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windydaboo · 07-31-2012, 01:09 AM

I have a 97 Discovery 36rs that has two propane tanks, one for the house and one for the genset. Because we can go weeks on the house tank but only a day or two of continuous genset use, I would like to find out how to connect the two tanks so that once the genset tank empties it switches to the house tank. I have seen TT's with auto switchover valves, could I install one of those to increase my capacity for the genset? It's a pain having to find propane every 2 or 3 fuel stops, especially since I have a full tank not being used. Has anyone done this mod and if so, what is needed? Thanks for the help.

jeffminsc · 07-31-2012, 01:27 AM

If it were me I would put a larger tank mounted in th frame. That way you could have 2 RV and 1big one for generator. But to answer your question yes you could hook both systems together and run a auto switch regulator. Hope this answer helps you. Jeff

windydaboo · 07-31-2012, 01:38 AM

I would prefer 2 genset tanks and 1 house tank. However, with the current 40 gal lp tank, a 90 gal fuel tank, and a 100 gal water tank, there isn't any more room for tanks down the centerline not to mention additional expense. Both tanks are filled in the side lp bay but the tank for the genset is only a fitting, no regulators or anything so I'm hoping someone has done this before and can let me know how they did it.

RV Wizard · 07-31-2012, 02:49 AM

If you are going to tie the two tanks together you will first need to find out if your generator is a vapor or liquid type unit. If you can photograph and post some photos I can help you out as to how to connect Genset to both tanks.

windydaboo · 07-31-2012, 02:56 PM

Quote:

Originally Posted by RV Wizard

If you are going to tie the two tanks together you will first need to find out if your generator is a vapor or liquid type unit. If you can photograph and post some photos I can help you out as to how to connect Genset to both tanks.

Whew, getting pics was harder than it sounded, but here they are:

I have a pic of the Genset lable, of the rear/house tank compartment where both tanks are filled from, and a pic of the fittings on the Genset tank. The fitting labled "liquid" goes to the genset, the top fitting is where it comes from the service bay/fill.

I greatly appreciate any advice you can give. I want to make sure it is done right. I really enjoy a large fire, as long as I'm not being engulfed in flames in the process

jeffminsc · 07-31-2012, 08:17 PM

Wow you do have a lot of LPG. OK from what I see in pictures your genset runs on liquid and you have no liquid outlet on house tank. While I still think you could run of of vapor there is no good way to tie the systems together. In hot weather you most likely could tie into the vapor outlet before regulator and run genset but in cold weather you would not have enough vaporization to keep up. Running of vapor alone could lead to a lean fuel mixture and do engine damage. So from what I see I would not recommend that you do this. If you want to go ahead you can pm me and I will tell you how but as I said I don't recommend that you do it. Hope this helps you. Jeff

windydaboo · 07-31-2012, 10:07 PM

Quote:

Originally Posted by jeffminsc

Wow you do have a lot of LPG. OK from what I see in pictures your genset runs on liquid and you have no liquid outlet on house tank. While I still think you could run of of vapor there is no good way to tie the systems together. In hot weather you most likely could tie into the vapor outlet before regulator and run genset but in cold weather you would not have enough vaporization to keep up. Running of vapor alone could lead to a lean fuel mixture and do engine damage. So from what I see I would not recommend that you do this. If you want to go ahead you can pm me and I will tell you how but as I said I don't recommend that you do it. Hope this helps you. Jeff

Thanks for the advice...
How do you know that the house tank valve is vapor? The outlet valve on both tanks is in the same location. I enlarged the pic a little and added arrows to show that there are two fittings already in the line (plus another quick connect on the genset tank for a bbq) I was hoping to be able to tie into one of those. One fitting is before the reg and the other is past it and they are different from each other. Is it possible that the fitting in front of the reg is liquid and the other vapor? Is there a way to find out without killing myself? I was under the impression that it was liquid from the tank and the reg turned it into gas, but I really don't have a clue. Thanks again for all the help...

jeffminsc · 07-31-2012, 11:40 PM

I'm on my phone right now. It's hard to hit these small letters so please forgive typos. When I get off work in morning I will get on home computer and respond better. But for now here is a quick LP lesson. Liquid propane expands 270 times its volume to become vapor. So 1 pound of liquid will become 270 pounds of vapor. Just to give you some idea what the difference is. Why is this important you ask. The line comming from the tank for genset is full of liquid so it will carry 270 more times the amount of fuel then the same size with vapor. So to hook up to vapor only the LP must boil in the tank to replace the loss of pressure. As the liquid boils it gives of heat but this heat is cold because LP is a cryogentic liquid so the harder it boils the colder it becomes in the tank as time goes by the tank gets so cold it cannot keep temperature to a level to continue to boil the LP and you run out pf vapor till temperature goes back up in tank. To answer your question about vapor on house tank all your other systems. Use vapor not liquid. The house tank has a pipe that goes up to the vapor space of tank so that you never get liquid. The tank for genset is called a motor fuel tank it has a pipe that goes down to the low part of tank so you get liquid all the time. Even though it is the same fuel in both tanks how you get it out is different. I'll give you more info tomorrow. Jeff

windydaboo · 08-01-2012, 12:03 AM

Very interesting Jeff, thanks for the lesson. I'll be eagerly awaiting your reply in the morning.
Of course if anyone else reading this post wants to school me as well, I'm all ears. (Well since I'm reading, I guess it would be all eyes!) This old dog loves learning new tricks!
Thanks,
Jason

RV Wizard · 08-01-2012, 03:10 AM

Jason, Jeff has covered this issue quite well and since your genset is set up for liquid LP It will not really be cost effective to try and retro fit genset into the house lp tank. Sorry, but you might want to consider finding a good diesel generator; possibly from a totaled out coach. This would be cost effective in the long run.

For those researching the reason you want a diesel generator in these units; this is a good example. Also LP is a lower btu rated fuel compared to gasoline or diesel.

windydaboo · 08-02-2012, 01:44 AM

Thank you Jeff and RV Wizard for the advice...

Replacing the Genset w/ diesel is out of the question until, if and when, this one gives up. I wasn't too keen on a LP genset when I was looking at this coach, however, this coach is the only one I could find that could sleep 8 (kids and their friends) and that is more important than what fuel the genset uses. Most DP's I came across are not family friendly and could only sleep 4.

I went to my local propane dealer/distributor today and they verified what I have already been told by you guys. They did make me a really nice hose to plug in my BBQ though.

After looking around under the coach I think the best solution is adding a 2nd tank, which was mentioned earlier. Now my problem is I can't seem to find a 40 gal lp motor fuel tank online. The rv sites I have found only go as high as 11.2 gal, which would be a waste of time and money.

Would anyone have any idea where I can find such a tank on the cheap?

Probably a stupid question, but since I can't see you roll your eyes or hear you bursting with laughter, I'll ask anyway... Would it be possible to use a vapor tank, but mount it upside down so the tube is in the liquid? That would certainly be cheaper and easier to find from a junk RV.

Thanks again for all the advice...

RV Wizard · 08-02-2012, 03:13 AM

The use of an ASME tank upside down will not work as the over fill protection valve float will not allow the tank to be filled. It will be upside down. Sure it can be rotated but it may not be at the proper height to only allow 80% filling. Also, the level gauge float will be upside down. Have you tried the manufacturer of tanks (Manchester) for a larger motor fuel vessel? You might find that you can install a larger one in place of the current tank.