Pump Drive Shaft Mechanical Seal

Function

A failing shaft seal allows hot bitumen to escape along the shaft, contaminating the drive coupling, PTO shaft or hydraulic motor and creating a fire risk on a machine that also carries a live burner flame. Early replacement at the first sign of weeping — confirmed during the daily inspection — prevents progressive damage to the pump casing bore and shaft journal, both of which are significantly more costly to repair or replace than a seal. The seal must also maintain face contact during start-up, when the bitumen is at its most viscous and shaft torque is highest.

Construction & quality

Seal type: single-spring pusher mechanical seal to DIN 24960 L1 or John Crane Type 1 interchange dimensions. Rotating face: reaction-bonded silicon carbide (SiC) or carbon-graphite — grade selected for bitumen service and operating temperature. Stationary seat: silicon carbide or high-alumina ceramic, precision-lapped to below 0.001 mm flatness. Secondary seals: high-temperature FKM (Viton) O-ring or PTFE wedge, rated to 240 °C (464 °F). Drive spring: Inconel or 316 stainless coil. Metal components: 316 stainless steel spring holder and drive collar.

When to replace

• Bitumen staining or crusted residue on the pump shaft outboard of the seal housing
• Bitumen droplets or film on the pump drive coupling, PTO shaft or motor adaptor flange
• Abnormal increase in shaft drag or elevated pump motor current draw
• Audible squeal from the seal area on start-up — indicating dry-run damage to the carbon face
• Rotating face visibly chipped or cracked during scheduled pump inspection