The Selection of Sealed Materials

The fluid seals have many different materials and structures, mainly gaskets in flanged connections, which are used in pump and valve compression packing. The first step of selecting the correct seal for any given application condition is to determine the required sealing performance level and the application conditions.

The gasket

The gaskets used for flange connections have a wide variety of materials, shapes and sizes. The use of organic or inorganic fibers, fillers and rubber adhesive for pressing sheet gaskets can be widely used in industry. There are many kinds of sealant formulations available, whether in general working conditions, mild corrosive medium to high temperature, high pressure and corrosive medium. It can also be used for gaskets containing special elastomer, which can contact the fluid and expand without losing its integrity and sealing effect. In the process fluid, these gaskets provide light compression loads for light flanges. It is better than the standard fiber pads, they can be sealed under low loads. At the same time, unlike most general gaskets that can only expand in oil, they are also suitable for use in water media. These gaskets can seal the flange under non-perfect parts and they are ideal for compressors, generators, pumps and other equipment.

For extreme temperature (1400~1000 F), high pressure (up to 2000 PSI) and corrosive medium, the graphite pads can withstand most non-oxidizing chemicals, and it can provide excellent compression force and low creep relaxation. In the case of serious corrosion, we usually choose PTFE gaskets, which can provide better anti-chemical corrosion performance. The modified polytetrafluoroethylene is used in the production of these gaskets, which can improve the anti-cooling and creep resistance compared with the traditional polytetrafluoroethylene. These improvements help maintain torque and save the need for repeated tightening of flanges. The polytetrafluoroethylene gaskets can withstand exposure to a large number of corrosive media, including strong acids, caustic soda, solvents, hydrocarbons and low temperature environments.

The gasket manufacturer provides detailed data for each of their products, including materials and physical properties, as well as sealing characteristics. The geometry of the gasket must also be taken into account when making the final selection of the data.

The properties of gaskets generally decrease with the increase of material thickness. The thicker pads require higher compression loads, which may not be available in certain operating conditions, for example, glass, non-metal or specially designed flanges. The thinner gaskets require a flatter flange, and there are many kinds of flanges surface defects which make the thin gaskets unsealed. But they are low cost and can improve the performance of flanged connections by reducing dissipation and product loss and enhancing anti-blow-out performance. We should select ring pads as much as possible instead of covering the entire flange face. In contrast, the annular pad can be combined in a bolt circle to reduce the compression load significantly for an effective seal.

The compression packing

A gasket material used for sealing valves, pumps, mixers, and other rotating equipment. It has different materials and structures.

Valves and pumps under high temperature, high pressure and high speed chemical conditions should be made of graphite lubricated carbon fiber or flexible graphite packing to reduce friction and reduce shaft wear and maintenance.

Flexible graphite filler can resist chemical and self-lubrication, which can be used to seal the leakage rate of one millionth of the level. The filler made of high graphite spun yarn is good at extreme temperature and pressure, and can provide excellent anti-chemical and thermal conductivity. Select the type of filler to make sure it retains its original volume and retains the flexibility to remove easily. The packing of polytetrafluoroethylene can withstand chemical erosion.

The preparation of polytetrafluoroethylene particles in polytetrachloride spinning is suitable for the valve. Pumps used in chemical and food processing industries are used impregnated and coated with silicone or other lubricated polytetrafluoroethylene woven packing.

There are also engineering packing parts designed for use in pumps and valves. For example, the recently developed application of industrial pumps to replace mechanical seal rotary seals, it can provide zero leakage and no dilution in the application of pump slurry. Excellent heat dissipation enables it to remain sealed with minimal water. Stem packing is being used in a simplified form of several components to achieve low dissipation.

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