Parking brake leaking air while driving. HME chassis Luverne
Hi, long time reader. Seldom post.
Okay brothers, here is our situation. We have this 1994 HME chassised Luverne engine. It has disc brakes all around. When the guys go on a call they run thru town hitting the brakes and releasing them. Hitting and releasing them. Each intersection, each car in the way. All the while the officer is hitting the air horn. Toot toot!
What happens is the rear brakes overheat.
What I believe is happening is the air pressure is dropping. The compressor unable to keep up with the demands. We do not have a shore line for air so I cannot say what the starting pressure is. It could be 70 psi or could be the full 130 psi.
What appears to happen is as the pressure decreases so does the air pressure in the spring brake system. When the air pressure throughout gets down to about 80 psi the brake is applied. As the pressure declines it is applied more.
Is this the correct way it is to act on a 1994 Fire Engine???
I would expect there to be a check valve that would maintain the highest pressure within the parking brake. Then if the system pressure gets below a set point it would allow the spring brake to activate in some way.
Pressure Protection Valve
I knew I kept those old NFPA stds for a reason. NFPA 1901-1991 std. is what your 1994 chassis should have been built too. Section 3-4.1.3 c) pressure protection valve to prevent the use of air horns and other air operated accessories when the air system pressure drops to 80 psi.
Easy way to check is set parking brake in neutral and with the engine running, pump the service brakes until the pressure gets down to around 100 psi. Then blow the air horn until the pressure drops to 80 psi. The air horn should shut off and the pressure should not drop lower. 80 psi is enough to fully release the parking brake and keep them from dragging.
If your chassis doesn't have, need to call the chassis manufactuer and have them pay to install.