The water used for the water brake is taken from inside the boiler at the back head of the boiler. This water is very hot “200 lbs approximately 380 F”. It then is injected into the exhaust porting of the cylinder saddle. When used the engine is meant to be in reverse. When in reverse the exhaust porting would be at or less than atmospheric pressure. Water of a temperature higher than boiling point will flash to steam as soon as it is moved in to the low pressure porting. The steam produced by the hot water now does two things.
1.) It stops cinders & smoke and other nasty things from being drawn in to the porting & cylinders.
2.) adds steam to the cylinders adding to the braking effect Phil talked about.
They call it a water brake but when used properly you don’t get water in the cylinders. If you manage to create a situation where a lot of water did fill the exhaust porting and the cylinders you would damage the heads or more.
Jack