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"300 Series" Rotary Union

Model:  300 Series / SRU-4086

Part N° Description Shaft Thread (A) Thread Hand Guide Price Quantity
R3S3747KNPT 1/8 NPT Right Quote Required
R3S2086KNPT 1/4 NPT Right Quote Required
R3S3862KUNF 5/8-18 UNF Right Quote Required
L3S3747KNPT 1/8 NPT Left Quote Required
L3S2086KNPT 1/4 NPT Left Quote Required
L3S3862KUNF 5/8-18 UNF Left Quote Required
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Corrosion resistant rotary union suitable for use in applications with space constraints.

300 Series Rotary Union

300 Series Rotary Union

Features and Benefits

  • Ideal for high speed air and water applications with limited space.
  • Corrosion resistant, all steel parts are nickel plated.
  • Small envelope dimensions make the 300 Series suitable for use in applications with space constraints.
  • Speed of 3,500 RPM.
  • Maximum working temperature of 250°F.
300 Series Dimensional Drawing

300 Series Rotary Union Dimensions

Shaft Thread (A) B Inlet C (NPT) DN F G H I
1/8 NPT 0.4 1/8 (RH) 0.15 2   1.7 .75 1.5
1/4 NPT 0.5 0.23
5/8-18 UNF 0.4 0.23

300 Series Rotary Union Specifications

Shaft Thread Right Hand Thread Left Hand Thread
Part Number Description Part Number Description
1/8 NPT 770359C R3S3747KNPT 770358C L3S3747KNPT
1/4 NPT 770357C R3S3086KNPT 770356C L3S2086KNPT
5/8-18 UNF 770361C R3S3862KUNF 770360C L3S3862KUNF
300 Series Performance Chart
Rotary Union Design

Rotary Union Design

While rotating joints come in many shapes, sizes, and configurations, they always have the same four basic components: housing, a shaft, a bearing (or bearings) and a seal.

Mechanical Seal

The heart of the Rotary Union or rotary joint is the seal.

The seal prevents the medium (water, oil, air, etc) from leaking outside the Rotary Union while the Rotary Union is in operation.

Duff-Norton uses four basic types of mechanical seals in its Rotary Unions: 1) pusher-type end face mechanical seal, 2) non-pusher type end face mechanical seal, 3) lip seals and 4) o-ring seal. Rotary Unions may have more than one seal.


The second most important part of the Rotary Union is the bearing. A Rotary Union may have only one bearing or multiple bearings.

Roller bearings, such as ball bearings and tapered roller bearings, or non-roller bearings, like graphite bearings and bronze bushings, may be used in the Rotary Union.

The bearings are always used to allow a part of the joint, either the shaft or the housing, to rotate.


The shaft is the component that carries the medium through the Rotary Union into the drum or roll. In many cases, the shaft will turn with the drum or roll. In some cases, like in larger flanged rotary Unions, the shaft may be stationary while the housing rotates. The bearings and seal are typically assembled around the shaft.


The housing is the component that holds all of the other elements of the Rotary Union together. The housing has an inlet port, which is a threaded port to which the hose supplying the medium will be attached .

The Rotary Union may also have an outlet port, if the same joint is being used both to supply fluid to a roll and to remove fluid from the roll. In smaller Rotary Unions, the housing is stationary. In larger Rotary Unions, the housing maybe bolted to the drum or roll using a flange. In these cases, the housing rotates at the same speed as the drum.

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