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CATEGORY LISTINGS > CATERPILLAR > Air Compressor / governor problem. [ REFRESH ]
Thread Title:

Air Compressor / governor problem.


Created On Friday November 22, 2013 21:02 Diesel Talk
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GSSign
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Note Friday November 22, 2013 21:02 View thread in raw text format
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Hay guys, not a Diesel topic but here goes.

1999 FL70 Freightliner 3126

While on the road I noticed when the air released it sounded different than usual for a few cycles then went back to normal for a few cycles. Now while at speed, the air releases every 4 seconds and releases for about 2 seconds.

I still have a constant 120PSI on the gauges.

I am guessing that the governor is failing causing the compressor to produce constant output. Until doing a little reading, I did not know the compressors were governed, I thought that the release valve just popped when the right pressure was reached. Rarely are things as simple as one would guess.

Does this sound right.

I have replaced chambers and such but have never worked with the actual air system.

Any help would be greatly appreciated.

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JoeZ
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Note Saturday November 23, 2013 05:43 View thread in raw text format
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If you are maintaining constant 120psi and not going over that or dropping to where the air compressor is kicking on and cycling again, either your air drier is going off erratically or your safety valve is defective. When you are building up air pressure, you should see the needle on the gauge flicker when the air governor cuts out.

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One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.
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GSSign
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Note Saturday November 23, 2013 20:58 View thread in raw text format
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JoeZ, thank you for the info.

I replaced the governor but this really did not change anything much. For 18.00 bucks, it was worth it to eliminate it.

At 1500 rpm or so, how often should the relief valve at the bottom of the dryer pop off?

Mine is now popping off every 10 to 12 seconds or less. Will be even less at 2,200 rpm at interstate speed.

I always have steady 120 lbs of air and I can see the gauges twitch when the governor cuts out

I did not drive the truck today, but last Friday, the pop off was so often that it would drive you nuts listening to it, even parked it was very excessive.

So when the compressor builds pressure, the governor puts pressure on the unloader to allow the compressor to stop building pressure. Until the brakes are activated or the system leaks down the compressor should not be building pressure. When the system bleeds down or the brake is activated, the governor disengages the unloader to allow the compressor to start building pressure. Is this correct? If my unloader is operating properly, I would not think that the release valve should be popping every 8 seconds or less should it?

When the pop off releases, the volume of air and pressure is quite violent, it is not just oozing out a little air, it has enough pressure and volume to erode the gravel where the truck is parked and loud.

At what pressure is the pop off suppose to release? And how often is average?

Thanks again for all of your help.
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Brent
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Note Saturday November 23, 2013 22:08 View thread in raw text format
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I had a air dryer last week that the check valve inside of it went bad and when it popped it was draining the wet tank to until the compressor kick back in. Its a milk truck and had to go and didn't have a new dryer so I put a check valve at the wet tank and fixed it. Put a gage in the wet tank and watch it if it drops off when it pop's. It should stay up in pressure till something use air and tells the governor to kick in.

Brent
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JoeZ
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Note Sunday November 24, 2013 06:12 View thread in raw text format
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There is a major sound difference between the air drier and the safety valve. The drier is a steady hissing sound and the safety valve is more of a buzzing sound. If you look at the safety valve, you should see evidence that it has been popping off. Also, you should be able to duplicate the problem by parking on a level place, block the wheels well, release the brakes and just run the engine up until it does it's thing. You can probably see the drier without crawling under the truck. Try that.

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One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.
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GSSign
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Note Tuesday November 26, 2013 17:05 View thread in raw text format
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Well I guess I was wrong, after replacing the governor and driving the truck Monday, nothing has changed.

After doing a little reading, it is the purge valve mounted on the bottom of the dryer. I guess you guys already knew that. I just did not know what it was called.

How do I know if it is working properly. I know that it does not sound like it has for the last 10 years that I have owned/driven the truck so I would think that this is the failing part. It does not leak off or anything, it just releases air every 4 to 6 seconds. Has the valve gotten weak and releasing air before the governor can kick out the compressor?

The purge valve has a heater and thermostat so it is not cheap. I can get one on ebay for 50 to 80 bucks, not sure what my local dealer is going to charge.

Is this my next step?

Thank you for helping.
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JoeZ
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Note Wednesday November 27, 2013 06:50 View thread in raw text format
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Just change it, bite the bullet....cleaning may help but not for long.

-------------------------
One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.
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GSSign
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Note Friday November 29, 2013 17:03 View thread in raw text format
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Getting irritated.

Changed governor, new unloaders, new purge valve. Nothing changed.

Sprayed soap/water on lines but have not found leaks. What else can I do? Replace line form dryer to governor?

I can have the brakes engaged or disengaged with the truck shut off and I loose no air all day.

Can it be the check valve in the delivery port in the dryer? The dealer did not have one in stock or I would have replaced it also.
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Brent
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Note Friday November 29, 2013 17:28 View thread in raw text format
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That is why I like to put a gage in the wet tank. If the tank drops off after the purge valve goes off. Find out where the air is going. Sometimes the fan hub is hooked into the wet tank and will drain it but not real fast. If the air is going out the purge valve and you can't get a check valve put a inline check valve on it or replace the hole dryer. Replacement is probable the best. What dryer is it?
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GSSign
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Note Friday November 29, 2013 18:09 View thread in raw text format
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It is a Bendix AD-9.

Well I hate to replace it if it is not bad but I have put enough in it now to have bought a reman. dryer.
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JoeZ
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Note Saturday November 30, 2013 06:40 View thread in raw text format
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From what I gather, you have detirmined the air release is coming from the purge valve on the drier. Have you fully serviced the drier? The purge valve is designed to release air with the cut out of the air governor. If it is constantly releasing air, either the compressor is cycling, there is a restriction in the line or the drier is malfunctioning. It's a fairly simple system.

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One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.
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trukdoc55
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Note Friday January 10, 2014 17:52 View thread in raw text format
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What it sounds like is the safety valve popping off. It is supposed to hold pressure to 150PSI and is a safety for the D2 air governor. If it is popping off at 120 it is no good and needs to be replaced. It is on the wet tank, this will be the first tank after the air drier. Usually 1/4 NPT with a round head not hooked to anything.

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Rupey's Diesel Service
Saltillo, Texas
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mobiltech
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Note Monday January 13, 2014 06:50 View thread in raw text format
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If anything in the unloader circuit is leaking it will keep cycling the governor and the dryer will blow off repeatedly. If you cant find a leak in the governor line to the dryer or a leak at the governor to compressor then it could be leaking on the seal inside the compressor on the unloader piston.

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mobiletech

Edited: Monday January 13, 2014 at 06:51 by mobiltech
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