the relief valves lifting pressure setting therefore fixes the maximum loading on the rams. This in turn limits the maximum torque that is exerted on the rudder stock and the maximum torsional stress is hence limited to about 34.5 MN/m2. The gear works on the well-known principle of the 'Rapson Slide' and knowing the maximum lifting pressure of the relief valves. Then the ram load is fixe, applying the leverage for distance to stock gives the torque exerted, which allows size calculations for the stock diameter, and horse power and sizes for the motor and pump. Higher pressure systems have relief valves acting at about 190 bar. For details of the pump block, see figure 5.9