Auxillary Compresser

[dale farley]

My Jun-Air compressor started acting a little strange this morning. When I turned it on, it pumps up to about 105 then pops off and bleeds down to about 75-80 lbs, then repeats the cycle. It takes a little less than two minutes to pump back up to 105. I have what appears to be a standard regulator, but I'm not sure if there is any adjustment to it or if I just need to replace it. Input would be appreciated.

[JIM KELLER]

Most common problem is the checkvalve.

[dale farley]

Jim,

Would the check valve be under the cover I am showing? I was thinking it was external to the regulator. I have never worked on one of the regulators, so I don't really know how it works.

[Gil_J]

What you are showing is a common well pump pressure switch. Some are adjustable, others are not. That, as you've described the symptoms, shouldn't be your problem. Your switch is turning off the compressor and then something is draining the pressure. There are so many places to look that a single answer isn't going to help. You say something pops off. That could mean you are hearing the air discharge. If so, localize which direction it's coming from.

It's possible, it's not a leak. Some aux systems are tied into Prevost's aux system and others are not. If it is, there is a protection valve between the 2 systems. If will not let the Prevost side feed the aux side unless the Prevost side is somewhere between 60-75 psi (or there abouts). I think, but know for sure, that the protection valve works both ways. To rule this out, simply start the coach and air up it's air system, turn off the coach, and see if the compressor still has a rapid drop in pressure.

[dale farley]

With the cover off, I can see something move (like a pop off) and then the air escapes inside the regulator.

[garyde]

The label says off at 100 psi so try adjusting opening it up some more.

[JIM KELLER]

Dale, Everything Gil said plus another back door testing approach.

With the Aux Compressor off start the Bus and watch the dash guage to see if the engine compressor is having the same issue keeping the air pressure supplied. Still sounds like the checkvalve.

[Gil_J]

Dale,

Here's what the inside of your switch should look like. There's isn't anything that should leak air and if it did it should be constant.
13279

Do you have a pressure relief valve on a T below the switch, maybe? They look like this:
13280

[JIM KELLER]

Gil, Boy you are computer savvy ! I can't even post a picture.

[dale farley]

The picture shows the right side of the regulator. You can see the adjustment spring just to the left of the pop off valve. The "L" shaped arm on far right is the pop off. When it reaches about 105 lbs, the arm goes down pushing the plunger that you can see in the picture. The plunger then releases air through 2 or 3 holes in the connector. You can see one of the holes just above the nut that attaches to the blue hose. The blue hose connects directly into the main line that attaches to the compressor.

I checked the compressor again before starting the bus. My bus air was over 100 lbs before turning on the compressor. The results were the same as yesterday. Ran until it reached about 105 lbs, opens the valve and bleeds to about 80 then the compressor runs again and repeats the cycle.

I then started the bus and ran it until it spit. The auxillary air gauges increased to about 120 and then fell to about 110. When the pressure on the auxillary reached about 105 the pop off valve in the picture opened again. Once the bus spit, I shut it off and the auxillary continued to bleed down until it reached about 80 lbs. Of course this didn't affect the primary air which was about 128.

[jack14r]

The L piece is opening a valve to release the head pressure on the compressor in order to help it start easer for the next cycle,it should only release air from the head pressure.

[dale farley]

As can be seen in this picture, the blue line goes straight from the relief valve in the pressure switch to the main compressor line. I don't see any other relief valve in the system.

[Gil_J]

Okay, now we have that thing positively identified. I've never seen one with the pressure relief/unloader option. Of course, I haven't seen many. Most compressors have the pressure relief mounted on them. The unloader function reduces the compressor's head pressure when the switch turns the compressor off. If the pressure relief function is not discharging air when the compressor is running, then it must be related to the switch. Although I couldn't find that exact model number I would guess the differential pressure should probably be 40 psi and it appears yours is set to about 30 psi 105-75, which may be correct. I'm guessing the level is depressing the unloader until the pump starts again. That's not correct. The lever should release pressure, then release the unloader to close and at some lower pressure start the compressor again.

If the unloader is triggered at 105 psi and you don't have a regulator between Prevost air and the aux side of the system, the unloader is going to be activated most of the time when driving. Even if the well switch is defective, replacing it with one that activates at 105 psi is not going to solve the problem when the engine is running, again unless there is a regulator between Prevost air and aux. From your description of the symptoms there is no regulator.

Let's backup a bit more. The unloader/pressure relief valve should have pressure markings on it. What is the pressure relief rating? It should be equal or less than the compressor's rating. What is the compressor's rating? If the compressor's rating is greater than the Prevost air system, then no regulator between the systems is needed. Is the unloader function necessary? It might be if the compressor maintains head pressure after it stops. Okay, lots of questions. So, where to start. If this air leak is something new, then your first step is determining if the switch can be adjusted or needs replacement.

Here;s the closest match to your switch: http://www.midwest-control.com/square_d_pressure_switches_9013FHG_up_to_230_large r.html

[Gil_J]

Our posts crossed each other. There's isn't a need for another pressure relief valve. The unloader appears to be configured as it should where it only unloads the compressor head pressure. That should be a check valve north of the T and attached to the yellow hose. That means Prevost air should not make it to the pressure relief/unloader valve. Check that check valve. This must be the one Jim was referring to.

[dale farley]

Looking at my receipts, I see that Parliament did install a brass check valve at the January rally. They changed all the fittings and added the water and oil separators at that time. Yesterday is the first time I have noticed the problem, but I assume it could have been doing it all the time while driving, and I would never have known the problem was there. I hardly ever run the compressor when the bus is in the garage. I did it yesterday because the belts were down and I didn't want to start the bus until the air tightened them. they normally stay tight for several days.

[dale farley]

The Jun-Air max pressure is 150 lbs. I assume the valve that is shown in the picture just above the T (below the yellow line) is a check valve instead of a relief valve since there is no vent to it.

[Gil_J]

Yep, the pressure relief valve is the one you hear air coming from.

[Joe Camper]

Gill U said

Here's what the inside of your switch should look like. There's isn't anything that should leak air and if it did it should be constant.

Not entirely correct. That regulator has a diaphragm with about 8 screws holding the 2 halves together.

Look at it from the bottom. I have replaced more than a few that were bubbling from that diaphragm flange.

I am pretty sure this is not Dales problem.

Some of the limits allow adjustment on both cut in AND cut out but not all. Most can only adjust a 20psi operating parameter up or down. Some others can make the cut in and cut out wider or narrower.

I put a manual override switch on mine so I could run it up to 120psi right before bedtime keeping it from running overnight. During auto operation I had it cutting out at 70psi.

[dale farley]

From all the comments and from the looks of the unit, it appears to me that my problem has to be with the switch. Is the screw on top of the spring the primary adjustment and is that where I should start?

[JIM KELLER]

Checkvalve checkvalve checkvalve.

[Gil_J]

Ditto to what Jim said. Very little air will come out of the unloader if the check valve is working.

[dale farley]

Jim,

Sorry I'm so slow at times, but I guess that the advantage of discussing things on this forum. They "may" eventually sink in! I got so hung up on the regulator that I was determined that had to be the problem, but after rereading all the posts, I think you were right in your initial and final diagnosis. The check valve does seem to be the problem. As stated in the posts, when my compressor shuts off, it should release just enough air to relieve the pressure from the compressor head, but if the check valve is bad, it will let the air continue to return out of the system until the pressure drops below the lower limit and turns the compressor on again starting the cycle over. I was thinking that since the valve is relatively new, it should be something else, but it may have been bad from the very beginning. I don't know if there is a warranty on such parts or not?

I see prices on the same Parker check valve from $13.53 to $57, so I think I will get the $13.53 one.

[JIM KELLER]

Parts purchased at a Rally event are not warranted.

[dale farley]

I ordered the original Parker valve and one for a spare for $27 including shipping. Among many more other items, Zoro.com has some really good prices on air valves, switches, etc.

[JIM KELLER]

Good price on the parts. Never heard of Zoro.com but as a kid Zoro was a friend of mine.

Just looked at this Website. Items are nicely displayed with a good description. I like how they tell you the name/manufacture of each tool or state " value brand."

[dale farley]

They are also very fair with shipping. A $5 fee for UPS on orders less than $25 and free shipping for orders over $25.

[dale farley]

About 20 minutes (including leak check) and a $12 part and my problem is solved.