|Copy from the design book of my supplier|
As the title indicates it would be a DEEP WELL pump. But, as I now understand it is not a deep well, but a shallow well pump, although the main pipe is quite long. Let me explain.
The first couple of weeks after installation in 2010 we had sometimes the problem that the pump could not prime very well, and we had to help the pump by filling the pump/pipe with water, just as you do with a hand pump if not used for some time. The plumber was here several times and eventually the problem was solved, mainly by putting "vulcaseal" on the fittings, to ensure the whole system was air-tight.
Some weeks ago we had suddenly the problem that the water was not clear anymore, it contained fine (river)sand. The usual solution to this problem is to disconnect the electric pump and connect a bigger gasoline pump and let it run for many hours or days. We did it for 2 days and after that the water was rather clean again. By doing so you remove all the sand near to the entrance of the pipe deep down in the ground. Our pipe is size 2 inch (schedule 40) 180 feet or 54 meters deep.
After connecting all the pipes again to the electric pump, we had the same problem as 3 years ago. Even adding "vulcaseal" didn't help.
My plan A was now to install new quality materials and to understand the problem I even bought a vacuum gauge and connected it to the sucking pipe section. However, the scale was too limited to really see any change in vacuum after the pump was stopped.
So I had to go to plan B, which was back to the specialists. I managed to get an employee of the supplier (Maramba, Dagupan) with a lot of experience for a couple of hours at my premises.
First potential problem was the new check valve which I had installed in the sucking pipe, as the spring seemed to be too strong, hence difficult for the pump to open the valve. So we decided to put back the old check valve, which was still good and the spring much weaker.
It seemed okay again, but next day we had the same problem again, so I went back to my supplier. Because the expert had seen our installation he could now advise a better solution, which was plan C, installing a straw, see drawing on top of this post.
Basically it is an inner pipe (the straw) in the outer pipe (the bottle) with at the lowest end a foot valve. It should be about 9 meters (30 feet) long, as they concluded that my pump was not a deep well, but a shallow well installation. This conclusion was deducted from the fact that the hand pump worked well on the same suction pipe. If it's deeper than 9 meters, a hand pump will also not work.
It was an easy decision to go for plan C. I bought the required materials, and made a special fitting for the straw pipe. The straw pipe is made from 1 inch PVC water pipe (blue in the Philippines) and step by step carefully loading pipe after pipe and connecting the in the 2 inch 2 pipes in steel pipe,and carefully securing the PVC pipe(s) to prevent them falling down in the depth of the outer pipe.
Since a couple of weeks it is working well now, no single problem and crystal clear water again.
The reason that it is working so well is of course the foot valve and the straw pipe. If the pump is primed for the first time, the water stays in the straw pipe from 9 meters deep up to the pump, because the foot valve is preventing the water to flow back in the well. So the next time the pump starts it has not to prime anymore as it is permanently primed.