Mechanical seals, also known as end seals, are primarily used for the sealing of rotating shafts in pumps, compressors, hydraulic drives and other similar equipment. The mechanical seal is a sealing device composed of a pair of planar friction pairs composed of a pair of moving rings and stationary rings.
The mechanical seal is a device for preventing fluid leakage by at least a pair of end faces perpendicular to the rotation axis under the action of the fluid pressure and the compensating mechanism elastic force (or magnetic force) and the cooperation of the auxiliary seals. The auxiliary seal of the compensation ring is a metal bellows called a bellows mechanical seal.
The composition of the mechanical seal:
There are mainly four types of components. a. Main seals: moving ring and static ring. b. Auxiliary seal: seal ring. c. Pressing parts: spring, push ring. d. Transmission parts: the magazine seat and the key or fixing screw.
Classification of mechanical seals:
According to the rotation or static of the spring element, it can be divided into: a rotary internal flow unbalanced single-end seal, referred to as a rotary type; a static external flow internal balance type single-end seal, referred to as a static type.
The static ring is located inside or outside the sealing end face and can be divided into: built-in type and exterior type.
According to the leakage direction of the sealing medium, it can be divided into: internal loss and outflow type.
According to the unloading situation caused by the media on the end face, it can be divided into: balanced and unbalanced.
According to the logarithm of the sealing end face, it can be divided into: single end and double end.
According to the number of springs, it can be divided into: single spring type and multi spring type.
Classified by elastic elements: spring compression and bellows.
Classified according to non-contact mechanical seal structure: hydrostatic type, fluid dynamic pressure type, dry gas sealed type.
Classified according to the temperature of the sealed chamber: high, medium, ordinary, low temperature seal.
Separated according to the pressure of the sealed chamber: ultra high, high, medium and low pressure mechanical seals.
Machine seal work should pay attention to the problem:
1. Precautions during installation
a. Pay great attention to avoid installation deviations during installation
(1) The upper pressing gland should be carried out after the coupling is aligned. The bolts should be evenly supported to prevent the end face of the gland from being skewed. Check the points with a feeler gauge. The error is not more than 0.05 mm.
(2) Check the fit clearance (ie, concentricity) between the gland and the outer diameter of the shaft or bushing. The circumference should be uniform. Check the tolerance of each point with a feeler gauge to be no more than 0.01 mm.
b. The amount of spring compression should be carried out according to the regulations. It is not allowed to be too large or too small, and the required error is 2.00 mm. Over the assembly, the end face is pressed and the other end face is worn. Too small will cause insufficient specific pressure and will not seal.
c. After the moving ring is installed, it can be flexibly moved on the shaft. After the moving ring is pressed against the spring, it should be able to bounce back automatically.
2. Precautions when disassembling
a. Care should be taken when disassembling the mechanical seal. Do not use the hand hammer and the flat shovel to avoid damage to the sealing components. A pair of wire hooks can be made, and the sealing device is pulled out in the direction of self-supporting profit and loss into the gap of the transmission seat. If the scale is not removed, it should be cleaned before disassembly.
b. If mechanical seals are used on both ends of the pump, take care of each other during assembly and disassembly to prevent loss.
c. For the mechanical seal that has been operated, if the gland is loose to move the seal, the static and dynamic ring parts must be replaced and should not be re-tightened for continued use. Because after the turbulence, the original trajectory of the friction pair will change, and the sealing of the contact surface will be easily damaged.
Machine seal normal operation and maintenance issues:
1. Preparation and precautions before starting
a. Thoroughly check the mechanical seal, and whether the attachments and pipelines are installed properly and meet the technical requirements.
b. Perform a static pressure test before starting the mechanical seal to check for leaks in the mechanical seal. If there are more leaks, you should find out the reasons and try to eliminate them. If it is still invalid, it should be disassembled and reinstalled. Generally, the static pressure test pressure is 2~3 kg/cm2.
c. Press the pump to turn the disc to check if it is light and even. If the car is struggling or not moving, check whether the assembly size is wrong and the installation is reasonable.
2. Installation and outage
a. Keep the sealed chamber filled with liquid before starting. For transporting a solidified medium, steam is applied to heat the sealed chamber to melt the medium. The car must be driven before starting to prevent the soft ring from breaking due to sudden start.
b. For mechanical seals using the pump external seal system, the oil seal system should be activated first. Finally stop the oil sealing system after parking.
c. After the hot oil pump is stopped, the cooling water of the sealing oil chamber and the end face seal cannot be stopped immediately. When the oil temperature of the end seal is lowered to below 80 degrees, the cooling water can be stopped to avoid damage to the sealing parts.
3. Operation
a. If there is a slight leakage after the pump starts, it should be observed for a while. If the leakage is still not reduced if the operation is continued for 4 hours, the pump should be stopped.
b. The operating pressure of the pump should be stable and the pressure fluctuation should be no more than 1 kg/cm 2 .
c. During the operation of the pump, evacuation should be avoided to avoid dry friction and seal damage on the sealing surface.
d. Sealing should be checked frequently. During operation, when the leakage exceeds the standard, the heavy oil is not more than 5 drops/min, and the light oil is not more than 10/min. If there is no improvement trend within 2-3 days, the pump plug should be stopped to check the sealing device.
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