Air brake systems and diagnostics

[DMiller]

Many of the Old World dump trucks I worked around YEARS ago never set up for trailers or pups and had hand valves, Driver could work the clutch & throttle, be dropping the load and using his hand to manage the brakes. Makes spreading much cleaner and precise.

 

[Truck Shop]

E7 valve.

 

[Truck Shop]

be dropping the load and using his hand

 

[doublewide]

From my manual;

 

[doublewide]

I will have to trace down the air lines coming into and out of the trailer control valve but, if I can trust the colors and considering that the valve is actuating the service brakes on the rear axle, I'm assuming that the trailer hand valve is currently plumbed into the primary air system and that it will need to be re plumbed into the secondary system. Notice the third smaller line at the back of the valve.

 

[mitch504]

One of the things I have thought about experimenting with on the spreader truck is two hand valves and two check valves plumbed into the rear wheel brakes so as to give me individual control, like a tractor.

 

[Birken Vogt]

One of the things I have thought about experimenting with on the spreader truck is two hand valves and two check valves plumbed into the rear wheel brakes so as to give me individual control, like a tractor.

http://www.vannattabros.com/truck6.html

 

[mitch504]

I haven't looked at that link yet, but I already know I love that Vannatta Brothers site, that was one of the very first things I found on the internet, back in the dial-up days.

 

[DMiller]

Will want to reroute the out line to that 2way check valve to the trailer glad hand side of TP valve off a secondary port.
The small third line most likely exhaust thru firewall into engine compartment.

 

[doublewide]

..... In all actuality it was installed for Just the truck brakes.

Yes. From the manual ;

 

[doublewide]

.......The small third line most likely exhaust thru firewall into engine compartment.

Yes. Exhaust through the firewall.

 

[Birken Vogt]

That is done that way to provide habitat for mud daubers and employment for mechanics.

 

[doublewide]

More on the trailer hand valve. With the air lines on the valve labeled and 'C' is exhaust, 'A' goes to the engine side of the Foot valve. It is connected to what I might guess is a double check valve with a stop light switch (also guess). 'B' goes to the left side of the cab side of the foot valve.

 

[doublewide]

My foot valve does not look exactly like the ones that I've seen from the Bendix website and the one that Truckshop posted above. It looks like 'B' is Primary supply which would make 'A' the Delivery side....

 

[Truck Shop]

What's that check valve in the last photo plumbed into?

 

[doublewide]

What's that check valve in the last photo plumbed into?

This one? Could this be a way of balancing the primary and secondary systems? From Bendix;
"BALANCED: PRIMARY CIRCUIT PORTION
When air pressure delivered to the brake actuators and air
pressure in the cavity on the delivery side of the primary
piston equals the mechanical force of the brake pedal application,
the primary piston will move and the primary inlet
valve will close, stopping the further flow of air from the primary
supply line through the valve. The exhaust valve remains
closed preventing any escape of air through the exhaust
port.
BALANCED: SECONDARY CIRCUIT PORTION
When the air pressure on the secondary side of the relay
piston approaches that being delivered on the primary side
of the relay piston, the relay piston moves closing the secondary
inlet valve and stopping further flow of air pressure
from the supply line through the valve. The exhaust remains
closed as the pressures balance."

 

[doublewide]

This is the right side of the valve 'in cab'. I still have to chase down where this goes.

 

[doublewide]

Question; Are the Primary Delivery ports 'common' ports? Meaning, The 1/2" green air line provides Primary air to the foot valve through the Primary Supply port on the engine side of the foot valve. Primary air is then available through any primary supply port on the valve without actuating the valve. If this is the case then primary air is being pulled off the primary air supply port inside the cab, plumbed through the supply port on the trailer hand valve, out of the delivery port on the trailer hand valve and into the double check valve on the engine side where it can supply air to the relay at the rear axle.

 

[DMiller]

Nothing is common to air brake systems
Will have two supplies both will feed a balance check for spring brakes then one feeds drive side service the other steer side.
Trailer will come off steer side for service.

 

[Truck Shop]

Notice the double check valve in photo, one hose comes from hand valve on one end of check, the check
is screwed into secondary/trailer/steer axle delivery port, then a hose runs from center of double check valve
back to tractor protection valve. This valve is a E6 but same basic principle. click to enlarge.