The first thing to consider when designing a vacuum system is what you are going to do with it. There are attributes that you can include in the vacuum system that may affect its usefulness for your planned activities. For example, a vacuum system capable of very high vacuum numbers may need to be dialed down quite a bit in order to do composite lay-ups with foam or honeycomb cores. Maybe you need to maintain a vacuum pressure, but the pressure would be too much if your pump ran continuously. Perhaps you only work on smaller projects, and don't need a lot of volume. Perhaps you only work on large projects, and want to make sure that your system can keep up with your potential bag leaks. Perhaps you have piped air in your workspace, and don't mind using that to create your vacuum pressure.

This boils down to three types of vacuum systems:

Venturi System: A Venturi vacuum system uses compressed air, forced through a small aperture to draw air through a small hole on the other side of the aperture. A vacuum-switching device senses the vacuum pressure inside of your storage device, and will cycle the airflow on and off to maintain a relatively consistent amount of vacuum. These systems are capable of decent vacuum pressures, and can be cycled on and off in order to maintain a vacuum pressure in a storage tank for prolonged use. Few moving parts, quick vacuum build, and low maintenance are all good things, but these systems are rather noisy due to the constant steam of air that it required to make them work.

Cycling Electric Pump: A Cycling Electric Pump system uses an electrically driven pump to pull air out of a storage device. A vacuum-switching device is used to sense the vacuum pressure inside of your storage device to maintain a relatively consistent amount of pressure. The type of electric pump will be discussed in further detail a little later on, and determines the efficiency, time it takes to draw down a lay-up, and the amount of noise it makes.

Continuous-Run Electric Pump: A continuous-run electric pump is like what you'd pick up on e-bay or Craig's list, and its only control is either a manual switch, or just plugging it directly into the wall. Once it gets going, nothing is going to stop it short of you switching it off, or pulling the plug. The down side of this is that you can't maintain a specific vacuum pressure, and the continuous running can be noisy, and advances the age of the pump quicker than if it were cycled on and off as needed. The good thing is that you don't need a storage device, and you don't have to buy all of those fittings, and switches, etc. It's cheap, quick, and dirty, but it sucks.

Along with the type of system you want to build, the size of your projects can largely determine your requirements. If you work on only large projects, you'll want a high CFM rating on your pump. Typical sized rocketry projects can usually get away with 1-3 CFM, but your draw down will be much longer for medium to large size projects. As long as you keep the leaks plugged, you shouldn't have too hard a time maintaining even high vacuum pressures. Some high CFM models can't reach all the way to 25.5" Hg, which you might be okay with, but if you want it to really suck, consider your application before you go cruising e-bay for a cheap pump.

Electric pumps come in at least three different styles:

Diaphragm Pump: Diaphragm pumps utilize an electric motor connected to a crank, similar to that of your car, which has a connecting rod bonded to a rubber diaphragm. On the down-stroke, the diaphragm creates a vacuum greater than that on the outside of the one-way check valve, and draws air in. On the up-stroke, the air is forced out of a one-way valve. These valves are usually a sort of reed valve, as opposed to the valves used in your car's engine. Diaphragm pumps create very good vacuum, sometimes in excess of 25.5" Hg (Mine will pull 29.5") but they have a low CFM rating - usually 1 CFM or less. These can also come with dual diaphragms, which is kind of cool, because it gives you options. You can use a dual-diaphragm pump to effectively double the CFM rating, maintaining the same efficiency of a single diaphragm pump. Or, you can use it as a dual-stage vacuum pump, pulling from your storage device, through the first diaphragm, and then through the second, you keep the same CFM as a single diaphragm pump, but with better efficiency, and more vacuum pressure. Of note: For both vibration issues, as well as the ability to use the pump as a dual-stage pump, most dual pumps have the cycles of their individual diaphragms shifted 180°. One solid benefit of a diaphragm pump is that it is completely oil-less, and usually suffers less from wear than other pump types. Maintenance/repair is usually just the replacement of a diaphragm set.

Rocker Piston Pump: It's called a "rocking" piston, because unlike a piston in a gas engine, which has a hinge pin both at the crank and at the base of the piston, this only has a hinge at the crank. The piston moves up and down, and actually rocks back and forth, to match the position of the hinge on the crank. This makes the components cheaper to manufacture, but doesn't really impact the performance of its ability to seal. These are also available in single and dual piston configurations, and like the diaphragm pumps, a dual can be used as either parallel or sequential. CFM numbers for these are typically a bit higher than diaphragm pumps, with the same vacuum capabilities, and comparable sizes. Their parts wear a little bit more, and even "oil less" do have some oil content - but remember, we're pulling air from the system, not forcing air into the system, so oil flow follows air flow.

Rotary Vane Pump: This pump has a compression chamber that shares it's axis with the rotation of the motor, but is offset just a little bit. The motor's output shaft has on it, a "block" of sorts that contains a number of "vanes" which are spring-loaded to contact the inside of the compression chamber. Because the motor is offset from the chamber, the vanes slide in and out of the block, changing the volume of the space defined by two adjacent vanes, the cylinder's wall, and the fwd & aft walls of the chamber. The inlet and outlet are usually close together. The inlet allows air to be sucked in between two vanes. As the vanes follow the contour of the chamber, the volume increases, drawing more air in. The next vane then closes off to the inlet, and the chamber begins to decrease in volume, increasing pressure. The outlet allows the volume to be forced out of the chamber as the first vane passes by it. Rotary Vane pumps usually have a much higher CFM rating than the other two types, but lower vacuum numbers. As their parts must come in constant contact with each other in order to make a seal, maintenance over the pump's life might be a bit higher, but they are usually rebuildable. The electric motors for Rotary Vane pumps are usually a bit larger, with higher horsepower ratings (and higher power draw) with a bit more noise, larger size, and more weight, but there aren't many other types of pumps that move more air. As a result of moving more air, they develop more heat - a consideration for your system, and any kind of "enclosure" that you come up with.

Why does a vacuum system work to apply pressure to bond things together? By removing the air from the inside of a closed bag or chamber, the atmosphere presses on the outside of the lay-up, applying even pressure. Usually, this is used to ensure that the lay-up is pressed tightly against a form or core material, and to squeeze out excess epoxy or resin. The amount of air that you remove from the chamber or bag determines the amount of pressure pushing against the lay-up. A perfect vacuum is impossible to achieve without an industrial autoclave, so we settle for something slightly less. "Vacuum Pressure" is a misnomer, because a vacuum, by definition is a lack of pressure. Vacuum is measured in inches of mercury, or in/Hg. But for this explanation I will use "vacuum pressure" to explain things. Just understand that it's an oxymoron, unlike the uber-moron that made this write-up.

Vacuum Pump (electric or venturi): This is the core of the system. It removes air from the system when it is turned on. If you purchase a pump from a third-party vendor, or slightly used, make sure that it has the appropriate capacitor(s) connected to it, that the capacitor is the correct rating for that particular motor, and that all of the wiring is done correctly. The capacitor is usually the first thing to go, next to brushes, and the motor can't typically get spinning without that extra bit of 'oomph' that the capacitor supplies.

Vacuum Pressure Controller: This device switches the vacuum pump on and off based on its reading of your vacuum reservoir and the screw setting. It also switches the MAC valve's ports. It uses a screw to adjust the threshold. Once the vacuum pressure drops to the set threshold, it will switch the vacuum pump on, and switch the MAC valve. Once the system builds back up to the threshold, it will turn switch the pump off, and switch the MAC valve. I'm sure they vary, but my system is usually within 4"Hg of my goal, so test yours, and account accordingly. If you can't go over 11", then you need to set it for 7".

MAC Valve: This electrically-controlled device is placed between the reservoir and the sub-reservoir. When the pump turns on, if it has a 'load' on it (vacuum pressure in the chamber) it will have a very hard time getting going, so the MAC valve switches to allow the pump to pull air from a sub-reservoir until it achieves the same pressure as your main reservoir, and overcomes the check valve. When the pump is switched off, the MAC valve closes again, and releases the pressure in the line and sub-reservoir between itself and the pump, removing the pre-load in the pump so it can start again for the next cycle.

Vacuum Reservoirs/Sub-Reservoirs: Once you build vacuum pressure, you need to store it. This is where it is stored. The larger your reservoir, the longer your system can operate without the pump running. The down-side of this is that once you have crossed the threshold of your vacuum pressure controller, you will need to pull down that entire volume. The amount of time this takes will directly affect the 'resolution' or accuracy of your system's nominal vacuum pressure, and is dependent upon the CFM rating of your pump. If you have a large volume, and you set your threshold to 11" Hg, your system will reach say 10.5, and during the time it takes to catch up to the loss of your system, could fall to 10, or even 9" before it can pull the system back down to 11. This is certainly something you should consider in determining the size of your reservoir. A Sub-Reservoir is a small chamber that helps to make sure that your pump isn't instantly slammed with sucking on vacuum pressure once the MAC valve opens.

Check Valve: This is a simple device that prevents the backwards flow of air. It is used on the MAC Valve to prevent the opening of the MAC valve from allowing the reservoir's pressure to drop from the introduced positive pressure in the line between the MAC Valve and the Vacuum Pump.

Vacuum Gauge: This is an important tool in any vacuum operation. How do you know how much vacuum pressure you have unless you have something that can tell you? This will tell you if there is a leak in your system or a leak in your bag, and help you to determine whether or not your system can keep up with the leak. I usually use two in my lay-ups, one on the system, and one on the bag to make sure that I'm getting the suction I need, everywhere I need it.

Ball Valve: You can store vacuum pressure in your reservoir, and connect your bag, and get everything ready, and then open the valve to pull down your bag. You can also shut it off, and save your vacuum pressure if you detect a leak that will take some time to fix, or if you notice that epoxy has reached your bag connector, etc. It's a handy thing to have.

Fittings: This system will use various fittings, elbows, air-line connectors, etc., which will vary by the complexity and arrangement of your components.

Vacuum System Schematic:

Vacuum System Electrical Schematic:

* One exception to the above electrical schematic would be if your pump draws more than 10A on startup, you may consider using a relay between NC of the Vacuum Controller, and the Vacuum Pump. Your fuse should be only slightly higher than the max current draw of your pump.

Now let's bring everything together, and see how this thing works. You plug your system into the wall outlet. On the one I made, I included an additional wall outlet, which is switched along with the pump, so I could power a light, or a heating element that was switched along with my vacuum system. First things first: Screw the adjustment screw on the Vacuum Pressure controller all the way in - this is the least amount of vacuum pressure that it can maintain. When you switch on your system, your pump will turn on, and your MAC valve will switch from ports 2 & 3, to ports 1 & 2 connected. The Check valve prevents any positive pressure in your Sub-Reservoir from rushing into your Reservoir. You vacuum pump will begin drawing the air out of your sub-reservoir until that pressure is lower than your main reservoir, and the check valve will begin letting you draw air out from your main reservoir. Once your reservoir's vacuum pressure has reached the set threshold on your vacuum control switch, the switch will turn off your pump, and will switch the MAC valve from ports 1 & 2 to 2 & 3 connected. This will allow air to flow through the brass breather into your sub-reservoir, allowing your pump to prime itself for the next startup. The gauge reads the pressure in the reservoir, and the ball valve prevents air from getting into the system, stealing your precious vacuum.

How you arrange all of the components, what size your reservoir is, if it's inside of an enclosed cabinet or completely exposed on a hand-truck or hidden from view under a work bench is entirely up to you. So long as the components are connected in the proper order, and are wired correctly, you can feel free to use your imagination! Do you have a narrow tall space up against the wall in your shop that you can fill? Do you want your system to sit on top of a cabinet out of the way? Do you have a long narrow cubby at the bottom of a cabinet that would hold it perfectly? This is where you get to use your creativity, and go wild.

My design is a bit different, and kind of interesting to look at. At first glance, because the pump isn't completely visible, you can't really tell what it is. It is specific to the pump that I used, and the materials that I was able to find locally. The tanks were pre-cut at Home Depot. The switch is housed in a section of tank that actually hides the MAC valve, Check Valve, Brass Breather, and most of my wiring. Because I knew that I was going to use my system for composites manufacture, I wanted to protect my pump as much as possible, so despite the fact that I have no filter, all of my tanks connected sequentially in a line. Meaning, I don't ever "Tee" off to another tank. One leads to another, leads to another. As well, the connectors from one tank to the next are never on the direct bottom of the tank. As a result, if I happen to get a bit of carbon dust, saw dust, or even epoxy in my system, it is very unlikely that it will ever reach my pump. My pump is well ventilated, despite the fact that you can hardly see it. Because it can hardly be seen, it also helps to absorb the noise that the pump makes. Operation of my system is very quiet indeed. The gauge has clear visibility from many angles, and all of the controls are located in one general area.

Think about how you would like to arrange your components. I would also suggest that you take a look at Joe Woodworker's gallery, for inspiration. People have done some pretty interesting things, and the inspiration for my design comes from one of the photos there as well. Can you guess which one? Take a look: Joe Wood Worker's Visitor's Presses

Now that we understand what goes into the system, we understand how the system works, and we know what components we will need to use in the system, let's figure out how to put them all together. If you are one that can place a number of parts in front of you, and just start throwing them together, so be it. Enjoy, and have fun. If you have access to CAD software, and know a thing or two about visualizing a 3D shape in a 2D view or views, then perhaps you can follow along with me. If you have no idea what you're doing, have no fear, we'll walk through it together.

First off, identify your major components - in this case, the pump, and your reservoirs. I used two 4" dia, 24" long tubes from Home Depot. They were pre-cut, and all I needed was caps to seal the ends. I also used one of the pictured 2" dia tubes as a portion of my main Reservoir. Like I mentioned before, they are linked together in a chain, rather than parallel. The other 2" tube is used for my sub-reservoir, and the third 4" dia tube houses my electronics, MAC Valve, Check Valve, and works as a foundation for my gauge, ball valve, and hose connector. The outboard cap on this tube has the switch plate attached to it, and all of the wiring is neatly stuffed inside, and out of view.

Admittedly, my design has certain drawbacks - It will only accommodate a certain size and shape of vacuum pump, and its parts are a bit on the fragile side, so it's not a tool that you can just beat around in your shop. Some of my own design shortcomings, I thinned out the structure a bit too much in some areas, and my screw joints which hold everything together suffered from a lack of meat to screw into, which adds to its fragility.

Because I have access and ability, I utilized CAD software to assist in the design of my system. After I understood all of the components I needed, I began on the arrangement. The first thing I did was draw my major components, using the real parts as a source for my dimensions, and layout. I knew what size and length of tubing I was going to use, but I didn't have any idea of how to arrange them. So I drew a couple of different renditions, and once I decided on an arrangement for my major components, I added and adjusted and rearranged what I needed to in order to make things fit. I did have to make a couple of educated guesses in several areas, which is risky, but I made sure to leave enough room to be able to account for my inaccuracies. I didn't bother with drawing this in 3D to make sure that everything fit the way it should because I knew enough about the materials and components, and I wasn't painting myself into any corners with aspects of the design. Instead, I simply drew everything in 3-view format.

From these 3-views, I was able to extrapolate patterns for each of the wood pieces, which I plotted on film. I used spray-adhesive to mount them to my wood, then went to work routing, and jig-sawing all of my parts out. After sanding and smoothing, I rounded over the edges that were to be exposed, and then used sanding sealer to put a finish on the wood. I applied three coats, sanding in between with progressively finer paper, and I think it turned out quite well. The block at the top of the handle is from a piece of scrap solid oak, and I used a small piece of plywood to make the shelf that supports the vacuum gauge, and that the vacuum pressure switch is mounted to, forming it by hand with a Dremel and some sandpaper. Once all of my parts were finished, I drilled and tapped all of my ABS parts after gluing caps to the tubes. I made sure to de-burr them, and remove all of the shavings afterward. I then worked from the pump to the quick-release connector, and assembled all of my fittings and air lines. My "Mystery Device of Doom" was assembled in a couple of sub-assemblies to make things easy. Lastly, I ran all of my wiring, soldered my connections, screwed the final cap on, and plugged it in, flipped the switch and tested the system out.

If you are coming up with your own configuration, be sure to account for everything that you know about. You may need to estimate the sizes of components, or wait until you have them in-hand to design certain aspects of a new design. Arrange them so that you can assemble all of your components, and be sure to leave room for wire and hose runs. If you do a thorough design job, you will have less to modify as you begin to assemble everything in your shop. Leave yourself plenty of room until you know exactly what goes where, and how big everything is.

I didn't have the forethought to keep my bill of materials for this project, but here is a recollection of the parts and components I used in the make-up of this system:

Other miscellaneous items you may need to include: wire, spade connectors, shrink-tubing, electrical tape, wire nuts, solder, Teflon Tape, PVC or ABS glue, various wood and machine screws, nuts, washers, and the like. Take a moment, and plan out your shopping list for the hardware store before you go, and take your list with you so you don't forget anything!

What about my own design?
Okay, so you're not building exactly what I built, so how do you figure out what you need? Once you figure out what you want to do with your major components, grab a piece of scratch-paper, and draw your components kind of like they will be in your final assembly, and make a big, spaced-out sketch of the things you need to connect together. Then plan your tubing routes, insert the appropriate fittings to make that work. I did mine in the hardware store, in the piping aisle, so I knew that what I needed, I could find. Once I had everything, I placed my paper in the bottom of the shopping cart, and started placing items on top of where they went on my paper to make sure I had the right thing, and I had enough of them.

The other thing you will need to account for is all of the stuff on the other side of your quick-disconnect air-line fitting. For my setup, I used regular barbed airline fittings, with a length of tube in between, and a couple of fittings on my bag connectors. I also took a length of tube, cut it in half, and using a Tee, and two air line fittings. With this, I obtained the ability to use two bag fittings on the same system, or even to draw from two different bags at the same time.

I got my bag connectors from Aircraft Spruce, which work really well, and have fewer issues to deal with than the items I originally purchased from Joe Woodworker's site. I also included a ball valve on my bag connectors so that I can draw a vacuum, and then seal it in while I deal with leaks, etc. or draw down another bag. Once, I even used it to set up my lay-up at a friend's house several miles away, packed everything in the car, drove home, and set the pump and my lay-up in the corner to finish its cure.

A system like this is kind of expensive compared to just turning a vacuum pump loose on a bag. After you get over the sticker shock, and you understand how much better parts and propellant you can make, and what kinds of avenues this opens up as far as construction techniques, let's get down to business.

I'm not going to go through the whole construction process, because we have a schematic, we have a parts list, and your design may differ from mine slightly or dramatically. But I will run through a couple of pointers that should assist you in your assembly, and caution you against mistakes that I made, which you can learn from, and not replicate and learn the hard way.

Teflon Tape helps to provide an air-tight seal if applied correctly. You want to apply the tape in such a way that when you screw a part into its mate, it will continually press the tape around the threads, as opposed to unraveling it. Most people will say that two to three complete wraps will suffice, but I like to do better than suffice. Brass pipe threads are not consistent - they are actually tapered. Putting five to six wraps gives a tighter fit, and allows you to ensure that your fittings are properly seated, and air-tight. Use Teflon tape on EVERY thread that you assemble in your system.

For my design, I assembled everything in the reverse-direction of airflow, from the pump all the way to the quick-disconnect, with a couple of pre-fabricated assemblies here and there to make things easier to put together.

Don't assemble and disassemble your parts if at all possible. Brass compresses a little bit when you thread things together, and tighten them down. This has the possibility of allowing for a leak in your final system.

Threading PVC or ABS isn't that tough, but I do suggest using an appropriate-sized NPT tap. First drill an appropriate-sized hole where you want a thread, and then come back with the tap and go to work. Keep in mind though, that the tap, like the brass threads that you will be screwing into this hole, is also tapered, so if you thread it in too far, you will be opening your threads more than you need to, and you may again have the possibility of leaks.

If you are screwing into the edge of plywood, make sure that you drill a pilot hole to prevent from splitting the plywood by forcing a screw into it. Pre-drill panel-face screw holes larger than the threads of your screw so that the screw can nearly slide through the hole. This will prevent the screw threads from tearing up the wood, and softening its structure by trying to tighten the two pieces of wood together with the screw. A countersink in plywood and harder woods for flat-head wood screws is also a good idea.

Finishing individual wood pieces is usually easier than putting a finish on the whole thing, assembled. But be cautious - wood glue doesn't like to stick to sealed wood, and in some designs, like mine, you can't assemble everything, strip the parts out of it, finish it, and re-assemble it. Looking back, wood glue would have been helpful in a couple of locations during assembly, but my design prevented that, because the handle holds the two smaller tanks in their hooks, so every part save three had to be finished separately, and assembled afterward.

Make extra sure that you have all of the parts for your compression fittings installed on your flexible tubes before you start threading them together, and make sure that your tubes are cut straight and square so that all of your fitting components go together the way they need to in order to make an airtight seal.

Use a wrench to tighten all of your fittings snugly to ensure that there are no leaks. If you need to align fittings, or line up an elbow and a riser, etc. tighten slowly. Get a feel for how many more turns your fitting will need in order to be tight so you can line things up like you need to, and not over-tighten, or have to back-off a fitting to make things work.

Check all of your wiring connections before you make anything permanent with solder, glue, or shrink-tubing. Be sure that you cover every single electrical connection that you make with either shrink-tubing, electrical tape, or seal them inside of an electrical junction box, with wire nuts. Accidents are unpredictable, and you never know what they will affect, so take the time, and go that extra step to make a safe, reliable system, and you won't have to worry about this device causing a short, a fire, or being affected by spills and the like.

If you've read this far, you should have a decent idea of what it takes to make a good vacuum system, and I hope that you are looking forward to finding all kinds of interesting ways to use it. The last thing that I suggest is to look around, do your homework, and make sure that you understand what's going on with everything that goes into this system. Be careful, take your time, plan ahead, and you should soon be sucking like no one's business.