plumbing
What materials are required to cap off a 3/8” water feed at the valve?
I had a dishwasher. Its feed line connected to the water service under my kitchen sink right at the hot water shut off valve. I’ve removed that hose and would like to continue to use the kitchen sink. What do I need in order to cap off opening?
I have a compression fitting cap that fits on the threads, but this, by itself, does not make a water tight seal.
I think what is leaking is the drain. Does it look like the object sticking out to the side in the below picture? If so, this is used to drain water from the house side of the supply when the valve is off.
It sounds like you over tightened it in the first place which started the leaking. If you've broken only the cap, you might be able to find a replacement. If the stem and threads are damaged, long-term you will need to replace the entire valve. As a short-term fix, you just need to block it some how. Marine epoxy is handy for emergency plumbing repairs.
Since it seems that you already have the lines, I think all you need is a compression adapter fitting like this:
http://www.amazon.com/LASCO-17-6759-4-Inch-Compression-Adapter/dp/B008E5CFC4/
It will screw onto the female 3/8" compression on the drinking water faucet and allow you to connect a 1/4" compression line to it (from the filter).
This is one of the most commonly sold compression adapter at Home Depot, so anyone in plumbing should be able to point you to it (if you're in the US... I'm sure Lowes and others sell it to. Quite common.
Best Answer
I recently dealt with a similar problem -- I installed a water accessory and was faced with a 3/8" compression male outlet and nothing needing to be connected to it. A cap was easy to find at the plumbing supply but it didn't seal well. Wrapping the male thread with teflon tape plus pipe dope slowed the leak to a very slow drip, but the fact is the threads on a compression joint just aren't intended to form a seal.
In this case I got away with sealing it by placing a thick o-ring in the bottom of the cap. It sealed the cap to the male fitting nicely.
I was concerned the o-ring might wrinkle or buckle in some way during assembly, allowing the leak to continue. Had that happened I also considered carefully placing a brass or acetyl/delrin ferrule (without any tubing) into the male fitting, then place the o-ring around that, and finally install the cap. Maybe the ferrule would seal between the fitting and the cap, but if it didn't, it could provide some structure to help keep the o-ring in place.