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Mechanical seal technology review

I Basic knowledge of mechanical seal:

1 Basic concept of mechanical seal:

mechanical seal refers to a device that prevents fluid leakage by at least one pair of end faces perpendicular to the rotation axis under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism and the cooperation of the auxiliary seal. The auxiliary seal of compensation ring is metal bellows, which is called bellows mechanical seal

2. Composition of mechanical seal:

there are mainly the following four types of components. a. Main seals: moving ring and stationary ring. b. Auxiliary seal: sealing ring. c. Pressing parts: spring and push ring. d. Transmission parts: Spring skip seat and key or fixed screw

II Problems needing attention in mechanical sealing work:

1 Precautions during installation

a. great attention should be paid to the production materials of the experimental machine of Jinan new era assay instrument Co., Ltd. the parameters of the high-end model are selected to avoid the installation deviation during installation, (1) the tightening of the gland should be carried out after the alignment of the coupling, and the bolts should be evenly supported to prevent the end face of the gland from deflection. Check all points with a feeler gauge, and the error is not more than 0.05 mm. (2) Check the fitting clearance (i.e. concentricity) between the gland and the outer diameter of the shaft or shaft sleeve, and the circumference should be uniform. Check with a feeler gauge that the allowable deviation of each point is not greater than 0.01 mm

b. the spring compression shall be carried out according to the regulations, and it is not allowed to be too large or too small. The error is required to be 2.00mm. If it is too large, the specific pressure of the end face will increase, and the end face will wear out at another speed. Too small will cause insufficient specific pressure and cannot play a sealing role

c. after the movable ring is installed, it can move flexibly on the shaft, and it should automatically spring back after pressing the movable ring against the spring

2. Precautions during disassembly

a. be careful when disassembling the mechanical seal. It is strictly forbidden to use a hammer and flat shovel to avoid damaging the sealing elements. A pair of steel wire hooks can be used to stretch into the gap of the transmission seat in the direction of self financing and pull out the sealing device. If scaling cannot be removed, it should be cleaned before disassembly

b. if mechanical seals are used at both ends of the pump, take care of each other in the process of assembly and disassembly to prevent one from neglecting the other

c. for the mechanical seal that has been operated, if the gland is loose and the seal moves, the dynamic and static ring parts must be replaced and should not be re tightened to continue to use. Because after the sample moves, the original running track of the friction pair will change, and the sealing practice of the contact surface has proved that the sealing property is easy to be destroyed

III Normal operation and maintenance of mechanical seal:

1 Preparations and precautions before startup

A. comprehensively check whether the mechanical seals, auxiliary devices and pipelines are installed completely and meet the technical requirements

b. conduct static pressure test before starting the mechanical seal to check whether the mechanical seal has leakage. If there are many leaks, find out the causes and try to eliminate them. If it is still invalid, it should be disassembled, checked and reinstalled. Generally, the static pressure test pressure is 2~3 kg/cm2

c. turn the gear according to the pump direction and check whether it is light and uniform. If the turning gear is hard or stationary, check whether the assembly size is wrong and whether the installation is reasonable

2. Installation and shutdown

a. keep the sealing cavity full of liquid before startup. When transporting solidified medium, steam shall be used to heat the sealing cavity to melt the medium. Mr. Bakker finally stressed that the turning gear must be carried out before starting to prevent the soft ring from breaking due to sudden starting

b. for the mechanical seal using the oil sealing system outside the pump, the oil sealing system should be started first. Stop the oil sealing system after shutdown

c. after the hot oil pump is stopped, the cooling water of the sealing oil chamber and end face seal cannot be stopped immediately. The cooling water can be stopped only when the oil temperature at the end face seal drops below 80 degrees, so as to avoid damaging the sealing parts

3. Operation

a. if there is slight leakage after the pump is started, it should be observed for a period of time. If the leakage does not decrease after continuous operation for 4 hours, stop the pump for inspection

b. the plastic food packaging of the pump is an article that consumers often contact in daily life. The operating pressure should be stable, and the pressure fluctuation should not be greater than 1 kg/cm2

c. during the operation of the pump, evacuation should be avoided to avoid dry friction and seal damage on the sealing surface

d. the sealing condition should be checked frequently. During operation, when the leakage exceeds the standard, the heavy oil is not more than 5 drops/minute, and the light oil is not more than 10 drops/minute. If there is still no improvement trend within a day, stop the pump plug and check the sealing device. (end)