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Old 03-31-2000, 11:31 PM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Seems like I just explained this system but it might have been on iATN.

The short answer is NO. The accumulators play no part in lifting the car.

The car is lifted by the strut portion of the shock. The car is slightly supported by these devices even unloaded. When a load is applied the valve is moved by the rotation of the stabilizer bar. Pressure is released into the system (both side are connected to this single feed so the pressure is always the same on both struts and both accumulators). Now picture this: the car is being supported substantially by the struts (now loaded). The hydraulic fluid is not compressable and the car hits a bump in the road.

What happens? .... well we haven't talked about accumulators so the system we have described would drive those ridged struts right up through the fenders. Now for the accumulator story.

The accumulator is a ball the size of a grapefruit. It has one hydraulic fitting/entrance. Inside there is a pressure of Nitrogen gas (probably around 500psi out of the box) against a diaphram and the whole cylinder in filled with the gas holding the diaphram against the walls. The car is started and the pump fills the line to the valve. The car is down so the valve releases pressurized fluid into the system. The fluid, not being compressable, instantly raises in pressure to the 500psi pressure of the Nitrogen in the chambers. The valve keeps letting fluid in as the car isn't yet rising and the pressure rises to say 800psi.

The diaphram has been pushed off the walls of the chamber and the chamber now is a quarter full of fluid with the resulting Nitrogen space reduced and the pressure at the matching pressure of 800psi. Some where around this time the car lifts and the valve shuts down (if too much lift is gained or if the load is reduced the valve lets fluid back out to the system resevoir).

So now we have a supported car riding along and we hit a bump, the strut collapses forcing the fluid to go into the accumulator chamber compressing the nitrogen till it hits 2000psi and the ball is nearly full of hydraulic fluid (quite a bump - think what would happen if that nitrogen is gone and the fluid already totally filled the accumulator chamber - solid as a rock) with the pressure this high the strut rebounds.

If the concept I described sounds something like a spring it is all the accumulators fault as the car is really riding on small high pressure balloons so to speak.

Since pressure is what lifts the car a dead accumulator just fills and when the pressure is right the car lifts. Since both sides are pressurized from one inlet all components receive equal pressure. If one side is lower it is because the steel spring is weak. You must remember the total lift is the pressure imparted by the struts (which is equal - baring some strut problem) plus the force of the steel springs. Alignment geometry can also alter the affect of either the steel springs or the strut force (but the strut force will be equal side to side as a principle of hydraulics - all force within a chamber with be equal).

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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