Toilets, Sinks, Showers, Tubs and Disposals - leaking around valve stems

Whenever I try to do any plumbing work, when I try to shut down the water at nearest valve, it always leaks around stem. The ONLY valve that doesn's seem to do this is main shutoff. It is the same as the others (it is NOT a ball valve, all valves are traditional ones you turn to open/close) When I worked on hot water tank and tried to shut off water at tank, I had a leak at the valve stem for week or so. It was slow trickle. I now need to work on sink. When I shut the valve, water came spraying out around stem and not just a drip, it was really spraying. I had to quickly open it back up and now it is dripping. Anything to do about this so I can work on things without shutting off all the water to entire house? Any way to prevent it? Are ball valves a lot better for this reason? If so, since I am likely going to put on a MAJOR addition to house I might just replace all the valves with ball valves to prevent this problem in future.

Thanks, hammer

Your description sounds like gate valves. If so, there is a nut under the handle. Open the valve and then tighten the nut until it stops leaking. The more you tighten it, the harder it will be to turn the handle. The nut is called a packing nut and has a fiber packing under it. When the nut is tightened, the packing is compressed against the stem to prevent leaks. Ball valves are preferred because: they don't have stems that leak, they allow a fuller flow through them, and they shut off quickly. Gate valves have a depression in the bottom that the gate seats in. After a period of time, this depression fills up with debris and calcium deposits which make it hard to shut off fully. Good luck.