Lessons learned: water pump

[DBBRanger]

For years I was annoyed by my water pump cycling when water wasn’t being used. Thinking there was a leak in the system, I tightened every hose clamp I could get to and inspected those that I couldn’t tighten. All seemed good - no leaks. So I finally decided that the pump was leaking backwards into the water tank and therefore there was nothing to worry about relative to leaking water. I was never real confident of that conclusion, but it did give some easing of the mind (except of course that it didn’t ease the mind of the Admiral!). So I finally decided to investigate more and realized that there is a check valve in the system just downstream of the pump. I removed that valve and found that it indeed did leak backwards. Great - so I replaced it with a more positive spring loaded check valve rather than the installed swing check valve. Well......it indeed did stop any leakage backward to the check valve, however there still was a backward leak through the pump. So now, instead of the pump cycling every hour or so, it micro cycled every minute or so! That is, the pressure in the line from the pump to the check valve (where the pressure switch is) lost pressure but because it was a very small amount of water contained in that line it didn’t take much of a leak to decrease the pressure and also didn’t take much to pump it back up hence the micro pump every minute. So now I removed the check valve entirely and the pump hardly ever pumps between uses. I think it’s OK to remove the check valve since I believe the purpose of it is to not allow the dockside city water connections to back flow through the pump filling/overflowing the water tank. I never use the city water connections - so no problem. I do think the pump should not allow back flow, but maybe someone will chime in and say if that can be fixed. I also have installed an accumulator which increases the time between cycling. The next thing I might try is to install the new check valve upstream of the pump but I’m not sure the pump can overcome the opening pressure of the valve satisfactorily. If it ain’t broke, don’t fix it!

 

[JamesTXSD]

We have been using pressure demand water pumps on RVs and boats for decades. Other than one motorcoach that had an accumulator tank, almost all of them have had that small "blip" from the pump as it tries to pressurize the line, with a minor backflow. I mentioned it once 20 years or so ago to an RV tech and was told, "They all do that. Don't leave your pump on all the time. Turn on the pump when you need it, then turn off the pump. You'll get that little blip when you turn on the pump and that lets you know it is working and ready to pump for you."

Yep. There is no advantage to leaving the pump on. In fact, if you leave the boat/RV with the pump on, and a leak develops in the lines, it will pump the contents of your fresh water tank into your conveyance. Avoid the annoying noise by leaving the pump off until you need it.

 

[BB marine]

If you do not use or have a city water hook up a check valve is not necessary. If you have city water hook up the check valve should be located on the suction side of the pump not the discharge side. The check valve is to prevent the water tank from filling when on city water. The check valve may cause some suction flow issues but is needed if city water is used. Having the check valve on the discharge side will cause pump cycling issues as you know.

 

[ALICE J]

There is a duckbill valve downstream (check valve) from the sump pump in the shower. It failed and would allow the sump pump to almost continuously run, basically recycling the gray water and not letting it go overboard. Removed it and all was right with the world. 😎