[Ran D. St. Clair]

Plumbers Rule

After installing my propane delivery system, I have a renewed appreciation for plumbers, but crack and all.

My primary concern was to design and build a safe propane distribution system that would stand up to long term vibration and not develop leaks, especially not leaks into the enclosed spaces like the living quarters. I figure a small leak into a well ventilated space, like under the truck, won’t do much except waste propane. As long as it can’t accumulate and find an ignition source I probably won’t blow myself up. A second concern is not to feed a vehicle fire that might get started from some other source. Of course, perfect safety isn’t an option. I do have other dangerous things in the truck like gasoline, diesel, etc.

Your typical home propane or natural gas installation involves hard piping to the vicinity of the appliance, and then about 5 feet of flexible stainless steel accordion tubing. That way they can plumb the house for a wide range of possible appliances and then you can hook up whatever you need. The long length of flexible tubing allows for a service loop, so you can plumb the dryer (or whatever) and then slide it into place with the extra tubing looped behind where you can’t easily see it or get to it.

I don’t like the idea of using that technique for an RV application. I am concerned that the long loop of flexible tubing will bounce, and possibly resonate with the road vibration, and eventually work harden and crack. I have similar, but smaller concerns with the solid copper tubing that is sometimes used with flare connections. I am using both the stainless steel flexible tubing and the soft copper tubing in my installation, but with special consideration for these concerns.

I decided to use heavy steel threaded pipe to connect to the appliances, in my case, the heater, range, and toilet. The heater for example comes with female thread for a 1/8” ID pipe that sticks straight down out of the bottom of the unit. Since it is mounted essentially on the floor, I can just drill a hole in the floor, screw in a section of pipe that extends through the floor and set it in place.

The range is plumbed in a similar manner except that I needed a combination of fittings to relocate the bottom facing 3/8” I.D female threaded coupling to miss a floor joist. Once the range is bolted in place I can insert the pipe through the floor from underneath the truck and then plumb it from there. In both cases I made sure that there was clearance between the pipe and the hole in thefloor so that any slight movement of the appliance would not stress the pipe or the joints. I will fill that gap with foam rubber insulation to reduce air intrusion later.

The toilet is a little different since it has a solid but soft copper tube with a compression fitting that comes out the back. I mentioned in earlier posts that I am not happy with how that pipe is supported even internal to the toilet so I added brackets to keep the internal regulator from bouncing around. In this case I brought hard steel pipe up through the floor where it is solidly mounted. I then used the appropriate brass fittings to connect to the shut off valve that comes with the toilet. From there it goes through the compression fitting and the soft copper pipe into the toilet itself. All of these appliances are firmly mounted to the floor, or in the case of the heater to the wall.

Once under the truck, there is a short length (about 1 foot) of the stainless steel, plastic coated, flexible accordion pipe that connects the appliances to the main distribution pipe. The idea is to mechanically decouple the main distribution piping from the individual appliances. I don’t want any heavy weights or long lever arms attached to the appliances that would put stress on any of the pipes or joints or the internal regulators. It would also be very difficult to get everything to line up perfectly if it were all hard piped, so the flexible tubing allows some dimensional slop and simplifies the design and installation.

By keeping the flexible tubing short and well supported, it is less likely to bounce, work harden, and crack. Also, If I should ever develop a small leak under the truck, the propane will just waft away, never reaching the concentration required to burn. Propane needs to be between 2.15% and 9.6% of the total propane/air mixture in order to be combustible.

My generator bay holds my two standard 5 gallon propane tanks, of the sort you would typically see used on a home barbeque. I am only using one tank at a time, so the other tank is just a spare. I am not crazy about having the propane in the same bay with a running generator, but there is no logical problem with it. The bay has a large filtered air inlet in the floor to provide cooling air to the generator. Propane gas is about 1 ½ times heavier than air, so any leak within the bay will drain out the large hole, hopefully before reaching an explosive concentration. When the generator is running, it could provide an ignition source, but the generator also pumps a large quantity of air through the generator bay for its own cooling. The propane leak would have to be massive in order to reach a combustible mixture.

I am using a standard barbeque style regulator that is connected to the propane tank. I have been warned that these regulators are for low volume use only, but fortunately all of my appliances require a low volume of propane. The regulator comes with a short length of rubber hose, which allows me to connect to either of my two tanks. I do not have any fancy system for disconnecting one tank while maintaining a continuous supply of propane from the other, at least not yet. The rubber hose has a flare connection which connects to a ¼ turn ball valve, and is hard mounted through the side of the steel bay.

Immediately on the back side of the steel bay is what amounts to a propane fuse. If a pipe should ever break and allow a free flow of propane, this safety valve will close and shut off the flow. It’s a clever magnetic technology, available at any home improvement store, and not even expensive. From there it goes through another short length of flexible stainless steel plastic coated accordion tubing to the main distribution piping.

The main distribution pipe is all standard ½” steel threaded “black” pipe. For some reason I don’t fully understand, I was told not to use galvanized pipe, but the availability of some fittings and lengths may dictate otherwise. I won’t bother with the details, as your installation will obviously be different, but there are a few things I learned. Don’t try to use 3/8”, ¼” or even 1/8” steel pipe except at the ends of the run where you might need to adapt to whatever the appliance requires. I would be concerned about the resistance to flow if you had to go very far, but beyond that, ½” pipe and fittings are just more available.

The distribution pipe is strapped to every floor joist and about every 18” when running along the underside of the wooden floor. I used standard straps for electrical conduit with wooden spacers where needed.

I marked the location of all the appliances and gas lines on the floor of the truck and then drew in all the piping in between. That helped to visualize the whole thing, at least in 2 dimensions. In some cases it was necessary to test fit various end sections in order to get an accurate measurement for the pieces in between. It took about 5 trips to the hardware store to figure out the best combination of pipe, couplers, etc., and I will admit to having a few pieces left over.

Don’t forget to allow for the change in length as you tighten the various fittings. Also, don’t forget to allow clearance for the next elbow, or whatever, to spin 360 degrees when it is installed. Sometimes it is very difficult to get a wrench where you need it, and sometimes you have to really think about the order of operations in order to get it done. It’s a 3D puzzle with multiple solutions. Some involve more swearing than others though.

All that planning paid off, because once I began the install, it was done in about 8 hours, with no real surprises. It can be quite a challenge to get the piping into place. I used standard lengths of pipe and nothing longer than 30” so I could work it into place above the truck frame.

The night before the install I used a wire brush to clean all the male pipe threads and then cleaned all the pipes and fittings with soap and water to remove any protective oil. Warning, pipe threads can be sharp.

I used TFE Paste pipe thread compound. You can also use Teflon tape, though I gather you need to use the yellow stuff for gas lines, not the white stuff that you would use for water lines. I am not sure what the difference is though. The TFE paste can be messy and more than once I touched the gooped up threads to something rusty or dirty, and had to clean the threads and reapply. It helps to have a roll of paper towels under the truck when installing pipe.

I leak tested the whole thing with soapy water when it was done. I actually did find one flare fitting that needed to be tightened. I hadn’t tightened that one fitting as much as I would normally because the heater was only installed temporarily for testing.

Two of my flexible pipe sections are literally within a stone’s throw of the left rear tires. I will be making some loose fitting aluminum covers to protect them.

I would be very interested in hearing comments from any “real” plumbers out there. I do my best to think about what will be correct and safe, but I don’t claim to know the various codes or how they apply to an RV application.

As always, pictures are available under keyword “Stealth”.

To be continued….