Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number HV 221 S3 1 POS 19 found under Valve Check by Bauer Nilsen A S. The National Stock Number assigned to this part is 4820251502731, and the Federal Supply Class is 4820 Valves Nonpowered. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like HV 221 S3 1 POS 19.