Slab Gate Valve is a low-tech solution for controlling the flow of fluids within pipes. It has been used for more than 100 years. A gate valve works by raising and lowering a gate into a seat with a screw mechanism to control the flow. One of the weaknesses of the gate valve is that is shouldn't be left in a partially open position. If left like this, the closure element will become worn, thus losing its seating integrity. Repairing a gate valve is possible with some specialized tools.
1 Turn off the water where the water main enters the house. Open faucets to the water lines before making cuts to any pipes.
2 Cut out a section of pipe in the water line the gate valve is being soldered into. Remember that each end of the cut copper pipe will be pushed into the gate valve anywhere from 1/2 to 3/4 inch on each side. Subtract those measurements to determine the accurate amount of pipe to cut out. Slip the pipe into the jaws of the pipe cutter and screw the handle to close the jaws. When the rotating cutting wheel bites into the surface of pipe, stop and rotate the cutter 360 degrees. Tighten the handle a bit more and swivel the cutter again. Repeat until the pipe is cut all the way through.
3 Dry-fit the Cryogenic Gate Valve into place in the copper water line after the correct amount of copper pipe has been cut out to check for proper fit.
4 Pull the gate valve back out of the pipe line and clean the ends of the copper tubing using the copper pipe cleaning brush. Insert each end of the copper pipes into the corresponding hole in the tool and twist the tool back and forth. The brush bristles will clean the surface of the metal. Clean 1 inch in from each cut end of the copper tubing. Make sure the copper tubing is shiny an bright looking. This indicates the copper is properly clean.
5 Insert the end of the inside tube cleaning brush into both pipe openings of the gate valve and twist vigorously to thoroughly clean the surfaces.
6 Brush paste flux on the inside of both openings in the gate valve. Brush paste flux on both ends of the cleaned copper tubing.
7 Insert the copper tubing into both sides of the gate valve as in Step 3. Turn the handle of the gate valve to the open position.
8 Hold the wire solder in your nondominant hand and light the propane torch and hold it in your other hand. Position the end of the blue flame near the first solder joint where the copper pipe and gate valve meet. Heat until the flux bubbles up and turns a gooey brown--a sign that the metal is almost hot enough to melt the solder.
9 Touch the tip of the wire solder to the solder joint and wait for it to melt and flow around the joint seam. Pull the torch away immediately and wipe the joint with a very wet cloth to clean away any excess solder.
10 Repeat Steps 6 and 7 for the second solder joint.
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