Fresh Water System Issue

[HopCar]

You said the problem is exactly like the OP’s problem. Does that include air being released from the faucet? If so you have a leak somewhere on the suction side. That air is getting in some how. The pump doesn’t make air.

The OP said he eliminated his problem by moving the pump closer to the tank. The distance to the tank wasn’t the problem. He had a leak on the suction side that got fixed when he moved the pump.

You said that this problem started when you installed a new pump of the same model number. I suspect you didn’t get one the connections sealed. See if you can tighten the connection to the pump on the intake side.

If no air is coming out, I suspect the accumulator tank is the problem.

The FloJet 4405 is designed to run continuously as long as a faucet is open. If the faucet is only open a little, the excess water being pumped is bypassed back to the intake side of the pump. This eliminates the need for an accumulator tank to prevent short cycling of the pump. While I don’t understand exactly what happens, I have heard numerous complaints of problems with this type of pump when connected to an accumulator tank.

I suggest you eliminate the accumulator tank or buy a regular pump that doesn’t have the bypass feature.

 

[Delfin]

The point behind having an accumulator tank is to allow longer rest times or less runs on the pump. I can't understand why the pump manufacturer doesn't want a tank unless it's so the pumps have a shorter life and get replaced more often. With a tank all the parts get less use, valves, motor, and diaphragm (if it's a diaphragm pump).
To find the cut in pressure, you need a pressure gauge in the line anywhere after the pump. Turn on a faucet and watch the pressure on the gauge where the pump starts.

Manufacturers have tried to provide models that don't need the accumulator. I had two Flojet VSD pumps designed this way. They work with variable speed motors that aren't just on-off, but will tap away at a sensed lowering of pressure by turning the pump on for as few as a single revolution. Sounds like that is what is happening now, and the manufacturer recommending against using a tank anyway is to avoid confusing the sensing mechanism in the pump and causing it to run when it shouldn't.

Change the pump or bypass the accumulator sounds like the approach.

p.s. I installed a 120 vac Headhunter pump and it is so far superior to any other system I have every used I finally understand the cost. Night and day. Likely be hard to fit for some, but if you can it is worth it.

 

[aboatman]

"I have a plumbing issue that is mystifying the yard,"

Sounds like a great time to find a better boat yard.

I agree. If you're paying people to fix a problem and have to ask folks on an Internet forum how to fix the problem because they don't know, it seems they don't know much and don't deserve your business.