air dryer purge

Topic: air dryer purge (Read 1072 times) previous topic - next topic

air dryer purge

March 25, 2020, 06:25:33 pm

have 2001 u270 with 350isc engine and playing with it do not hear the purge cycle does this coach not have an air purge on the dryer

Re: air dryer purge

Reply #1 – March 25, 2020, 06:59:43 pm

YES, when the air pressure reaches CUT-OUT PSI (generally around 120 PSI, you should hear the "sneeze"/purge from the air dryer.

But if you don't, first question is how old is your air dryer??

Re: air dryer purge

Reply #2 – March 25, 2020, 07:46:35 pm

Quote from: wolfe10 – March 25, 2020, 06:59:43 pm

...first question is how old is your air dryer??

2nd question: What do your dash air pressure gauges indicate when driving down the road? (highest pressure, lowest pressure)

Re: air dryer purge

Reply #3 – March 25, 2020, 07:55:17 pm

Mine is set to cut in at 95psi and out at 125psi. The gauges will gradually decrease going down the road depending on the type of road-on a straight flat road with no braking they will take quite a while. On a curvy road with lots of up and down, with braking added, they will cycle more frequently.

Re: air dryer purge

Reply #4 – March 25, 2020, 08:34:34 pm

Brett mine goes from 110-130. Not as much braking at 95. I do not need the retarder much at the higher air pressure

Re: air dryer purge

Reply #5 – March 25, 2020, 08:43:29 pm

sitting at idle here in yard the back gauge reads 128 and the front 105 but no cycling my other coach would cycle at 125 down to 92 and back
guess I need to replace the purge valve

Re: air dryer purge

Reply #6 – March 25, 2020, 10:24:23 pm

Quote from: Caflashbob – March 25, 2020, 08:34:34 pm

Brett mine goes from 110-130. Not as much braking at 95. I do not need the retarder much at the higher air pressure

Higher air pressure in your tanks slows you down so retarder is not needed? 5 or 10 psi. brake application needed for slowing coach why should it matter if the tanks have 100 or 130psi?

Re: air dryer purge

Reply #7 – March 25, 2020, 11:46:28 pm

Quote from: bvectra – March 25, 2020, 08:43:29 pm

sitting at idle here in yard the back gauge reads 128 and the front 105 but no cycling
guess I need to replace the purge valve

Brian,

Don't jump to conclusions...yet. Need more info. Try a simple test:

Sitting in your yard with engine running at idle, try "fanning" the brake pedal to lower the pressure in the air tanks. "Fanning" means depress and release the brake pedal rapidly so that the brakes cycle on and off. This will deplete pressure in the brake tanks.

While doing this, watch the dash air pressure gauges closely. You should see both gauges fall more or less together to some pressure where the engine air compressor will kick in. Note that pressure and stop fanning the brake pedal.

Watch the pressure gauges. Do they both increase together? At the point where they stop going up (compressor cuts out), you should hear the air dryer purge. Open the driver window if necessary so you can hear the dryer purge.

Both pressure gauges should now be indicating the same pressure. If they are not, then you might have a faulty pressure gauge.

What is the pressure where the dryer purges?

Get back to us after you try this test. It's possible that you only need a new D2 governor.

Re: air dryer purge

Reply #8 – March 26, 2020, 12:18:11 am

Doug the "cans" on the wheels receive the chassis air. I think the system has metered flows. Being fed from a higher pressure reservoir made a noticable increase in my same pedal efforts braking effect.

At 95 to 110 you had to push harder to get the same braking effects.

Then I had the rears totally rebuilt. New caliper bushings.

I start out cold now and go down a fairly steep hill just below my house and storage and the coach now has the ability to stop safely in a emergency without deglazing them and/or warming them up.

I do keep my hand ready to turn on the retarder at that particular point in my route but the coach will stop fairly hard if I get into the brakes.

this is with no tow.

Re: air dryer purge

Reply #9 – March 26, 2020, 10:58:41 am

Quote from: Caflashbob – March 26, 2020, 12:18:11 am

Doug the "cans" on the wheels receive the chassis air. I think the system has metered flows. Being fed from a higher pressure reservoir made a noticable increase in my same pedal efforts braking effect.

At 95 to 110 you had to push harder to get the same braking effects.

Then I had the rears totally rebuilt. New caliper bushings.
[/quote

Having the least amount of throw in your slack adjusters will give you the most noticeable effect regarding effort on the brake pedal. Having your brakes rebuilt and adjusted most likely was the reason your brake pedal takes less effort and not the 10psi increase in your tanks, in my opinion.

Re: air dryer purge

Reply #10 – March 26, 2020, 02:24:23 pm

Doug everything was done in steps to separate the results. Took years.

Meritor disk brakes self adjust with a hard pedal pressure application. See their manual.

The D2 up pressure was first. Very noticeable. Everything else worn.

There is a DOT(?) chart that shows various D2 pressures required(allowed?)per application.

School bus I think was the 110/130 one.

The chart had minimum pressures shown as the safety was the key.

I think DOT max allowable is 135.

Re: air dryer purge

Reply #11 – March 26, 2020, 02:28:31 pm

My brakes improved a bunch when using a new D2@ higher pressures. The old was 110/85 ish and now it is 125/105.

Re: air dryer purge

Reply #12 – March 26, 2020, 02:59:23 pm

Ok, I'm confused. I thought that the brakes were spring activated. IOW the springs will lock up the brakes. Having air pressure releases the brakes by overcoming the springs. When you press your brake pedal you are releasing air on the cans which allow the springs to apply the brakes. Same with the park brake, pull it and it releases the air allowing the springs to lock the brakes. That's why you have to build up air pressure before your park brakes will release.
So what I don't understand is what if any difference does a higher service air pressure have to do with the amount of braking?
Please correct my thinking if I'm wrong.

Re: air dryer purge

Reply #13 – March 26, 2020, 03:04:32 pm

Service brakes (brake pedal) is AIR applied.

Parking/emergency brake is SPRING applied, air released.

There are two cans on each rear brake-- one for service brakes, one for parking/emergency brakes.

There is one can on each front brake-- the service brake.

Re: air dryer purge

Reply #14 – March 26, 2020, 03:37:38 pm

Thanks Brett. All these years I was wrong! Makes sense now reading this and the other discussion.
See newbies, don't be afraid to ask a question that seems silly to you.

Re: air dryer purge

Reply #15 – March 26, 2020, 03:45:47 pm

OK anybody have a part number for a d2 govenor had this problem on my other coach

Re: air dryer purge

Reply #16 – March 26, 2020, 04:15:53 pm

Quote from: bvectra – March 26, 2020, 03:45:47 pm

OK anybody have a part number for a d2 govenor had this problem on my other coach

There are two ways to approach a mechanical problem on your coach:

1. Analyze the symptoms and, with some simple diagnostic tests, try to determine the exact point of failure .

2. Randomly throw parts at it until something finally makes the problem go away.

If you prefer solution #2 just go to any NAPA store or truck parts dealer and ask for a D2. They will sell you what you need.

Re: air dryer purge

Reply #17 – March 27, 2020, 11:01:06 am

has anyone changed the purge valve on the dryer was told they should be changed every few years to work good but he was also talking like a big truck if the governor is working but the vavle does not open and close this could be a problem too i think this motorhome had set for sometime before i bought it i never shut the lp off when i park coach fpr a couple of weeks because i may want to leave in a hurry and then forget to turn on with fridge on

Re: air dryer purge

Reply #18 – March 27, 2020, 11:06:01 am

If you mean the brass valve on the side of the dryer, yes,can find it on Ebay.

Re: air dryer purge

Reply #19 – March 27, 2020, 11:06:26 am

Rather than servicing the air dryer (replacing the filters) a very good idea is to replace the dryer with a factory (factory that made it) reman. The factory reman units come with all new valves, heater, etc.

Do this at three years, then at 6 years just replace filters, 9 yearsfactory reman............

Re: air dryer purge

Reply #20 – March 27, 2020, 03:28:25 pm

anyone know the dryer on a 350 isc motor 2001 u270 can get a new or reman

Re: air dryer purge

Reply #21 – March 27, 2020, 03:34:00 pm

Make and model of dryer should be on a tag on the dryer.

Re: air dryer purge

Reply #22 – March 27, 2020, 04:22:57 pm

thanks brett will look now rain has stopped then figuring out the trailer connection prople do alot of different things this coach had a hoopy attatched and seven pin plug guess they put the hoppy in place to do a 4 pin or 6 pin plug they make adapters fpr both now to get rewired to work my way

Affiliate Notice