Pumps won't make shut-off
Pumps won't make shut-off
(OP)
I started up two Grundfos CR 5-7 pumps yesterday. The pumps are marked with a shut-off head of 225.6 ft. I have a curve that shows the same, as near as I can read, not sure of the .6. The curve indicates a 3501 RPM speed. These pumps are driven with 2 HP 3450 motors, and I wired them across the line (design driver includes a VFD) for startup. Suction is taken from a tank three feet away overflowing with 10 feet of clear, cold potable water. After venting air from the pumps, they were individually started and both made 172 feet of shut-off pressure. Allowances were made for suction pressure (10 feet) and gauge location (5 feet above floor level, and yes the tank sits on the floor). Why ??? I hade a new mechanical gauge and a new, very expensive, instrumentation pressure transmitter. Both gave the same readings.
Steve Wagner
Steve Wagner





RE: Pumps won't make shut-off
Also I don't know if there is a possible impeller trim which of course would affect your head.
RE: Pumps won't make shut-off
RE: Pumps won't make shut-off
Check the inlet side pressure (by gauge), maybe you have a blockage.
RE: Pumps won't make shut-off
Most likely it is something suggested above by Valvecrazy or Artisi especially now that I see it is one of those multistage centrifugals.
RE: Pumps won't make shut-off
Thanks!!!
Steve
RE: Pumps won't make shut-off
RE: Pumps won't make shut-off
RE: Pumps won't make shut-off
RE: Pumps won't make shut-off
If it isnt this, then the speed check is next step in case you have dropped a phase in the motor.
Let us know how you get on...
Ash Fenn
www.cdrpumps.co.uk
RE: Pumps won't make shut-off
Steve
RE: Pumps won't make shut-off
Was he actually out of the factory or from a representative? I am surprised because the factory in Fresno is very close by and has a good reputation (although I have never used a Grundfos because they don't make the ANSI end suction industrial type pumps that I typically use).
RE: Pumps won't make shut-off
BTW, Grundfos now owns Peerless. So I think they now make ANSI end suction type pumps.
RE: Pumps won't make shut-off