Smooth surface clearance seals can be used as liquid and gas seals with a pressure difference of 100MPa or more, and the sliding speed and temperature are virtually unlimited. The cylinder gap seal is provided with a sealing ring, a sleeve, etc. The impeller seal ring of centrifugal pump, the lubrication of hydraulic components and cylinder liner, and the simple seal of back pressure jacket of high pressure reciprocating pump all rely on the hydrostatic pressure effect of cylinder annular clearance throttling to reduce leakage.
First, sealing ring
In order to improve the volumetric efficiency of the centrifugal pump and reduce the liquid leakage and wear between the impeller and the pump shell, a detachable sealing ring is installed on the outer edge of the pump shell and the impeller inlet.
The flat ring type sealing ring has simple structure and convenient manufacture, but the sealing effect is poor. Because the leaking liquid has a considerable velocity and flows vertically into the liquid main stream, there is a large eddy current and impact loss. The radial clearance S of this sealing ring is generally between 0.1 and 0.2mm. The axial clearance S1 of the right-angle sealing ring is much larger than the radial clearance, generally between 3 and 7mm, because the leakage of liquid after turning 90° its speed is reduced, so the vortex and impact loss is small, and the sealing effect is better than the flat ring type. Because the labyrinth sealing ring increases the resistance of the sealing gap, the sealing effect is good. However, the structure is complex and difficult to manufacture, and it is rarely used in general centrifugal polymerization.
The wear of the sealing ring will reduce the efficiency of the pump, and it should be replaced in time when the tight clearance exceeds the specified value. Sealing rings should be made of wear-resistant materials, commonly used materials are cast iron, bronze and so on.
Second, sleeve seal
The sleeve seal has simple structure, compact and small friction resistance, but it has a certain leakage amount, and the leakage amount increases with the increase of the seal gap.
The gap between the outer diameter of the sleeve and the shell is greater than the gap between the inner diameter of the sleeve and the shaft. When the fluid passes through the inner diameter, the pressure gradient is generated, while the outer diameter is uniformly compressed by the liquid, so that different pressure differences and deformation are generated on the axis of the sleeve. The higher the pressure, the greater the reduction of the home. In order to control the clearance and pressure gradient in the axial length direction, the sleeve can be made into a variable section structure.
The interval between the horizontal reciprocating piston pump sleeve and the shaft varies according to the pressure, such as when the pressure is 600MPa, the clearance is 0.013-0.043mm.
The gap between the outer diameter of the sleeve and the plunger is 0.045~ 0.11mmi. When the pressure is 100MPa, the gap between the sleeve and the plunger is 0~0.024mm, and the outer gap is 0~0.031mm. The clearance of the hydraulic component takes the surface roughness of the plunger of 0.004 ~0.008mm RA-0.20 ~0.25μm, the inner hole of the sleeve Ra= 0.20 μm, and the outer ring Ra= 1.6~2.0pm. The plunger material is GCr15, W18Cr4V. The sleeve is W18Cr4V. Broken bronze, 30Cr3MoWV, etc.
Sleeve seal has a long service life, suitable for high temperature, high pressure, high speed, and can also be used in combination with other sealing structures. Due to the inevitable leakage of the sleeve, it is necessary to have a pressure control system and a leak recovery device.