Molly Ayala
Building an electric air compressor is a challenging project that requires careful planning and execution. An air compressor has three main components: a pump, a motor, and a tank. The first step is to determine the purpose of the compressor and calculate the required air volume (CFM) and pressure specifications. This information will guide the selection of the motor size and other critical components. Safety is a key consideration, especially when working with tanks, as they need to be carefully inspected and tested to prevent the risk of explosion. It is recommended to source parts from scrap yards or repurpose old compressors, as building one with new parts can be significantly more expensive.
Characteristics and Values of an Electric Air Compressor
| Characteristics | Values |
|---|---|
| Main Parts | Pump, Motor, Tank |
| Sources for Parts | Scrap Yards, AC Compressors, Car Compressors, Harbor Freight Tools |
| Motor Sources | Motor Repair Shop, Scrapped Washing Machine, Electric Lawn Mower |
| CFM | Dependent on Application and Number of Tools/Users |
| Type | Reciprocating or Rotary Screw |
| Voltage | 110V or 240V |
| Tank Size | Dependent on Application, 30-80 gallons suggested |
| Safety | Wear Safety Glasses and Closed-Toe Shoes, Ensure Flat Surface, Check Pressure Regularly |
| Use | Powering Tools (Wrenches, Grinders, Paint Sprayers), Nail Guns, Cleaning |
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What You'll Learn
Sourcing parts from scrap yards
Start by looking for a pump, as this is the core component of an air compressor. Scrapped compressors from cars, lawnmowers, or even AC units can be a good source for pumps. You may find usable pumps in these discarded items, or you might need to make some modifications to get them working for your project.
For the motor, you have several options. Electric lawnmowers, washing machines, or even gasoline engines (with a pneumatic clutch) can provide the necessary power. Gasoline engines might be more readily available at scrap yards, but they will require additional parts to function safely in your compressor. Electric motors are a more straightforward option, and you can often find them at local auctions or motor repair shops for a reasonable price.
Tanks are relatively inexpensive, so you may want to consider buying a new one. However, if you're determined to source a tank from a scrap yard, be cautious. Ensure that any tank you consider has been completely drained of pressure and fluids. Look for a tank with a petcock or a safety valve at the bottom, as these features make it easier to drain any remaining pressure or fluids.
While scrap yards can be a treasure trove for compressor parts, keep in mind that you may not find everything you need in one place. Be prepared to visit multiple yards and be patient in your search. Additionally, when working with second-hand parts, always prioritize your safety. Consult experts or online resources to ensure that your chosen components are compatible and that you're assembling them correctly.
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Understanding tank safety
Relief Valves: Safety valves, also known as relief valves, are critical safety features in air compressor tanks. These valves automatically release air when the pressure inside the tank exceeds safe levels. It is imperative never to adjust, bypass, or remove these valves, as they prevent dangerous pressure buildup.
Drain Valves: Proper drainage is essential for maintaining tank safety. Electric drain valves should be positioned at least one and a half feet above the ground to prevent moisture accumulation. Regularly draining the tank helps prevent corrosion and reduces the risk of catastrophic failure due to metal fatigue.
Shutoff Valve: Always keep the shutoff valve within reach when operating the air compressor. This valve allows you to quickly cut off the air supply in case of an emergency.
Guards for Moving Parts: Air compressors have moving parts, such as flywheels, belts, and pulleys, that can pose a safety hazard. Ensure that these components are adequately guarded to prevent accidental contact or entanglement.
Workspace Air Circulation and Humidity: Air compressors can introduce pollutants and carbon monoxide into the workspace. Maintaining proper air circulation and ventilation is crucial to ensuring safe working conditions. Additionally, keep an eye on the humidity levels in your workspace, as high humidity can lead to moisture buildup in the tank and potential corrosion issues.
Electrical Safety: Always plug your air compressor into a correctly grounded outlet to avoid damaging the machine's electrical circuitry and prevent the risk of fire. Lock open the electrical switch and tag it to prevent accidental activation.
Rust Prevention and Regular Cleaning: Rust is one of the most significant dangers associated with air compressor tanks. Regular cleaning with soapy water or a lye solution helps prevent rust and improves the performance and longevity of the compressor.
Lubrication: Proper lubrication is essential for maintaining the compressor's parts. However, avoid using oils with low flashpoints, as they may combust due to the high temperatures generated during operation.
Testing and Inspection: Regularly inspect your air compressor tank for any signs of corrosion or metal fatigue. While there is no standard service life for a tank, older tanks, especially those over 40 or 50 years old, may require hydrostatic testing or recertification to ensure their integrity. Ultrasound testing is also a popular method to measure tank wall thickness and identify corrosion.
Remember, safety should always be a priority when working with air compressors. By following these guidelines and staying vigilant, you can significantly reduce the risks associated with electric air compressor tanks.
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Compressor types and uses
Air compressors are categorized as either positive displacement or dynamic displacement, based on their internal mechanisms. Positive displacement compressors encompass a variety of different air compressors that generate power via air displacement. Air compressors in this category work with different internal mechanisms, but the principle for each is the same: air is stored in a cavity inside the machine, then the cavity is slowly compressed to increase the air pressure and potential energy. Positive displacement compressors include reciprocating compressors, rotary screw compressors, and scroll compressors.
Reciprocating compressors are typically found at smaller work sites such as garages and home construction projects. They utilize pistons and cylinders to compress air efficiently and come in single-stage and two-stage configurations, allowing for different levels of air compression. They can be oil-lubricated or oil-free.
Rotary screw compressors are large industrial-sized machines that can be either lubricated with oil or run oil-free. They generate energy via two internal rotors that turn in opposite directions, with air getting trapped between them and building up pressure. They are some of the easiest types of air compressors to take care of, as they are equipped with an internal cooling system that doesn't require much maintenance.
Scroll compressors, the third main type of positive displacement compressor, utilize two interlocking spiral-shaped scrolls to compress air. These compact and quiet compressors are commonly used in medical and dental applications and do not require oil.
Dynamic compressors, on the other hand, rely on high-speed impellers to create compressed air. Dynamic compressors include centrifugal and axial compressors. Centrifugal compressors are ideal for large industrial facilities, delivering high flow rates and handling high-pressure applications. They require regular maintenance and care for optimal performance.
Axial compressors are commonly used in aircraft engines and gas turbines, relying on rotating blades to compress air. They offer high flow rates and low-pressure ratios, making them suitable for power generation and petrochemical industries. They are smaller and lighter than centrifugal compressors, operating at higher speeds. Axial compressors are not typically used in construction projects due to their high costs.
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CFM, tank size, and HP
When building an electric air compressor, it is important to consider the CFM, tank size, and HP to ensure the compressor meets your needs and is efficient. CFM, or Cubic Feet per Minute, is a measure of the compressor's airflow and its ability to perform a task continuously. PSI, or Pounds per Square Inch, measures the pressure or force the compressor can exert. Balancing CFM and PSI is crucial for the compressor's efficiency and performance. A higher PSI means a lower CFM and vice versa.
To determine the required CFM, consider the number of users or tools connected to the compressor and the volume of air needed. As a rule of thumb, each person in an automotive shop may require 4-5 CFM, while a body shop may demand 12-15 CFM per person. Multiply the estimated CFM by 1.25 to determine the total CFM needed to choose the right compressor.
The tank size, or air receiver volume, is another critical factor. It determines the compressor's capacity to store compressed air. The larger the tank, the more air it can store, resulting in longer run times and reduced cycling. However, larger tanks also increase the overall size and weight of the compressor, making it less portable and suitable for stationary use.
Finally, HP (horsepower) is essential for delivering the airflow. The higher the HP, the greater the CFM and the compressor's ability to perform tasks. For example, a 5-7.5 HP compressor is suitable for 3 mechanics requiring 15-19 CFM total.
Online CFM calculators can aid in determining the CFM output and demand for your specific application, ensuring you build an electric air compressor that meets your airflow requirements efficiently.
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Startup, operation, and shutdown
Startup
Before starting your electric air compressor, ensure that you are wearing the proper safety gear, including safety glasses and closed-toe shoes. Place the compressor on a flat surface and check the pump oil level. If you are using a tank from an old compressor or welding your own, ensure that it has been checked and tested to handle the required pressure safely. Any tank that accepts air needs to be safe to avoid the risk of explosion.
Next, connect the air hose to the regulator valve and the power tool to the hose. Ensure the pressure switch lever is in the "OFF" position, then plug the power cord into a properly grounded outlet. Avoid using an extension cord, as this may cause the motor to overheat.
Operation
Once your setup is complete, move the lever on the pressure switch box to the "AUTO ON" position. The air compressor will now start building up pressure in the air tanks until the correct pressure is achieved. When the pressure drops with usage, the air compressor will start automatically to build additional pressure. Set the pressure to the tool PSI specification by adjusting the pressure regulator knob. Never exceed the pressure recommended by the tool manufacturer.
Shutdown
To shut down the air compressor, first move the lever on the pressure switch to the "OFF" position, then unplug the unit and disconnect the air hose. Drain the air from the tanks by releasing air with the pressure relief valve. Once the air tank pressure gauge registers under 10 pounds, open the air tank drain valve to drain any moisture. Allow the air compressor to cool down.
If your air compressor shuts off unexpectedly, this could be due to the use of an extension cord.
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Frequently asked questions
An electric air compressor has three main parts: a pump, a motor, and a tank.
Building an electric air compressor can be dangerous, especially when dealing with the air tank. Any tank that accepts air needs to be checked and tested to ensure it can handle the pressure to avoid the risk of explosion. Always wear safety glasses and closed-toe shoes when working with power equipment.
You can source parts for your electric air compressor from your local scrap yard. You can also purchase parts from hardware stores, such as Harbor Freight Tools, which sells compressor pumps.
