Acting, not reacting: How leakages can be detected at an early stage and their causes can be eliminated

Processes in many industrial manufacturing applications need to be heated – for example when producing plastic products, drying wood or heating presses or chemical reactors. For a temperature range of 200 to 400 °C thermal oils are usually employed in such systems. The systems require special heat transfer fluid pumps, whose reliable operation is fundamental to the functioning of entire production lines.

The failure and consequential downtimes of such a system can very quickly lead to massive costs, clearly exceeding the total value of the pump with a single mechanical seal.

Also: If, in the event of a failure of such a pump, hot heat transfer fluid (e.g. thermal oil) escapes, there is a significant risk of fire and/or environmental damage as such fluids are usually combustible and hazardous to the environment.

For this reason, natural wear or impending damage should be detected as early as possible to prevent incalculable risks and unscheduled downtimes.

Even the 4EYS mechanical seal, which has been specially developed for operation in thermal oil systems and for use with the SYT pump series, only has a limited service life. It is normal for a small, practically invisible amount of thermal oil to escape at all times. This minor leakage is actually desired as it ensures lubrication of the seal faces and is necessary for the mechanical seal to work properly. This function-related leakage is clearly below one gramme per hour for an intact mechanical seal.

However, if the leakage rate increases over time when the pump is in operation, this indicates progressive wear of the seal faces. Should such damage occur at a single mechanical seal, larger quantities of fluid may escape to the environment and may become a hazard to persons and the environment.

It is common today for synthetic high-performance heat transfer fluids to be used in demanding processes. Given the potentially environmentally hazardous properties of these fluids we recommend an additional safety measure for heat transfer fluid pumps: the KSB Leakage Sensor for monitoring the leakage rate.

The KSB Leakage Sensor is an intelligent monitoring system for measuring and displaying on site the leakage of single mechanical seals . The system consists of a leakage rate measuring unit and an analysing and display unit which emits acoustic and light signals when the adjustable warning or alarm threshold is exceeded.

The benefits of continuous leakage monitoring are obvious:

• Increased operating reliability by preventing consequential damage and unscheduled downtimes
• Cost savings thanks to longer maintenance intervals and more predictable maintenance and repair cycles
• Fast and easy commissioning as well as integration into the customer’s process control system

In addition to a single mechanical seal, KSB offers a double mechanical seal, type 4EYT, for use with Etanorm SYT and operating mode to API Plan 52 (unpressurised tandem arrangement). For safety reasons, the double mechanical seal should generally be used for synthetic heat transfer fluids with a vapour pressure above 1 bar at operating temperature.

The 4EYT double mechanical seal is designed with a space filled with unpressurised compatible buffer fluid (e.g. a mineral oil) between the inboard mechanical seal and outboard mechanical seal, so it is impossible for any leakage of the fluid handled to escape to atmosphere. A supply system ensures that this space is always filled with buffer fluid to provide sufficient cooling (or lubrication) of the seal faces and to rule out any leakage of the fluid handled.

The use of a double mechanical seal also prevents any contact between the fluid handled and the rolling element bearing grease. Synthetic high-performance heat transfer fluids have a distinct tendency to creep. The double mechanical seal makes sure they cannot attack the rolling element bearing grease.