Irrigation pump sucking air

[My Old Tools]

I went out yesterday to check sprinkler heads and found my irrigation pumps (from the lake) were sucking air and wouldn't hold prime. This system is 20 years old and I inherited it with the house. I rebuilt the pumps a couple years ago. The suction line is buried and goes across and down to the lake pretty far from the pumps. It really makes no sense. Anyway, it was sucking air. i reprimed it but no joy, it wouldn't pull from the lake. Since the old line was buried and I couldn't see any cracks in the exposed areas, I took a chance and bulit a new suction line. I glued it all up and let it set awhile. I put it in the water today and primed it. Sure enough it ***** just fine now. Just glad it wasn't the pumps again. When the weather cools down we'll do a more permanent install.

 

[nadogail]

Sounds like you have done the the best you can to get things working again.

 

[yatg]

I pull out of an irrigation canal, about 10' lift to the pump. Even the smallest air leak will cause great frustration. I leave the suction line on the surface and remove it in winter.

The two pumps in series is interesting.

 

[My Old Tools]

It's a 20-30 foot lift to the sprinkler heads. It needs both pumps to get pressure up there.

 

[larry_g]

I think that I would try to blow down the old pipe and see if you can find the leak from the rising bubbles in the lake.... However if your sucking air the leak is not under the water...

 

[yatg]

Did/can you check the foot valve?

 

[Innovate1]

It's a 20-30 foot lift to the sprinkler heads. It needs both pumps to get pressure up there.

The question is still why two pumps. I pump up 80 feet elevation change and run sprinklers with one pump. You must need a lot of flow or have low pressure pumps. 20-30 feet is only about about 10-15 psi drop.

 

[finn]

Another suggestion to look at the foot valve. Mine sucked up sand from the lake bottom and would lose prime immediately upon shutdown.

Cleaned the sand out and it’s been fine for six weeks now.

 

[My Old Tools]

Did/can you check the foot valve?

No foot valve, just a 2" pipe with a backflow valve. It's suspended a couple of feet off the bottom. And remember, it worked for 20 years and failed in a day. And yes, I back flushed it before I built the new one. You need considerable pressure to run 6-10 sprinkler heads. There is no pressure tank or cistern, they run off the pumps.

 

[Innovate1]

Could be you are both talking about the same type of valve. If you have a foot valve can you pressurize the intake pipe and see where the water shoots out? Might even add a little coloring.

 

[kbs2244]

I would guess the 2 pumps are due to the height of the lift
you are at the ragged edge of the max lift
a better system would have the pumps closer to the lake for less lift and a pressure line up the hill

 

[My Old Tools]

The pumps are about as far down the hill as is safe, 20 feet to the water, 8-10 feet lift. It's much further up the hill from there, probably another 200 feet and 40 feet of lift. You loose pressure the more you have to lift.