To optimally control a load depending on power capacity by forming two or more exhaust ports on a connecting tube between the delivery port of a pre-stage compression chamber and the intake port of a post-stage compression chamber, providing each exhaust port with a solenoid valve and controlling the solenoid valve, when drive current for an electric motor becomes equal to a load control start current value.
A two-stage compressor for feeding the compressed air to a pneumatic work machine such as a pneumatic nail driver, has a connecting tube 6a for connecting the delivery port 4b of a pre-stage compression chamber 2 and the intake port 5a of a post-stage compression chamber 3 to each other, and the delivery port 5b of the post-stage compression chamber 3 is connected to a compressed air reservoir 7 via a connecting tube 6b. In this case, exhaust ports 8a and 8b are formed on the connecting tube 6a, and respectively fitted with a first and a second solenoid valves SV1 and SV2. A control part 10 makes judgement about the load status of an electric motor 1 on the basis of a current value measured with a measurement means for measuring current flowing in a drive circuit. When the drive current becomes equal to a load control start current value, both of the solenoid valves SV1 and SV2 are controlled, thereby causing the valves SV1 and SV2 to control a load on the electric motor 1.
YOSHIDA TSUTOMU
TABUCHI YASUHIRO
