Seal selection and Cylinder classification

2024-02-27

The selection of the right seal profile and material for a given application requires consideration of many factors. This section supports the selection of the right seal for typical hydraulic seal applications and existing cylinder designs. For any application factors outside of the ordinary, or to specify sealing systems in new hydraulic cylinder designs, a certain amount of expertise may be required.

 

Before seals can be selected certain application parameters and information should be collected. The following most common application considerations are nearly always required when selecting hydraulic seals:

 

Fluid pressure range,

the range of operating fluid system pressure, as well as the frequency and severity of pressure peaks

Temperature range,

the range of the fluid and cylinder assembly, both when operating and at rest

Speed,

the stroking speed of the reciprocating piston rod

Fluid media,

the type and viscosity of fluid used in the system

Hardware dimensions,

the rod and bore diameters, seal groove dimensions and gaps (if already specified), cylinder overall length and stroke length as well as surface finish specifications (if already specified)

Application of the cylinder,

the type of equipment the cylinder will be used on and how the cylinder will operate in the equipment as well as installation, duty cycles, and environmental factors (external temperature, contaminants)

 

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 (2 300 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 (3 625 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 (5 800 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

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