Common sealing methods are as follows.
Gap seal
Gap sealing is a commonly used sealing method that relies on small gaps between mating surfaces of relative moving parts to prevent leakage.
According to the axial flow theory of annular gap, the leakage is proportional to the cubic of the gap, so the leakage can be reduced by reducing the gap. The general clearance is 0.008 ~ 0.05mm, which requires the mating surface to have a high processing accuracy.
Piston ring seal
The piston ring seal relies on the elastic metal ring installed in the annular groove of the piston to seal against the inner wall of the cylinder.
Ring seal
Seal ring seal is the most widely used in hydraulic system of a kind of seal, seal ring has O shape, V shape, Y shape and combined type, etc., its material is oil-resistant rubber, nylon, composite polytetrafluoroethylene and so on
(1) V-shaped sealing ring
The cross section of the V-shaped ring is V-shaped, and the V-shaped sealing device is composed of a pressure ring, a sealing ring (ring) and a supporting ring.
When the working pressure is higher than 10MPa, the number of V-rings can be increased to improve the sealing effect.
When installing, the opening of the V-ring should face the side with high pressure.
(2) Y-shaped sealing ring
The cross section of the Y-shaped sealing ring is Y-shaped and belongs to the lip sealing ring.
The sealing effect of Y-ring depends on the close contact degree of its lip edge to the coupling circle. Under the action of pressure oil, the lip edge produces a large contact pressure to the coupling surface, so as to achieve the purpose of sealing; When the liquid pressure increases, the lip and the coupling surface are more tightly attached, the contact pressure is higher, and the sealing performance is better.
When the Y-ring is installed, the lip end face should be on the side with high pressure. When the pressure changes greatly and the sliding speed is high, a retaining ring is added on the back side of the lip as a support ring to fix the sealing ring.
The basic requirement of the design or selection of sealing device is to have good sealing performance, and to automatically improve the sealing with the increase of pressure, in addition, the friction resistance should be small, oil resistance, corrosion resistance, wear resistance, long life, simple manufacturing, convenient disassembly.
(3) O-ring seal
The cross section of the O-ring is round. When there is no liquid pressure, pre-contact pressure is generated on the contact surface by the elasticity of the O-ring to achieve initial sealing. When the sealing cavity is filled with pressure oil, under the action of liquid pressure, the O-ring is squeezed to one side of the groove, and the contact pressure on the sealing surface rises, improving the sealing effect.
Any shape of the sealing ring in the installation, must ensure the appropriate amount of pre-compression, too small can not be sealed, too large friction increases, and easy to damage, therefore, the installation of the sealing ring groove size and surface accuracy must be strictly guaranteed according to the data given by the relevant manual.
In the dynamic seal, when the pressure is greater than 10MPa, the O-ring will be squeezed into the gap and damaged, so it is necessary to set a stop ring made of polytetrafluoroethylene or nylon on the low pressure side of the O-ring, its thickness is 1.25 ~ 2.5mm, when the two-way high pressure, both sides should be added to the stop ring.