by Jeffery Zurschmeide
Compressed air is one of the most useful features you can put in your shop—a good air system is second only to light and heat in making your shop a more useful place. The best news is that compressed air is not expensive or difficult to install, so you should absolutely plan to install a compressor and air tank.
Plan to purchase and install the largest and most capable compressor you can find. You never hear someone complain about having too much compressed air, but you do hear people complain all the time that their compressors are too small and the tanks don’t hold enough air to keep the motors from cycling constantly while they’re working.
When you plan your air system, think about stations where you want to use air, and plan for a quick-disconnect fitting at each station. Don’t forget to install a few overhead where you’ll be working on cars. It’s great to just reach up, grab an air hose, and plug in a wrench.
This project installs a compressor with hard-line plumbing and a soft-line hose reel. The compressor installed in this project is a 240-volt upright model, hard-wired to a dedicated 30-amp circuit using flexible metal-clad cable. The distance from circuit panel to compressor is approximately 30 feet.
Cost: $60 to $250, plus the price of the compressor
Time to complete: 2 hours
• Wire and conduit
• Conduit supports and connectors
• Junction boxes and switch boxes as needed
• Circuit breaker
• Air couplings
• Schedule 40 3/4-inch PVC
• PVC primer and glue
• Galvanized iron fittings
• Hose reel and air hose
• Bolts or screws for hose reel mounting
• Construction screws
• Flathead and number-2 Philips screwdrivers
• Tools appropriate to your conduit type
• Power drill/driver and drill bits
• Crescent wrench
Follow these steps:
- Determine the amperage requirement of the compressor—this defines the gauge of cable you need to run according to your local code. In general, choose 12/3 for 20-amp circuits, 10/3 for 30-amp, 8/3 for 40-amp, and 6/3 for 50-amp circuits. Read the sticker on the electric motor that drives your compressor. It tells you the amperage drawn by the motor. Make your circuit more capable than your compressor requires.
- Position the compressor where you would like it to stay, and carefully plan and measure the circuit from the panel to the compressor. Note where you plan to install any junction boxes or switches, and then use a pencil to mark the walls or ceiling where each component goes. Measure and note the distance between each fixture. Place each fixture in its desired position, and use the drill to make holes in the studs or walls as needed to thread the cable from point to point. Next run the lengths of cable. Don’t forget to support the cable within 2 feet of the panel and at least every 6 feet to the compressor.Metal-clad cable works well for compressors. You can also buy the individual wires and a length of flex conduit and pull your own metal-clad cable. But don’t forget to pick up anti-abrasion plugs for the ends of the conduit!
- Locate the electrical connection box on the compressor. This is usually a small plastic box held to the compressor with a screw. The on-off switch is usually located on or near the box. Open the box and follow the installation guide instructions for making the connection.The white and black wires in this 240-volt circuit are both hot. The white one should be wrapped in black tape to code it as a hot wire. The green one goes to ground.
- Close the compressor connection box and go to the circuit panel. Make very sure the power is turned off at the main breaker. Install the new 240-volt circuit breaker and label it on the panel. Attach the cable or conduit to the side or back of the panel and route the wires to the circuit breaker and to the neutral and ground bus bars. Close the panel and reset the main breaker, then turn on the breaker and test the new circuit by turning on the compressor. Don’t forget to stand to one side when you throw the switch. Most compressors have a brief break-in period when they should run without pressure, so this is a good test.
- Turn off the compressor at the breaker and start plumbing the pipe from the port provided for the air line. This is generally a 3/4-inch NPT-threaded hole, but may be larger or smaller depending on the unit. Smaller compressors may come with an air coupler already installed. This usually is an industrial interchange format, but check to be sure. Start the plumbing with galvanized or black iron pipe, because this is easily removed later without damage. Use some kind of thread sealant such as Teflon tape or liquid pipe thread sealant or the joints may leak. Take the plumbing to the nearest wall before switching to PVC or some other pipe. Make the first piece of your hard-line installation out of galvanized pipe. That way you can remove the cap to add more hard line without breaking or cutting the PVC.
- Once at the wall, run the PVC or dedicated air pipe upward to the ceiling or attic—or simply far enough to get to where you want the air without being in the way. Rafters and joists are a good place to run air lines because the line is easily attached to the wood. You’ll want supports at least every 6 feet or so.Support the PVC air line with conduit support straps at least every 6 feet.
- Use 3/4-inch PVC Tee fittings to drop air-access points where you want them—usually this is over working bays and at the workbench. If you have free-standing tools that use air, such as a blast cabinet or air-powered tire mounter, drop a coupling near those tools as well. You can use a tee fitting to drop an air line from the ceiling. Use a brass reducer to get to 1/4-inch pipe thread for the air connector. You can also put an extension on the bottom with a cap to use as a simple water drain.
- When you put in an air coupler, note that most couplers use a 1/4-inch NPT fitting, male or female, but you’re likely using 3/4-inch PVC for the pipe. You need to reduce this, generally with a 3/4- by 1/2-inch elbow and then a 1/2- to 1/4-inch brass reducer fitting.
- Be sure to plan for drainage. Compressed air generates a tremendous amount of water, especially if you live in a humid climate. As a rule, you want the system to have a little drop from one end to the other, so the water flows to a drain. A drain can be as simple as a PVC cap on a short extension from the air couplings. The initial run of pipe drains back into the tank and you can use the bottom drain on the tank to eliminate that water. An in-line water collector is a good idea; it makes it easy to drain the condensation out of the system.
- Mount the hose reel in a convenient location near a hard line. Ideally, you should place the reel where you won’t bump into it all the time, but where it’s easy to unreel the hose. Spring-loaded hose reels can go overhead, but if you have to crank it to recoil the hose, make sure you have space to do so.
- Make an appropriate connection to the tail of the hose reel. The hose reel tail may have a 1/4-inch NPT fitting, or it could be bare hose requiring a barbed fitting and a hose clamp. You may need to make a longer hose or use a purchased hose if you plan to install the hose reel farther than a couple feet from the line.
- Connect the hose reel to the compressor and let the system build up pressure. When the compressor turns itself off, note the total PSI in the system—there’s usually a gauge on the compressor. You can adjust the PSI, usually by turning a screw under the cap with the electrical connections, but be sure the circuit breaker is turned off before you open that cover. Also, be very cautious about increasing the pressure beyond the manufacturer’s specification, usually 90 or 125 psi. Never disable or eliminate the emergency pressure valve; you could end up with a disaster at worst and a broken compressor at best. Many automotive hobbyists get by with a simple hose reel for years, and never feel the need to plumb hard lines into their system.
- Test the system with your most demanding air tool. If it works, you’re ready to go.
You can use the air system with just a hose reel for as long as you like, and then upgrade to a hard-line air system. But you might find that the hose reel works well enough that you don’t need to spend the money—this is especially true if you do most or all of your work alone. If there’s only one person using tools, you can get by with just one connection.