The seal is of critical concern

To prevent product leaking out of the rotary valve, or oxygen entering the process, we developed the optimum shaft seal. This special seal, is based on an air purge-seal, with a monitored gas flow. An alarm signal is generated if the gas flow deviates from the set point. Operators than can choose what action to take in accordance with the agreed protocols; monitor the situation, perform maintenance at the next scheduled opportunity, or stop the plant immediately for further investigation.

 

Flow-control box
A lip seal or double gland packing is used as an external shaft seal in combination with a labyrinth seal for the internal seal. The labyrinth seals are provided with an equal gas flow at a pressure of 200 mBar over the full diameter of the rotor shaft, which prevents product from entering the seal. The electronic control unit not only compensates the pressure fluctuations but also registers the actual gas flow to each seal. Alarms are generated when the preset deviations of the flow, positive or negative, are exceeded.

 
Flow deviation

A positive flow deviation could be caused by a leaking pipe joint or damage to the shaft seal (lip seal or gland packing). A negative flow deviation could be caused by a partial failure of the purge gas supply or partial blocking of the labyrinth seal.
It goes without saying that this seal option could be combined with the rotary valve as an autonomous security system; in this case the rotary valve is shock-proof and flame-proof.