Spring actuator
Guide to Controls (BG 83/2023) written by John Marrow and published by BSRIA in June 2023, states in relation to spring actuators or power fail actuators: ‘Sometimes, a control valve needs to fully close or open quickly during a high temperature or power failure condition. In this case the actuator is provided with a spring or power return feature. On excess temperature a separate high limit device, such as a thermostat, can be used to break the power supply. This releases a clutch within the actuator which takes control away from the normal sensor. The spring will quickly close the valve or, in some applications, open it to relieve the high temperature. The same would also happen in an unmanaged electrical supply failure.’
--BSRIA
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