KST Double Sphere Rubber Expansion Joint

Front view of KST double sphere rubber joint

Side view of KST double sphere rubber body with blue flanges

Rubber Expansion Joints

KST Double Sphere Rubber Expansion Joint

The KST double sphere rubber expansion joint is a flanged flexible rubber joint designed for higher movement compensation and vibration isolation in pumps, HVAC, water and industrial piping systems.

Also commonly searched as a double sphere rubber joint, twin sphere rubber expansion joint or twin sphere rubber joint.

Published Size Range: DN40–DN600
Available Length: 165–400 mm, depending on size
Axial Extension: 30–35 mm, depending on size
Axial Compression: 50–60 mm, depending on size
Lateral Displacement: 35–45 mm, depending on size
Angular Deflection: 30°–40°, depending on size
Rubber Options: NR / EPDM / CR / IIR / NBR / FKM
Flange Options: GB / HG / ANSI / DIN / BS / EN / JIS

Stock / Fast ShipmentMany common sizes and configurations are kept in stock for faster shipment; actual availability is confirmed according to size, rubber material and flange configuration.

CustomizationRubber material, flange configuration and project-specific dimensions can be reviewed according to confirmed operating and installation requirements.

Project Configuration

Mingchao can customize the product configuration based on the technical information, operating conditions and dimensional data you provide. Final configuration can be reviewed and manufactured to the approved project drawing.

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KST Double Sphere Rubber Expansion Joint Overview

The KST double sphere rubber expansion joint uses two flexible rubber spheres between flanged ends to provide increased movement capability while isolating vibration and reducing noise in connected piping systems.

Compared with a compact single-sphere design, the double-sphere configuration provides greater published axial, lateral and angular movement capacity and uses a longer installation length. This makes KST suitable where the required movement exceeds the capability of a standard single-sphere connection and adequate installation space is available.

Typical applications include pump and valve connections, HVAC and building services, water supply and drainage, water-treatment systems, industrial piping and general utility piping.

Movement Capability & Key Specifications

KST is designed primarily for applications requiring greater multidirectional movement than a compact single-sphere rubber joint. Published Mingchao data identifies axial extension, axial compression, lateral displacement and angular deflection as the principal movement modes.

DN	inch	Length L (mm)	Axial Extension (mm)	Axial Compression (mm)	Lateral Displacement (mm)	Angular Deflection
40	1.5	165	30	50	45	40°
50	2	165	30	50	45	40°
65	2.5	175	30	50	45	40°
80	3	175	30	50	45	40°
100	4	225	35	50	40	35°
125	5	225	35	50	40	35°
150	6	225	35	50	40	35°
200	8	325	35	60	35	30°
250	10	325	35	60	35	30°
300	12	325	35	60	35	30°
350	14	325	35	60	35	30°
400	16	340–400	35	60	35	30°
450	18	340–400	35	60	35	30°
500	20	340–400	35	60	35	30°
600	24	340–400	35	60	35	30°

Exact movement and dimensional values depend on nominal size and the selected product configuration. Final data should be confirmed against the approved product drawing before order.

Size, Length & Flange Options

The published KST size range is DN40–DN600, with available face-to-face length varying from 165 mm to 400 mm according to nominal size. The flange configuration must be selected to match the connected piping or equipment.

Mingchao source material lists GB, HG, ANSI, DIN, BS, EN and JIS flange options. Exact drilling, dimensions and pressure class should be confirmed according to the selected project standard and approved drawing.

Rubber Materials & Double Sphere Construction

The KST uses a double-sphere flexible rubber body with flanged ends. The two-sphere geometry provides the additional flexible length required for higher movement accommodation while the elastomeric body helps isolate vibration and noise from connected piping and equipment.

Rubber material selection must be confirmed together with the medium, temperature and actual operating conditions.

Item	Confirmed Configuration
Structure	Double-sphere flexible rubber body with flanged ends
NR	Available rubber option
EPDM	Available rubber option
CR	Available rubber option
IIR	Available rubber option
NBR	Available rubber option
FKM / Viton	Available rubber option

Applications for Pumps, HVAC, Water & Industrial Piping

Pump & Valve Connections

Provides flexible connection where pump or valve vibration and piping movement must be accommodated.

HVAC & Building Services

Used in chilled-water, heating and building-services piping where vibration isolation and movement flexibility are required.

Water Supply & Drainage

Flexible connection for water supply and drainage systems according to the selected rubber and flange configuration.

Water Treatment Systems

Suitable for water-treatment piping and connected equipment requiring vibration isolation and multidirectional movement.

Industrial Piping

Used in industrial piping systems where higher movement capability is required within the confirmed KST operating conditions.

General Utility Piping

Provides flexible connection for utility piping where axial, lateral or angular movement must be accommodated.

How to Select a KST Double Sphere Rubber Joint

KST should be selected when the required movement exceeds the practical range of a compact single-sphere joint and the piping layout provides sufficient installation length for the double-sphere construction.

Nominal size / DN
Required axial extension
Required axial compression
Required lateral displacement
Required angular movement
Face-to-face / installation length
Medium
Working pressure
Operating temperature
Rubber material
Flange standard / drilling
Quantity
Project drawing or existing joint information

Final configuration is confirmed against the supplied service conditions and project drawing.

KST Double Sphere vs. KXT Single Sphere Rubber Joint

Product Type	Configuration
KXT Single Sphere Rubber Expansion Joint	Structure: single sphere. Primary search intent: single sphere rubber expansion joint. Selection character: compact general-purpose flexible rubber connection. Published size range: DN32–DN1200. Movement: lower published movement capability than KST.
KST Double Sphere Rubber Expansion Joint	Structure: double sphere. Primary search intent: double sphere rubber expansion joint. Selection character: higher movement option where additional installation length is available. Published size range: DN40–DN600. Movement: higher published axial, lateral and angular movement capability according to Mingchao product data.

Installation & Piping Support Guidelines

Confirm the selected KST configuration and approved piping arrangement before installation.

Confirm Selection

Confirm DN, flange arrangement, rubber material, movement requirement and operating conditions before installation.

Piping Alignment

Align the piping correctly before final tightening.

Avoid Torsion

Do not twist the rubber expansion joint.

Misalignment

Do not force the joint to correct excessive pipeline misalignment.

Movement Limits

Avoid installation beyond the confirmed extension or compression range.

Pipe Weight

Support connected piping so the KST joint does not carry unintended pipe weight.

Flange Tightening

Tighten flange bolts diagonally, gradually and evenly.

Large Suspended Water Lines

For suspended water-supply service above DN200, provide appropriate fixed support or anti-pull-off protection according to the approved piping design.