Air brake system - any experience - equipment recommendations? $150 name brand tester found zip, gun shy getting too spendy for limited usage, anyone lease them? Thanks - John

I have and use an Amprobe ultrasonic leak detector on air brakes. It works well. When using it on an oil burning engine the atomizer and blower create so much background noise that it is almost impossible to use. We charge the air system from the house air and search air leaks when the engine is cold and everything is quiet. The model we have, ULD-300, has several options for listening and many settings for sensitivity which meets our needs well. It is a piece of testing equipment and so needs to be treated accordingly, it will suffer if not used carefully.

.

Kelly reminds me of an experience I had when I served on the Amtrak BOD. We were asked to authorize a multi million dollar purchase order to buy test equipment to indicate where rough track existed and needed to be fixed.

I recalled riding with my Dad as a young kid on his CRRofNJ office car. Under the desk in the left rear seat position was a pedal which when pushed discharged yellow paint onto the track when rough track was experienced. That yellow paint on the ROW told that section gang to fix that rough spot.

At the start of each journey Dad always filled a tall water glass almost to the brim and placed it on a freshly starched white napkin on that rear desk and he would note at the end of each segment if the napkin remained dry.

I suggested to our staff that perhaps we could use the millions better elsewhere and use my Dad's old fashioned methods?? They said it wouldn't work in the "modern" world.

We bought the expensive new stuff which I'm guessing didn't tell them anymore than the yellow paint pedal and dry napkin did???

Ross Rowland

Put a ball bearing in a larger metal hemisphere so it can roll in any direction. Place an insulated metal ring at the top edge, so the bearing will close a circuit if it rolls too far. Use this to energize a solenoid with a return spring that works the 'pedal' when someone isn't sitting ready to mark it...

A similar approach was quietly used to redesign the main arch supports on the Hernando de Soto bridge in Memphis. The bridge and its piers can move more than several feet out of line, and will come back to stable equilibrium afterward. Gives you some idea of the expected displacements from a New Madrid fault event...

We had an Ultraprobe that also had a Stethoscope probe. We used stethoscope to find water and steam valves that wouldn't shut off tight and to check steam traps. If your amprobe has a probe you would need to check every fitting or valve by touching it with the probe. I would emagine with microphone you would have to get pretty close to a leak to detect it, up in the underframe of a car.

WABCo always uses/used soap suds, soap suds for detecting leaks, not detergent suds nor "modern-day" leak detection fluids. This probably has to do with soap's inability to react with the rubber goods and lubricants inside the valves. When it comes to internal leakage tests, every leakage port on every test rack I've ever encountered has been coated with a thick layer of slimy soap residue.

Joy dishwashing liquid. A good healthy squirt of it in a spray bottle with softened or distilled water. Use it liberally. The tiniest of leaks will grow a bubble beard after a few minutes. I have yet to run across another soap product that foams as well as Joy.

My two cents.

Older WABCO test codes specify leakage limits in terms of bubble timing, e.g. "a 1/2 inch bubble in 10 seconds is permitted." Not very scientific! Later test codes used a "Leakage Indicator" which is essentially a manometer. You press the hose into the port which is leakage and time the rise of the water between two marks. Don't try putting the valve into release while doing this or you'll get a shower! The last generation of test codes refer to a "flowrator" which is a modern, variable area floating ball flow meter, and give the leakage figures in scim (cubic inches per minute at standard temperature (room temperature) and atmospheric pressure).

Typical numbers are 3 scim to 25. This is for things such as the lap of a slide valve on its seat. The leakage rates for valves and fittings is much lower.

By comparing different vintages of popular test codes, one can create a map between the "calibrated bubble" method and actual CIM. Unfortunately I can't find my notes at the moment. But I did this once and concluded that the viscosity of the bubble fluid that WABCO had in mind was much thicker than what you'd get with say dishwashing soap and water. I should try mixing up a small bar of Ivory soap in water and see how that reacts.