The
seal is an agent that prevents leakage of oil from the hydraulic
elements and protects the system from dust/dirt. A hydraulic seal is
usually used to arrest both internal and external leakage of
oil/gas/steam. It maintains pressure, prevent loss of fluid from the
system and keeps out contamination in the system to enhance its service
life and functional utility. In any kind of pressure actuated system,
seal is necessary for rotary or reciprocating, static or dynamic system,
steam, hydraulic or pneumatic medium. Types of Seals
Seals may be categorized as per methods of sealing, areas of application, seal material, geometrical shapes of the seal used in the system etc.
Sealing may be
(a) Positive sealing that prevents even a minute amount of fluid from getting past (b) Non-positive sealing that may allow a small amount of internal leakage such as the clearance of a spool in its bore to provide a lubricating film.
Most commonly hydraulic seals are classified as:
(a) Static seals that are used when no relative movement occurs between the mating parts. The seal is usually compressed between two adjacent parts securing the two stationary parts together by fasteners.
(b) Dynamic seals are used between the surfaces of hydraulic parts where movement occurs and controls both leakage and lubrication. In certain dynamic seals wipers or covering boots are used to keep away dirt and other foreign materials. The motion encountered by dynamic seals may be either reciprocating or rotating or a combination of both.
