I got my school bus driver’s license just before I set out to buy a bus in the summer of 2021. I didn’t know whether the bus I would end up buying would have conventional hydraulic brakes as cars do, or pneumatic (air) brakes as many larger vehicles do. To cover all the bases I also studied for and took the test to add the air brakes endorsement to my CDL. This turned out to be helpful in troubleshooting the issue covered in this episode.The parking brake on my bus is an air brake. I can release the parking brake only if there is sufficient pressure in the air tank. Recently I discovered that an air leak was preventing the compressor from filling the tank. Until I got that fixed the bus could go nowhere. I have a roadside assistance program good for a tow to the dealership, but with the brakes locked, that would have been a challenge for a 35 foot bus.So with more than a whiff of desperation, I set out to diagnose and repair the problem, with guidance from the dealership. I bought and installed a replacement purge valve (crawling under the bus, with a tarp laid over a puddle of ice water - good times.)Apparently it’s not uncommon for air to leak from this valve. So if you own or may be buying a vehicle with air brake components, you may want to have a look at this short episode.Click the image below and watch episode 30 on my YouTube channel. And while you’re there, click the Subscribe button so you don’t miss subsequent episodes.