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Solenoid Valves

        The choice to use solenoid valves was made early on as part of the buoyancy and resurfacing system design process. The exact type of solenoid valves to be used was not finalized until much later and required much deliberation. Solenoid valves use an electromagnetic coil which is energized by an external power supply to actuate a plunger to open or close a port in the valve. Typically the solenoid valves are designed such that the plunger is held in either the open or closed position by either a spring or (in the closed case) the pressure of the fluid the valve is being used to control. This means that the electromagnetic coil only needs to be energized when the flow is switched from on to off or vice versa. Because of these factors one must be careful when choosing a solenoid valve so that the electromagnetic coil will only need to be energized periodically. 

Solenoid valves are rated by their minimum and maximum pressure as well as their operating voltage and current. The main criteria used by group 6 when choosing the solenoid valves to be used in the robot were that the solenoid valves must run on DC current, fit inside the 4” diameter housing, and be rated to operate at the pressure of the carbon dioxide (1000 psi - 1200 psi). Unfortunately, these two criteria seem to be mutually exclusive for commonly available solenoid valves as despite checking multiple vendors the team was unable to locate a solenoid valve that meet both specifications.

Ultimately, the group chose to use a solenoid valve that ran on 24VDC current with a draw of 400 mA that was rated for 500 psi. While this solenoid valves appears to be inadequate the group determined that it was the best choice possible given the selection available. The decision was made to purchase four of these solenoid valves based on the facts that they fit in the housing (see Appendix A for dimensions), and operated on an attainable voltage and current level, had the highest pressure rating of any DC solenoid valves that were available and with the expectation that perhaps the valves were engineered with a high margin of error for their maximum pressure rating.