On a smooth trail
When you are riding on a smooth trail and the shock absorber is compressed slowly and only a small amount (low shaft speed and short stroke), the damping oil is forced through the double-acting rebound/compression adjuster in the piston shaft, fig 1 flow 3.
    The oil displaced by the piston shaft is forced through the independent compression damping adjuster out into the external reservoir, fig 2 flow 3.
    The floating piston in the reservoir is forced to move, compressing the gas behind it.
    When the shock absorber extends the gas pressure behind the floating piston will force the oil through a one-way valve, past the compression adjuster and back into the shock absorber body, fig 3 flow 1 and 2.
    The oil under the piston returns through the double-acting rebound/compression adjuster in the piston shaft, fig 4 flow 3.

Hitting a big bump
When you hit a big bump the shock absorber is compressed quickly and almost totally (high shaft speed and long stroke).
    The oil can not be forced " fast enough" through just the valve in the piston shaft. The pressure in the shock absorber increases and force open the shim stack (thin steel washers stacked as a pyramid) covering the compression orifices in the piston, fig 1 flow 2.
    Also, oil displaced by the piston shaft can not be forced " fast enough" through just the valve in the reservoir. The pressure increases and a shim stack, parallel to the valve, opens, fig 2 flow 1 and 2.
    The floating piston is forced to move compressing the gas.
When the shock absorber extends, the floating piston will force the oil through the one-way valve back into the shock absorber body, fig 3 flow 1 and 2.
    The pressure is still high in the shock absorber and the flow can not be forced through just the valve in the piston shaft. The shim stack covering the rebound orifices in the piston opens and the oil returns, fig 4 flow 1.

All are tailor made
By changing the number, diameter, and thickness of the shims in the stacks and by using different jets in the valves, your Öhlins shock absorber is tailor-made for your snowmobile. The set-ups are not guesswork but the results of true tests with a snowmobile exactly like yours!