Header tank Identification.

Hello all.
Can any of you kind folk help me identify a Merlin Header Tank. Sorry haven’t got any photo’s.

Information I have is off the data plate and is as follows –

Standard Air Products Inc.

Part number = SA-3800-5 (maybe S)
PP-5398.

Serial number = 29610.

Contract number – W20-17-AC-863

Water Capacity =2 gal -2 pnts
Air Capacity =2 gal -2 pnts

Cheers

Mick.