HYDRAULIC BUFFER SEALS 991/00110

SinoHyva   is China’s leading hydraulic seals manufacturer.

Our functional parts, such as hydraulic seals and o-rings of advanced technology in processed synthetic rubbers, are used not only in the commercial vehicle industry, but also in a wide variety of other industries. We have developed into the number-one reliable company in this field while leveraging the technology and know-how acquired since the star-up of operations.

SinoHyva has created the products full of dreams. While SinoHyva products vary from miniature to man-sized, they are all cared equally with the closest attention.

Starting from the field of hydraulic seals, SinoHyva has been changing its corporate image to the extending of having cutting-edge technology and development relating to heavy engineering.

SinoHyva’s products and technology are not outwardly visible. However, SinoHyva is always with you. We are committed to providing the innovative products to perfectly meet our customers’ needs, while contributing to the global community. SinoHyva’s dreams are infinite and everlasting.

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

Rod and buffer seals maintain sealing contact in sliding motion between the cylinder head and the piston rod. Depending on the application, a rod sealing system can consist of a rod seal and a buffer seal or a rod seal only . Rod sealing systems for heavy duty applications typically consist of a combination of both seal types, whereas the buffer seal is arranged between the rod seal and the piston in the cylinder head. Rod seals determine the tolerance for the rod diameter d.

In addition to the sealing function, rod seals also provide a thin lubrication film on the piston rod that lubricates themselves and the wiper seals. The lubricant also inhibits corrosion of the piston rod surface. However, the lubrication film must be thin enough so that it returns to the cylinder during the return stroke.

Selecting profiles and materials for a rod sealing system is a complex task, considering all possible cylinder designs and application criteria. SKF supplies rod and buffer seals in many different profiles and in a wide range of materials, series and sizes, which make them appropriate for a wide variety of operating conditions and applications.

Items	Draft
Polyurethane U-cup rod seals
S1S profile ZBR profile SIL profile
Energized U-cup rod seals
PTB profile STD profile
Hybrid rod seals
DZ profile DZR profile
Polyurethane U-cup buffer seals
RBB profile
Buffer seals incorporating slide rings
S9B profile RSB profile

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