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Old 06-26-2009, 08:36 AM   #1
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is this possible?


hi - is it possible for air to be trapped in a pump intake line (at a high point in the run) and remain there, even if the pump is sucking water and appears to be holding prime?

my intake line runs out at a slight downward grade from pump (camp) to a holding tank / cistern - at the tank it turns upward a bit, into the tank , and then down again to the foot valve (I do not have a bulkhead fitting at the bottom of the tank - only at the top). So the tank entry point is a high spot. I pulled the water up to the pump (bladder pump) to prime it 1st time. The entire run appears to be leak free. When the pump stops, I lose about 10lb pressure, then it holds steady - making me think there must be a pocket of air in the line somewhere...?

thanks
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Old 06-26-2009, 09:35 AM   #2
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is this possible?


An air pocket sitting there in the same spot and not flushing through while the pump is running is like a seal balancing a beach ball on his nose. It's possible, but I think a leak is more likely. Can you post a pic? I'm also a little unclear on the pipe run.
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Old 06-26-2009, 10:16 AM   #3
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is this possible?


Aggie67 - thanks for the reply - I'm hoping to get out there (camp) this weekend or asap - guess a pic would help - sorry my descriptions are a bit ambiguous.

it start out as a "typical" shallow well run (constant downward grade) - at the end the pipe is at the same grade as the bottom of the cistern. Since I have no fitting there to connect directly into the bottom of the cistern, the pipe turns 90 deg up to top of tank (about 4 feet) - then 90 deg into existing side opening in tank - and 90 deg down to foot valve. If I had a bulkhead fitting at the bottom of the tank these bends would not be there.

I keep thinking leak too - but also wondering why I don't seem to be continuously losing pressure. As soon as pump turns off the water does blast back out like there wasn't even a foot valve - in a split second I lose the 10 lb - but then it hits 30 and then stops dead and holds there. would it not continue to steadily drop off if I had a leak? I even replaced the (brand new) foot valve thinking maybe that wasn't working 100%. I'm probably missing some simple concept here so thanks for any feedback

Last edited by rtoni; 06-26-2009 at 10:26 AM. Reason: add'l info
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Old 06-26-2009, 10:37 AM   #4
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is this possible?


Air in high spots on lines is a common problem in commercial piping (where I spent many happy years as a design engineer). In commercial piping, there are usually a series of automatic air bleed valves at high spots to eliminate the problem. This is not the case in residential work, since an air bleed valve is relatively expensive, and the runs are usually not too long in residential work.

I have seen cases where air gets trapped, and does not "flush out" even when the pump is running. This is especially common if there is a small air leak that constant feeds air into the line, sufficient to maintain a rough balance between the air pushed out by the water, and the air that leaks in.

The simplest way to address the problem is to make sure the line is at a constant positive slope, that way air cannot get trapped. If this is not possible, you can install an automatic air bleed valve on the line at the high point. This requires a box for the valve at the surface, the valve goes in the line.
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Old 06-26-2009, 01:30 PM   #5
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is this possible?


Thanks Daniel - the only way I can get a constant positive slope is to dig out the side of the cistern, bust out / drill the bottom wall, and install some kind of bulkhead pipe fitting to eliminate the upward bends / section. Was hoping not to have to do this but maybe I have to - if "relatively expensive" means more that the cost of a roll of poly pipe..

Last edited by rtoni; 06-26-2009 at 01:33 PM.
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Old 06-26-2009, 02:41 PM   #6
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is this possible?


Daniel, an air eliminator won't work on his suction line. He's drawing water up a column, so it'll be under vacuum.
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