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HOMOGENEOUS U-CUP PACKINGS

Standard "AN" Design

Homogeneous U-Cup Packings are available in a full line of sizes for hydraulic and pneumatic applications. They are especially adapted to rod and piston assemblies with reciprocating motion or where there is a definite space limitation. Sealing is accomplished by means of the contact made by the U-cup's flexible lips, which are designed to be preloaded when installed. The solid section design at the heel is narrower than the packing groove to eliminate binding in service. Homogeneous U-cups are available in a variety of compounds to meet specific conditions. They have low frictional qualities and are completely automatic in action.

HUVA Design

HUVA-Cups are a proven advancement in homogeneous rubber U-cup packings for both static and dynamic sealing. They offer definite advantages over standard U-cups of the AN design in a wide variety of hydraulic sealing applications.

1. Space savings - smaller cross section facilitates product design.
2. Ability to withstand higher pressures.
3. Greater stability and pressure resistance - made possible by 80-durometer hardness.
4. Greater sensitivity to lower pressures due to the special angle of the lips.

HUVA-cups can be used without additional back-up rings ar pressures up to 1500 psi. They will perform at higher pressures if the clearance behind the cup is bridged with a suitable back-up material.

HUVA-Cups are furnished in a Buna-N compound for most hydraulic and pneumatic cylinder applications. Ohter compounds are available for services such as fire-resistant and high temperatures.

Design & Installation

Standard AN design U-cups and HUVA-cups are essentially the same kind or type of packing. The differences are in hardness, cross-section and application. Although both can be manufactured in a variety of compounds, U-cups are usually supplied in 70 durometer and HUVA-cups in 80 durometer hardness.

Recommended rod surface finish is 16 RMS. (max.) with internal gland thread offset to avoid damage to the U-cup lips upon installation. Also, all sharp edges and corners in the packing installation areas should be removed. In reciprocating service, avoid any design in which the U-cup must pass over corners, holes, ports or over a step diameter.

U-cups are generally used in pneumatic cylinders for pressures up to 500 psi. HUVA-cups can be used in both air and hydraulic cylinders for pressures up to 1000 psi. HUVA-cups will handle pressures up to 5000 psi if back-up rings are used to bridge the clearance behind the packing and prevent extrusion. Generally, the back-up rings are cut from 1/16" thick gasket sheet material. Recommended finishes for the use of HUVA-cups are 16 RMS on a dynamic surface and 32 RMS on a static surface.

Groove Dimensions

U-cup and HUVA-cup groove dimensions can be calculated with the formulas shown below. If back-up rings are used, the groove length (Dim. A) must be increased by the thickness of the back-up ring.

Dimensions A = Groove Length B = Cylinder Bore C = Maximum Diametral Clearance G = Piston Groove Diameter L = Length of HUVA Cup M = Rod Bearing Diameter N = Gland Diameter P = Piston Diameter R = Rod Diameter W = Nominal Cross-Section of HUVA Cup	Recommended Maximum Diametral Clearances Type of Service Up To 1000 psi Over 1000 psi Light Duty Medium Duty Heavy Duty .020 .015 .010 .015 .010 .005