Excavator Parts Hydraulic Cylinder Seal kits

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Hydraulic seals and guides

Hydraulic cylinder seals are used to seal the opening between various components in the hydraulic cylinder. There are two main types of hydraulic seals in the system:

. Dynamic seals
They seal between components in relative motion. In a hydraulic cylinder the rod sealing system seals dynamic reciprocating motion between the piston rod and head, while the piston sealing system seals dynamic reciprocating motion between the piston and cylinder bore.

. Static seals
They seal between components fixed together without relative motion. Hydraulic cylinders use static seals in various locations depending on the design and construction. The most common are static seals between the piston and piston rod and between the head and cylinder bore tube.
Each dynamic seal in a hydraulic cylinder has a special function to contribute to the performance of the system:

Piston seal functions
. act as pressure barrier and prevent fluid passing the piston – important for controlling the cylinder motion or maintaining the position when at rest

Rod seal functions
. act as pressure barrier and keep the operating fluid inside the cylinder
. regulate the fluid film which extends with the surface of the piston rod – important to inhibit rod corrosion and to lubricate the wiper seal and the rod seal itself
. accept the lubrication film back into the cylinder when the rod retracts

Buffer seal functions
. protect the rod seal from fluid pressure peaks in excess of system pressure
.attenuate the fluctuations in system pressure, thereby improving rod seal performance by allowing the rod seal to deal with more constant or gradually changing pressure
. act as an internal excluder to keep system contaminants, such as metal particles, from damaging the rod seal

Wiper seal functions
.exclude external contaminants from entering the cylinder assembly and the hydraulic system
.accept the lubrication film back into the cylinder when the rod retracts

Guide rings (rod and piston) functions
.prevent metal-to-metal contact between components
.react the radial load caused by side loads on the cylinder assembly
. keep the piston rod and piston accurately centred in the cylinder assembly-important for performance of the rod sealing system and piston sealing system

Cylinder classification

The type of cylinder and the application in which it is used are two of the main criteria when selecting the appropriate seals and guides. Applications are referred to as light duty, medium duty or heavy duty applications. These classifications are somewhat subjective but the duty levels are typically characterized by the following criteria.

Light duty cylinders
Light duty cylinders, e.g. cylinders used for stationary equipment indoor in a factory environment, may be characterized by: 
. system pressures up to 160 bar (2300 psi)
. temperatures up to 70 °C (160 °F)
. rare pressure peaks in excess of system pressure
. minimal side loads acting on guides
. environment with moderate temperature fluctuations and relatively free of contaminants

Medium duty cylinders
Medium duty cylinders, e.g. cylinders in agriculture off-highway equipment, may be characterized by:
. system pressures up to 250 bar (3625 psi)
. temperatures up to 90 °C (195 °F)
. moderate pressure peaks in excess of system pressure
. moderate side loads acting on guides
. environment with temperature fluctuations and typical external contaminants such as dust and --------moisture

Heavy duty cylinders

Heavy duty cylinders, e.g. cylinders in off-highway earthmoving or forestry equipment, may be characterized by:
. system pressures of 400 bar (5800 psi) or more
. temperatures exceeding 90 °C (195 °F) with peaks in excess of 110 °C (230 °F)
. regular pressure peaks in excess of system pressure
. heavy side loads acting on guides, usually due to heavy components and/or high accelerations
. tough environment with wide temperature fluctuations and typical harsh external contaminants

Telescopic hydraulic cylinders

Telescopic cylinders are a special design of hydraulic cylinder which provide an exceptionally long output travel from a very compact retracted length. Typically the collapsed length of a telescopic cylinder is 20 to 40% of the fully extended length depending on the number of stages. Some pneumatic telescoping units are manufactured with retracted lengths of under 15% of overall extended unit length. This feature is very attractive to machine design engineers when a conventional single stage rod style actuator will not fit in an application to produce the required output stroke.

Telescopic cylinder (ISO 1219 symbol)

Heavy duty telescopic cylinders are usually powered by hydraulics, whereas some lighter duty units could also be powered by compressed air.

Telescopic cylinders are also referred to as telescoping cylinders and multi-stage telescopic cylinders.

An application for telescopic cylinders commonly seen is that of the dump body on a dump truck used in a construction site. In order to empty the load of gravel completely, the dump body must be raised to an angle of about 60 degrees. To accomplish this long travel with a conventional hydraulic cylinder is very difficult considering that the collapsed length of a single stage rod cylinder is approximately 110% of its output stroke. It would be very challenging for the design engineer to fit the single stage cylinder into the chassis of the dump truck with the dump body in the horizontal rest position. This task is easily accomplished, however, using a telescopic style multi-stage cylinder.

Hydraulic Seals For Telescopic Cylinder		Size
	Wipers	From 90 to 260 mm Deep Hole / Step Hole
	Seals	From 90 to 260 mm Deep Hole / Step Hole
	Rod Bearing	From 90 to 260 mm Deep Hole / Step Hole
	Static Seals	From 90 to 260 mm Deep Hole / Step Hole

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