Rotary-vane compressor

A rotary-vane compressor comprising:

• a main housing formed with a high-pressure chamber;
• a front-housing plate secured to said main housing and formed with a low-pressure chamber;
• and
• compression means arranged within said main housing;
• said compression means comprising a pump housing comprising a cam ring formed with a substantially eliptical cam surface and first and second ring plates mounted on said cam ring to close said cam ring, a rotor rotatably supported within said cam ring and formed with a plurality of substantially radially extending slots and a plurality of back-pressure passages each held in fluid communication with an radially inward end of the corresponding slot, and a plurality of vanes each received slidably in the corresponding slot, lubricating oil in said high-pressure chamber being conducted to said back-pressure passages;
• said cam surface of said cam ring and an outer peripheral surface of said rotor forming a pump chamber;
• said cam ring being formed with first and second intake ports which respectively communicate at their one ends with said low-pressure chamber and at their the other ends with said pump chamber and a pair of discharge ports which respectively communicate at their one ends with said pump chamber and at their the other ends said high-pressure chamber, wherein
• said pump housing is formed with a first by-pass passage which is open at its one end to said first intake port and at its the other end with said high-pressure chamber, and provided with first by-pass valve means so that said first by-pass passage is opened when an external signal is supplied, and
• said first ring plate is provided with an one-way flow check valve to block fluid communication between said first intake port and said low-pressure chamber only when said first by-pass passage is opened.