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Senior Member
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Discussion Starter #1
how can I adjust the pressure the governor allows the compressor to build? I installed a new compressor yesterday, and at first the pressure would build to 130 psi a few times (which is high I know) but now it will only build to about 110-115 (the 2 needles aren't even with each other, never were).

I removed the plastic cap on the end of the governor, and there is a lock nut and the bolt has a slot to turn it. I'm guessing thats all I need to do, BUT if I push on the end where the bolt/jam nut are the whole inside of the governor moves, like there is some free-play in there. do I have to set it at a certain free-play, or just adjust the bolt/jam nut to I get the desired pressure.

I know this is probably easy but I don't want to screw anything up.
 

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Highway to Hell
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130 is normal for todays trucks 120 was the cut out on older trucks but it seams that they upped the psi cut out a little.

I think the tighter you turn in the bolt screw etc.. the higher the cut out will be. Its been a few years but I think thats how it works.

last week I started the truck after 4 weeks of sitting It started fine but the compressor never cut out . I was at 155 psi!! I pushed inthe trailer emergency and drained the air tanks to get it back down. I was worried about it that high and still very cold.
 

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TDG Mafia Member #64!
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Not saying its good on things but we had a freightliner century that had over 175 in the tanks, the truck was hooked up to the shop air that cut out at 200 so we got lucky with no damage.
 

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To answer your question, and it is a good one, turn the screw with the slot in it (under the plastic cover) OUTWARD to increase the govornor cut-out pressure setting, and INWARD to decrease it. When you are satisfied with the setting, tighten the jam-nut while holding the slotted screw firmly, then replace the plastic cover.

Cut-out must be measured with an accurate gauge, and after the compressor has stopped pumping. So, don't measure cut-in. The differential pressure (cut-out minus cut-in) is not adjustable.

130 PSI is the current standard, but anything from 120 to 130 is acceptable.

Every vehicle with air brakes leaves the factory with a safety valve that as others have mentioned, "pops" at 150 PSI to prevent a tank from exploding. Most modern systems have TWO. One on the "wet" tank (as ALL systems MUST have), and another at the compressor discharge to save the compressor in the event of a discharge line freeze-up.
 

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Discussion Starter #6
thanks John_G, I'll give that a try. I appreciate all the help!!
 

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dondiesel444 said:
I removed the plastic cap on the end of the governor, and there is a lock nut and the bolt has a slot to turn it. I'm guessing thats all I need to do, BUT if I push on the end where the bolt/jam nut are the whole inside of the governor moves, like there is some free-play in there.
There isn't much inside of the governor. Basically a plastic or nylon plunger with a couple of o-rings on it, a spring.
 

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TDG Mafia Member #64!
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chris142 said:
Your supposed to have a pop off valve in the system. If I remember corectly it should pop @ 150 psi.
This thing never popped, mabye its something to do with the air dryer? if so you have to have the key on. who knows:squish
 

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Shouldn't need to have the key on for the pressure relief. It is a spring loaded valve.
 

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Discussion Starter #10
when I installed a new governor on my old Mack, the first time I started it the pressure went to at least 150 and then there was a wierd noise as the pressure blew off somewhere in the system. I'd think all trucks would have this as a safety...
 

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Hybrid_4x4_Superduty said:
This thing never popped, mabye its something to do with the air dryer? if so you have to have the key on. who knows:squish
It's just a simple mechanical safety valve.

You SHOULD never hear it, unless something is bad-wrong with the air govornor.
 

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Fire App. Mech.
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John_G said:
Every vehicle with air brakes leaves the factory with a safety valve that as others have mentioned, "pops" at 150 PSI to prevent a tank from exploding. Most modern systems have TWO. One on the "wet" tank (as ALL systems MUST have), and another at the compressor discharge to save the compressor in the event of a discharge line freeze-up.
The one on the compressor head is supposed to be a special 250 psi model just for that purpose. The pulses the compressor puts out in normal operation will often be over 150 psi therefore popping a regula valve slightly and wasting air. The purpose of saving the compressor is to prevent shards of it from getting loose inside the diesel engine!

I agree governor settings are to be done with a known accurate test gauge only, dash gauges are next to worthless.

Birken
 
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