problem, but I think sugar sand is lodging in my check valve and preventing it from closing tightly. I always have a lot of sand clogging my sprinkler heads and zone indexing valve.


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