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Adjusting Air Bag Pressures For Smoother Rides


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#1 gfarmcafe

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Posted 09 September 2013 - 06:27 PM

I recently talked to a truck driver friend who asked if I could adjust the amount of pressure in the air bags of my 1997 Beaver Marquis. We were discussing how good of a ride we have on our Gillig chassis when the pavement is good, but can be extremely rough on bad pavement. He thinks adjusting air in these bags will help the ride. Apparently this can be done on trailers.

 

Has anyone explored, or installed pressure regulators on the air bags? Just curious. I don't think the shocks are bad since they're not leaking nor bottoming out, but the ride can be hard on the bladder on lots of expansion joints and pot holes! I have 102 lbs of air in front tires and 100 lbs on the rears.

Thanks for your input.


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#2 hwarkentin

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Posted 09 September 2013 - 07:00 PM

I don't know for sure but if the airbag pressure was "adjustable" don't you think it would always be set incorrectly? I am pretty sure the load dictates the pressure? From there the shocks take the blame for being too firm or allowing too much "floating." I am the same in our CC magna....some roads are just awful but others are very good. Smarttire made a living on incorrect tire pressure, I doubt they could duplicate the feat with airbag pressure.


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#3 DickandLois

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Posted 09 September 2013 - 07:24 PM

gfarmcafe,

 

Air pressure levels the ride system that are set more for load, then for ride.

 

The item with the largest impact are the shocks, having said that; systems are equipped with ping tanks that allow air to move within a set of parameters, that allow for a portion of the air within the system to move in a predetermined range and pattern. Primarily with the use ride height controls set at a predetermined starting height that changes as the road surface varies.

Shock absorbers on the other hand are designed in a number of ride control ranges for a soft or stiff ride.

 

Hope that helps answer your question. The total answer gets into a lot of Physics.

 

Rich.


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#4 wolfe10

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Posted 09 September 2013 - 08:02 PM

Yes, as Rich said, you can (and should) NOT contemplate adjusting air bag pressure.

 

Ride height valves control suspension height and therefore PSI. Set too low, and your coach can easily bottom out on bumps.

 

I find it hard to believe anyone would suggest changing this-- could be a VERY expensive experiment, as even a small deviation from correct ride height can adversely affect ride and handling and in the rear (very short drive shaft) cause extreme wear to U-joints and transmission.

 

SO, with harsh ride first thing to do is set RIDE HEIGHT. Check with Gillig for the proper specs.

 

Brett


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#5 desertdeals69

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Posted 09 September 2013 - 08:03 PM

I recently talked to a truck driver friend who asked if I could adjust the amount of pressure in the air bags of my 1997 Beaver Marquis. We were discussing how good of a ride we have on our Gillig chassis when the pavement is good, but can be extremely rough on bad pavement. He thinks adjusting air in these bags will help the ride. Apparantly this can be done on trailers.

 

Has anyone explored, or installed pressure regulators on the air bags? Just curious. I don't think the shocks are bad since they're not leaking nor bottoming out, but the ride can be hard on the bladder on lots of expansion joints and pot holes! I have 102 lbs of air in front tires and 100 lbs on the rears.

Thanks for your input.

Are your tires inflated to the correct pressure according to the chart?  Changing the air pressure in the bag just changes the ride height.  The ride height is controlled by the height valve and really doesn't have anything to do with pressure.  On my front bags the correct height is 65 to 70 lbs air pressure in the bag.


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#6 DickandLois

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Posted 14 October 2013 - 05:04 PM

One is always learning!

 

I just looked over some Chassis air system drawings and noticed that they had a PPV(Preset Pressure Valve) in the air ride supply system. The Pressure setting on the valve feeding air to the ride height system was 65 LBS.

 

This system does not have ping tanks in the ride height system. So now I'm going to have to see if this is the new norm on systems with out ping tanks.

 

There are drawing without ping tanks that run the same pressures that my setup has.

Now, I was sure that the ride height pressure on my chassis is running at 120 PSI / the compressor governor is set at 125psi. and the pressure gauge on the air supply for the ride height varies from 90 to 120psi as the pressure in the secondary air tank changes with demand.

 

Rich.


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#7 wolfe10

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Posted 14 October 2013 - 05:34 PM

Perhaps a little clarification:

 

PSI in the air bags is not more related to system pressure than is your tire pressure to the tire shops 150 PSI line pressure. Both have a "controller" determining when to let air in and how much-- ya one is automatic and the other "manual".

 

In the air system, the ride height valve opens to allow air in, closes, opens to let air out based on the ride height dimension.

 

Many air suspensions limit air PSI to the front suspension, as the rear  axle is quite a lot heavier and they don't want to torque the chassis by raising the front abruptly and then having the back end slowly catch up.

 

Extreme example of HUGE variations in air bag pressure-- dump trucks with rear air suspension.  The same ride height is maintained with the dump empty or loaded with 50,000 pounds of gravel.  You bet the PSI is much more when loaded to maintain the same ride height.

 

Brett


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