Thread: Advice about solenoid valve block rear suspension.

Hi Lewy, I'm not really sure of the function of the dump valve. At the moment I'm planning using two D 2 solenoid blocks. The dump valve looks like it allows the compressor to pump into the central port for raising but opens to atmosphere when the solenoid valve is lowering it maybe has a minimum pressure function as well to prevent the air bags emptying. I'll set up the system on bench and test it before fitting to the car. If I need one it should show up during the test. cheers simmo

the dump valve lets air out of the bags when the sensors tell it to.

I was found out the 2 rocker switches are only three poles, that calls for another plan

This one is a bit simpler I think, I'm still using the two D 2 WABCO solenoid blocks. cheer simmo.

that should work,Just don't hit the wrong switch when you are on a big lean,The other thing is how will you know if you are over extending the bags.Or will you rely on the shock to stop that.

Hi Lewy, good question, the bags are permitted to operate up to 80 psi. I will have manual control and can see the pressure in the bags when inflating, I might see 80 psi once in a blue moon. With over extension yes, i think the shockers can manage that, they currently limit the extension of the existing springs, what do you think? How do they do it on D-2? I have tried my existing OME shockers, (2" lift"), and they allow articulation up to the bump stops, and a lot of travel on the way down.

I can check that out before i put the wheels on, and ask Brendan what is the the maximum allowable extension of the bags. He's given me a longer bag to accommodate the 2" lift. I'll know next week anyhow when i fit them cheers simmo

The limit is set by the shocks on the disco when on full droop,However the sensors tell the pump to stop pumping when the gap between the chasis and axle reaches tolerance,If the shock wasn't there the bag would pull apart although the rear sway bar may stop it happening.

Simmo,

I get the impression from your comments that you will manage your air bags by the pressure you see on the gauges in the cab.

From my experience, that will not work. When I bought my Disco the air bags had been removed and it had coils. Rebuilding the system took me a little while to get everything together and I started with just the air bags with a short piece of tube and a Shrader (tyre) valve on the end. I just pumped them up and away I went until I got the compressor and valves all in place.

To set the height, I would just park the vehicle on level ground and pump up the bags measuring the guard to wheel centre heights with a tape.

Firstly I noticed the pressure can be very different from one side to the other, varying up to 10psi.

Next thing I noticed, If I got the heights all perfect with a full tank of fuel, the vehicle could go up be near 2 inches when fuel was almost empty.

I believe (at least with standard LR air bags) air bags are very progressive. To explain that a little, I under as far as I under stand a linear coil spring rated at 100lbs for example will take 100lbs of weight to compress it by 1 inch then 200lbs of weight to compress it to 2 inches and so on. A progressive coil spring (depending on the rate of progression) might take 100lbs to compress it 1 inch but then take 300lbs to compress it 2 inches. Now with airbags I believe they are a very low rate spring that is also very progressive. This makes them soft around centre. By this I mean they are very low rate so it only takes a very slight change in weight to compress them a little, maybe only 50lbs will compress them the first inch but then it might take 400lbs to compress them 2 inches. I have no idea what the actual figures are but I know it doesn't take much weight change to cause them to go up or down an inch or 2. This is why LR have a separate computer to control the height by inflating or deflating as required the maintain correct height. Just stopping and my 20kg kid jumping in the back calls for more air.

As a suggestion for something you might like to look at is how trucks control their air bags. They have a manual 3 way air valve fixed the the chassis and a lever that extends to the axle. If the axle moves toward the chassis, the lever opens the valve and inflates the bags, if the axle moves away from the chassis the lever moves the opposite way and exhausts the bags.

Or if you are dead set on controlling it your self, maybe look at how the Disco 2 height sensors work. (I carry a spare that I could check if you need) Maybe if it's a simple variable resistor then you could have a couple of gauges that show the height of the vehicle rather than the pressure.

Basically I am saying I don't think pressure is a reliable measure of the height of the vehicle.

Also 80psi seems pretty low. I think the Disco 2 bags are rated over 300psi and from memory it took over 70psi to set the vehicle level when empty.

Happy Days

Hi Joel, you posed some interesting questions. I'll be fitting them next week, so I'll let you know how they go. The pressure to lift the car depends a lot on the diameter of the airbags. I think the airbag man air bags are larger in diameter so they need less pressure, they will also be less change of height for the same load reduction.I think 80 psi was the stated maximum pressure by the maker. They sell them with solenoids and switches etc and a pressure gauge. But I want use landrover parts so i can get parts easily for that, yes I can appreciate the back will raise up a bit when you remove 80 liters of fuel. I'm not sure how much weight is on the back axle of a defender, but I would say at least 600 kg per wheel at a reasonable load, a 60 kg fuel burn is a change of about 5%, on the the axle load. Interesting days ahead .
I'll keep the forum informed on how it goes. Have a merry and safe Christmas all, and hopefully a prosperous new year. cheer simmo