Building your own blast gates is one way to save yourself some money, especially when you are planning to put in as many as I plan to. I made enough parts to make 18 blast gates. It makes sense to make them all at once so that you can use all the same material, and you have the jigs set up to cut everything the same exact size.
For my system I am using 4” sewer and drain PVC pipe. This has an outside diameter of 4 ¼ “. I am using 1/2” plywood for the gates because I wanted plenty of surface to glue the pvc onto the wood. My wood just happened to be some 8” wide prefinished flooring that I salvaged out of a dumpster.
Cut the wood 7 ¼” square. Using my “Jasper circle cutting jig”, (which is one of my favorite shop tools) I cut a 4 ¼” diameter hole. Notice that I set up a jig so that I could cut three at a time. The center of the hole wants to be 3 ¼” from the back of the gate.
Most of my gates use this dimension. However some of them will want a smaller hole for the bottom of the gate. This would be the case if the gate was feeding a 2”, 1 ½”, or 1 ¼” hose. Whatever size the bottom is, it still wants to be centered at 3 1/4” from the back.
Cut your pvc 2 ¾” long to glue into the ½” plywood hole. Use two-part epoxy for this. It’s important that this is a strong joint. Be sure to place some wax paper under the plywood when doing this. After the glue is fully set up, run the piece across a sander to make sure have a smooth surface.
Next I used 3/16” thick plywood for the spacers to sandwich the two gate pieces together. Rip the plywood ¾” wide. When gluing the spacers on, use extra spacers from side to side to make sure that the inside width is consistent. Make sure you don’t overdo it with the glue. You absolutely don’t want any glue squeeze-out. This is why I went with ¾” wide spacers so that there would be enough surface to glue everything together without having the glue so close to the inside edge. The back spacer ended up needing to be only 9/16” wide.
For the gate itself, I used 1/8” panelboard Masonite because it slides easily and because it is thinner than the 3/16” thick spacers. The gate is 8” long and 5 ¾” at the widest part. 1 ½” from the back, offset the width in 5/16” on each side, for a total width of 5 1/8”. Also cut off a little on the back corners. This is in case a little sawdust builds up inside the back corners that you are not able to clean out.
With a magic marker, draw a line on the Masonite, where the gate is completely closed. Then slide the gate partially open until it just barely still covers the 4” hole. Make a second line on the Masonite. This is so you will know if some sawdust is preventing the gate from closing all the way.
Make some little pieces for stops so that the gate won’t slide clear out. Screw these pieces on, but don’t glue them on, so that you can remove the gates later on if scraping excess dust out of the back of the gate is necessary.
For adapting the 4 ¼” outside diameter pipe to fit inside a 4” inside diameter flexible hose, you can buy adapters for this or you can form your own. To do this, cut a 4” diameter hole in a 2×6. Then rip the 2×6 down the middle of the hole.
Cut two 1/4” wide by 1 ½” long slots out of the end of the 4” pipe. Then, with a heat gun, soften the pvc enough to squish down in the form. Use pvc glue to re-glue this formed end back together.
Where you are going to use 2 1/2” flexible hose, I used schedule 40 (thick wall) 2” pvc. The outside diameter is 2 3/8”, which will work if you tighten down the 2 ½” hose tightly with the hose clamps. For a little better fit I made a plug to stretch out the end of the pipe to a full 2 ½”.
Just heat up the end of the 2” pipe and drive the plug expander in.
You can cut some 4 ¼” diameter adapters from a 2×6 for whatever size hose you have coming out of the wye fittings.