Water Pump Cycling On\Off

[Theb2b]

Last trip out the water pump on my Jayco White Hawk was cycling on and off, number of cycles increased as the fresh water tank emptied out. Less water in the tank the more often it would cycle. Found no leaks, all faucets are/where fully off. Wondering if it may be due to the pump going bad or drain back going bad or perhaps the pump diaphragm could be bad. TT is on its 3rd season believe it has a Shurflo 4008?

I was able to confirm the cycling increase's with tank level as we had to refill the tank during the week+ we where out.

Thoughts or advice on what to check for?

[4x4van]

SoundGuy wrote:

SoundGuy wrote:
Leaking city water inlet check valve is the most obvious place to start.

Theb2b wrote:
I'll start here, not sure what I'm looking for but start the trace and see what I find.

Obviously you want to know if the city water inlet check valve isn't seating properly and therefore leaking air into the system. Simply seal it with a threaded water inlet plug and if solves your problem you've found the culprit. If not, continue looking at the rest of the system ... no magic here, you've got air leaking into the system somewhere.

It is impossible to leak air "into" a pressurized system; whatever is in the system will leak out, not the other way around. A leaking city water inlet valve will leak water "out", dribbling down the outside of the RV. And tank level will not affect it if that is occurring. The only way for air to get "into" a pressurized system is for there to be a leak in the line between the tank and pump (on the vacuum side), so that the pump is sucking air in.

However, a leak in the pump's check valve allows the pressure in the system to drop enough for the pump to cycle as the water leaks back into the tank. It's possible that a higher water level in the tank exerts a (slightly) higher the pressure on the tank side (in essence "pushing back" against the leak), explaining the higher rate of "cycle" as the tank level decreases. That (the differing cycle rate corresponding to differing tank level) is the clue that points to the pump check valve.

[wnjj]

I don't see how the tank level would have any effect on the city connection check valve. The only thing that makes sense is the pump. When the water level is lower in the tank, there's a lower pressure in the suction line, increasing the chances of leaking back through the pump.

[Bobbo]

SoundGuy wrote:

Theb2b wrote:
Thoughts or advice on what to check for?

Leaking city water inlet check valve is the most obvious place to start.

This is what it was when mine did it. We were on a 2 week camping trip. The screw in plug held it till we got home, then I replaced the backcheck valve.

[Theb2b]

Won't have a chance to mess with the pump for a few days, let you all know what I find out.

Thanks for the pointers.

[marcsbigfoot20b]

May need an adjustment of either pressure or bypass pressure switch.

[SoundGuy]

SoundGuy wrote:
Leaking city water inlet check valve is the most obvious place to start.

Theb2b wrote:
I'll start here, not sure what I'm looking for but start the trace and see what I find.

Obviously you want to know if the city water inlet check valve isn't seating properly and therefore leaking air into the system. Simply seal it with a threaded water inlet plug and if solves your problem you've found the culprit. If not, continue looking at the rest of the system ... no magic here, you've got air leaking into the system somewhere.

[Theb2b]

mtofell1 wrote:
When my tank gets low the pump will start cycling and running constantly. It's very sensitive to being on a hill when the water is presumably falling away from the pump. I don't think anything is wrong. You just must keep enough water in the tank to satisfy the pump.

That spot I was on was one of the flatter spots I have had so don't think that is it. The pump still cycled just longer periods between the cycling.

SoundGuy wrote:
Leaking city water inlet check valve is the most obvious place to start.

I'll start here, not sure what I'm looking for but start the trace and see what I find.

[SoundGuy]

Theb2b wrote:
Thoughts or advice on what to check for?

Leaking city water inlet check valve is the most obvious place to start.

[LadyRVer]

2 x to me. Once was outside shower faucet was not turned completely off and the other was a bad diaphragm in the pump itself.

[mtofell1]

When my tank gets low the pump will start cycling and running constantly. It's very sensitive to being on a hill when the water is presumably falling away from the pump. I don't think anything is wrong. You just must keep enough water in the tank to satisfy the pump.