Stimuli are signals that trigger the senses. Receptors detect the stimuli and neurons send the signals to the brain where they're interpreted. Each sense organ includes receptors that capture relevant stimuli for transmission to the brain. The receptors in the skin are mechanoreceptors and thermoreceptors.
AWWA Butterfly valves are quick opening valves that consist of a metal circular disc or vane with its pivot axes at right angles to the direction of flow in the pipe, which when rotated on a shaft, seals against seats in the valve body. They are normally used as throttling valves to control flow.
Electric actuator (blue cylinder) on a valve in a power plant. A black handwheel is visible on the actuator, which allows manual positioning of the valve. The blue valve body is visible in-line with the pipe. The valve actuator opens or closes the butterfly disc of the valve based on electrical signals sent to the actuator. Another valve actuator is visible in the background, with windows to indicate the valve position. A valve actuator is the mechanism for opening and closing a valve. Manually operated valves require someone in attendance to adjust them using a direct or geared mechanism attached to the valve stem.