The disclosure provides a pump device capable of suppressing hydraulic amplitude and reducing noise or vibration associated with hydraulic amplitude while simplifying the structure. The pump device includes: a housing which defines a suction port, a discharge port, and an accommodation chamber; and a pump unit which is arranged in the accommodation chamber and which defines a pump chamber that expands and contracts to exert a pumping action including a suction stroke and a pressurization and discharge stroke on a fluid. The housing includes an air introduction hole that is opened to introduce air into the pump chamber at a predetermined opening timing immediately before the suction stroke is completed.

An automatic transmission has an oil pump driven by a travelling driving source. An air vent structure that expels air bubbles contained in automatic transmission fluid during pump operation has an air vent hole whose one end communicates with an outlet port of the oil pump and whose other end opens toward the oil pan. An air vent tube is connected to an opening end of the air vent hole. The air vent tube is extended up to a strainer lower side gap area located between a strainer and the oil pan, and a tube opening end of the air vent tube is placed in oil of the automatic transmission fluid.

A momentum pump apparatus for mechanically pumping fluids includes a pump housing defining a housing inside. A housing front side has a fill aperture extending through to the housing inside. A housing back side has a supply aperture extending through to the housing inside. A fluid line is coupled within the pump housing and is in fluid communication with the supply aperture and the fill aperture. A pump is coupled within the pump and is in fluid communication with the fluid line to bring fluid from the supply aperture to the fill aperture. A gear system is coupled within the pump housing and includes a weighted disc to maintain momentum once spinning. The gear system is in operational communication with the pump. A handle assembly is coupled to the pump housing and is in operational communication with the gear system to operate the pump.

An automatic transmission has an oil pump driven by a travelling driving source. An air vent structure that expels air bubbles contained in automatic transmission fluid during pump operation has an air vent hole whose one end communicates with an outlet port of the oil pump and whose other end opens toward the oil pan. An air vent tube is connected to an opening end of the air vent hole. The air vent tube is extended up to a strainer lower side gap area located between a strainer and the oil pan, and a tube opening end of the air vent tube is placed in oil of the automatic transmission fluid.