One of the main contributors of water hammer can be the choice of check valve type. Valve types, such as swing, tilting disc or piston style check valves, depend on gravity and the reversal of flow to return the valves to the closed position. This causes water to slam into the valve mechanism, creating a pressure wave that propagates through the piping system. Silent or spring-assisted check valves, on the other hand, are fitted with an internal spring that silently moves the valve into closed position before flow reversal, thereby reducing or eliminating the possibility of water hammer. Air chambers are also an effective water hammer solution. These systems consist of a short segment of pipe, usually in the form of a tee-fitting, with an empty/air-filled chamber that serves as a cushion (shock absorber) for the water to expand when it changes direction suddenly. This reduces the magnitude of shock that would otherwise be directed towards the pipeline.