That is a very old commercial vac made by NSS, a longtime producer of commercial cleaning equipment. They’re best known for the legendary M1 “Pig” heavy duty canister vac. Judging just by the look, I'm guessing it’s probably from the ‘50s or early ‘60s.
If it's anything like the Doyle Vac-It at the gas station I worked at in the early 70s, it will have unremarkable water lift but tremendous airflow. Looks like it uses a 2-1/2" hose, and the motor appears to have a separate cooling fan, which could mean it's a wet/dry machine. If it's operable, please post a YT video of it running. It's definitely a machine to hang onto if you have the room.
The National Super Service Co. is still in the commercial floor care business as NSS Enterprises. Below is a link to their products page.
That vacuum is a TREASURE-From the famous NSS company"Enterprise" as known today.Yes,besides the world famous M1 commercial "canister" vacuum they build wet-dry vacuums and commercial floor and furnishings care equipment.Lets see this vacuum work!