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Application Range of Hydraulic seals for Reciprocating Motion
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Terminology The terms "cylinder", "piston" and "rod" will always be used in this brochure in relation to the arrangement and function of the seals, namely: The term "cylinder" indicates a component of hydraulic and pneumatic installation and may be classified in four basic types as shown in figure 1 through 4.
Figure 1	Figure 2	Figure 3	Figure 4
Rod Seal The static seal on the external diameter while the relative motion of the metal surface occurs on the internal diameter.   Piston Seal The Static seal on the internal diameter while the relative motion of the metal surface occurs on the external diameter.

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Item No.	Description	Item No.	Description
1	Piston Rod	15	Packing Washer
2	Cylinder Barrel	16	Rod Wiper
3	Head end Cap	17	"O" Ring Seal for Ball Check Retainer
4	Cap end cap	18	N/A
5	Rod Bushing	19	Wave Spring
6	Retainer Plate	20	Cylinder Barrel O-Ring
7	Piston	21	Wear Ring
8	Cushion Plunger	22	Tie Rod Flex Loc Nut
9	Cushion adj. Needle	23	Teflon Ring Seal for Cushion adj. Needle
10	Ball Check Retainer	24	N/A
11	Ball Check	25	Jam Nut for Cushion adj. Needle
12	N/A	26	Tie Rod
13	Block Vee Packing	27	Self-Locking Cap Screw
14	Rod Vee Ring Set	28	O-Ring for Floating Cushion

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U-cup packings conforming to the drawing below are generally recommended for operating pressures up to 1500 psi. On installations where operating pressures exceed 300 psi, diametral clearances at the heel of the cup should be held to .004" - .006".

V-Packings

USE OF BACK-UP RING
When the packings are used for high pressyre or the extrusion gap is too large, the heel of a packing may protrude to suffer damage (Firgure BR-1). In such cases, a back-up ring will prevent extrusion (Figure BR-2).

USE OF WEAR RING

Wear rings are used as bearings of a piston to prevent scuffing the piston and cylinder, minimize eccentricity, and improve durability of packings.

Material	Fabric-reinforced phenol resin	Tetrafluoroethylene resin
Features	Standard wear ring. Biascutting is made at one spot. Excellent wear resistance.	It is made into a hoop (10m per roll) and used by cutting to required length. Low friction resistance.
PV limit (in oil)	See the following chart for PV limit.

NAMES OF PACKINGS

Figure P-1 (Packings Installed in Hydraulic Cylinders) (1)Dust Seal (2)Rod Packing (3)O-ring (4)Piston Packing (5)Wear Ring

EXAMPLES OF PACKING COMBINATIONS BY APPLICATIONS

Table PCA-2 lists examples by type of application. (1 of 2)

Type Piston Seal Rod Seal Power Shovel Miniconstruction Equipment Bulldozer Dozer-shovel Because of no inversion and small coefficient of friction, no stick-slip occurs even at low speed. It can also be used at high pressure. The life of the packing is extended by interrupting impact pressure with HBY and protecting IDI packing. Because oil film is thin with HBY and IDI, DWI with high dust resistance is used as dust seal. Power Shovel Miniconstruction Equipment Bulldozer Dozer-shovel When lateral load is small and there is no fear of 'scuffing' between piston head and cylinder tube, full function can be achieved with only one wear ring (WR) and the piston head can be made smaller. HBI interrupts pressure and protects the packing same as above, but it is used for extremely short strokes. Power Shovel Miniconstruction Equipment Bulldozer Dozer-shovel Inversion does not occur and coefficient of friction is small like SPGW but it can be used at lower pressure than SPGW. When impact pressure does not occur very often, bufferings of HBY and HBT are unnecessary. It can be used in an appropriate groove and DKBI is used for dust seal considering its low oil film scraping performance. Shovel-loader Minibackhoe This is example of use where lateral load is small and there is no fear of 'scuffing' between piston head and cylinder. SPG is used at less than 280kgf/cm(2). When impact pressure is very low and extrusion gap is small, it can be used without back-up ring. Dumptruck When lateral load is small and piston must be made compact but still requiring pressure resistance, it is used by combining SPGW packings and WR. It is used when impact pressure rarely occurs. Dumptruck It is used at less than 280kgf/cm(2) with large lateral loads. HBY is used to interrupt impact pressure.

A cylinder uses pressurized fluid or air to create a linear force/motion as shown in See A Cross Section of a Hydraulic Cylinder. In the figure a fluid is pumped into one side of the cylinder under pressure, causing that side of the cylinder to expand, and advancing the piston. The fluid on the other side of the piston must be allowed to escape freely - if the incompressible fluid was trapped the cylinder could not advance. The force the cylinder can exert is proportional to the cross sectional area of the cylinder.

A Cross Section of a Hydraulic Cylinder

Single acting cylinders apply force when extending and typically use a spring to retract the cylinder. Double acting cylinders apply force in both direction.

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