Transducer Converter Spoiler control Locked wheel comparator Locked wheel Pressure bias modulator Summing amplifier Valve driver Valve Deceleration reference Velocity reference Velocity comparator Lead Transient control Left inboard wheel card To right inboard  lock wheel  comparator Figure 13-109.  A Boeing 737 antiskid control unit internal block diagram.  position of the valve. Brake pressure increases, decreases,  or holds steady depending on this value. a voltage output that is sent to the summing amplifier to do  this. A lead output from the comparator anticipates when the  tire is about to skid with a voltage that decreases the pressure  to the brake. It sends this voltage to the summing amplifier as  well. A transient control output from the comparator designed  for rapid pressure dump when a sudden skid has occurred also  sends voltage to the summing amp. As the name suggests, the  input voltages to the amplifier are summed, and a composite  voltage is sent to the valve driver. The driver prepares the  current required to be sent to the control valve to adjust the  Anti-skid control valves are fast-acting, electrically  controlled hydraulic valves that respond to the input from  the anti-skid control unit. There is one control valve for  each brake assembly. A torque motor uses the input from  the valve driver to adjust the position of a flapper between  13-64 Anti-Skid Control Valves