Frequently Asked Questions
Brakes

How does the brake for Valvcon AC actuators work?

The primary AC brake component is a small electric solenoid.  When the motor is not energized, the solenoid applies pressure to the motor shaft via a brake pad on the cooling fan. When the motor and brake are energized, the solenoid withdraws the brake pad from the fan allowing the motor to spin freely.

When is a brake recommended or required?

A holding brake is recommended on butterfly valves, resilient-sealed valves and dampers.  Excessively long brackets and couplings may require holding brakes to overcome "wind-up" introduced in the design of the coupling.

Why is a brake necessary?

Because of the high efficiency of the spur gear system, the drive train can be back driven.  Pressure from resilient seats and fluid/gas dynamics can act on the disc of the valve to move the actuator off the end of travel position.  Unless a brake holds the actuator in place, this condition can cause a "hunting" condition as the actuator attempts to relocate the commanded position.

How can such little pressure from the brake provide enough holding force?

Example: If the gear reduction is 3000:1, then one ounce of force from the brake generates 3000 ounces of holding force at the output.

What is the difference between a holding brake and a stopping brake?

A holding brake is an electromechanical device used to hold the valve in position against the pressures of the fluid dynamics or the resiliency of the seat.  Typical holding brakes include solenoid, cork, relay, and spring and are ordered as optional (all DC positioners have relay brakes standard.)

A stopping brake is an electronic device used to stop the motor shaft instantly to prevent coasting and overshooting.  Valvcon incorporates this electronic function in all positioner boards.

What is the difference between an AC motor brake and a DC motor brake?

The AC brake utilizes a solenoid to apply a force against the motor fan, which in turn stops the motor.  The DC brake is a relay that completes a circuit across the input leads of the motor.  This creates an internal magnetic braking force in DC motors.