How long should my coach retain air pressure after I stop and shut the engine off?

Mine drops to 50 pounds in 24 hours.

Mine will drop from max (125 Lbs) to recharge (100 LBS) in 3-4 days.

A lot will depend on what the air system is responsible for. I only have disc brake actuators and emergency/parking brake. If you have full air suspension air pressure will drop faster over time.

I have 2 tanks, one for front brakes and one for rear brakes. A few years ago my pressure would drop at first 25-30 lbs over night and got worse with time. Finally it would drop to 0 over night.
Found the regulator separator between the tanks to have a leak. Replaced that and now the pressure will drop only a few Lbs in 24 hours.

If you have vacuum generator that is a venturi type (to run the HVAC controls), that will also deplete the air quickly over time.

What is yours doing?

The pressure will drop to zero overnight. I also have two tanks. I think there is separate pump for the AC system.

The system has an emergency valve that closes when the tank pressure drops to 65psi. If your shows less that valve is damaged or has failed. It is spring loaded and uses no electricity. It is located near the drier, whch can also be the culprit that is allowing the leak down. There are three valves in the electric compartment on my '93 that have 1/4 turn wings on them. You can connect a compressor or gauge to them and determine which system - front brakes, rear brakes or suspension is leaking. They are there to allow service without running the coach compressor.

I have been suspecting some of the same culprits. When I get the time I am going to start the coach and time the air buildup. The way it goes now is Air 1 builds up to around 85psi then Air 2 starts. Air 1 builds up reasonably fast but Air 2 is often agonizingly slow. Sometimes I am afraid that Air 2 isn't even going to start building up. After Air 2 reaches around 85psi both systems continuing to build pressure to around 105 or 110 psi. It usually never gets to 115 or so until I am actually driving and the engines RPM is higher than 800 rpm. It may be very informative to get actual times. I will update when I do this procedure.

Sounds like your issue is just like what I had. My two tanks is actually one tank with a divider in between. There is a regulator check valve between the two tanks known as pressure protection regulator. This regulator is what will allow tank one to fill first to 80+/- Lbs and then will open and allow filling of both tanks until the regulator on the compressor allows the compressor to freewheel, usually about 120 Lbs.

The pressure protection regulator serves two functions, the first as mentioned above and the second is to prevent tanks from depleting each other. As long as the system pressure, (the compressor and tank one) is above 80+/- Lbs tank two is connected and both tanks act as one. At about 90 +/- Lbs the compressor will again come on line and restore the system to 120 Lbs.

When parked and engine off the pressure protection regulator is there so that if either tank system has a leak, the system will deplete to about 65 +/- Lbs and the regulator will close and the check valve "should" prevent loss of pressure from the tank system that has no leaking.

In my case, the pressure protection regulator had a hole in the diaphragm of the regulator, the diaphragm separates the tank systems so with a hole there both tanks would go to "0" over night.

The pressure protection regulator I replaced is the one with the green air line connected to it. Find that device and blow some soapy water around it and I am sure you will see bubbles.

quote:

When parked and engine off the pressure protection regulator is there so that if either tank system has a leak, the system will deplete to about 65 +/- Lbs and the regulator will close and the check valve "should" prevent loss of pressure from the tank system that has no leaking.

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Thanks Ed, I did not know the check valve is why my tanks will stay at about 50 pounds for several weeks. Mine must be regulated to about 50 or the gauge is off 15 pounds.
Thanks Mwrench!

It may be that Gillig chassis has different regulator than Spartan chassis.

My original regulator would start charging tank two after tank one reached 60 Lbs. The new regulator starts tank two at 80 Lbs.

Originally my coach had two vacuum venturi generators in the air system used to run the HVAC controls and cruise control. I had a vacuum leak and a vacuum generator would continually operate drawing air. If the engine was off, the vacuum generator would continue to operate until air system got to 50 Lbs and then would shut off.

The vacuum generator also had a regulator that would shut off the vacuum generator if sir pressure dropped. Before I took out the vacuum generators, my air pressure would drop over night to 50 Lbs and then stay there for a week or more.

I replaced the vacuum venturi generators (NLA) with an electric vacuum pump for the HVAC and cruise is electric servo activated.

quote:

Originally posted by MWrench:
Originally my coach had two vacuum venturi generators in the air system

Ed I am pretty sure my 2nd venturi was removed when the cruise was replaced. Where was it located in the back? I have not come across it and don't hear it.

Yes there was one in front for the HVAC controls and one in the back about mid engine on the passenger side for the cruise.

I have finally been able to start up my coach and time the build up of air pressure. Here are the results.

Engine startup to Air 1 at 85 psi: 1 min. 18 sec.
Engine startup to Air 2 at 85 psi: 3 min. 13 sec.
Engine startup to Air 1 at 110 psi: 4 min. 3.8 sec.
Engine startup to Air 2 at 110 psi: 4 min. 9.4 sec.

Time between events:
From Air 1 at 85 psi to Air 2 at 85 psi: 1 min. 55 sec.
From Air 2 at 85 psi to Air 1 at 110 psi: 51 sec.
From Air 1 at 110 psi to Air 2 at 110 psi: 5.6 sec.
There are some times when I am seriously worried that Air 2 will never start to build up. When that happens again I will try and remember to time it. This time it performed as expected.

I then let the engine run at idle for about fifteen minutes and the pressure in both systems dropped to 108 psi.

Then I shut the engine off and observed the air pressures as follows indicated as AIR 1/AIR 2.
1 hr after shutdown: 55/50
2 hrs after shutdown: 45/32
3 hrs after shutdown: 40/32

I then went to bed and checked the pressures the next morning, about 11 hrs after engine shutdown. Both systems were at zero psi.

More to follow.