The role of sealing: to prevent the pressure inside the cylinder, the leakage of the working medium and to prevent the invasion of foreign dust, dirt and foreign bodies. There are two kinds of sealing parts for night pressure cylinders: one is the part without relative movement, the other is the part with relative movement. The former adopts static seal, and the latter uses dynamic seal.

Hydraulic cylinders need to use static sealing parts: piston and piston rod between the connecting parts (more two-way seal); cylinder and the end of the cover (one-way seal).

The hydraulic cylinder to the dynamic sealing parts between the piston and cylinder hole (with seal, piston two-way or one-way) seal, hydraulic cylinder, gear pump to prevent the high pressure cavity on the cavity between the piston rod and the cylinder head; the guide sleeve (or one-way seal) seal, hydraulic cylinder to prevent leakage.

The requirement of static sealing is mainly to the requirement of elasticity, there is a certain margin of compression. Besides the elasticity, the requirement of dynamic seal has good abrasion resistance and long service life, and the friction force should not be too big. Static seal usually adopts O ring and combination (or soft metal) gasket; a movable seal in addition to the traditional V, U, Y, YX seal, now also often uses the combined type hydraulic cylinder seals, hydraulic cylinder has a better way to solve the problem of dynamic seal.