Central swivel joint composed by the housing and the mandrel, the casing attached to the upper body to the lower body mounting the mandrel. Open on the mandrel and has an equal number of tubing annular groove, from the housing to the hydraulic oil tank through the hole from the vertical flow of the travel motors on the mandrel, so that even when the housing continuously with the upper portion of the rotary body, the mandrel The trench also with the oil port on the housing remain open. Hydraulic oil can freely in and out. Failure to timely replacement of hydraulic oil filter, the filter can lead to open the bypass valve, hydraulic oil due to unfiltered impurities in the oil directly into the sliding surface finishing center swivel joint variable pump ', sealing it on Circle damage variable pump maintenance ', the machine while walking due to the pressure side of the oil leak caused by walking on both sides of the motor speed is not the same, resulting in a machine running deviation. Remedy is: rotary joint replacement center seal; hydraulic oil and filter replacement. Piston variable displacement pump variable pump Schematic diagram, figure; the drive shaft is rotated by a diesel engine with and promote the cylinder rotates, the cylinder piston and the cylinder rotates together. Swash plate does not rotate around its center point just swing around. The left end of the spherical portion of the plunger to slide on the swash plate. When the figure at the top of the plunger to the following variable pump specializing 'in the axial position of the plunger from the lower dead point went dead and go on a trip. In this case the suction of the plunger a certain amount of oil. As the plunger continues from a lower position to an upper position again when it and from the top dead center in the axial direction come lower dead point, the suction of a quantity of oil discharged from the drain hole. This is the pump discharge pressure oil. Each cylinder 1 a plunger, which is spinning cylinder with oil pump continuously from the hydraulic tank suction and discharge pressure of the hydraulic oil. Variable pump repair phone 'crystal to create a hydraulic (certified), variable pump from Jinan Jing Chong hydraulic machinery Limited. Jinan Jing Chong Hydraulic Machinery Co., Ltd. (www.jnjcyy.com) (www.jnjcyy.com) Shandong Jinan, mining machinery leaders, over the years, the company is implementing the scientific management, innovation and development, the principle of honesty and trustworthiness, the maximum meet customer needs. In the crystal to create a hydraulic leadership with the staff warmly welcome all inquiries negotiations to create the crystal to create a better future for the hydraulic.