Fixing fresh water pump chatter

Christo

Christo

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Oct 4, 2019
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Weymouth, MA
www.cruzingear.co
Whenever I pump from the fresh water tank in my coach, the pump chatters (rapidly cycles on and off). Since this shortens the life of the pump, stresses the system, and gets on my nerves, I went looking for a solution. It came in the form of a one liter accumulator, otherwise known as a pressure tank, which acts as a small pressurized reservoir in the system. Some folks use larger residential-style ones, but I didn't want to take up that much space and I also want an earlier/more frequent activation of the pump in case of a leak.

All of these units have a flexible bladder inside which gets inflated to roughly the turn-on pressure of the pump, which in my case is 40 PSI. There's a standard Schrader valve on the top of the unit for this purpose. When the pump runs, the bladder acts as a spring pushing back against the water flowing into the accumulator. There's enough reserve pressure for a quick flush or hand rinse without activating the pump.

The installation of the accumulator was easy, inexpensive, and effective. They can be mounted at any angle. Maintenance-wise, they're self-draining for winterization purposes but one does have to check the bladder pressure (with the water system depressurized) every once in a while. As far as I'm concerned, these should be standard equipment on all RVs. This season I decided to stop using my city water connection because I want to know if I spring a leak before it turns into a disaster, plus it's super easy to just turn off the pump at night and when I'm away from the coach.

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Speaking of water pumps, mine also cycles on and off. It doesn’t bother me that much but it is very old and I’m not sure how much longer it will hold up. If/when it gets replaced, what is the correct pressure for our plumbing system?
 
I intend to just put a length of closed-off PVC pipe in the bathroom wall when I put things back together. It won't have the bladder, but those really only come into play in extremely long-term usage when the water dissolves all the air in the headspace. I also won't be able to precharge the tank, so I'll get less effective storage with the same volume. But still, it should make handwashing with a trickle of water much less obnoxious.

Regarding leaving the pump on...
I've also pondered putting my water pump on a momentary switch with a latching relay. I can't count on everyone who uses the coach to shut it off when they will be away. So you could push a button, and the water pump would be activated for an hour or however long you prefer. Then no one has to remember to shut it off. Maybe I'll implement something like that someday. And by latching relay, I probably mean a functionally similar circuit built around a MOSFET so I don't have anything like a relay coil consuming unnecessary power.
 
pvfjr said:
I intend to just put a length of closed-off PVC pipe in the bathroom wall when I put things back together. It won't have the bladder, but those really only come into play in extremely long-term usage when the water dissolves all the air in the headspace. I also won't be able to precharge the tank, so I'll get less effective storage with the same volume. But still, it should make handwashing with a trickle of water much less obnoxious.

Regarding leaving the pump on...
I've also pondered putting my water pump on a momentary switch with a latching relay. I can't count on everyone who uses the coach to shut it off when they will be away. So you could push a button, and the water pump would be activated for an hour or however long you prefer. Then no one has to remember to shut it off. Maybe I'll implement something like that someday. And by latching relay, I probably mean a functionally similar circuit built around a MOSFET so I don't have anything like a relay coil consuming unnecessary power.
Click to expand...
For a timed water pump switch, my PO added a 2nd (parallel) switch in the bathroom under-sink cabinet. It's an automotive rear window defroster switch with a built-in 10 minute timer.
 
My pump from 1995 recently started leaking and I replaced it with this -

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It uses a “back-flow valve” to prevent rapid cycling of the pump, so if you’re running the water at a trickle and need a small amount of additional pressure, the pump kicks on with some pressure going into the plumbing (to bring the pressure back up) and the rest going back into the water tank. This results in a longer pump cycle as opposed to frequent starts and stops. Seemed to work well on our outing this weekend. No cycling and very quiet compared to the old Shur-flo it replaced. It says in the instructions that an accumulator isn’t needed, although it could prevent the pump from cycling on at all when using only a small amount of water. We’ll see how reliable it is over time…
 
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An accumulator will work wonders to delay the pump turning on and off. I have a variable speed pump, which is even better, IMHO. I've played with both types in a product I designed and by far the best way to go is the variable speed. The negative is cost...A VSP is quite a bit more money vs a single speed pump and a small accumulator.
 
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