Gasket is a kind of sealing spare parts used for machinery, equipment and pipelines as long as there is fluid. It uses internal and external sealing materials. The gasket is made of metal or non-metal plate material, which is made by cutting, stamping or cutting. It is used for the sealing connection between pipes and the sealing connection between the machine parts(like centrifugal pumps). According to the material, it can be divided into metal gasket and non-metal gasket. Metal has copper gaskets, stainless steel gaskets, iron gaskets, aluminum gaskets, etc. Non-metallic asbestos gaskets, non-asbestos gaskets, paper gaskets, rubber gaskets, etc.
How to choose a gasket
Important Factors Affecting the Selection of Gaskets Gasket selection is not an easy task, especially in the selection of gasket sealing materials. The variables that appear at the flange joints seem to be endless, and all of these uncertainties affect the sealing effect of the gasket. In the past, the parameters "TEMP" (temperature, application, medium, pressure) seemed to be sufficient. However, today, the processing quality of the flange, the amount of bolt thread insertion, the amount of flange rotation, the amount of bolt tension, the filler of the medium and the surface treatment of the flange all affect the sealing effect of the gasket. Therefore, various parameters must be considered in order to make appropriate choices.
(1) Temperature
In most types of selection, the temperature of the fluid is a primary consideration. This will quickly narrow down the selection, especially from 200°F (95°C) to 1000°F (540°C). Higher levels of material should be used when the system operating temperature reaches the limit of the maximum continuous operating temperature of a particular gasket material. This should also be the case at certain low temperatures.
(2) Application
The most important parameters in the application are the type of flange and the bolts used. The size, number and level of bolts in the application determine the payload. The effective area to be compressed is calculated from the gasket contact size. An effective gasket seal pressure can be derived from the load of the bolt and the contact surface of the gasket. Without this parameter, you won't be able to make the best choice among the many materials.
(3) Medium
There are thousands of fluids in the medium, and the corrosive, oxidizing, and permeability of various fluids are very different. Materials must be selected based on these characteristics when selecting. In addition, the cleaning of the system must also be taken into account to prevent the cleaning fluid from eroding the gasket.
(4) Pressure
Each gasket has its highest ultimate pressure, and the pressure resistance of the gasket decreases as the thickness of the material increases. The thinner the material, the greater the pressure bearing capacity. The selection must be based on the pressure of the fluid in the system. If the pressure often fluctuates drastically, you need to know the details to make a choice.
(5) PT value
The so-called PT value is the product of pressure (P) and temperature (T). The material's pressure resistance is different at different temperatures and must be considered comprehensively. In general, the manufacturer of the gasket will give the maximum PT value of the material.
Sealing gasket installation requirements
Gasket
1. The sealing gasket and flange sealing surface should be cleaned, and there should be no defects such as scratches and spots that affect the connection sealing performance.
2. The outer diameter of the sealing gasket should be smaller than the outer surface of the flange sealing surface. The inner diameter of the sealing gasket should be slightly larger than the inner diameter of the pipeline. The difference between the two inner diameters is generally 2 times the thickness of the sealing gasket to ensure the sealing gasket after compaction. The inner edge does not protrude into the container or conduit to prevent interference with the flow of fluid in the container or conduit.
3. The pre-tightening force of the gasket should not exceed the design regulations, so as to avoid the excessive compression of the gasket and the rebound ability.
4. When the gasket is pressed, it is best to use a torque wrench. For large bolts and high strength bolts, hydraulic tensioners are preferred. The tightening torque should be calculated according to the compression of a given gasket. The hydraulic pressure of the hydraulic tensioner should also be determined by calculation.
5. When installing the gasket, tighten the nuts in order. However, the design value should not be reached once. Generally, it should be circulated for at least 2 to 3 times so that the stress distribution of the gasket is uniform.
6. For pressure vessels and pipelines with flammable and explosive media, safety tools should be used when replacing gaskets to avoid sparks caused by the collision of tools with flanges or bolts, resulting in fire or explosion accidents.
7. If the pipeline leaks, it must be replaced after the pressure reduction treatment or adjust the installation of the gasket. It is strictly forbidden to operate with pressure.
Special installation requirements
1. When installing the sealing and winding gasket matched with the protruding plane flange, care should be taken to ensure that the sealing member is concentric with the pipe. Generally, the outer reinforcing ring is placed in contact with the inner circumferential surface of the bolt to be positioned, and eccentric mounting is not allowed. When installing the basic type of wound gasket in the flange of the groove surface sealing surface, be careful to keep the gap with the groove wall surface.
2. When installing a metal-coated gasket with a narrow width, a steel plate with a certain thickness should be placed on the outside of the gasket, and then the flange should be pressed to prevent the coating of the metal gasket from being pressed after the metal gasket is pressed. (or lap) expand and damage the metal coated gasket.
3. When the working temperature of the flange is higher than 200 °C, a sealant should be applied between the flange sealing surface and the sealing gasket to prevent the sealing gasket from sealing with the flange sealing surface at high temperature, and to increase the inspection and replacement of the sealing gasket. trouble.
4. When the sealing surface is not flat, sealant can be applied on the sealing surface before installing the sealing gasket. The sealant is generally composed of manganese dioxide, lead dan, graphite powder and linseed oil (dry oil). The corresponding type and grade of liquid sealant can be selected according to the conditions of sealing medium, working temperature and medium pressure.
5. For the installation of octagonal metal ring gaskets, when the metal ring gasket and flange sealing groove are not ideally processed, it can be closely fitted by matching research. For large-diameter metal ring gaskets, it is difficult to match the research. In order to fill the small unevenness of the metal surface, a sealant can be used.
