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Topic: Treadle Valve Question (Read 640 times) previous topic - next topic

Treadle Valve Question

As I am under the steering gear box trying to find the oil leak that has left a 12" puddle under the front, I have been able to eyeball the treadle valve.  On the bottom of the valve there is an 'open to the atmosphere' port or opening, with no cover.  There doesn't seem to be any threads where there is something missing, but still...I did see one photo from several years ago where it seems that there is some kind of sight glass, or translucent cover over that opening.  Can someone enlighten me?
Thanks, Mike
Mike Brady
'97 U320 SE. #5137
'13 Honda Fit
Willow Springs, MO

Re: Treadle Valve Question

Reply #1 –
I Googled "treadle valve", went to images...lots of pictures.  The majority of them seem to have a kinda bell-shaped port on the bottom, labeled "exhaust".  If this is what you are looking at, then it is probably the exhaust port.  In which case I would imagine it should indeed be "open to the atmosphere", or at most covered with some kind of thin filtering device to keep dirt/mud daubers out.  Just guessing here - I'm sure you will get a more knowledgeable answer when everybody wakes up.

PS: More info here:    http://www.bendixvrc.com/itemDisplay.asp?documentID=4907
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Treadle Valve Question

Reply #2 –
It is conceivable there was some type of "chintzy" push in air filter just to keep stuff out. Thus there would be no threads to indicate a screen filter. Yours probably came out over time. I would check with the manufacturer--or FOT's Mike Grimes to find out what you need and where to get it.
Nitehawk,  Demolition Lady, & our NEW master, Zippy the speeding BB cat.
1989 Grand Villa 36' ORED
Oshkosh chassis, 8.2 DD V8
2006 Saturn Vue AWD

Re: Treadle Valve Question

Reply #3 –
A couple of things about treadle valves. When you step on the valve, the effort increases not from air pressure, but because a spring(s) is pushing back. The effort replicates the feel of a car's brake pedal and is designed to safely stop the coach without inadvertently locking the wheels. On our later fire trucks, the pedal effort was much less and all six wheels could easily be locked up with moderate effort.

Many air brake systems have a reserve tank and in case of total loss of air pressure, as soon as the treadle valve goes past a certain point, the reserve air is introduced into the system to stop the vehicle.

In case of maximum treadle valve application, the air system is designed not to allow a parking brake application to increase the pressure on the rear cans and possibly damage the components.

On manual shift vehicles, there may be an optional steering column hand operated valve to hold the vehicle on hills and not allow it to roll backwards while letting out the clutch. Later models had a return spring so the valve could not be accidentally left on or used to park the vehicle.

The parking brake releases air pressure allowing the springs in the REAR ONLY to deploy and apply pressure. The braking effort is only a fraction of the normal service brake operation.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Treadle Valve Question

Reply #4 –
Here is a great explaination of the treadle valve and it also ends with how the bottom exaust port comes into play.

TREADLE VALVE.dv - YouTube
 

Re: Treadle Valve Question

Reply #5 –
That is a pretty good video.  I guess there is some sort of cover missing, but not that critical.
Thanks, Mike
Mike Brady
'97 U320 SE. #5137
'13 Honda Fit
Willow Springs, MO