Type: Adjustable Auto-Cycling
Vacuum: Electric Pump
Page: 6 of 11
Build the PVC Reservoirs
There are three PVC reservoirs that need to be built. This is another easy part of the system and it shouldn't take more than 60 minutes to assemble. The first two tanks, which we'll call the "main reservoirs" are made from 4" solid core schedule 40 or 80 PVC which can be found at most plumbing shops. The reservoirs are used to hold spare vacuum. They prevent the vacuum pump from having to cycle on and off too frequently.
|Parts used in this section:
4" PVC Pipe (2 at 15"L)
4" PVC Caps (4)
1.5" PVC Pipe (1 at 6"L)
1.5" PVC Caps (2)
Pipe Tap (optional)
7/16" Drill bit
1/2" socket & ratchet
Check your local plumbing supplier for the PVC pipe. If they have one or two small pieces sitting around, they might give them to you for free. If they don't have any in stock, I've found this grade of PVC at Home Depot (oddly, Lowes does not carry it). Be sure that it is solid core schedule 40 or 80 PVC. If you cannot find this type of PVC, ask your local plumbing supplier to order it for you. Do not substitute any other type of PVC. Foam core PVC and black ABS pipe reportedly collapse under negative pressure.
For the main reservoirs, you need 2 pieces that are 15" long. With more available reservoir space, the less the unit has to cycle on and off. This minimizes the wear and tear on the Mac valve and pump. The 15" lengths of PVC will make an adequate reservoir system that will give you the right amount of vacuum reserve without making the overall system too heavy. Two schedule 40 or 80 end caps are used to make the reservoir ends.
This system also uses a "sub-reservoir" to maintain proper life of the vacuum pump valves. For the sub-reservoir, a 6" piece of 1.5" schedule 40 or 80 PVC is used. You'll also need two 1.5" PVC caps to complete this piece.
Tap the Caps
There are two ways to tap the reservoir caps. The first involves the use of a dedicated pipe taping tool. This is the easiest method and produces the cleanest threads. The second method involves using the fitting itself to cut the threads and requires a bit of strength and patience.
You only need to tap 2 of the 4 caps for the main reservoirs and one of the sub-reservoir caps!
The easiest and most reliable way to create the threads is with a dedicated 1/4" NPT tap. Note that pipe tap sizes do not refer to diameter. The actual outside diameter
of a 1/4" NPT pipe thread is .54 inch. Most hardware stores carry pipe taps for about $9 but you can save a couple of bucks and pick one up at VeneerSupplies.com.
To create the threads use a drill press and a 7/16" bit. It is critical that the hole be drilled straight through the top center of the cap. To do this, be certain to drill into the cap from the top as shown. If the cap is drilled off-center, it will not fit the manifold and carrier correctly. I've also had excellent results drilling the caps on my lathe. Click here to see a picture.
Use a pair of Vise-Grips or a ratchet with a 1/2" socket to hold the tap. Carefully screw in the tap using about 3/4 of the tap length. Then test the threads with a brass fitting. If it is too snug, re-tap the hole and screw it in a bit further to slightly widen the hole. Be sure to tap only two of the four caps in the system.
If you don't have a tap, you can make your own using an old 1/4" NPT brass fitting. Simply bevel the leading threads and then cut an angled groove in them with a hacksaw so you have something similar to what is shown in the picture to the right. The sharp brass edges won't last long but will hold up for a couple of uses. Thanks for Mark Porter for the suggestion and picture.
If you prefer to tap the caps with the brass fitting itself, you can drill a 31/64” hole into the cap and create the threads with the ¼" pipe thread of the fittings.
To create the threads in the cap, use a wrench or socket to insert a brass fitting. Any fitting with 1/4 " NPT threads and a hex nut on the top will work fine. Remember, you will be threading the fittings into unthreaded plastic so work slowly. A small amount of light oil will assist in the threading process. After you have inserted the fitting completely through the hole, remove it and repeat the process on the other cap. Be sure to tap only two of the four caps in the system.
From Mike Lonchambon of Houston, TX
After I drilled the caps out at the drill press, I chucked a brass fitting into the press and lowered it down to the cap. I gave the chuck a few twists by hand to get it started straight and true and then removed it from the press and continued with a wrench. This ensures that the fitting goes in perfectly straight which is difficult to do by hand.
Build the Main Reservoirs
Cut two pieces of 4" PVC to 15" in length. They must be the same length. This will make it easier to attach them to the carrier.
You can now cement the caps to the PVC pipe to make one of the reservoirs. Remember to use one tapped and one untapped cap on each of the two reservoirs. Use regular PVC cement and apply it generously to both sides of the mating areas. Give the cap a slight twist (1/4 turn) as the parts slide together. For goodness sake, do this in a well-ventilated area.
Before assembling the second reservoir, measure the length of PVC pipe between the two caps on the first reservoir (on my system, the measurement was 10.5"). Now, attach one of the caps to the second reservoir using the cement. Measure from the edge of this cap to the length you just measured on the first reservoir and mark the PVC with a pencil. Apply cement and attach the last PVC cap. Slide it up to the pencil line to ensure that both reservoirs are the same size. This moderately important. Otherwise they will not easily attach to the carrier.
Assemble the Sub-Reservoir
Cut a piece of 6" length of 1.5" diameter PVC. One cap should have a hole drilled in it. The other cap should be solid (no holes). Use regular PVC cement and apply it generously to both sides of the mating areas. Give the caps a slight twist (1/4 turn) as the parts slide together. Again, be sure do this in a well-ventilated area.
Attach the Reservoirs
Be sure that you have applied thread-sealing tape to the male threads that are remaining on the tees. Then screw the PVC reservoirs onto the main manifold system. Attach the sub-reservoir to the upper brass fitting on the sub-reservoir manifold as shown in the picture on the right. You can click on the picture for a larger image.