Overflo mod

**315RLTSinPA** · 05-12-2019, 08:05 AM

Had a valve on the overflo, but more than once forgot to open it to let air back into the tank. So it was time to redo it. I don't know if the check valve is high enough, but it is up against the bottom of the floor. I would think the top of the tank is a little lower if the overflo pipe comes out of the top of the tank. If it doesn't work I'll run it over and up into the front compartment. I also moved the shutoff valve out to the side, so no more crawling under the trailer to use it. I had to make a bracket to attach the new valve.

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**Walaby** · 05-12-2019, 08:08 AM

Interesting

Is there a reason a shut off valve for the overflow is necessary? Just wondering what Im missing, and trying to learn more.

Mike

**TucsonJim** · 05-12-2019, 11:51 AM

Originally Posted by 315RLTSinPA

Had a valve on the overflo, but more than once forgot to open it to let air back into the tank. So it was time to redo it. I don't know if the check valve is high enough, but it is up against the bottom of the floor. I would think the top of the tank is a little lower if the overflo pipe comes out of the top of the tank. If it doesn't work I'll run it over and up into the front compartment. I also moved the shutoff valve out to the side, so no more crawling under the trailer to use it. I had to make a bracket to attach the new valve.

I really like this solution. I'm going to have to clone it! Thanks much.

Jim

**TucsonJim** · 05-12-2019, 11:55 AM

Originally Posted by Walaby

Interesting

Is there a reason a shut off valve for the overflow is necessary? Just wondering what Im missing, and trying to learn more.

Mike

Mike - When you're filling the tank, it's a good idea to have a valve to open up. If you fill it to the brim, the overflow will come out of the valve, and not up at the top next to the membrane.

Jim

**Walaby** · 05-12-2019, 03:56 PM

Thanks

So doesn't the overflow tube that is already in place (sans valve) work the same, just not controlled with a valve?

Im probably missing something really obvious and I'll feel like an idiot.

Mike

**TucsonJim** · 05-12-2019, 04:24 PM

Originally Posted by Walaby

Thanks

So doesn't the overflow tube that is already in place (sans valve) work the same, just not controlled with a valve?

Im probably missing something really obvious and I'll feel like an idiot.

Mike

Mike,

There is a long history behind this. The way that GDRV installs the overflow, some models are prone to significant spillage while driving down the highway. Whether it's due to sloshing or siphoning is irrelevant. The solution that many owners use, including myself is to put a valve on the overflow. Then, when underway with a full tank, the valve is shut and the water is retained. The issue is that the valve is hidden, and if an owner forgets to open it when setting up camp, the tank will essentially be at a vacuum and water won't flow correctly.

The solution is to route the discharge port higher than the tank. This minimizes the sloshing or siphoning action. However, when filling the tank, the water will still want to come out of the re-routed overflow when the tank gets full and the water hose is turned on. The way that the OP routed his overflow, the excess water can run out and saturate the bottom of the floor if the filling hose is still pressurized. However, by adding a bypass valve and hose at the bottom of the line, he can open it up when filling up and the majority of the excess water will bypass the discharge near the floor. Once the tank is full, that bypass valve can be closed, and the tank will still be vented and prevent the vacuum that others encounter.

Jim

**315RLTSinPA** · 05-12-2019, 05:46 PM

Yes, what Jim said. Except water can't come out the top. I used a check valve. Air can be sucked in, but water can't come out.

**powerscol** · 05-12-2019, 05:56 PM

Will the check valve you installed pass air both ways? I know some don't that are spring loaded. Just a thought. It looks high enough too - nice clean install. It also looks like your valve is at the low point for winter draining.

Its similar to what I did except using an air/vac valve that allows air both ways. I still need to remember to open the drain valve when filling as water will not pass through the air/vac https://www.mygrandrv.com/fo...263#post196263

**Walaby** · 05-12-2019, 06:19 PM

Thanks for the explanation... I got it now. Sorry if I sounded like an idiot.

Makes sense now. Learn something new everyday.

Thanks

Mike

**powerscol** · 05-12-2019, 06:24 PM

Originally Posted by Walaby

Thanks for the explanation... I got it now. Sorry if I sounded like an idiot.

Makes sense now. Learn something new everyday.

Thanks

Mike

That's what is so great about this place. No need to fear when asking questions or sounding dumb (i am an expert at asking dumb questions). Folks are great to share and help. Even when my CRS kicks in folks will give me the answer again