As stated in my initial blurb, the pump sits at 200 feet. I cannot find any data (from the installer) that states the depth of the static water level; however, I know there likely is hardly any draw-down during use, since the well digger said he'd never seen so much water. This tells me the static water level isn't too far above the pump. And, as mentioned in my follow-on comment, if the leak is at the pump and the surface check valve I install retains the water column, then there shouldn't be a column of water slamming into the check valve when the pump starts (since the water is already there, right?).
Surface Check Valve??
- Thread starter RetMil
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Suppose there is a tiny tiny leak at the check valve at the pump. Suppose no leak on the up-top check valve. Suppose the water in the well is 40 ft or more down. Suppose there is no above-water air leak. As the water drains, there will be a vacuum leaving the drop pipe to contain water that is maybe 32 ft (depending on current atmospheric pressure) above the surface of the water in the well. Above that will be a vacuum.
As the pump turns on, that column of water goes up, filling the vacuum. The water is moving at a pretty good clip by the time it gets to the poppet on the upper check valve.
I don't know of anybody who does this, but suppose you put a valve in parallel around the topside check valve? Then you could choose what works best for you at a given time.
Something else that I don't know of anybody who does, suppose the pressure switch is set to 40/60. You tee off to a pressure tank before the above-water check valve, and you set the air precharge to 58 or 62 psi. Would that gracefully absorb the energy? I don't know.
As the pump turns on, that column of water goes up, filling the vacuum. The water is moving at a pretty good clip by the time it gets to the poppet on the upper check valve.
I don't know of anybody who does this, but suppose you put a valve in parallel around the topside check valve? Then you could choose what works best for you at a given time.
Something else that I don't know of anybody who does, suppose the pressure switch is set to 40/60. You tee off to a pressure tank before the above-water check valve, and you set the air precharge to 58 or 62 psi. Would that gracefully absorb the energy? I don't know.
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LLigetfa
DIYer, not in the trades
You may want to educate yourself on the physics of how a mercury barometer works. If the static water level in lower than 30 feet, that column of water will fall and draw a vacuum. How much lower than 30 feet will determine the actual size (and weight) of that column. When the pump starts, that column will shoot up like a rocket aided by that vacuum which will cause not only water hammer when it slams into the check valve but also upthrust that can grind the tops off the volutes.
LLigetfa
DIYer, not in the trades
One generally does not install a pump deeper that it needs to be with a margin of safety. IF there is no drawdown, the margin of safety can be less. I would guess that the static level might be at 150 feet, so that column of water will certainly fall just like the mercury does in a barometer.
You clan choose the highest quality check valve that might survive the water hammer, but the existing pipe might not. Then again, there is the upthrust concern.
Upthrust happens when the pump starts against a vacuum or no head. But then the resulting water hammer that happens when the projectile of water between the two checks hits the upper check causes massive downthrust. The downthrust from water hammer goes all the way to the bottom and can even shatter the thrust bearing in the motor. Multiple check valves are not good anyway you do it.
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