A fluid spray gun include a pressure vessel, a valve disposed in the pressure vessel and configured to be actuated between an open position and a closed position, a trigger actuatable to actuate the valve between the open and closed positions; and a valve actuating mechanism assembly partially disposed in the pressure vessel and coupled to the trigger. The valve actuating mechanism assembly includes an axle, a valve contacting member disposed along the axle and configured to contact the valve, a first sealing element disposed in the pressure vessel and configured to create a first seal against the axle and a first seal against the pressure vessel, a second sealing element disposed in the pressure vessel and configured to create a second seal against the axle and a second seal against the pressure vessel, and a fastener including threads and a hole configured to receive a portion of the axle.