When I started to build my dust separator, I found that all the stores I shopped had the very same 20 gal. galvanized trashcan. Nothing heavier. I purchase the least expensive one I could find and went ahead with the project. Everything worked as planned except I experienced the ?oil can? effect many have talked about. In order to solve the problem, I first bought a second trashcan and, cutting off the top and bottom, I inserted it inside the original can and essentially made a double walled can. A lot better, but still some oil-canning if the vacuum hose was blocked. Then, I thought I might come up with a relief valve that might be cheap and easy to make. The following photos show the results. And it works! All parts were purchased from my local True Value hardware store.
VACUUM RELIEF VALVE
Parts List:
?-20 x 6? full thread hex head bolt (1)
?-20 nylon inset lock nuts (4)
?? x 1-1/2? steel fender washers (2)
?? x 2? rubber fender washer (1)
?? standard steel washers (2)
7/16? x 2-1/8? compression spring, Century Spring #C-676 (1)
3/8? lamp nipple with set of nuts, lock washers and washers
2? PVC pipe cut to 5-1/8? (1)
2? PVC pipe cap (flat ended) (1)
2? PVC pipe slip union (1)
8 x 3/8? automobile trim screws with points ground down (3)
6 x 5/8? machine screws (3)
?? MDF to make 2 disks
?? MDF to make one disk
Special Tools Needed:
Adjustable circle cutter - for precisely cut disks ? use on drill press
3/8? Forstner drill bit - seems to work better than standard drill bits
Theory:
Disk on right end of photo is secured in pipe with 3screws. Middle and left disks move as a piston. When vacuum tube is blocked, suction moves piston down pipe until middle disk clears the inlet holes in pipe. Outside air bypasses the trashcan and normalizes pressure until blockage is cleared. Once blockage is cleared, spring returns piston to normal position and full pressure comes through dust separator.
Construction and Assembly:
Disks: These are the critical parts. If they are not made to the correct size, the valve will not work smoothly. MDF works better than plywood or hardwood. Keep in mind that PVC pipe interior is not perfectly round or smooth. Middle and left disks must move freely. Carefully measure the inside of your pipe and, using the adjustable circle cutter on a drill press, cut disks to be as big as possible and also allow this movement. Right disk can be a little snugger. Don?t be afraid to remake disks to get the right size. Drill 6 air holes in middle and right disks with 3/8? Forstner bit. Try drilling small pilot hole for each air hole and enter from each side with Forstner bit to avoid break-out. Drill 25/64 hole in center of right disk for 1-1/4? to 1-1/2? length lamp nipple. Assemble with bolt, nuts, washers and spring as shown. Left disk is solid. I suppose it could be made with the ?? MDF, but there must be enough room between the middle and left disks to let in air.
PVC Union: In order for the union to fit on the 2-1/2? ?T? I used, I had to stretch one end of it. I did this using a heat gun. I heated the end for several minutes and forced it over a 2-1/2? disk I had cut from ?? plywood and screwed to a flat board. The same can be done using an oven, boiling water or boiling oil. I find the heat gun the easiest. Be sure to use gloves! I used a short piece of PVC pipe inserted in one end for leverage, but be sure it is scrap pipe because it may deform also. You can either wait for the union to cool off gradually, or dip it in water.
PVC Cap: Be sure you purchased a cap with a flat top and not one of the rounded type. Find the exact center and drill a 1-3/4? hole using the adjustable circle cutter on a drill press. In order for the cutter to not damage the hole you are cutting, I found it best to cut a ?? plywood disk and insert it inside the cap. This gives the center drill something to steady itself on when the cutter goes through the PVC.
PVC Pipe: 6 holes should be drilled with your 3/8? Forstner bit. They will be about 1-1/4? apart. Position them so their centers are exactly under the middle of the middle disk. This keeps air from flowing through the valve under normal air pressure. Be sure the inside is smooth, and no burrs interfere with the piston.
Assembly: I assembled the PVC with screws instead of glue so I could disassemble it and adjust it if needed. Drill pilot holes and attach cap end with short screws. Be sure points are ground down so they do not protrude onto the interior. Position slip union on other end and drill pilot holes. Insert piston. It should protrude past the pipe end (not the union) about 3/16?. Push it level with the pipe end and fasten it with three 5/8? screws. Screws go through the union and the pipe and into the disk.
Use: All my system uses 2-1/2? fittings. I have used a 2-1/2? ?T? between the dust separator and the vacuum. I put the relief valve on this T. Under normal use, the relief valve is closed. When the hose is blocked with trash or my hand, the relief valve opens, letting outside air into the vacuum, and the trashcan does not collapse. If I do not want to use the relief valve, I put a modified 2-1/2? PVC end cap over the opening. I stretched the cap the same way I modified the PVC union described above. Can this valve be scaled to a 4? system? Make the same valve and connect with an adapter.
It is possible there is another way to do this, but this is what I originally drew up and it seems to work as planned. My only experimentation was with springs. The first one was way to strong, but my second try worked. I did try making the pipe a little shorter to get more pressure on the spring, but I went back to the original length. So feel free to experiment all you want, but this plan does work if built as described and shown. Good luck!
VACUUM RELIEF VALVE
Parts List:
?-20 x 6? full thread hex head bolt (1)
?-20 nylon inset lock nuts (4)
?? x 1-1/2? steel fender washers (2)
?? x 2? rubber fender washer (1)
?? standard steel washers (2)
7/16? x 2-1/8? compression spring, Century Spring #C-676 (1)
3/8? lamp nipple with set of nuts, lock washers and washers
2? PVC pipe cut to 5-1/8? (1)
2? PVC pipe cap (flat ended) (1)
2? PVC pipe slip union (1)
8 x 3/8? automobile trim screws with points ground down (3)
6 x 5/8? machine screws (3)
?? MDF to make 2 disks
?? MDF to make one disk
Special Tools Needed:
Adjustable circle cutter - for precisely cut disks ? use on drill press
3/8? Forstner drill bit - seems to work better than standard drill bits
Theory:
Disk on right end of photo is secured in pipe with 3screws. Middle and left disks move as a piston. When vacuum tube is blocked, suction moves piston down pipe until middle disk clears the inlet holes in pipe. Outside air bypasses the trashcan and normalizes pressure until blockage is cleared. Once blockage is cleared, spring returns piston to normal position and full pressure comes through dust separator.
Construction and Assembly:
Disks: These are the critical parts. If they are not made to the correct size, the valve will not work smoothly. MDF works better than plywood or hardwood. Keep in mind that PVC pipe interior is not perfectly round or smooth. Middle and left disks must move freely. Carefully measure the inside of your pipe and, using the adjustable circle cutter on a drill press, cut disks to be as big as possible and also allow this movement. Right disk can be a little snugger. Don?t be afraid to remake disks to get the right size. Drill 6 air holes in middle and right disks with 3/8? Forstner bit. Try drilling small pilot hole for each air hole and enter from each side with Forstner bit to avoid break-out. Drill 25/64 hole in center of right disk for 1-1/4? to 1-1/2? length lamp nipple. Assemble with bolt, nuts, washers and spring as shown. Left disk is solid. I suppose it could be made with the ?? MDF, but there must be enough room between the middle and left disks to let in air.
PVC Union: In order for the union to fit on the 2-1/2? ?T? I used, I had to stretch one end of it. I did this using a heat gun. I heated the end for several minutes and forced it over a 2-1/2? disk I had cut from ?? plywood and screwed to a flat board. The same can be done using an oven, boiling water or boiling oil. I find the heat gun the easiest. Be sure to use gloves! I used a short piece of PVC pipe inserted in one end for leverage, but be sure it is scrap pipe because it may deform also. You can either wait for the union to cool off gradually, or dip it in water.
PVC Cap: Be sure you purchased a cap with a flat top and not one of the rounded type. Find the exact center and drill a 1-3/4? hole using the adjustable circle cutter on a drill press. In order for the cutter to not damage the hole you are cutting, I found it best to cut a ?? plywood disk and insert it inside the cap. This gives the center drill something to steady itself on when the cutter goes through the PVC.
PVC Pipe: 6 holes should be drilled with your 3/8? Forstner bit. They will be about 1-1/4? apart. Position them so their centers are exactly under the middle of the middle disk. This keeps air from flowing through the valve under normal air pressure. Be sure the inside is smooth, and no burrs interfere with the piston.
Assembly: I assembled the PVC with screws instead of glue so I could disassemble it and adjust it if needed. Drill pilot holes and attach cap end with short screws. Be sure points are ground down so they do not protrude onto the interior. Position slip union on other end and drill pilot holes. Insert piston. It should protrude past the pipe end (not the union) about 3/16?. Push it level with the pipe end and fasten it with three 5/8? screws. Screws go through the union and the pipe and into the disk.
Use: All my system uses 2-1/2? fittings. I have used a 2-1/2? ?T? between the dust separator and the vacuum. I put the relief valve on this T. Under normal use, the relief valve is closed. When the hose is blocked with trash or my hand, the relief valve opens, letting outside air into the vacuum, and the trashcan does not collapse. If I do not want to use the relief valve, I put a modified 2-1/2? PVC end cap over the opening. I stretched the cap the same way I modified the PVC union described above. Can this valve be scaled to a 4? system? Make the same valve and connect with an adapter.
It is possible there is another way to do this, but this is what I originally drew up and it seems to work as planned. My only experimentation was with springs. The first one was way to strong, but my second try worked. I did try making the pipe a little shorter to get more pressure on the spring, but I went back to the original length. So feel free to experiment all you want, but this plan does work if built as described and shown. Good luck!