4-Way Solenoid Valves (VERSATILE) These valves offer the most versatility as they can be used for anything. They actually have 5 ports: One port is for air going IN from your compressor. Two ports are for air going OUT to your prop's cylinders. 2 ports are for exhaust. *1/4" air ports. 1/8" breather ports. Includes: (1) 5/2 1/4" Solenoid Available with 12-Volt, 24-Volt, or 110-Volt Flying Lead (3) 1/4" Male Straight Push-In Fittings (2) Breather Vents These valves are required for Double-Acting Cylinders.Why? Because they actually switch the direction of the airflow from going in the BOTTOM of your cylinder's inlet, to going in the TOP of your cylinders other port.This causes the cylinder to open or close very rapidly! Other Benefits of 4-Way Valves: More exhaust control to adjust speed of props. Generally larger diameter inside the solenoid allows for more air to flow when needed. Can also be used for any solenoid need that the one or two-way valves can do.