Water Pump Cycling Problem

[charliem]

[font size="3"]This pertains explicitly to the Shurflo 4008-101-X65 in the Camplite CLs but might also apply to truck campers and toy haulers depending on what pump is used.

The major symptom was pump cycling every 2 minutes at night with no water being used. It was not a long run but just a short brrrp. I also noticed a very annoying  temperature variation caused by pump cycling during showers. The pump would not run continuously even with the shower wide open. I first suspected a leak or faulty check valve, but no leaks could be found and there was no evidence of the FW tank filling when city water was connected.

The problem ended up being that the pump was cycling between two closely spaced points in the 25-35 psi range. Somehow the pressure switch had "drifted" out of adjustment such that the on/off points became low and very close together.  I don't know if this indicates wear or degradation in the pressure switch diaphragm or an initial misadjustment. The screw was not loose so I doubt it backed off by itself.

The fix was to adjust the switch to raise the on/off set points. The 5/64" Allen head adjustment screw is on top of the pressure switch which is near where the power wire connects. Turn the screw clockwise into the pump until the pump runs continuously with shower not quite wide open.  This sets the upper limit to 50-60 psi as originally shipped. Now the shower runs at a constant temperature and pressure without the pump cycling. When no water is being used the pump holds its pressure and does not cycle for least 12 hours, at which time I quit watching and went to bed.[/font]

[diversteve]

Great tip. Thank you for posting.