M923A2 not building pressure past 75 PSI

[vb1119]

My fire dept. has a m923a2 and it will not build pressure past 75 psi. both primary and secondary tanks fill evenly. if tanks are empty it takes about 5 minutes to build to that PSI at 2000 RPMs. The truck was at 140 psi and sat for 14 hours and primary tank is at 90 PSI and secondary is at 60 PSI, so no major leaks. no air is dumping into the intake u when its not supposed to. Q2 valve is working properly. I took the Governor line off the top of the compressor and there was no change. no difference if parking break is set or not. aslo just replaced the treadle valve. pressure protection valve seams to be working properly also. any Ideas?

 

[simp5782]

My fire dept. has a m923a2 and it will not build pressure past 75 psi. both primary and secondary tanks fill evenly. if tanks are empty it takes about 5 minutes to build to that PSI at 2000 RPMs. The truck was at 140 psi and sat for 14 hours and primary tank is at 90 PSI and secondary is at 60 PSI, so no major leaks. no air is dumping into the intake u when its not supposed to. Q2 valve is working properly. I took the Governor line off the top of the compressor and there was no change. no difference if parking break is set or not. aslo just replaced the treadle valve. pressure protection valve seams to be working properly also. any Ideas?

No air from the bottom of the air dyer? Can be hard to hear while the truck is running. This would allow it to dump air before ever reaching your tanks that the gauge reads off of.

You need to remove the line from the compressor. and install a fitting on that line that will allow you to charge the truck air system with a compressor from that line. Mostly its a 1/2" pipe into the back of the compressor and you simply just can install a gladhand on that and hook another gladhand on it. This allows air to go thru every bit of the system . Charging thru the gladhands bypasses the air line on the frame rail to the dryer from the compressor and the air dryer.


You may not hear a leak but the air dryer can dump all its air before you turn the truck off to hear it leak. It also will not let any air from the wet tank backfeed into it to leak since it has a 1 way check valve on it. The same with the primary and secondary tank they have check valves that dont leak back thru.

 

[vb1119]

No air from the bottom of the air dyer? Can be hard to hear while the truck is running. This would allow it to dump air before ever reaching your tanks that the gauge reads off of.

You need to remove the line from the compressor. and install a fitting on that line that will allow you to charge the truck air system with a compressor from that line. Mostly its a 1/2" pipe into the back of the compressor and you simply just can install a gladhand on that and hook another gladhand on it. This allows air to go thru every bit of the system . Charging thru the gladhands bypasses the air line on the frame rail to the dryer from the compressor and the air dryer.


You may not hear a leak but the air dryer can dump all its air before you turn the truck off to hear it leak. It also will not let any air from the wet tank backfeed into it to leak since it has a 1 way check valve on it. The same with the primary and secondary tank they have check valves that dont leak back thru.

ok so i found a few things. I traced the line from the compressor back to the air dryer, when the truck is running the dump valve is sticking open. the put a gauge on the compressor line, still only builds to 75psi at high idea and as soon as the compressor turns off it looses all air pressure in that line. i then back fed 50 psi in that line and found the unloader gasket was leaking and what sounds to air in engine. so new air dryer or rebuild kit and compressor are needed. also i was able to ajust the pressure protection valve back to 65psi because it was set at 95psi. tested governor and it starts blowing air at 130psi so it seems to be working also. am i missing anything else?

 

[simp5782]

ok so i found a few things. I traced the line from the compressor back to the air dryer, when the truck is running the dump valve is sticking open. the put a gauge on the compressor line, still only builds to 75psi at high idea and as soon as the compressor turns off it looses all air pressure in that line. i then back fed 50 psi in that line and found the unloader gasket was leaking and what sounds to air in engine. so new air dryer or rebuild kit and compressor are needed. also i was able to ajust the pressure protection valve back to 65psi because it was set at 95psi. tested governor and it starts blowing air at 130psi so it seems to be working also. am i missing anything else?

Sounds like you found it.

Try to redo the head on it and see if that will hold up.

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