Maybe my experience will save you some $$ and/or aggravation...

Last summer the Cobett waterer behind a pond began filling slowly. I cobbled together a camlock coupler with a Schrader valve to fit the male camlock end of the tube that feeds the waterer tank, and a few blasts of air from an air tank returned the waterer to normal flow rate.

A week ago, the waterer suddenly had NO water coming in--not just slow. I grabbed my camlock coupler & valve and gave it the compressed air treatment again. Nothing. I ended up putting 18 psi in the line, opened a hydrant at the back of the pond (the waterer is 50 yards farther down a slight grade--which will be useful information later) and some air hissed out. So I took the coupler off at the waterer and the air bled out but no water came.

This is getting serious! If air (but no water) comes out of the hydrant with the line pressurized, and air comes out at the waterer when I remove the coupler that's holding the pressure in, then the line from the hydrant to the waterer must be open....which only leaves a problem with the pipe under the dam (1 1/4" PVC installed 30 years ago) or the riser pipe in the pond. I had NO IDEA what could be causing the problem.

So today I rented a mini-excavator and dug up the plumbing at the hydrant. When I loosened a PVC pipe union near the hydrant air hissed out....but this was on the pond side of the hydrant. And when I got the union looser both air and water began squirting out. Wierd! But there was an old brass gate valve below this union, so I thought it was somehow stopped up.

After I got enough apart I could see that there was no restriction in any plumbing. With everything disconnected, the line to the waterer was submerged as I worked on things. I walked down to the waterer and...it was full of water. So I reconnected everything and turned cows back in...and now the waterer flow is fine.

Finally, my miniscule recollection of plumbing and sewage lines kicked in and I figured out what must have happened....

Last summer I had put brief blasts of compressed air in the line, then let the air and water gush out for a bit before before another blast of air. But this week I had put a lot of air in the line (partly because after a short blast of air still nothing came out). I left the waterer end open for three days and got no water coming out.

I think the reason was an air bubble. There's a slight belly in the line between the hydrant and the waterer--unavoidable due to the terrain. I think my 18 psi of air made it past the water in that "belly" area. The water in the "belly" (maybe 40 feet long) provided just enough resistance to keep the air above it (i.e., on the hydrant side of the belly), and the air was just enough pressure to counteract the head pressure from the pond (maybe 7 feet of head).

So taking the line apart at the hydrant let the air bubble escape and let the water flow. (If I had just opened the hydrant for 30 minutes the air bubble could have bled off without a trip to town, $300 excavator rent, and one boot completely full of muddy water.)

PHOTOS:  the reason for the long trench going away from the hydrant was to get water out/away from where I needed to work, to keep the plumbing visible (above the muddy, 37-degree water).

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