Abstract: A flow test chamber for diminishing and diverting the flow of a high pressure stream of water while testing a fire pump has a hollow chamber supported on a main support frame for receiving a high pressure stream of water forced by the fire pump through standard playpipes and nozzle tips retained in a stable position adjacent the hollow chamber on a playpipe support frame mounted on the main support frame. Screens suspended within the chamber diffuse and divert the flow of water as it enters the chamber with the water subsequently exiting through a discharge opening at a reduced rate of flow and diffused over a large area. An under carriage supports the main support frame for movement of the flow test chamber over the underlying surface in a generally horizontal orientation for easy positioning adjacent the fire pump to be tested.