Guy's we are having a problem with one of our cond. pmps. When it is starting up whether in auto or man. it just sits there freewheeling for about a minute and then all of a sudden bam off it goes with a slug of water. 0 psi to 220psi just like that. this would be with 1 pmp already running and this 2nd out of 3 pmps starting up. Do you think there is some cavitation going on there? And also can the vent line or seal water line have anything to do with this problem? Any advice will be appreciated. Thanks

Maybe checkvalve in discharge line sticking?

If you are seeing the sudden bam and have a check valve it could be stuck and breaking free with the slug of water passing through. might consider installing a recirculating system to prime and load the pump prior to putting it in service with the system. Also consider bleeding the air in the lines or install an auto breather kit. Check the sizing of the piping/ flow orifice and flow rate required to the suction side of the pump for ideal discharge pressure against the CV curve...might not be per the spec with pump 1 in operation and calling to operate pump 2 or 3.
thanks

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O&M Manager-BSME, MSME, P.E.