When i came across the dry motor submersible pump the motor has a limitation that it cant be used above 20m.whereas the wet motor submersible pump can be used till 350m.can i know why?pls advice.
Is the answer not the dry housing pressure rating? A dry housing would conceiveably have a limitation of 20 m depth, whereas a wet motor could operate presumedly at much greater depths.
If that's not the answer, I don't know what is. We'll see if anybody else can suggest something different.
The answer is the delta pressure. “Wet” motors used in the petroleum industry are installed to depths exceeding 15000 feet (4572 M) without problems. Submerged static pressures > 6000 PSI are not uncommon. The trick is to keep the pressure inside the motor and outside the motor equalized. Dry motors and / or water well type motors are limited by collapse pressure of the motor housing.
Very good point. I wasn't considering collapse pressures, as the maximum depth mentioned by the OP was 320 m, but that is probably getting into the depth range where it needs to start being considered for housings without specially designed reinforcement.