The invention discloses a double-acting 
retarder, which comprises a frame, a speed changer and a transmission shaft, and the double-acting 
retarder is characterized in that an output shaft of a speed changing box is connected with a 
cam and a 
brake disc body, two sides of the 
cam and the 
brake disc body are respectively and symmetrically provided with a 
plunger pump, the 
plunger pumps are connected with a heat radiating 
oil tank through an oil inlet 
pipe with a one-way valve A, the oil inlet 
pipe is connected with a one-way valve B through a tee joint, the other end of the one-way valve B is connected with a 
brake device through an oil outlet 
pipe, the oil outlet pipe is also connected with a throttling valve through a tee joint, the throttling valve is connected with the heat 
radiation oil tank through an oil return pipe, the outer side of each 
plunger pump is wrapped by a brake slide groove, a thrusting 
air chamber is arranged between the bottom end of each 
plunger pump and the brake slide groove, the front end of each 
plunger pump is provided with a guide wheel, the guide wheel is matched with the came and the brake disc body, the thrusting 
air chamber is connected with an air 
storage tank through a retarding switch, and both the retarding switch and the throttling valve are connected with a 
control unit.