Gaskets: what they are and what type of seal they are used for?

Fluid sealing is essential for the proper functioning of mechanical equipment and the insertion of gaskets is one of materials most used.

They are easy to install and suitable for virtually all types of fluids, be they of different pressure and temperature ranges.

What are gaskets?

Gaskets are o-rings seal that can be applied to static systems such as, for example, greenhouse doors and sealing of inspection and manhole covers. But they can also be applied to dynamic systems, as a seal in valves, pumps and reactors.

Used in systems with axial elements such as cylinders, pistons and axles in general, the sealing provided by the gaskets is due to the pressure that the material exerts against the wall of the axial element.

Gaskets provide sealing for low-voltage systems, medium and high pressure. The specifications of each material used in its production determine the operating conditions for each product.

Simple features and mechanics, they contain a high degree of innovation in their materials used (fibers and lubricants), that must have resilience, adequate chemical and mechanical resistance.

How the gasket works

Gaskets work under compression. Mechanical or pressure packings consist of several rings that are inserted into the annular space (stuffing box) between the rotating or reciprocating member and the pump body or valve.

When tightening the gasket press against the upper or outer ring, pressure is transmitted to the gasket set, which expands the rings radially against the side of the stuffing box and seals.

Proper operation of gaskets used in rotary or reciprocating pump service typically depends on a film of fluid to cool, lubricate and reduce friction.

Residual leakage is expected, but the amount of leakage considered normal depends directly on the type of gasket. However, The acceptable leakage limit is 50 drops per minute.

Those that do not leak are compression gaskets used on valves that move slowly or infrequently., or static operations.

How to choose the most suitable gasket

When talking about gaskets, there are several braid configurations, fibers and material combinations. Therefore, Selecting the most suitable sealing material for each application may not be such a simple process..

There is, nonetheless, some attributes that must be considered when finding the ideal gasket. They are:

• Size: directly influences the type of gasket to be used. It is also important to know the diameter of the shaft where it will be applied..

• Temperature: directly influences the performance of gaskets. The higher the temperature, more meticulous should be the choice of gasket, since the wrong option can burn and carbonize the material, which would make the gasket unable to perform the sealing function.

• Application: It is essential to know the type of equipment in which the gasket will operate to indicate the most suitable material.

• Fluid: The gaskets are built to operate in the most diverse types of fluids, nonetheless, know if it is gaseous or liquid, abrasive or clean, helps select the most suitable sealing material. Its attributes must have chemical compatibility with the fluid.

• Pressure: each gasket is also designed to withstand a certain pressure range. If it is applied to equipment with pressure greater than the supported limit, there may be serious accidents. Fluid pressure indication ensures good gasket performance.

• Speed: a good quality gasket is made of resistant materials to guarantee good operation also according to the rotation speed of the shaft.

Where gaskets are applied

Compression gaskets are used in mixers, agitators, dryers, valves, soot blowers, rotary pumps, centrifugal pumps, reciprocating pumps and many other types of mechanical equipment that can be divided thus:

Dynamic equipment → Can be subdivided into rotating equipment and alternative equipment:

• Rotating equipment: pumps of the most varied types are part of this group. Gear pumps can be mentioned, centrifugal pumps, vacuum pumps, screw pumps etc.
• Alternative equipment: In this group there is equipment such as piston pumps that can use gaskets as a form of sealing, depending on your size.

Static devices → In this group are industrial valves that, despite having a rotating axis, have a very short and seasonal turnover — that is, the valve does not work by rotating constantly. There are several types of valves that have gaskets between their components., Examples include piston valves and control valves..

Types of gasket materials

Gaskets can be composed of different materials to meet the different possible applications. Below, Check out some of the most used materials for its manufacture:

Acrylic: presents good mechanical resistance and provides excellent dimensional stability. These gaskets are recommended for applications up to 230 °C.

Aramid: It has excellent mechanical resistance and is capable of withstanding temperatures up to 280 °C. Made of dense and flexible material, this model Suitable for abrasive applications, waste pump sets, piston pumps, refiners, between others.

Graphite / Carbon: are conformable materials with high thermal conductivity and chemical resistance. The combination of graphite and carbon makes the gaskets three times more resistant to extrusion compared to unreinforced graphite ones. Due to the great chemical resistance of the raw materials used, a Carbon Graphite Gasket can be used in practically all media such as saturated or superheated steam, chemicals, gases, thermal fluids and solvents, with the exception of strong oxidizing agents, being widely used in boiler valves, hydrocarbons and the petrochemical industry in general.

Phenolic: has high thermal stability, good chemical resistance and excellent lubricant retention, what makes it these gaskets a recommended solution for use in applications with abrasive particles. They are used to seal abrasive fluids in steel industries, cement, among others.

PTFE: It has excellent chemical resistance and a low coefficient of friction. Due to the characteristics of its main compound, PTFE gaskets their strong points are their non-toxic attribute, excellent chemical resistance and sealability. Therefore, They become an excellent option for sealing valve stems, chemical industry rotating equipment shafts, petrochemistry, pharmaceutical, paper and cellulose, food and others.

Heat sealing: made of ceramic, these gaskets are recommended for thermal insulation at high temperatures. As this type of product has a high melting point, it is possible to achieve low thermal conduction and low heat storage, allowing the equipment to work correctly at all times. These gaskets are recommended for applications that work at high temperatures, as sealing oven and stove doors, thermal insulation of pipes, furnace and boiler inspection doors, i.e., where high capacity thermal insulation is required.

GFO: It is a high-performance product aimed at industry in general where the purpose is to operate the equipment for a longer continuous period of time, i.e., with fewer interventions for adjustment or replacement. Its excellent continuity due to fibers and interlacing guarantees operational savings by reducing friction, minor leak, maintenance and continuity of the production process. Composed with 100% the GFO, these gaskets can be used for an extensive list of applications within industry, like various bombs, including centrifuges, rotary, turbines and pistons. They are also used in valves, agitators, mixers, dryers and refiners. For its wide range of services, they can be used as a standard gasket solution.

Learn more about sealing

Gaskets are just one of the materials used in sealing, but there are many others. Here at our website, you have access to different types, application sites and also information on how to apply them in your industry and the sealing sector.

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