Utilities are widely used shut-off valves — they are in all water inlets in the house and each apartment. Earlier these devices were made of iron or steel: casing — cast iron, and the remaining parts (except seals) — steel. Such gates are still many in the water supply systems, although most of them are not working: their thread has long since rusted and the stocks firmly rooted to the heads. And these are “rarities”, playing only the role of coupling, but unreliable, as the water through the hole in the head stem still leaks.
Modern valves — bronze, brass, or stainless steel, and corrosion cannot handle them. But using valves from case to case when it is necessary to turn off the water to replace the worn gasket in the faucet or the faucet itself. But just this circumstance contributes to their withdrawal from the system over time on the thread stems from the constantly falling water is delayed, as in the pipes, so solid salts and oxides that wrap, if necessary, the valve costs a lot of efforts, which often cut off the edges of the tetrahedron flywheel or stock, and often breaks off, and the stock.
Extend the life of the valves both from ferrous and non-ferrous metals is possible by simple retrofit.
The old black valve you can try to revive, since its replacement by “color” because of their different lengths will entail more and replacement sleeves (and if the connection is not, and reconstruction of part of water). To this end, a special fluid (or kerosene), softening the rust, it is necessary to Unscrew the head together with the rod and nut and try to separate the part in a vise. If it succeeds, then clearing all the items from rust and polished with the valve seat in the housing and the lower surface of the head, gather the node and upgrade the valve to set the knot in place.