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Old 10-13-2013, 09:19 PM   #1
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Join Date: Nov 2003
Location: Richmond Hill, GA USA
Posts: 623
Experimental Adjustable Motion Control for Air Bags

After reading a lot of posts, primarily on the Freightliner Forum, about the Super Steer Motion Control Units, I decided to try to use some commonly available hardware to accomplish the same effect. Below I've posted what I've done to date and hope that if anyone else decides to try this method, that they will publish their results also.

A fellow RV'r on the Freightliner Forum pointed me to STCValve.com to look at the "Flow Control Valves", which are adjustable devices for controlling the flow of compressed air. My coach has 1/2 inch air lines going to the bags, so I purchased two slip on 1/2 inch flow control devices (made of plastic). Luckily, I also purchased two 1/2 inch slip on unions, thinking that if my idea did not work, or the flow control valve failed, I could replace the valve with the union and not be stranded.

I cut the lines to the front air bags, and installed the plastic flow control valves. The plastic flow control valve was rated at 150 psi, so I thought this would work great with a system regulated to a max of 125 psi. This was a bad assumption, as I discovered that the psi goes up momentarily when you hit a bump and the air bag is compressed. The coach was obviously more stable with the flow control valves in place, but I only drove it about 3 miles. Then, one of the plastic flow control valves blew apart when I hit a good bump. I quickly installed the unions in place of the valves, and drove back home. The plastic unions can stand the temporary pressure increases as they are molded as one piece. (The plastic flow control valves are molded in two or more pieces and then attached together by some process that did not stand the temporary pressure increase.) I ran the coach about 800 miles with the unions installed with no problems.

After consulting with STCValve, they suggested I try the panel mount, metal construction flow control valve with metal threaded adapters to convert the valve to slip on installation. Their engineers stated that the rating was the same 150 psi, but the internal construction was much stronger.

I ordered these metal valves and installed them on the front motorhome air bags. I did a 30 mile test drive today with good results. I initially adjusted the flow valves so that the time to dump the air bags was extended about 10 seconds. I plan to experiment further with different settings when time permits. My guess is that the more you restrict the air flow, the "rock and roll" will be reduced but the ride quality may become more harsh.

The below links are to the company where I purchased the parts. There are probably other manufacturers with similar components. If you decide to try this, be sure you get the components for your size air line.

Solenoid Valve, Air Valve, Fittings, Pressure Regulator

Here is the link to the page with the 1/2 inch panel mount flow control valve (near bottom left of page):
Stainless Steel Fittings - STC Fittings

Here's what I ordered from STC Valve company:

4 each MC 1/2 N 1/2 K Male Connector 1/2 OD Tube X 1/2 NPT $3.03 each
2 each ASC N 1/2 1/2" NPT Panel Mount Precision Flow control Valve $19.65 each

If you decide to do this, I highly suggest purchasing two 1/2 inch slip on unions so that if you experience a failure on the road, you can easily remove the flow control valve and install the union. This is what I did when the first plastic flow control valve failed.

The slip on unions are
SU 1/2 K Straight Union 1/2 OD Tube $2.36 each

Total cost before shipping = $56.14

Additional ideas and/or comments welcome.


Fred & Vicki
Richmond Hill, Ga
2000 H.R.Endeavor/Freightliner/330 Cat
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Old 12-13-2013, 08:52 PM   #2
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Join Date: Nov 2003
Location: Richmond Hill, GA USA
Posts: 623
Additional info: Just completed a 4000 mile trip with the flow control valves installed. Coach is more stable, and does not ride harsh. It significantly reduces the rebound effect when crossing a speed bump at an angle, and it feels better on the curves.

I may experiment with different settings on the flow control valves, but have not had time to do so yet.


Fred & Vicki
Richmond Hill, Ga
2000 H.R.Endeavor/Freightliner/330 Cat
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Old 12-13-2013, 09:01 PM   #3
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Join Date: Dec 2006
Location: St. Augustine, FL
Posts: 3,579
Thanks for the write up and info.
'02 Ultimate Advantage 40J Spartan MM - Cummins ISC
2013 Jeep Rubicon JK Unlimited
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