Plourde’s Toolbox Bargains. Slightly Used ARO 1/4 5/3 Alpha Stacking Dual Solenoid Pneumatic Valve, 120 VAC, A722SD-120A. Brand: ARO, Ingersoll-Rand Part #: A722SD-120A. 1/4, 3-Position Alpha Stacking Solenoid Valve See pictures above for more details. It is assumed that the unit(s) will be installed and operated by qualified personnel.