Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 501-1819 PC. NO. 9 found under O Ring by Portland Valve Llc. The National Stock Number assigned to this part is 5331001661001, and the Federal Supply Class is . Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 501-1819 PC. NO. 9.