Re: Parking break release
Posted: Mon Feb 10, 2020 10:49 am
Well Walter, prepared to be underwhelmed.
First, a very special warning: modifications to air brake systems must be done with every consideration that the modification will not affect the function of either the service brakes or the parking brakes. If a modification is made, the whole braking system must be tested using DOT test procedures. Further, I am not an air system expert and I am only describing what worked for me.
The simple answer that worked for me was to simply remove the service interlock valve from the system. The modification was very simple as shown in the photo below:
The service interlock valve is shown on the right and the simple bypass line is shown on the left.
This essentially connects the PP1 (parking brake valve on dash) directly to the diaphragm which compresses the parking spring (via the normal relay valves).
I made this modification many years ago and it has worked flawlessly since then.
Again, I want to make sure that it is clear that I did a ton of testing before I put the bus back on the road. On paper, it would appear to be a straight forward modification, but air brake system are complicated.
I did not do a good job of documenting the function of the PP1 valve. My best recollection is that I used the original Eagle PP1 valve, but I think I had to remove one air line. Best guess is that it was a small air line to the service interlock valve that provided a signal to move the check valve.
Jim
First, a very special warning: modifications to air brake systems must be done with every consideration that the modification will not affect the function of either the service brakes or the parking brakes. If a modification is made, the whole braking system must be tested using DOT test procedures. Further, I am not an air system expert and I am only describing what worked for me.
The simple answer that worked for me was to simply remove the service interlock valve from the system. The modification was very simple as shown in the photo below:
The service interlock valve is shown on the right and the simple bypass line is shown on the left.
This essentially connects the PP1 (parking brake valve on dash) directly to the diaphragm which compresses the parking spring (via the normal relay valves).
I made this modification many years ago and it has worked flawlessly since then.
Again, I want to make sure that it is clear that I did a ton of testing before I put the bus back on the road. On paper, it would appear to be a straight forward modification, but air brake system are complicated.
I did not do a good job of documenting the function of the PP1 valve. My best recollection is that I used the original Eagle PP1 valve, but I think I had to remove one air line. Best guess is that it was a small air line to the service interlock valve that provided a signal to move the check valve.
Jim