Novice trying to figure out fresh water pressure issue

[crowlegs]

Greetings all...

I've got a Shurflo 4000 model 804-009-01 and over the last few months, I've noticed that the pump will kick on to pressurize the collection tank while no water is being used anywhere on the boat. So, there's probably a leak either on the pump/tank or in a fresh water line. I don't find any water where it shouldn't be along the fresh water lines, so my guess is the pump/collector. Has anyone else had this problem with a similar setup and how did you remedy the problem?

The second issue is that the pump won't consistently pull water up from the lower of my 3 water tanks and the pump just runs and runs until I turn on one of the higher placed tanks. All three tanks feed into a piece of stainless which has two outputs, one to the hand pumps and the other to the Shurflo system. I've taken off the feed and vent on the lower tank and blown air through each hose and none of them feel restricted. To get the lower tank to feed water, I have to turn on a higher tank until I see water backflowing into the lower tank. I assume then that there is no air trapped between the tank and the stainless flow control piece. Once I turn on the faucet, the water will run nicely for about 5 mins, then the pitch of the pump motor changes to a higher note and the water flow eventually dwindles down to nothing.

Any observations, instructions or suggestions would be greatly appreciated!

Thanks everyone.

[Thumbs Up]

You have a leak in the lower feed line that is sucking air (does the tank have a dip tube?) and you either have a leak on the pressure side or a bad check valve in the pump. If it is the pump check valve you could install an external check valve on the pressure side of the pump.

[MarkJ]

A tiny leak can spray mist so fine it never settles so it drip. There are difficult to find.

[newhaul]

It sounds like a hoseclamp needs to be tightened on the feed line from the tank and the pump check valve is leaking by and allowing pressure to drop you can install new check valve inline or now that you know the reason for the pump cycling its not a problem won't cause the pump to fail and usually happens to all pressure pumps eventually

[GordMay]

Greetings and welcome aboard the CF, crowlegs, and newhaul.

[mitiempo]

Originally Posted by crowlegs

The second issue is that the pump won't consistently pull water up from the lower of my 3 water tanks and the pump just runs and runs until I turn on one of the higher placed tanks.

Pumps always push better than they draw. The pump should not be mounted higher than the tank ideally.

[Harvey Mason]

I agree with the other posts that a small leak is probably the issue. In the case where your water tank is below the pump and the pump suction must draw the water up to a higher elevation net positive suction head, NPSH, is a common issue if the water is warm such that vapor pressure is lowered allowing vapor to form in the lower pressure suction line. The pump then cavitates as vapor replaces liquid and suction is lost. You can have a similar problem due to pressure drop in the inlet pipe if it presents excessive flow resistance due to tight bends or long lengths of small diameter tubing.