The SSA 10 seat is a basic form of seats applied mostly to ball-type smalldimension fittings designed for cold-media and/or moderate-pressure applications. They are made mostly of pure PTFE (pure PTFE provides the smallest possible friction factor and good chemical resistance), or of PTFE filled with carbon or graphite. Metal/graphite and/or impregnated synthetic graphite compositions are not so popular. Though it is a very cheap structure, applications to high pressure and/or temperature systems are somehow restricted regarding resistance and/or creep p roperties. In case PTFE is considered, s econdary s ealing (in t he body) is not required, because the seat can satisfy this need.

The SSA 11 seats without housings can be made as multi-component PTFE structures. Such a design can be fire-safe, practically with no modifications of the structure. This is a multi-component seat of principally PTFE and graphite. In regular applications, the sealing is of a PTFE-metal type. In case of fire (PTFE is burnt off) sealing of the ball is transformed in a metalgraphite composition. Since the profile of SSA 11 has practically the same dimensions as a SSA 10 profile, adjustment of the internal sealing structure to fire hazard requirements is restrained to modification of the seat only.

Designing ball-type fittings suitable to meet high technical requirements, abrasive media, and/or big diameters, their ball seats have to be tear reinforced and erosion protected. One of possible solutions is installation of a sealing component between external ring (tearing) and internal ring (erosion). Such a structure can be applied to seats of PTFE and/or PTFE composite material, as well as to sealing components of carbon and/or graphite. Depending on material of a seat and/or the shape of a sealing ring back, secondary sealing can be avoided. Such a structure allows for using floating seats.

The SSA 30 seats of fittings, trilaterally enclosed in steel housings, have the highest strength properties and/or erosion resistance. It can freely move inside the body, according to the structure concept. Such a structure requires to install secondary packing between the body and seat. The structure can be used as a fire-resisting product with a seat of PTFE. In case of fire, upon PTFE is burnt off, the steel housing operates as a sealing. Either PTFE composite materials or carbon/graphite materials can be used, as well as other suitable materials on a customer requirement, as for instance polymer materials.

The SSA 40 seat is a popular type for ball-type fittings, because secondary sealing can be avoided, and they can be used in great axial-movement applications. The structure is designed for seats with sealing components made of PTFE or PTFE compositions. The metal component protects against erosion of the disk spring. The outside ‘soft’ cylindrical surface of the seat provides leak-proofness, even when moving. The steel ring can be used also as an emergency fireresistant sealing. For such an application, it should be machined.

Intending to prevent failure of ball cocks having seats made of brittle materials, e.g. made of synthetic carbon or graphite, shrinkable steel mountings are used. Between the mounting and the seat, there can be inserted glue (caulking), and inside the mounting structure a room for secondary sealing can be constructed.

Seats of a SSA 50 profile are applied mostly to ball-type taps with balls supported on trunnions (trunnion ball valves). The seat has to be held down to the ball by pressure thrust, because the ball itself is fixed. There are a number of various seat structures having capacity to move under pressure, and their geometry is designed to reduce thrust of the seat against the ball when the valve is opened, hence life of the valve is extended. Regarding the SSA 50 structure, the basic part of the sealing is the steel component, whilst the sealing piece itself is a pad of a relatively small section.