Split mechanical seals are mechanical seals that can be mounted and dismounted – either completely or in part – radially to the shaft. A distinction is drawn between semi-split mechanical seals, in which only the wearing parts are split, and fully split mechanical seals, in which all components are of split design.

Their main fields of application and typical operating conditions are for large shaft diameters and relatively low speeds (up to approximately 1000 rpm) under low to medium pressures, such as are met with in shipping (stern tube seal), in water turbines, in rolling mills and in drum driers.

A fully splitting mechanical seal for sealing a pipe housing pump in a sewage desalination system

The splits are made:

• in brittle face materials by breaking and enclosing the broken halves in elastomer materials, or
• in metallic components by high-precision machining, pinning and bolting together of the cut faces
• in elastomer secondary seals by cutting and subsequent bonding or cold vulcanization.

At the first fitting, the wearing parts and elastomers are often installed in unsplit form. It is not until the time comes to repair them that the split replacement rings are mounted in their place; to do so, the initial rings are destroyed. The reason is that unsplit mechanical seals generally have far less leakage. Internal pressure (internal pressurization) must be avoided with split mechanical seals because it forces apart the joints – especially of flexible seal faces – and results in high leakage.