Expansion joints

A rubber expansion joint is a flexible flanged sleeve that absorbs movement between two pipe sections. KTN Valves manufactures EPDM expansion joints with DIN and ANSI flanged connections, fitted to protect pumps, flanges and bearings from thermal growth, pump vibration and flange misalignment.

What an expansion joint does

An expansion joint mechanically decouples two pipe runs. The elastomer takes the movement steel cannot take, so thermal growth, vibration and misalignment stay inside the joint instead of reaching the flange, the mechanical seal and the pump bearings. Against a steel expansion loop it needs a fraction of the space and damps structure-borne noise; against a metal bellows joint it accepts more lateral offset in water service.

Types manufactured by KTN

KTN supplies flanged rubber expansion joints, the standard format for water, air and aqueous solutions.

• Flanged expansion joints, drilled to DIN or ANSI pattern to match the mating flange.
• Full expansion joint range within the accessories catalogue.
• Special executions built to drawing when size or drilling is non-standard.

Axial, lateral and angular movement

A rubber joint works on three axes at once. Axial movement is compression or extension along the pipe axis: a straight 20 m carbon steel run heated from 20 °C to 80 °C grows around 14 mm, at 12 µm per metre per degree. Lateral movement is perpendicular offset from settlement or off-centre flanges. Angular movement is rotation between flange faces. The three ratings share one budget: on two axes the allowable travel is split, never added.

Anchors and tie rods

Internal pressure pushes both flanges apart with a force equal to pressure times effective area. A DN 100 joint at 10 bar develops roughly 13 kN, close to 1.3 tonnes. Where pipework is anchored on both sides, the fixed points carry that thrust. Where it is not, tie rods become mandatory: they link the backing flanges, cap maximum extension and take the pressure thrust. Without anchors or tie rods the joint elongates until it fails.

Elastomer, media and temperature

EPDM is the standard elastomer on KTN expansion joints. It handles cold and hot water, glycol mixtures, compressed air and dilute aqueous solutions, with continuous service around 100 °C. It is not compatible with mineral oils, diesel or hydrocarbons, which make EPDM swell and lose mechanical strength. Ask KTN for the alternative execution before fixing a size. Chemical attack also lowers the usable temperature, so media and temperature are validated together.

Connections and installation at the pump

Flanged joints carry swivel flanges drilled to DIN EN 1092-1 PN10/PN16 or ANSI B16.5 class 150 and clamp against the mating flange face. Install as close to the pump as the layout allows, on suction and discharge, because that is where vibration starts. Check bores against the DN to inches conversion table and the flange face types guide.

How to select an expansion joint

• Function: thermal growth, pump vibration or misalignment.
• Size and connection: DN and drilling, DIN PN10/PN16 or ANSI class 150.
• Media and temperature: EPDM compatibility and continuous service.
• Pressure: working pressure, pump start-up peaks and water hammer.
• Movement: axial, lateral and angular travel, split across axes.
• Accessories: tie rods whenever the line is not anchored.

Applications and industries

KTN rubber expansion joints are installed in pumping stations, water treatment and desalination, HVAC circuits, chemical processing, food and beverage, pulp and paper, mining and marine service. Typical media are cold and hot water, glycol mixtures, air and aqueous solutions, on lines where a pump or a temperature swing moves the pipework.

Buying direct from the manufacturer

KTN sells direct from its own factory: price at source, common sizes in stock for immediate despatch and special executions to drawing. Every order ships from Rubí, Spain, with a certificate of origin, and with a 3.1 material certificate when the project requires it. Send DN, pressure, media, temperature and flange standard to receive a quotation.

Why KTN

KTN Valves (Kara Technology News, S.L.) is a Spanish manufacturer with its plant in Rubí, Barcelona, running an ISO 9001 quality system with Bureau Veritas inspection. Sourcing the joint from the same European manufacturer that supplies the valves and the strainer keeps flange standards consistent along the run. Distributor enquiries are welcome in the UK, France, Poland, Vietnam and Egypt.

Related categories

The same pumping line takes Y strainers upstream of the pump, check valves on the discharge and butterfly valves for isolation. Complete it with sight glasses, safety spray shields and the rest of the industrial accessories, within the industrial valves range.

Frequently asked questions

When are tie rods required on a rubber expansion joint?

Whenever the pipework is not anchored with fixed points on both sides of the joint. Tie rods take the pressure thrust and cap maximum extension. On pump discharges resting on sliding supports, or on runs with assembly gaps, they are fitted as standard rather than as an option.

Can an EPDM expansion joint handle oil or diesel?

No. EPDM swells on contact with mineral oils and hydrocarbons and loses mechanical strength, even at low temperature. Those services need a different elastomer. State the exact media and temperature when requesting a quotation and KTN will confirm the correct execution.

How far from the pump should the joint be installed?

As close to the pump flange as the layout allows, on both suction and discharge. The further away it sits, the more pipe mass vibrates before reaching the flexible element. Leave room to tighten the studs and to inspect the rubber without dismantling the run.

Rubber or metal expansion joint: which one?

Rubber absorbs more lateral and angular movement per unit of length, damps vibration and suits water and aqueous solutions. Metal bellows handle higher pressures and temperatures, which is why steam and hot gas lines use them. Media temperature usually decides before anything else does.

What is the service life of a rubber expansion joint?

There is no single figure: ageing depends on temperature, pressure, cycle count and exposure to ozone and sunlight. Inspect at every shutdown for cracks in the arch, permanent set and loss of stud torque, and replace before leakage appears rather than after.

Request a quotation

Send DN, working pressure, media, temperature and flange standard and KTN will confirm the execution and lead time. Request a quotation or call +34 937 818 219.