Patent ID: 7422421

Claim:
A plunger pump apparatus comprising: a body; an electric motor mounted on one side of the body for rotating a pump drive shaft having an eccentric cam portion; at least one of pumps provided in the body and having a plunger reciprocated by the eccentric cam portion; a reservoir chamber formed between a motor casing of the electric motor and the body, and communicating with a vent passage provided in the electric motor to thereby communicate with an inside of the electric motor; and a drain port provided in the body having an external open end thereof oriented downwardly so as to communicate the reservoir chamber to an outside, wherein a capacity of the reservoir chamber below the vent passage is set to become larger than a sum of a cooling contraction amount of air in the electric motor and the reservoir chamber which contracts according to cooling by water covering the pump apparatus which has been warmed up under an operating environment and a pressurizing compression amount of air in the electric motor and the reservoir chamber which is compressed by a water pressure applied from the drain port when the pump apparatus is submerged.