1

At a place I'm staying, there is a borewell whose design and construction I ignore and I have no means to figure out (total depth, cap etc.)

The entire house runs on a limited electrical supply from solar panels, therefore, the setup is NOT designed to run automatically (no floatswitch). Thus, every week or two, the pump is manually turned on in order to fill a couple of elevated tanks.

  • The pump's inbuilt check-valve is not working properly.
  • The pump is 1 metre long.
  • The pump's outlet port is 2 metres below the water level.
  • The pump's outlet port is 9 metres from ground level, connected to a PVC pipe.

Last few weeks when trying to perform the tank filling operation, the pump shows a near 80% failure to start pumping while the motor can clearly be heard rotating from above. One detail worthy of note is the owner of the house was always trying --futilely-- to "fill the water pipe" from above in the false belief the failing check-valve made it necessary to "prime" the pump.

After extracting the pump and testing it within a filled water tank, the pump was working fine, and majestically pumping water out of its 9m long pipe. It had a 100% success rate at starting and pumping.

However, in this "experimental" setup, it was easy to induce an airlock condition, where the pump would rotate but not move water at all by intentionally making sure the pump had air inside while a column of water was sitting above the unreliable but slow draining check valve.

Now, I utterly and thoroughly fail to imagine where air could come from while sitting 2m. below the water surface. But I'm not a physicist or engineer so I'm not sure if there could actually be a certain phenomenon, unknown to me, that could cause air entering the impeller section of the pump --except, perhaps, assuming the well's water level could drift below the pump's intake level--.

Assuming that I'm correct in assuming no air could enter the pump 2m. underwater, and once it is discarded or confirmed a possible water level drift, I suppose the well should be checked for dirt, leaves etc. that might be clogging the pump's intake. No?

geeheeb
  • 23
  • 3
  • Steam behaves like air. Add enough energy in water and make steam. There are also gasses dissolved in water that the agitation caused by a pump can bring out of solution. Busted check valve might also cause pump to work in reverse, sucking air down. Replace busted parts. Lots of possibilities when your constraining parts are malfunctioning. – Abel Jul 22 '23 at 11:41
  • maybe the pump empties the well to the point where it starts to suck air – jsotola Jul 22 '23 at 22:13

1 Answers1

2

You have a submersible jet pump. In the bottom of the well, there will usually be a screen surrounding the pump to keep it from sucking up sand or pebbles out of the aquifer and getting them caught inside the pump. If the screen is plugged up, the pump will instead suck down all the "loose" water inside the well casing (where the pump is suspended), spit that water upwards into the well casing, suck it up again, etc. and churn it into a mix of water and water vapor and air. if the check valve is "above" the pump inside the well casing, then a leaky check valve will let the well pipe water level fall to the level of the aquifer, making it easy for the pump to suck the pipe dry and cavitate (go into endless churn without delivering any water).

So: start by replacing the check valve first, then test. if the system still pumps itself dry, unplug the screen.

niels nielsen
  • 14,708
  • 1
  • 13
  • 30