Add manual information for WSP

Author: peternewell

Source/Documentation/Manual/physics.rst

@@ -3166,6 +3166,28 @@ To control the application and release rates on the brake use the ``EngineBrakes
 The ``SteamBrakeFX`` special effect, if added to the wagon, will turn on and off with the brake operation 
 and can be used to model steam leakage of the steam brake cylinder, etc.
 
+Wheel Slide Protection
+----------------------
+
+Open Rails supports the use of Wheel Slide Protection (WSP) on trains with air brakes. WSP operates as described below.
+
+During braking wheelslide control is effected throughout the train by additional equipment on each vehicle. In the piping to each 
+pair of brake cylinders are fitted electrically operated dump valves. When axle rotations which are sensed electrically, differ 
+by a predetermined speed the dump valves are operated releasing brake cylinder pressure to both axles of the affected bogie.
+
+Dump valve operation will cease when differences in axle rotations are within specified limits or the axle accelerates faster than 
+a specified rate. The dump valve will only operate for a maximum period of seven seconds after which time it will be de-energised 
+and the dump valve will not re-operate until the train has stopped or the throttle operated. 
+
+Dump valve operation is prevented under the following conditions:
+
+- When the Power Controller is open.
+- When Brake Pipe Pressure has been reduced below 36 psi (250 kPa).
+
+To enable WSP ``ORTSWheelBrakeSlideProtection (1)``. If it is desired that emergency braking should not be impacted by WSP, then use 
+the ``ORTSEmergencyBrakingDisablesWSP (1)`` parameter.
+
+
 Dynamically Evolving Tractive Force
 ===================================