One of the nice things about the bus is that it has an air system for the air brakes, which means that it has a compressor that runs off the engine with a mechanical pressure regulator and a dehydrator for the system, which doesn’t mean that it makes apple chips, but rather that it helps keep water from building up in the brake lines (which can be a big deal in the winter!). You might ask why this is a nice thing, since your car most likely gets along fine without such things.

Well, first, it offers the possibility of refilling tires if need be, or, if you like, any number of air-powered accessories, like tools (impact hammers/wrenches, drills, jacks, etc.), or an ‘air seat’ for the driver (highly over-rated from my experience on school buses that have them), or air suspension bags (to aid the shocks and smooth the ride), or to run air horns. However, one of the things that our bus didn’t have as part of its air system was an auxiliary tank.

Air brakes for a single unit vehicle only need one tank with three partitions. The first partition (wet tank) is the place where air is stored for future use, and to trap more of the moisture that might have made it through the dehydrator. The second partition feeds from the first tank and serves to provide air to the front brakes, and the third (also fed from the first) provides the air for the rear brakes. This is why, on a vehicle with air brakes, there are either two pressure gauges (one each for the second and third partitions) or a single pressure gauge with two differently colored needles, each indicating one of the two brake partitions. (Multi-unit vehicles with air brakes usually have a separate gauge for the trailer brake tanks.)

Now, some of the people on the Skoolie board had just tapped into the first tank for a ‘service’ air line for tools (or in a pinch, to hook a compressor to, in case the one on the engine failed), but it’s not something to tamper with if you want safe brakes. I wanted to be able to use an air line for tools, as well as run air horns, and have the possibility to upgrade to air suspension bags in the future if we decided we wanted it. In order to do this, we needed an auxiliary tank.

I found an auxiliary tank online that was a 20 gallon one that would fit alongside the air brake tank under the bus. While one might think that this would be a simple matter of running a line between that first partition of the brake tank over to the auxiliary tank, you can’t do that, because there is a maximum amount of time your air brake system can take to get up to “working pressure” of about 85 psi from starting with no pressure. If you hook a 20 gallon tank up to that first partition, you have to bring that whole storage area up to the 85 psi threshold within that minimum time, which just doesn’t work.

In order to get around this problem, I had to install a pressure valve in the line between the two tanks. This valve stays closed until the pressure in the brake tank partitions get up to about 90 psi, then opens, allowing the compressor’s air after that bring the whole system up to pressure over a longer period of time. One of the things that ends up happening here is that I have a lot more air available for my brakes when the system is up to pressure (120 psi), as the 20 gallon tank can feed air back to the brake tank as long as the system pressure is over 85 psi.

The pressure tank I got had a whole lot of ports, but none on what I wanted as the bottom (because of the placement of the ‘feet’ for attaching it), and one on what I wanted as the top, so I ended up having to support it from underneath, rather than bolting it directly to the floor. The location of this port to be facing down was important so that it could be used as a drain to get rid of excess moisture, and I did double-duty in putting in a pressure release valve in, so if the system over-pressured (150 psi +), it would let the excess pressure out and save other elements from stress. , but I could also manually activate it as a drain.

So, one port was the pressure relief valve, another was the air coming in from the brake tank, and, for now, only one port would be used for feeding up through the bus body to two air sounding devices. The first was a Leslie Supertyfon RS-3L that was originally installed on a Conrail Diesel locomotive that my father had acquired somewhere (more on this later). The other was an ‘air chime’ which, when used nautically ends up meaning an air horn, but in this case was the closest I could get to a steam whistle. It channels the compressed air through four different chime pipes, a rich sound compared to the air horn.

The next thing to do was to lift the tank into place, which is actually tougher than it sounds, as I was attaching it to the bottom of the floor and to the side of the bus’ ‘skin’ where it drops down.  In order to hold the tank in place, I decided to use a nice floor-jack and lift it, but this also was trickier than it sounds, as the tank was balanced just so and having the supports catch on the brake tank or the skin of the bus could cause it to tilt and slide off the jack.

To be continued (in Part II) …

And for a really nicely detailed explanation of air brake systems, look to this great Army informational film from 1967: