Old tub---what is this mechanism and how to fix?

[Chuckles]

As far as I know, our bathtub (shown in the sketch) is original to the house, c.1920. There is a handle you turn that goes through the wall and makes a rod go up and down. This is supposed to control whether the tub drains or not.

Well, the tub no longer drains and the handle has no effect. This is not a blockage due to hair; we've done the snake/Drano bit. As far as I can tell, the plug is no longer connected to the vertical rod, so pulling the rod up and down makes no difference. (I have disconnected it from the rotary mechanism, and it goes up and down freely with a lot of travel but it has no effect.)

Of course I can't see the plugging mechanism itself because it is inside the cast-iron piping.

Could someone please tell me what this kind of mechanism is called and/or give me a link to someplace where it is described? (It is not described in my home repair manuals.) I guess what I really want to know is what the options are for fixing it or replacing it with something appropriate for an old house bathroom.

I will get a plumber, I certainly can't handle cast-iron pipe disassembly, but I want to know what the good options are so I don't get stuck with a bad solution if suggested by the plumber.

Many thanks,

 

[hj]

drain

It is called a "direct lift drain with concealed overflow". The tub does not have an overflow opening in the front wall so the water rises in the concealed tube until it reaches the top of the inner pipe at which time it "overflows" it and begins to flow down the drain to maintain a set water level in the tub. Usually that entire inner tube is lifted by the turning handle.