In most submersible systems, dynamic shaft seals are a recurring reliability problem. Friction, wear and chemical attack eventually cause leaks, allowing water to reach sensitive components.
According to Ronn Garland, program director at ARM Automation’s SplashBotix division, the SplashValve team eliminated that risk by removing the seals entirely. Rather than transmitting torque through a rotating shaft, they used a magnetic coupling to drive the valve spool through the sealed stainless-steel housing.
Garland explained that this decision was pivotal for lifetime reliability: by isolating the drive system, the design achieved precise motion without exposing the motor cavity to the environment.
How Magnetic Coupling Works
A magnetic coupling employs two concentric magnet assemblies—one inside the sealed chamber, one outside—separated by a thin non-magnetic wall. The inner magnet ring attaches to the servo output shaft inside the housing, while the outer magnet ring connects to the valve’s drive hub in the fluid. Magnetic flux lines transfer torque through the barrier with no physical contact.
Garland notes that this configuration maintains complete isolation between the actuator and the external fluid while still allowing smooth, controlled motion.
Performance Under Load
Torque-transfer efficiency was a primary focus during design. Garland and his team optimized the coupling using rare-earth magnets arranged in alternating polarity pairs to achieve the required operating torque within the limited available space.
Even with a compact motor, the coupling reliably rotates the valve spool through its 90-deg. range. Because torque transmission occurs magnetically, wear and backlash are virtually eliminated, supporting precise control and long service life.
Garland adds that consistent torque behavior also improves the performance of the embedded PID control loop.
Why it Matters for System Designers
Garland highlights two design principles embodied by the magnetic coupling:
- Isolation for longevity. Keeping the actuator completely sealed from the environment drastically reduces failure risk and maintenance demands.
- Simplicity for control. Fewer mechanical interfaces reduce variability, improving predictability for motion-control algorithms.
These lessons apply broadly—from underwater valves to medical pumps and compact robotic actuators—where reliability depends on keeping the drive mechanism protected from its operating environment.
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