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Mid-Valves and Base Valves
Finally computer software to tune a shim
Two types of valves are used in suspension systems: mid-valves and base-valves. The base valve controls compression damping and the mid-valve controls rebound. On the mid-valve the check plate can be replaced with a valve stack for use in augmenting compression damping. The ReStackor models both types of valves through specification of the input keywords BVc, MVc and MVr.
ReStackor pro input file specifies valve type through the keywords BV, MVc or MVr.
Base Valve (BV)
During compression the damper rod is forced into the shock body and forces oil to flow out through the base valve. The oil flow rate through the base vale is defined by:
Mid-Valve (MV)
During rebound the oil trapped between the mid-valve and damper rod is forced through the mid-valve. The flow rate through the mid-valve is defined by:
Difference in oil flow rate between mid-valve and base valve
For typical fork dimensions of drod= 12.5mm and dvalve= 24 mm operating at a velocity of 100 in/sec the oil flow rate through the base valve is 2.9 L/min and the flow rate through the mid valve is 7.8 L/min. The mid-valve processes nearly three times more oil then the base valve. Due to the higher oil flow the mid-valve is capable of producing much more damping than the base valve. Due to the different oil flow rates the mid-valve stack needs to be configured differently than the base valve.
Damping force
The damping force produced by the mid-valve is created by the pressure difference between the compression and rebound face of the valve. During rebound the damping force is defined by:
During compression the total damping force is the combined force produced by the base and mid-valve:
The differences in these two expressions required the MVr and MVc keywords in the ReStackor input file so the code can figure out if the mid-valve is operating in the rebound (MVr) or compression (MVc) phase of the shock absorber stroke.
