Fresh Water pump sucking air.

[JanisM1956]

Problem: My freshwater pump is sucking in air instead of water once the water level drops below a certain point.

During my trouble shooting, once the pump stopped pulling water and started to sucked air, I pulled the freshwater drain and water drained at the full volume for at least 10 seconds. So, there was plenty of water in the tank. I was at a campground where the plumbers were shutting off water for the whole weekend. I refilled my tanks to the max and the pump pulled water correctly. Luckly, the water outage was postponed but I continued to live off pump water for a couple of days. Then, with water in the tank, the pump sucked air and all faucets sputtered. More trouble shooting. I replaced the pump, the filter screen was tight with no leaks, and all connections on the Nautilus panel were tight.

I haven't dropped the bottom lining yet, because I am on a 75-day trip and most campgrounds don't permit maintenance. To rub salt into this wound, we normally stay at full hookups. We only use the pump for road potty breaks and emergency's such as water shut off and our latest, a boil your water orders from the city. It was at our last camp that we couldn't draw our fresh water and had to boil or buy water.

I have concluded that I must have a water tank bulge, or the tank is slipping from its supports. I can't think any other reason why the intake tube would be high and dry with water in the tank. Other posters have said the tanks are flimsy and poorly supported. Plus, I have sinned several times by traveling with my tank over half full. I am asking the group if my conclusion is correct. If not, what else can it be?

[DougW9876]

This is a very common problem. The water tank is not very deep, it is wide and flat. The pickup for the water pump is almost always on the side of the tank, an inch or two above the bottom of the tank so it will suck air when there is still nearly a third of a tank of water left. The only real cure would be to put a water pickup in the bottom of the tank, not always an easy thing to do.

I really wish the manufacturers would build the tanks with a small sump and the water pickup in it but they just don’t seem to care about this issue.

[jmbopp]

I measured my tank - there's 6 gallons of water left between the time the pump starts sucking air and an empty tank. I did modify the pump pickup by T-ing into the drain line and extending the pump winterizing line to the drain.

[JanisM1956]

Thanks for your reply. I measured the remaining water in my freshwater tank when the pump started sucking air. There were about 14 gallons of water still in the tank. That is about 25% of the tank's capacity which seems to be a lot of water remaining to be just poor design or sloppy installation.

[LincolnGuy]

Fresh water pump sucking air... When I purchased a RL295 150 from the dealer in 2019, he gave an introduction to the systems. One thing he did NOT cover was the vent from the freshwater tank. I had what sounds like the same issue. No water but the pump was working. I discovered the freshwater vent by looking under the RV and noticing a blue rubberized line coming out of the coroplast with a ball valve. Wondering what that was and attempting to figure out the no water issue, I rotated the valve. It made a little whooshing noise. Aha! I went to the Nautilus and turned on the freshwater pump and opened the outside faucet. Eureka! Nowhere in the Ops manual was any description of the valve or what it was for. I did some research and it's important to have the vent open while filling the tank and while using the water pump. Caution is to be observed if one travels with water in the freshwater tank because if it is open while traveling, water will slosh out! Maybe this will help.

[Hoopy Frood]

I've never heard of a ball valve in the vent lines from the factory. That would be a recipe for disaster. This was a brand new trailer?

[LincolnGuy]

I've never heard of a ball valve in the vent lines from the factory. That would be a recipe for disaster. This was a brand new trailer?

It was a year old when purchased. The RV is a 295RL 150 Series. The Freshwater tank does indeed have the ball valve on the vent line from the freshwater tank. When the old tank fell out I was able to inspect where it is attached. It is attached to the highest point on the side of the freshwater tank. There is no other vent for the air to dissipate when filling or allowing air into the tank when draining. Those tanks need venting, otherwise when filling, the tank WILL expand and could cause damage. When using the 12vdc water pump, the tank needs venting to allow air to replace the water. While traveling the ball valve should be closed, otherwise water will be sloshed out. I believe the ball valve was installed to prevent the sloshing while traveling. It all looked dealer installed.

[Hoopy Frood]

It just seems so unlikely since that kind of installation puts a pretty large liability on the dealer. If there would be a problem with the tank, basically the dealer, or whoever installed the ball valve, will get the blame. They are an almost necessary add-on on some trailers, but I've just never heard of any installed, unrequested, by a dealer.

[LincolnGuy]

It just seems so unlikely since that kind of installation puts a pretty large liability on the dealer. If there would be a problem with the tank, basically the dealer, or whoever installed the ball valve, will get the blame. They are an almost necessary add-on on some trailers, but I've just never heard of any installed, unrequested, by a dealer.

So - how would you propose to vent the freshwater tank? How is yours vented? Do you have a Nautilus System? Just asking!

[JanisM1956]

Fresh water pump sucking air... When I purchased a RL295 150 from the dealer in 2019, he gave an introduction to the systems. One thing he did NOT cover was the vent from the freshwater tank. I had what sounds like the same issue. No water but the pump was working. I discovered the freshwater vent by looking under the RV and noticing a blue rubberized line coming out of the coroplast with a ball valve. Wondering what that was and attempting to figure out the no water issue, I rotated the valve. It made a little whooshing noise. Aha! I went to the Nautilus and turned on the freshwater pump and opened the outside faucet. Eureka! Nowhere in the Ops manual was any description of the valve or what it was for. I did some research and it's important to have the vent open while filling the tank and while using the water pump. Caution is to be observed if one travels with water in the freshwater tank because if it is open while traveling, water will slosh out! Maybe this will help.

Thanks for your response. I'm at the GDRV National Owner's Rally and will bring this up to the tech guys tomorrow.