Large valves enable autonomous safety system

Edited by the Engineeringtalk editorial team Nov 21, 2007

Special consideration has been paid to conditions when the valves start from cold or are rapidly subjected to fluctuating high temperatures.

Rota Val has recently completed an order for 13 large valves to be used as autonomous safety system devices.

The valves will be working at a maximum of 120C, are rated at 10bar(g), and comply with the required ATEX rotor clearance for safe flameproof operation at that temperature.

Specific features have been designed to cope with fluctuating temperatures and the potential for differential expansion between the rotor and housing during start-up and normal running operation.

Special consideration has been paid to conditions when the valves start from cold or are rapidly subjected to fluctuating high temperatures, creating possibilities for differential expansion between the rotor and housing assemblies which could put the valve at risk of metal to metal contact and the potential for loss of the ATEX flame-proof status.

This situation is contained by employing skilled engineering techniques to ensure very close rotor to housing clearances, together with the addition of the RotaSafe Rotor Monitor, which instantly senses possible rotor to housing contact and cuts power to the motor, avoiding damage to critical components and therefore preventing any potential for flame propagation.

Comprising seven HD600 valves, plus a BS500 blowing seal equipped with vent dividers, and five HD600 valves without the vent, the order was placed by a major European plastics manufacturer for its plant in Holland.

SEW Zone 21 motors were supplied fully fitted and wired, together with thermistors, all piping, pressure regulators and solenoids.

The HD600 rotary valves are expected to handle up to 13,000kg/h of plastic powder with an average grain sise to 14um.

The blowing seal is designed for a throughput of 8000kg/h.

Bearing housings are carried in subassemblies to speed in-situ bearing replacement without disturbing the rotor alignment.

Enhanced performance is assured by using the RotaSafe Rotor Monitor.

As already noted, these units detect rotor contact with the housing and shut down the drive motor to minimise valve damage, preserving valve integrity and its function as an autonomous safety system.

Using a sophisticated control system enables the Rotor Monitor to distinguish between actual rotor contact and spurious signals caused by conductivity in the powder being handled.

Ceramic-lined drive shafts and sleeved bearing housing electrically isolate the essential components and provide protection to the rest of the manufacturing plant.

Paul Bailey, Senior Contracts Engineer, comments: "This order demonstrates Rota Val's ability to take standard products and make detailed changes to meet the very precise requirements of demanding applications".

"Customers can have confidence in valve performance to ATEX standards without the high costs usually associated with custom-designed equipment".