04-05-2014, 01:28 PM
The brake gauge dropping out faster than the supply gauge means that the larger leak is in the brake system. That certainly needs to be fixed as loss of brakes is seriously dangerous. The leak is most likely at a fitting but a leak in one of the brake tanks is also possible. There is a check valve to prevent a leak in the supply system from draining the air brake tanks back into the supply tank. I have had to replace that check value on mine.
The air bags are filled from rectangular tanks located along the coach rails. Those tanks, in turn are filled from the supply tank. The problem you are having appears to be that their are multiple leaks resulting in the brake tanks, the suspension tanks and the supply tanks all running out of air. To refill all of those tanks requires a significant amount of air. Both the engine mounted air compressor and the 120 volt air compressor feed into the supply tanks but air will try to go to fill the brake tanks first (larger hoses). It is common for the brake and supply gauges to go down at different rates but unless you are pumping the brakes, the supply tank typically goes down much faster as there are so many fittings and opportunities for leaks.
The best methods for detecting air leaks are 1) sound and 2) bubbles from spraying leak detector solution (or soapy water) on each valve and fitting. Where you see bubbles forming after the solution is sprayed on (or using a sonic leak detector when you hear the leak as the probe nears the fitting or valve) you have found one potential leak. You have to fix each one, air it up, confirm that it isn't leaking at that location any more and then move on to the next location. It takes time but eventually you will get it sealed up fairly tight and the system will refill much faster.
Check the ride height valves (one in the front near the center of the coach and one on each side of the drive axle) for cracking. I have had to replace all three of my travel valves. When the plastic cracks, they can lose an enormous amount of air but may only do it when the valve is in certain positions. I have one that when the coach was on a level surface in the shop at Newell, no leak. But as soon as I took it outside to a sloped parking space and started to level it, you could hear the air rushing out of the valve. The suspension six-packs (front and rear) are a potential source of leaks, I changed all of mine at about 13 years. It is also possible to have an air leak under the dash at the brake valve. It usually doesn't happen in 13 years but the individual air tanks can start getting pin sized holes from rust if they are not kept dry. I have put the lanyard type valves on mine so I can easily drain them. The downside is that the lanyard type valves tend to not center and leak more than the petcock drain valves that are typically installed. Not sure what is causing the air pressure to read differently when the key is turned on. I have a supply gauge that used to increase as soon as the pressure started increasing but now I see the brake gauges slowly increasing and when they get to about 40 psi, then the supply gauge jumps from 0 to 40.
The air bags are filled from rectangular tanks located along the coach rails. Those tanks, in turn are filled from the supply tank. The problem you are having appears to be that their are multiple leaks resulting in the brake tanks, the suspension tanks and the supply tanks all running out of air. To refill all of those tanks requires a significant amount of air. Both the engine mounted air compressor and the 120 volt air compressor feed into the supply tanks but air will try to go to fill the brake tanks first (larger hoses). It is common for the brake and supply gauges to go down at different rates but unless you are pumping the brakes, the supply tank typically goes down much faster as there are so many fittings and opportunities for leaks.
The best methods for detecting air leaks are 1) sound and 2) bubbles from spraying leak detector solution (or soapy water) on each valve and fitting. Where you see bubbles forming after the solution is sprayed on (or using a sonic leak detector when you hear the leak as the probe nears the fitting or valve) you have found one potential leak. You have to fix each one, air it up, confirm that it isn't leaking at that location any more and then move on to the next location. It takes time but eventually you will get it sealed up fairly tight and the system will refill much faster.
Check the ride height valves (one in the front near the center of the coach and one on each side of the drive axle) for cracking. I have had to replace all three of my travel valves. When the plastic cracks, they can lose an enormous amount of air but may only do it when the valve is in certain positions. I have one that when the coach was on a level surface in the shop at Newell, no leak. But as soon as I took it outside to a sloped parking space and started to level it, you could hear the air rushing out of the valve. The suspension six-packs (front and rear) are a potential source of leaks, I changed all of mine at about 13 years. It is also possible to have an air leak under the dash at the brake valve. It usually doesn't happen in 13 years but the individual air tanks can start getting pin sized holes from rust if they are not kept dry. I have put the lanyard type valves on mine so I can easily drain them. The downside is that the lanyard type valves tend to not center and leak more than the petcock drain valves that are typically installed. Not sure what is causing the air pressure to read differently when the key is turned on. I have a supply gauge that used to increase as soon as the pressure started increasing but now I see the brake gauges slowly increasing and when they get to about 40 psi, then the supply gauge jumps from 0 to 40.