MCI air brake pressure.

[rgrauto]

1967 MCI -5A, when you apply the brakes,how much air pressure,PSI, is applied to the front and rear brake canisters,thanks Glen.

[buswarrior]

As much, or as little as you direct to them via the foot valve?

a typical boring stop at the corner stop sign might put 10 -15 lbs in the chambers?

happy coaching!
buswarrior

[Iceni John]

I have a dual air pressure gauge for brake application force, and a typical traffic slowing or stop takes about 20 to 25 PSI.   Over 30 PSI is a quicker stop than normal, and anything over 40 PSI is serious.   I think I would be launched off my seat if I applied full air pressure!   I have 6"-wide front brakes with 24 chambers, 10"-wide rears with 30/30 chambers, both with 16" drums, i.e. slightly larger than most buses.

John

[brmax]

Its great if you have a dual or seperate gauge showing the application as John has. The treadle is varible as we apply it.  So just viewing a single volume gauge can be tough.
What are you experiencing or just being curious is always good.

http://www.bendixvrc.com/itemDisplay.asp?documentID=6854

We have to do some math with that app psi to our chamber diameter size to get more info.

Floyd

[rgrauto]

The reason I asked ,this bus has never had enough stopping power to please me. Brakes are adjusted correctly,lots of friction material on the shoes so I was wondering will the brake valve apply the full 120 lbs. to the brake chambers.  MCI 5A, DD3 rear chambers. Thanks Glen 

[brmax]

Glen in shops many times they use an air brake balance test, just checkin out or troubleshootin obviously leaks but mechanical parts also at the tested axle. Also axlescan have different readings so some relays are to be corrected to a specfic set point or rebuilt. In any event most legal checks a 90psi minimum at the chamber when applied for a test.
When doing checks from mfg's they many time want an inital check of 75 minimum and then on to other progressive type readings and then generally lower test points. And so do ask for a smaller guage to check finer issues below 60. Relay valves can be a big deal in designed ways of a particular axle or say fleet type just as shoe surface choices. I can really only say a check of this type is standard on the ole sheet the shop foreman, would ask if the tech performed on a tough one.

Floyd

https://youtu.be/afyM_k9krRw

[buswarrior]

with some brass fittings and a pair of air gauges, loosen off a hose at a front and a rear brake chamber and measure the applications.

Relay valves are a hiding devil, they have been known to deliver less than called for air pressure.

And the typical brake checks won't uncover this.

happy coaching!
buswarrior

[uncle ned]

I believe there are several different kinds of brake lining for our coaches.

some softer that others.

and there is the lining for trucks that is very hard to make up for the weight.

uncle ned

[Oonrahnjay]

     I noticed that the video on the function of a relay valve shows "normal" pressure to the chamber as 30-psi with an "increased" pressure of 60-psi.  Of course, a simple educational exhibit should be taken with a big grain of salt, but since our systems run a basic pressure of about 120-psi, I thought that that was interesting.

[brmax]

I believe it may raise on that other gauge as the relay equalizes what it gets as a signal amount from the treadle. But i may have been doing popcorn 🍿 i have been known to do that in some shop training.
In any event im kinda glad its a varible or i would be doing the parking brake stops a bunch, them DOT guys would be stoping in for a coke cola sayin hey Floyd i see your doing some brake checks again, might as well go through the inspection papers.  

Have a good day there everybody
Floyd

ps. Them broken springs always drag last on break checks even though still wrkn?

I seen this video a it helped me see a regulating part of our basic air brake treadle valve
https://youtu.be/hU3aSQDfEcE

[rgrauto]

Thanks Guys for the advice,videos ect. I think the next step is to get some fittings , gauges and find out just how much pressure I'm getting at each chamber.  Thanks Glen,