responding to http://www.homeownershub.com/mainten...et-716374-.htm
Abacab wrote:

dumbstruck wrote:


Thank you to those who answered accepting the premise of my
question. I will try some cobbling in series, although it is hard
to buy online because I don't know the terms for what I need. I
don't have good access to local plumbing contractor places...
I just found shutoff valves with threads only on the output end,
but will try more....

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I doubt you will find a new shutoff valve that will screw directly onto the old seized shutoff valve. This is because the outlet on a shutoff valve is designed to be connected to a pipe/tube, and not to another fitting. Having said that I believe you can achieve what you want by connecting a faucet water supply line (which may be the existing one or a new one) to the old shutoff valve outlet, and then connecting a new shutoff valve to the other end of the supply line. Obviously you will need to match the supply line outlet with the inlet of the new shutoff valve (e.g. a 1/2" MIP/FIP connection).

I have observed this setup on more than one occasion. I believe it is possible to crimp the existing supply line, or use a C-clamp on the existing supply line, to stop the flow of water without shutting off the water to the building. An alternative is, if you have access to the building shutoff valve, to shut if off for a minute while you connect the new supply line/shutoff valve and turn it back on again quickly. While many buildings with common water supply have an "official" policy of 24 hour written notice, in practice many maintenance staff just turn off the water for short periods of time without notice.

The problem you describe is not at all uncommon. In California, for example, there were many apartment complexes converted into condos. There are thus no individual unit water shutoff valves, or common-area maintenance staff. I am aware of one complex that was converted and where new faucets were installed in all units, along with all new appliances. However the old shutoff valves were left in place, almost all of which are seized up. Replacing a faucet or swapping out a dishwasher now "officially" requires a condo owner to give advance notice of water shutoff to up to 20 other units. In practice this is often not done.