I am having problems with my diaphragm switch sump pump. Sump pump model is little giant 6-cia-ml / catalog number = 506160 (drainosaur). The sump pump sits in a basin (506065 model wrsc-6). The diaphragm switch went bad so the pump ran constantly. We replaced the diaphragm switch and things appeared to be working again. However, we remembered that the vent pipe wasn't connected. Once we re-connected the vent pipe, we tested the pump again by filling the basin with water. The pump turns on then immediately kicks off and will continue to do this until it manages to pump enough water out. Obviously we can't keep running it this way or it will shorten the life of the pump.

I called little giant and they said the vent pipe must be vented to open air and it sounded to them like the vent pipe to the building wasn't venting to open air somehow. Does anyone have any ideas what we should try to correct the problem? Does it sound correct that the building's vent pipe doesn't vent to open air? If so, I am curious why it was working before the switch went bad in the first place. Is there anything I can do to test or prove that the buildings vent pipe doesn't vent to open air?

thanks in advance

I could see a pressure switch functioning on and off it it were the air inside an unvented sealed pit because drawing water out would change the pressure. But your switch should be operated by water pressure which does NOT change when the air pressure changes. Therefore, it will take more investigating and testing to determine what is actually happening. Your power cord may have a small "vent tube" from the pressure switch, and if so and it gets moisture in it that will severely affect the operation of the switch.



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I think the pressure in the tank being reduced, because of a lack of venting, would cause the pressure switch to cycle. If you look at the reverse of this and pressurized the tank, the water would exert more pressure against the switch, so a vacuum has to have an opposite effect.

IT would have to "lift" the water which cannot happen. Pressure pushes down on the water which is an entirely different dynamic.

fyi everyone. The pressure differential was indeed the problem. I pipe clamped my wet/dry vac onto the building's vent pipe and let it blow for several minutes. When I connected the pump vent pipe with the building's vent pipe, everything appears to be functioning normally now. Thanks for the replies.



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