Ok to replace a Shurflo 4 gpm pump with a 3 gpm?

[JCWDCW]

If the pump primes from a bucket, it could be the pump is worn enough that it will not lift water from the tank. To prove this you will need to put the bucket outside and run a longer hose...pain...I know!

You could also try priming the pump from the tank with the discharge open; that usually gives the pump a chance to establish full flow.

Everything points to weak pump or something open and leaking in the lift tube from the tank.

The pump can run dry but as the diaphragms ran for an extended length of time they may have over heated and developed a small crack in one of the three diaphragms which reduces the ability of the pump to develop enough suction lift from the tank

I also repaired an old pump that was touchy about priming. The kit was less than a new pump and quite easy to install. Worked like a charm after that!
JCW

[idroba]

Originally Posted by JCWDCW

I also repaired an old pump that was touchy about priming. The kit was less than a new pump and quite easy to install. Worked like a charm after that!
JCW

I am being cute now: "Worked like a charm after that!" I have never had good results from charms, so I am assuming you are saying it didn't work after the repair? LOL, Grin, and so on. (bows head in shame, but still giggling).

[featherbedder]

I have replaced old style piston type pump that was in 1976 AS with new type pump, and went bad replaced again, lot's better than repair plus about same cost considering maybe didn't fix original problems, so new is better. Pumps are not expensive, plus some model AS need upgrade for pump as AS is not known to install higher pump, or better pump. As for draining water tank AS did NOT INSTALL DRAIN VALVE IN FRESH WATER TANK.... in 1976 AS 31 footers Same as today use cheapest availble components. Ps I camped with Holiday Rambler some yrs. ago same grouch about things I had . This only trailer I have owned with out drain in fresh water tank including slide in truck campers.