what was this old valve used for?

It is a manually opened valve that is mounted on or in some water controls or a water column to show the water level in a steam boiler. They were used as a "just- in- case" indicator if the gauge glass had become compromised or plugged or to check the water level in addition to the gauge glass. Do this, "GOOGLE" McDonald Miller control #157 or #193 to get a picture of the placement of those valves. Those three holes in line on the vertical surface would each have 1 of those valves. By the way, they are called tri-cocks and are used as a set of 3.

Hello, I've got an old gauge column that looks sort of like this. The valves were operated by pulling a chain, which lifted the iron weight, opening the valve. They operated this way as the valves might have been up high on a big boiler, but served the same purpose as a hand-wheel.

Yours, Larry

Also bleeder valves for hot water radiators

They are called tricocks and they used to mount three on the column of the old boiler installs. Now you see One Fifties on the boilers instead. Remember, steam has always been a hands on way to heat and a plant of any size had a resident fireman/ custodian
The really old schools in Winnipeg 1911 ,1895 had seperate living quarters for the caretaker and his family. The boilers were fired on cord wood in those days. Just to point out what a different time that was , the suites were all on the top floor and they had a seperate stairwell just for the caretaker and his family, no one else could use it because it was the entrance to a private home. The apartments were also very nice , the trim was quarter sawn oak, solid oak floors three bedroom, dining room, living room, antichamber and of course kitchen and washroom. I remember Lauria Secord school , the backdoor for the suite opened onto the top floor of the school and the only mechanical equipment was a large exhaust fan, the space was so large you comfortably play soccer with ten friends. Stay Well and Be Blessed Jack