Wax motors did not originate with the Neptune. My understanding is that they have been around a long time. Their advantage is that they are generally cheap and reliable ways to actuate valves and locks. They are much slower than solenoids, however. For water valves they may be preferred because their slower action doesn't cause water hammer.
From:
From
http://www.ark-les.com/products/custom-products/actuators-wax-motors/default.html
"Wax Motors"
A Wax Motor is an actuating device that consists of a positive temperature coefficient thermistor (PTC) mounted to a sealed vessel filled with a solid wax. As the solid wax is heated to a controlled temperature by the energized thermistor, the wax melts and expands, driving a spring-loaded piston outward. Depending upon the orientation of the vessel within its housing and the configuration of the spring, this piston may pull in or push out a load. When the thermistor is de-energized, the liquid wax cools and the spring returns the piston to its original position.
Wax Motors should be considered for applications where quiet, smooth, and efficient actuation is desired which include: liquid and detergent dispensers, air flow control, water diverter valves, thermal time delays, door safety locks, and noise dampers.
Common Operating Parameters
Please note that these are thermal devices and are affected by ambient conditions.
Voltage rating: 12VDC/120/240VAC, 50/60 Hz.
Current: 100mA maximum steady state (50 mA typical), 1A maximum inrush
Temperature Rating: Max. operating ambient of 70°C & 60°C for high & low temperature models respectively
Actuation Stroke/Time: 0.196” minimum travel in 90-seconds. Plunger begins to move in 45-50 seconds.
Retraction Time: Dependent upon electrical soak time and ambient conditions. Typically, a 2-minute soak time will have a retraction time of 60-80 seconds; an 8-minute soak requires 120-140 seconds to retract
Actuation Force: The assembly is tested with a 5 lb. load during manufacturing testing. The assembly can provide forces up to 30 pounds with decreased travel. Actuation force is a factor in rated cycles, and therefore we recommend not exceeding the 5 lb suggestion.
Power: 1 foot – pound < 1 Watt
Life Cycles: 10,000 cycle minimum, although this is somewhat application dependent. In certain applications the life of the product has exceeded 75,000 cycles.
Also:
en.wikipedia.org