In the event you find yourself in the desperate need of a vacuum pump but aren’t desperate enough to pay for one, then you’ll have to use some of your resources and this article to build one yourself. This is assuming you have some vital components and are mechanically inclined.
Step 1 - Get a Refrigerator Unit
You can obtain one for relatively cheap from a local refrigeration reseller if you don’t have one in mind. You’ll need a pair of strong cutting pliers in order to cut the tubing that goes in and out of the unit. You won’t want to use a saw because the metal dust may enter the unit via the tubes and be a problem later on. Be sure that you leave plenty of tubing because you can always cut more but it’s not easy to replace if you cut too much. You’ll want 10 cm. Seal the tubing at the ends for transport.
It is important to leave the oil inside of the unit. It will contain Freon and is a menace to the environment. Be careful not to spill any of the oil because these units will heat up quickly without adequate lubrication. Some will say to replace the oil and there are different opinions as to the use of the Freon to help cool the unit. It’s a safer bet to just keep the original oil inside.
Step 2 - Get the Glass Syringe
A glass syringe can be obtained from a pharmacy or medical supply store. Do not use a plastic syringe because it will not last long. The rubber from the bicycle air tube will be used to protect the glass syringe.
Step 3 - Collect the Rest of the Materials
A manometer can be found at a car supply store and is meter used to check the aspiration of the fuel pump and doesn’t cost much. It will be used to set the depression valve precisely as to not cause the foam core form to collapse on it. A vacuum depression of -0.4 bar is the max depression you want to use.
Everything else can be found around your house, garage, or in a department store.
Step 4 - Understand the Basic Concept
Before beginning it is important to understand the basic principle. The compressor will pump when connected. Vacuum pressure moves the piston of the syringe up and this releases pressure on the microswitch until the OFF position is reached. The Piston will go back down due to vacuum pressure leaking, pushing the microswitch back ON. The syringe acts as a regulator. It is vital that the system is fixed in a vertical position.
Step 5 - Build the Housings
A box needs to be built out of plywood so that hazardous parts can go inside safely. The electrical junctions should be installed in an isolated box that is on the top of the wooden box. The separation will be handy for later maintenance.
Step 6 - Install the Refrigerator Compressor
The unit should be firmly placed on a wooden plate with the rubber damper that came along with it. Cut the tubing to 8cm. Identify the IN and OUT tubes by starting the compressor and being careful of oil that may spurt out.
Fix a 20cm tube to the OUT tube and guide it vertically on a piece of wood of about the same dimensions. Connect the ping-pong ball to the end and drill small holes in the ball for air ventilation. This ball will serve as an oil recuperator.
The vacuum tube is to be fixed to the IN tube with a T added so that one tube will go to the bag while the other will go to the inlet of the regulation. The manometer can be added by using another T but must be secured as to not add more air leakage.
The syringe should be fixed firmly using rubber cut from bicycle tubing. Piston movement should be limited so that it only moves enough to fully press the switch ON, not any lower. This can be done with a nail or two.
Seal all links with silicone and ties and let dry. Test and troubleshoot.