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Air Suspension Pressure regulator

I am going over the coach and trying to understand a bit about what this adjustable air pressure regulator should be set at.  This seems to be an odd amount, but nowhere in my Foretravel manual (or HWH Air suspension manual) can I find what this SHOULD be set at.  Any air system folks out there with guidance?  Pictures attached of the entire leveling air system diagram, the adjustable pressure valve, and the gauge.  It *seems* to me that this 66 PSI is low and should be raised ABOVE the threshhold of the auxiliary compressor shutoff pressure (whatever that is)...else the auxiliary compressor would cycle on faster as this valve releases pressure too early.  Am I on track?


Re: Air Suspension Pressure regulator

Reply #1 –
Brad,

Everything I have seen in Forum posts on this subject suggest the pressure should be set around 60-65 PSI.  HOWEVER, I can offer no reference or link to any "official" factory guidance on the matter.  So take it for what its worth.

You have a much newer model coach, so your air system is more complicated than mine.  Your reasoning about the aux compressor may be valid, but does not apply to my coach, so I can't comment.

Some Forum members (in the past) have questioned if this regulator even has any real purpose.  The "story" is that it prevents the front end of the coach from going up to ride height faster than the rear end, so the operator does not drive off with the rear end too low (tires rubbing in the wheel wells).  I believe this reasoning is faulty.  I would love to hear a more logical justification for having the regulator.

Re: Air Suspension Pressure regulator

Reply #2 –
Well every once in a while, when the compressor is on, I can hear what I at first *thought* might be a leak.  I finally tracked it down to this relief valve, doing its job.  When I turn the auxiliary compressor off, the valve takes less than a minute to stop releasing air.  So I strongly suspect that the output of the not-adjustable auxiliary compressor is higher than 66 PSI.  I have noticed over the years that the lower the outside temperature, the more often that auxiliary compressor comes on.  I think I am seeing why.  I am just waiting for someone to tell me that I should raise the valve to 70 or more.

Re: Air Suspension Pressure regulator

Reply #3 –
I was told, all the bag and step pressure regulators are to be set at 60#.
Happen to be at MOT, one was stuck, none adjustable/stuck!  Had both front and rear replaced.  And bought a spare, as front, rear and steps all used the same regulator.  Then I wrote 60# on the box.

The D2 governor has a start at 110, and off at 125# for the system, mostly for dash gauges and brakes.

Re: Air Suspension Pressure regulator

Reply #4 –
If this is the regulator that hangs about center of the front axle, its primary purpose (supposedly) is to keep the front from achieving ride height faster than the rear so that folks don't drive off before the coach is fully at ride height all the way around (the rear being heavier takes much longer).

60-65 psi per Triana many moons ago.  Replacements can be bought in the air tool department at Lowes for (last I checked) around $20.

Re: Air Suspension Pressure regulator

Reply #5 –
Quote from: Michelle –
...its primary purpose (supposedly) is to keep the front from achieving ride height faster than the rear so that folks don't drive off before the coach is fully at ride height all the way around (the rear being heavier takes much longer).
Same "reason" I have always heard, but does it really compute?  I suspect there are very few (if any) owners who fire up the coach and immediately drive off while the air system is still coming up to pressure.  I always wait until our air compressor has unloaded at least once before I would even think about taking off.  In my opinion, the regulator serves no purpose (other than being a common location for an air leak).

Re: Air Suspension Pressure regulator

Reply #6 –
Quote from: Chuck & Jeannie –
Same "reason" I have always heard, but does it really compute?  I suspect there are very few (if any) owners who fire up the coach and immediately drive off while the air system is still coming up to pressure.

Foreforums members are smarter than the average bear  ;)

You'd be surprised at how many people think that because the front stopped rising, the back must be done as well.  I'm guessing it was added at some point many moons ago after one too many issues.  It's the kind of thing that gets put in place because of such things (damage to wheel wells, etc.)

BTW, Brad, it is part of the suspension, not related to the aux compressor setpoints.  The only time that regulator on ours ever leaked air was when the regulator itself had failed.  You should not hear any sound from it.

Re: Air Suspension Pressure regulator

Reply #7 –
"I always wait until our air compressor has unloaded at least once before I would even think about taking off." That's usually my cue, too. There is a hidden sensor that senses when I'm hooking up the car and unloads when my back is to the coach. Happens every time. Most of the time it happens when I'm right by the thing, but sometimes I'm too quick and on the other side.

Re: Air Suspension Pressure regulator

Reply #8 –
Quote from: Chuck & Jeannie –
Same "reason" I have always heard, but does it really compute?  I suspect there are very few (if any) owners who fire up the coach and immediately drive off while the air system is still coming up to pressure.  I always wait until our air compressor has unloaded at least once before I would even think about taking off.  In this case, the regulator serves no purpose (other than being a common location for an air leak).



This is a little confusing. I am assuming that if the pressure regulator is set to 60#. Then that is the design pressure the system operates at. Not 125# system pressure that the coach develops. What am I missing here?

Re: Air Suspension Pressure regulator

Reply #9 –
Quote from: Res777 –
This is a little confusing. I am assuming that if the pressure regulator is set to 60#. Then that is the design pressure the system operates at. Not 125# system pressure that the coach develops. What am I missing here?

That is sort of my thought. Maybe the brake system is higher and the bag, bladder and step systems are lower. 

I'd like to have a better understanding,  so when the coach makes air noises, I can know whether it is doing something smart...or there is something wrong.  I spent the entire rest of the day out there cleaning all the bugs off of the front end from our 8,000 miles of summer travels...and I heard no more noise whatsoever.  So why ever it chose to bleed off some pressure when it did, I don't know.  But I do have the coach sitting higher than normal, and all is fine.

Re: Air Suspension Pressure regulator

Reply #10 –
Yes, there are 2 separate systems. Brakes are high pressure, and the air bags are just what is needed for the Foretravel ride. 

Air can get released after parking from the HWH system, as it "wakes up" I believe every 20 minutes and checks "level".  I have heard discharges of air after being parked, or even the next day, as HWH drops a high corner.  Those releases are at the manifold on your drawing.
Also there is a check valve at the 12 volt air pump, it's a simple brass nipple, near the water collection bowl, and stamped with an arrow, that is easy to miss noticing.  Mine allowed system air to leak out the bowl discharge.  Aubry at MOT showed me the place on my air diagram that he drew way back in 1997.  MOT had the part in stock.

Re: Air Suspension Pressure regulator

Reply #11 –
Quote from: Res777 –
This is a little confusing.
I agree with you.  As I said in Reply #1, I don't buy the "story" about why we have this regulator.  The reasoning is not logical.

Look at the air system diagram posted by Brad in the initial post.  Or look at the diagram for your own coach.  The regulator in question is inserted in one of the air lines coming from the front brake tank.  This line is downstream of the protection valve.  The protection valve will not allow air flow out of the front brake tank until it opens, usually at about 60-70PSI.  When the protection valve opens, air then flows to the pressure regulator, which is set for 60-65PSI.  When air pressure upstream of the regulator exceeds 60-65PSI, the regulator will allow air to flow to the front 6-pack manifold.  It will maintain the pressure flowing to the front manifold at 60-65PSI, regardless of the upstream system air pressure, which usually varies from about 100PSI to about 125PSI (depending on D2 governor setting).

BUT, what does ANY of this have to do with how fast the front end of the coach rises to travel height when the engine is started!

On my coach (HWH 600 Series leveling system) if the HWH panel is OFF and I start the engine, the coach immediately tries to go to travel height.  Air flow to the front (and rear) air bags is being controlled by the height control valves.  If my air system pressure is depleted and the coach is sitting all the way down on the hard stops, the height control valves will direct air flow to all the air bags (via the travel solenoids) as the system attempts to attain travel height.  The front height control valve is supplied by a separate unregulated air line from the front brake tank (via the protection valve).  Air pressure going to the front height control valve will be exactly the same PSI as the pressure going to the 2 rear height control valves.

Based on the way MY coach works, I cannot see how the pressure regulator in question can have ANY influence over how fast the front end of the coach rises.  In fact, I have yet to find any logical explanation for having it in the system.  If anyone can tell me why it is there, I'm all ears.  Neither of the HWH manuals linked down below offer any explanation for having the regulator.

Note:  In spite of my above described skepticism, I DO retain the front manifold air pressure regulator in place on our coach, set to 60PSI.  Even though I don't understand the purpose, I am not so arrogant as to think I am smarter than the folks who designed the system.

https://www.hwhcorp.com/ml20635.pdf

https://www.hwhcorp.com/ml11148.pdf



Re: Air Suspension Pressure regulator

Reply #12 –
Quote from: Brad & Christine Slaughter –
That is sort of my thought. Maybe the brake system is higher and the bag, bladder and step systems are lower. 
I can understand the purpose of the other regulators on these coaches.

The regulator for the air steps/door is to reduce system air pressure going to the activation cylinders.  Why subject them to 125PSI if all they need to operate effectively is 60PSI?

Besides the air step regulator, my coach has a regulator upstream of the Bendix cruise control activation cylinder (which is also used for our air throttle).  Same reasoning: it only needs 60PSI to operate, so higher system pressure is reduced by the regulator.

My coach also has a exhaust brake.  The brake valve is operated by a air cylinder.  Guess what - there is a 60PSI regulator in the supply line to the cylinder.

Slide air bladders I know nothing about, but I suspect they also only require a lower pressure to operate effeciently, so high system air supply pressure is regulated.

BUT, this reasoning falls down when we look at the pressure regulator on the supply line to the front 6-pack manifold.  If the regulator is there to "protect" the HWH manifold from the higher system pressures, then logically there should be a matching regulator (set to a higher pressure) protecting the rear HWH manifold.  Yet there is none to be found.

Re: Air Suspension Pressure regulator

Reply #13 –
On the 1997 U295  when I was airing up from being dumped the front would come up way before the rear would come up. 

My guess is the the regulator is to only let 60 or so PSI go into the front bags when trying to level (not travel mode).  Looking at the parcel drawing the ride height sensors get their air from another connection.  Why subject the bags, fitting, valves to pressures higher then 60 lbs if 60 lbs is all that is needed to raise the front of the coach all the way up.

On an air compressor the only time I have heard the pressure regulator let out air is when I was adjusting the pressure down from it being on a higher setting. 

Re: Air Suspension Pressure regulator

Reply #14 –
Quote from: turbojack –
My guess is the the regulator is to only let 60 or so PSI go into the front bags when trying to level (not travel mode).  Looking at the parcel drawing the ride height sensors get their air from another connection.  Why subject the bags, fitting, valves to pressures higher than 60 lbs if 60 lbs is all that is needed to raise the front of the coach all the way up.
Perhaps...

In the HWH Air Leveling Systems Text Book (link in Reply #11), under the paragraph "Vehicle Air Supply" it says:

"Although it may vary between different vehicles, it normally takes at least 60 psi to start lifting a vehicle. Most vehicles will require 90 psi to obtain maximum lift. Some may require up to 130 psi to obtain maximum lift."

Based on that statement, limiting the front manifold air supply to 60PSI seems overly "protective" to me.  All of the air lines, fittings, and valves on our coaches are supposed to be DOT quality.  They can handle at least 150PSI without any strain.  Surely the HWH components are designed to at least as high a standard.

When the coach is trying to level (auto or manually), it is sometimes necessary for the front end to be raised to maximum height.  If it only requires 60PSI to accomplish this with the front air bags, then why subject the rear manifold to full system pressure (125PSI)?  Does the additional weight in the rear require twice the pressure to achieve full lift?  I think not.  Yet there is no regulator on the rear manifold supply line.

Easy to test.  With the air system fully bled down, add pressure from a external compressor 10PSI at a time.  After each 10PSI increase in system pressure, try using the "RAISE" button on the HWH panel to raise the coach.  Monitor the bag extension at both ends.  Record the pressure when the front air bags first reach full height, and when the rear air bags first reach full height.  I am GUESSING all 8 bags will be fully extended by about 80-90PSI.  May be higher with newer coaches (slides and/or tag axle).

Coincidently, the rear 6-pack air system low pressure warning switch is triggered when pressure drops below 85PSI.



Re: Air Suspension Pressure regulator

Reply #15 –
My rear needs over a 100 Psi to fully extend. If the air tank was full and I hit raise, without the regulator the front would fully extend much faster than the rear. Don't know why that would make a big difference though.

Re: Air Suspension Pressure regulator

Reply #16 –
Quote from: craneman –
Don't know why that would make a big difference though.
Exactly, because you are using the leveling system.  You are not trying to drive away prematurely with the rear tires rubbing.  When manually raising the coach, who cares if the front goes up faster than the rear?



Re: Air Suspension Pressure regulator

Reply #17 –
Quote from: Chuck & Jeannie –
Exactly, because you are using the leveling system.  You are not trying to drive away prematurely with the rear tires rubbing.  When manually raising the coach, who cares if the front goes up faster than the rear?

I don't think FOT would have added the regulator unless they felt it was necessary since extra cost to do.

As I was writing the above an Eliot Musk quote came to mind, don't remember exact wording.  Question everything, no mater who told you or how long it has been used. He never want to hear "It has always been done that way"

Re: Air Suspension Pressure regulator

Reply #18 –
Quote from: Chuck & Jeannie –
Perhaps...

In the HWH Air Leveling Systems Text Book (link in Reply #11), under the paragraph "Vehicle Air Supply" it says:

"Although it may vary between different vehicles, it normally takes at least 60 psi to start lifting a vehicle. Most vehicles will require 90 psi to obtain maximum lift. Some may require up to 130 psi to obtain maximum lift."

Based on that statement, limiting the front manifold air supply to 60PSI seems overly "protective" to me.  All of the air lines, fittings, and valves on our coaches are supposed to be DOT quality.  They can handle at least 150PSI without any strain.  Surely the HWH components are designed to at least as high a standard.

When the coach is trying to level (auto or manually), it is sometimes necessary for the front end to be raised to maximum height.  If it only requires 60PSI to accomplish this with the front air bags, then why subject the rear manifold to full system pressure (125PSI)?  Does the additional weight in the rear require twice the pressure to achieve full lift?  I think not.  Yet there is no regulator on the rear manifold supply line.

Easy to test.  With the air system fully bled down, add pressure from a external compressor 10PSI at a time.  After each 10PSI increase in system pressure, try using the "RAISE" button on the HWH panel to raise the coach.  Monitor the bag extension at both ends.  Record the pressure when the front air bags first reach full height, and when the rear air bags first reach full height.  I am GUESSING all 8 bags will be fully extended by about 80-90PSI.  May be higher with newer coaches (slides and/or tag axle).

Coincidently, the rear 6-pack air system low pressure warning switch is triggered when pressure drops below 85PSI.

I think having two air bags to side will change as to how much air is needed to raise the coach compared to a coach that only has one bag.

An example with my Active Air I have a screen that lets me know how much air is required in each bag for the coach to be at ride height.  My drive axle have more weight on it then the front or the tags but has the least amount of air required per axle.  (I can not find my weighed axle weighs.)

Left tag      81 lbs    single bag per side
Left Drive    66 lbs    2 bags per side
Left Front    98 lbs    single bag per side
Right Front 98 lbs    single bag per side
Right Drive 75 lbs    2 bags per side
Right Tag    85 lbs    single bag per side

Re: Air Suspension Pressure regulator

Reply #19 –
Quote from: turbojack –
I don't think FOT would have added the regulator unless they felt it was necessary since extra cost to do.
Which is why I still have the regulator in place on our coach.  I figure it must have some purpose...I just don't understand what it is.  :help:

On our coach, the front GAWR is 10,000 and the GAWR is 19000.  At our last 4-corner weigh we were real close to actually weighing that much on both ends.  So our coach is basically almost twice as heavy in the rear as in the front.  And, as you know, we have 2 bags on each corner.  If the relationship between air bag pressure and lifting force is linear, then I guess it makes sense that if the front manifold can raise 10,000 pounds while regulated to 60PSI...then the rear manifold might possibly need the full 120PSI system pressure to raise (almost) twice that weight.