[Dan]

No doubt my 12v pump was added by one of the previous owners. So glad they did!

Just like the back-up cadet heater I added to the water bay in case the first one quits …

[Archived]

As a follow-up to why you Should shut-off your 110v water pump when running down the road:

Apparently in my vintage year coach (newer Marathon coaches have an automatic switch which shuts off the 110v and turns on the 12v water pump when you turn on your bus), if you’re running down the road and your 110v water pump is on, and your fresh water tank is not 100% full, air can build up in the tank, which then turns on the 110v water pump constantly, eventually burning them out.

For whatever reason, Marathon has not had issues with the 12v water pumps doing this.

One more thing to add to my departure checklist …

[Archived]

Tim,

Uh huh, looks like your tiny micro departure list just got one more item added! :o)

Safe travels to you and Cindy.

Mark

[Tim]

THAT IS BOGUS, TIM

As amateurs I am sure we get told stuff sometimes just so we go away and quit bothering the experts. But to say the 120 V pump needs to be off because of air build up in the water tank is BS.

Let’s apply a little thought to that statement. Both pumps draw water from the bottom of the tank. Each has a check valve or some means of preventing pressurized water from flowing back into the water holding tank because if water were to drain back into the tank the pumps would be cycling all the time to maintain water system pressure.

But there is a second reason water and air will not be an issue if they diid flow back into the tank. The tank is not a sealed vessel. If it was the first time water was drained from the tank by usage, and no air entered because it was sealed eventually the space previously occupied by water would be filled with the tank until if broke or cracked or otherwise failed. With atmospheric pressure at around 14 PSI you can imagine how quickly the tank would cave in from air pressure outside. That is why all tanks are vented and as water is drawn from the tank it is replaced with air. Conversely if by some unknown means a pump was able to introduce water to the tank it would escape through the vent which is usually the tank overflow.or if there was no vent it would not be long before the tank would explode.

Keeping a 120V pump automatically turned off and using instead a low current draw 12 V pump makes sense in the context that if you are not hooked to shore power or have the generator running, you could be trying to cool the coach by running A/C units through the inverter. If the 120V pump kicks on, like the A/C units there is an intial high starting current draw and if that happened a lot it would trip breakers or overload inverters so a coach without OTR is likely to have current draw issues that make the addition of a heavy water pump load undesirable.

[Larry & Diane]

Jon beat me to the punch. My BS meter was pegged when I read that one. Total BS!!!!!!

The only reason to turn off the pump is in case you had something break, like a water valve that would flood the bus in some fashion. I know, because I had one do that under the kitchen sink last summer. I did not hear it go, but my wife did and we were able to get it shut off fairly quickly, but still used up lots of towels getting it cleaned up.

If my wife had not been with, I would not have known about it until water started running down the stairs by the driver’s seat.

[Archived]

Hold on there rose pedal owners, Tim’s info is correct. Your assumption that this 110v pump sucking air is BS, you better look in the mirror.

If my fresh water tank is anything less than 1/2 full and I run with the pump on, it sucks air and when I get stopped, I have to shut off the pump, drain all faucets, then with all faucets open, turn the Headhunger back on and all is back to normal. One correction for Tim, the Headhunter won’t harm itself, it times out and needs the reset button pushed if that happens.

I now only run with a full water tank, eliminates the chance of sucking air and I have learned over the years you never know what’s coming down the road and running out of water is a bad day.

I got your back Tim, these rose pedal experts now think they know more than Marathon.:)

[needtocamp]

Boys,

I’m the messenger on this one. They stated they have documented 110v water pump failures because of this air issue and, that’s why in the newer Marathon coaches, when you turn the bus on, it disengages the 110v water pump and engages the 12v water pump.

Maratahon says this is one of the reasons why they now put in two 12v Shurflo water pumps instead of the 110v. For me, it fairly easy though since I have a water pump button in my water bay where I unhook anyway, so it won’t be a big deal to shut-off my 110v water pump when I travel, and turn it back on when I arrive. I do have to go to the otherside of the coach to turn on my 12v water pump. But it’s not worth the price to automate this process.

I think you Liberty guys are jealous that there is no “Leon” at Liberty 🙂

[Larry & Diane]

Explain to me how it can “suck air” if the tank is not full. The tank has to be vented, so how does this happen in a Marathon and not my current coach a Liberty, nor my previous coach a Legendary with a Headhunter pump, which I never shut off either. Neither one has ever had an issue with what you described.

[Archived]

I really want to hear how a water tank that is low on water can allow air to enter the 120V water pump. Is the inlet to the 120V pump such that it gets cavitation? I cannot imagine how low the water level must be for that to happen. Surely the tank has internal baffles so no matter how the coach is driven that will not happen until the tank is almost empty. Half full? No way. Even 1/4 full I cannot imagine a pump sucking air.

I am going to presume we are talking about a Headhunter type pump. That pump has the ability to suck a lot of water all at once, but in order to do so there has to be no restrictions to the discharge side. Otherwise the inflow and outflow are going to be quite low because when the pressure switch calls for the pump to turn on, it is usually to provide some modest flow while the system re-pressurizes.

BTW, this is a secondary issue. Tim said in his post air can build up in the tank and that is not going to happen, and I have an equally hard time imagining a tank with even a modest couple of inches of water causing the pump to suck air unless the coach is on the 30 degree banking at Daytona.

[Archived]

My statement of “air can build up” was not accruately stated. I meant that because the tank was less than half full or lower, there was a lot of air in the fresh water and the pressure from that air somehow turned on the water pump.

Again, I have “no” exerience with this issue, but since Marathon did a redesign of their coaches which now switches the 110v pump to the 12v pump when you turn your bus on, they must have felt it was a significant problem to redesign this change.

[Archived]

Hang on Tim, they’ll be lobbing grenades at ya.

I don’t know what causes it to happen, but learned quickly how to deal with it. It’s never a problem 1/2 full or more.

[Bryan]

I’ve dug a foxhole to hang-out in while these Liberty guys go on the attack 🙂

[Archived]

It’s not a Liberty thing versus a Marathon thing, but a question as to how a tank and pump can be designed so the pump ingests air when there remains an abundance of water in the tank.

If water is very low relative to the opeing to the pump a high demand from the pump can pull a lot more water into it than the contents of the tank can keep up with. I get that. But at levels discussed previously something is wrong. If I have opened my plumbing system such as to get rid of all pressure so I can work on it I will get air pockets in the water lines. But after the initial pressurization and after I have run water through all the pipes the need to burp the system is over.

I never turn off the Headhunter when we are in the coach regardless of whether we are driving or not and regardless of the water level. I have driven the coach and used the pump when the Headhunter water level sensor has been flashing and the single lowest red light is the only indication there is still some water in the tank, although it is probably only a couple of inches.

When the toilet is flushed there is still no indication of the disctinct sound made when there is air in the lines. My tank has a single 3/4″ outlet feeding directly into the Headhunter so there is no magic. How is the Marathon plumbed and what makes it draw air even with what seems like substantial water in the tank?

[Harry]

So after doing a little more investigatiion and interviews, here’s some additional information:

As you’re rolling down the road, air “can come in” thru your vent pipe on the roof. There is no check valve in this vent pipe. But it especially is susceptible building up air when your fresh water tank is less than half-full of water.

In addition, while rolling down the road, even with a check-valve in the water pump, the pressure switch on your 110v water pump can sense that pressure is taken off it when the water flows away from the pump. For these two reasons, Marathon did a design change.

Don’t shoot the messenger …

[Tim]

I’m not sure where you are getting this information but it gets weirder by the minute.

If you house plumbing system vent that goes through the roof is connected in any way to the fresh water tank vent you literally have a direct connection between your waste holding tank and your fresh water tank.

I don’t think so. Somebody is making this stuff up.

Relating to the water pump, of course when you draw water the pressure drops and the water pump kicks on to restore pressure. Which pump does that is unimportant because that is how the system works and there has to be a check valve to prevent pressure from pushing water back into the water tank.