What to do.

For the air bags get the 4 way valve that sets each bag separate, you get less body roll in the corners. When you T an axle together with only 2 valves, The air in the outside bag of a turn goes to the inside bag like right now and she will roll over like an ocean liner. I have the 4 way valve now after having the 2 way, been there did it, I then added sway bars front and rear so she will carve a corner now.
Bill

Bill, can you provide a link to someone who sells this 4 way valve? all the ones for heavy trucks have a common outlet even if more then one port is used.
It may be suprizeing to learn that on hevy trucks and trailer they normally use only one valve per suspension (one for drive, one for trailer) and only on heavy haul, where off-center loads might be expected, are two valves used to control roll, and then you have the problem of sync'ing them so one doesn't take the lions share of the load. I often thought that a valve with isolated outputs would be a good idea, but have never seen one offered in the truck market.

I used Ridetech.com, also known as Air Ride Technologies.
This is the gauges and switches I used,
http://www.ridetech.com/store/4-way-rid ... panel.html
This is the valve block I used, it runs 1/4" air lines, they are electrically controlled valves.
http://www.ridetech.com/store/ridepro-4 ... block.html
If you need more volume for the big trucks, they have the BigRed valve blocks that use 3/8" line.
http://www.ridetech.com/store/4-way-big ... valve.html
Bill

Ahh, I mis understood, I thought they had a automatic level valve that sets the ride height of the suspension, but had four independant outputs that are isolated from eachother, but controlled from a common valve. That would solve body roll while still maintanining ride height. What they have are just solonoid valves where the driver set the pressure manually. That would not be good for trucks.
With the loads that truck suspension carry it is critical that the ride height be correct for pinion angles and to not over stress the componants when they go over uneven ground.

The 1500 medium duty vehicles where I worked have air springs controlled by three leveling valves. One for the front axle and left and right separate for the rear axle. I chose to use HOLLAND NEW WAY because the company used another brand. I bought my valves at KENWORTH TRUCK Parts. They were about $75 each. You can see we did in the L,R,S build with L110 Shorty.
The complete suspension for our project was under $1000 including the valves, lines, springs and compressor.

In theory, adding air to air springs should not change the pressure in the "bag" if the vehicle has not increased in weight. The vehicle should rise as the air volume in the springs increases. The vehicle should weigh the same at any height and it is the weight/resistance that determines spring pressure.

-except that the pressure does change. My KW dump truck has air bags. I have a pressure gauge on the dash and when the truck is empty the pressure is usually about 21-22 lbs. One day I noticed the pressure was up around 24-25 lbs and the truck was sitting a couple inches higher than normal and discovered the bolt that clamps the adjustment lever on the valve was loose. After I set the ride height back where it belonged the pressure was back at 21-22 lbs.

I post this merely as a point of interest since it really doesn't matter to the OP and drivers everywhere of bagged vehicles as long as the systems do what they're supposed to to. Not trying to argue with you, Nikki, just thought you might find it interesting. I think as the airbag gets taller, the shape changes a little bit and hence the difference in pressure.

Yes, but in trucks, the weight is changeing all the time or at least daily, and the sytems are not tight, so a fixed amount of air can't be expected to stay in indefanatly. Automatic level valves are used, but with the left and right sides tied together, they are less stiff side to side then spring ride. Duel level valves are often found on heavy haul tractors and trailers to stiffen the side to side spring rate.
On a tandem suspension the front to back trasfer of weight between the two axles of the tandem does far more then the springs (be they air or steel).
The Neway level valve just has two tire valve cores inside with a T attached to the lever arm, some have a viscus semi fluid grease to slow down the movement of the T to prevent the valves from opening and closeing over every small Bump (So called controlled responce level valves) while others don't (imediate responce valves) It is not the air entering and venting from the bags that dampen the bumps as many think, but the transfer of energy front to back. The amount of air that can enter or vent from the system is very small compared to the volume of the whole system.
With dual valves, the hard part is make sure they are set correctly so the load is shared equally left to right. If one is set just a little higher, that side will take the lions share of the load. That is why I wondered if an auto level valve has been made that has two outlets that are not connected together (so air can not pass side to side) but controlled from the same control arm such that the pressure (or volume if you will) will be the same side to side.
Many air suspensions are plumbed so the single level valve go to a T fitting between the left and right side, and each side has a seperate line going front to back, and not a single feed tieing all bags in series (ie down one side and back up the other) to try an minimise left to right transfer of air.

There is no argument here. Air springs, often do not have lots of travel. I would think that the increased pressure you witnessed may have been from the spring reaching the end of its working length and the pressure increased. The loose valve could cause this to happen. These "bags " will likely resist as much pressure as a common air system can deliver.
Air suspension on multiple axle working trucks can be complicated out of necessity. It is about load, control and terrain. Some of the heavy haul, many axle,some steered, combinations that go to Fort McMurray, Alberta are genius. Check You Tube.

I have pulled and worked on multi axle trailers some of which I could steer from the cab while driveing.
I have also seen the damage that can happen from over pressure, or "hyper extending" the bag, Bead plates bend and crack, useally around the attachment points.
On one trailer I owned, I had a problem with the beadplates cracking even when the ride height was set properly, The problem was solved by running seperate lines for each side of the trailer so air could more freely pass front to back on each side. At some point in its past, someone had run one line connecting all the airbags, it went from right front, to left front, to left rear and finely to right rear, this limited the exchange of volume between the front and rear on the right side, and made the left side line try and handle a greater volume then it should, this ment when loaded, passing over a hole, the bags would extend to their limit with high pressure in them, pulling the beadplate away from the mount and cracking around the studs.

Cornbinder,they also have a kit with leveling valves for all four corners that automatically adjusts the pressures. It has an electronic control that can set 3 different pressure settings that you program into it, like parked, light load or heavy load. The nice is you get to set what they are and the leveling valves maintain which one you set them at.
http://www.ridetech.com/store/levelpro- ... ystem.html
Explore what else is on the site.
Another option is Kelderman, they do airride for pick-ups and medium duty trucks, including IH
http://kelderman.com/product/medium-duty
Bill

Thought I would add a few pics of my progress.