Simple structure, small number of parts, high durability and reliability, high displacement controllability at high speed, low pressure loss with inner side air suction, large internal chamber volume, excellent pulsation reduction effect, further pulsation reduction with one-way air suction and evacuation valve, small number of kinematic pairs, low running noise, low suction noise with all-rubber sucker, small number of sliding friction pairs, low no-load torque, low weight with high percentage of aluminum alloy