PRESSURE C     [bv force + press]     P.mv - P.bv = bv force
P.mv is the pressure variable in the bv force.  This press is determined by the stiffness of the bv stack.  A stiffer bv will create HIGHER pressures, and have higher bv dyno force numbers. P.bv is dependant on the icspr, and does not fluctuate with valving changes, but will increase slightly as the temperature increases. The press increases due to thermal expansion of the oil (there is no actual gas with an icspr). Consider P.mv as the primary pressure, and P.bv as secondary.  'bv force' comes from  P.mv - P.bv. Note:  If the bv is stiffened, and P.mv is higher, P.r will also be higher by the same amount. i.e.  If the P.mv graph line goes up, the P.r line has to follow.  See graph below.