Many home craftsmen are thinking about how to effectively use old household appliances, and compressor from a refrigerator is one of the most popular projects for the garage. An old unit that is no longer capable of cooling food often retains excellent sealing and pressurization capabilities, making it an ideal base for a homemade air pump. Such a homemade tool is useful for painting a car, inflating tires, working with pneumatic tools or blowing parts.
The main advantage of this solution lies in the availability of materials and the relatively low cost of the final product compared to factory-made analogues. Hermetic piston compressorsinstalled in household appliances, have a low noise level and are able to operate in long cycles without overheating. However, in order to turn an assembly from a refrigerator into a full-fledged pneumatic station, it is necessary to correctly select additional components and follow the assembly technology.
In this article we will analyze in detail the entire conversion process, starting from preparing the equipment and ending with the final testing of the system under pressure. You'll learn what tools you'll need, how to choose the right receiver, and why you shouldn't ignore installing safety valves. A properly assembled unit will last for many years, providing stable pressure for your needs.
The operating principle and advantages of a homemade compressor
The basis of our future installation is piston compressor, the operating principle of which is based on the reciprocating movement of the piston inside the cylinder. When the piston lowers, a vacuum is created and air is sucked into the compression chamber through the intake valve. As it moves up, the volume decreases, the pressure increases, and the compressed air is pushed through the exhaust valve into the system. This simple but reliable scheme has been used for decades.
Why is the refrigeration unit so popular among home-made people? Firstly, it is initially designed to operate in a closed circuit and is capable of creating a pressure sufficient for most household tasks, usually ranging from 6 to 10 atmospheres. Secondly, such motors are equipped with an effective cooling and lubrication system, which allows them to operate for years without serious maintenance.
⚠️ Attention: The refrigeration compressor is not designed to pump large volumes of air, like industrial models. Its productivity (liters per minute) is lower, so it may not be suitable for powerful sandblasters without upgrading.
The key difference from open compressors is the sealed housing, which houses the electric motor and mechanical part, immersed in oil. This provides excellent noise insulation lubrication of rubbing parts. However, it is precisely this feature that dictates certain operating requirements: such units are afraid of moisture inside the system and require the installation of high-quality filters at the air inlet.
Necessary tools and components
Before proceeding with assembly, it is necessary to prepare all components. The basis is already there - it is itself refrigeration compressor, which can be removed from an old refrigerator or bought assembled at disassembly. It is important that it is in good working order: when turned on, it should hum and create a noticeable flow of air at the outlet, and not just vibrate.
The second most important element is receiver, or a container for storing compressed air. Old gas cylinders (propane or fire extinguishers) that can withstand high pressure are often used as a receiver. You will also need pressure gauges to control pressure, a reducer to adjust the output flow and a piping system.
- 🛠️ Tools: a set of wrenches, screwdrivers, a hacksaw for metal, a drill or screwdriver, a soldering iron or welding machine (for metal pipes).
- ⚙️ Accessories: adapters, fittings, high pressure hoses, clamps, check valve, safety valve.
- 🧪 Consumables: motor or compressor oil, sealant, degreaser, coating paint housings.
Pay special attention to the selection of hoses and fittings. They must be rated for pressures greater than the maximum operating pressure of the compressor. The use of ordinary water hoses is unacceptable, as they may burst under stress. It is best to use specialized pneumatic hoses braided.
Preparation of the compressor unit and receiver
The first stage of assembly is the preparation of the “heart” of our system. If you are using the unit from a refrigerator, it usually has three tubes: two copper and one steel (most often). To determine which tube is suction and which is discharge, briefly turn on the compressor. The tube from which air blows is the outlet (discharge), and the one that draws in air is the inlet (suction).
After identifying the tubes, they must be carefully cut, leaving a margin of length for connecting the fittings. Copper tubes are easily soldered, but to ensure a reliable connection with threaded elements, it is better to use special adapters or crimp couplings. There is no need to touch the steel pipe (muffler), it serves to return oil to the crankcase.
Now let's take care of the receiver. If you are using an old gas cylinder, it must be carefully prepared. Remaining gas must be completely vented, and the internal surface must be washed with water to remove condensation and odor. For fire extinguishers, the procedure is similar: make sure that the body is free of corrosion and mechanical damage.
| Component | Material | Function | Requirements |
|---|---|---|---|
| Compressor | Steel/Copper | Air compression | Tightness, good winding |
| Receiver | Steel | Air accumulation | Working pressure > 15 atm |
| Pipeline | Copper/Steel | Transportation | Vibration resistance |
| Hoses | Rubber/Polyurethane | Flexible connection | Reinforced, oil-resistant |
It is important to correctly position the inlet and outlet holes in the receiver. The inlet (from the compressor) should be at the top of the cylinder to minimize condensate entering the line immediately. It is better to make the outlet hole for air intake slightly above the bottom, but below the level of possible water accumulation, or use an internal tube that takes air from above.
Assembling a pneumatic system and installing automation
Assembling the system begins by installing the compressor on a frame or solid base. Vibration is inevitable during operation, so use rubber pads or anti-vibration mounts. The compressor must be fixed rigidly, but with damping, so as not to destroy the fastenings over time.
Next, we install the air preparation group. Immediately after the compressor, before the receiver, it is necessary to install a check valve. It will prevent compressed air from leaving the receiver back into the compressor after it stops, which protects the piston group from turning in the opposite direction. After the check valve, a tee with a pressure gauge and a pressure switch is installed.
- 💡 Pressure switch: automatically turns the engine on and off when specified limits are reached (for example, switching on at 4 atm, switching off at 8 atm).
- 🌡️ Safety valve: emergency element that bleeds air if the pressure switch will fail and the compressor will continue to pump.
- 💧 Moisture separator: it is advisable to install it after the receiver to remove condensate before supplying air to the tool.
The connection of all elements is made using threaded fittings. To seal threaded connections, use FUM tape or anaerobic sealant. After assembling the entire pneumatic line, but before the first start-up, purge the system by briefly turning it on, checking the joints for leaks with a soap solution.
☑️ Checking the system assembly
Electrical diagram and connection of the pressure switch
The electrical part is the brain of your installation. Standard pressure switch (pressostat) has two groups of contacts: normally closed and normally open. To control the compressor, a circuit is usually used where the relay opens the power circuit when the upper pressure threshold is reached.
The connection is made through the terminal box on the relay. The incoming phase and zero from the 220V network are connected to the input contacts, and the output contacts go directly to the compressor motor windings. Grounding is a mandatory safety requirement, since the metal case and the possibility of condensation create a risk of electric shock.
⚠️ Attention: The power of the relay contacts must correspond to the current consumption of the motor. If the compressor is powerful, be sure to use an intermediate electromagnetic relay or starter so as not to burn the pressure switch contacts.
The relay is adjusted by rotating the adjusting screws under the cover. One screw sets the cut-off pressure (upper limit), the second sets the delta (the difference between turning on and off). Do not set the range too small, otherwise the compressor will turn on and off too often, which will lead to rapid wear of the contacts and the motor.
Why may the compressor not start under load?
If the compressor stops when the receiver is full and cannot start again until the pressure drops, then the unloader valve is missing or faulty. It bleeds air from the compressor head after stopping, making it easier to restart the engine.
Starting, testing and safety measures
The first start is the most crucial moment. Make sure all fasteners are tight, the crankcase oil is level (check the sight glass or dipstick if equipped), and the outlet valve is closed. Plug in the compressor and monitor the pressure gauge readings.
During the pumping process, listen carefully to the device. Unusual knocking, grinding or excessive vibration indicate problems. Check the temperature of the case: it should heat up, but not to the point where it is impossible to touch it with your hand. If the compressor is working normally, check the operation of the automation: it should turn off when the pressure is reached.
Safety when working with compressed air (compressed air) is priority number one. A pressure of 8-10 atmospheres has enormous energy. Never point the air stream at people or animals. When working with pneumatic tools, always use safety glasses, as flying particles or dust can cause serious injury to the eyes.
- 👓 Eye protection: mandatory for any work with pneumatics.
- 🔧 Regular draining: condensation from the receiver must be drained after each use to prevent corrosion from the inside.
- 🚫 Prohibition on modifications: Do not try to artificially increase the pressure beyond the rated limits (above the nominal), this can lead to rupture of the receiver.
Possible malfunctions and methods for eliminating them
During operation, you may encounter a number of typical problems. For example, the compressor hums, but does not pump air or pumps very little air. Most often this indicates worn piston rings or sticking valve plates. In such cases, disassembling the cylinder head and troubleshooting parts is required.
Another common problem is frequent engine starting. This may be caused by an air leak in the system (whistle in the connections) or incorrect setting of the pressure switch. Also, the cause may be too intense air intake, exceeding the capacity of the pump.
If the compressor gets very hot and turns off by the thermal relay, check the oil level and the cleanliness of the cooling fins. Working in a poorly ventilated area or in direct sunlight can also contribute to overheating. In some cases, it is necessary to replace the starting capacitor if the engine hums but does not start.
What to do if the compressor throws oil into the pneumatic system?
This is a common problem with hermetic compressors. The solution is to install a high-quality oil separator (separator) at the outlet of the compressor, in front of the receiver. Also, the reason may be an overflow of oil above the permissible level or wear of the piston group that allows oil to pass into the compression chamber.
Can this compressor be used for airbrushing?
Yes, but with reservations. Airbrushing requires very dry and oil-free air, as well as stable pressure. You will need a multi-stage filtration system (oil separator, dryer, fine filter) and a high-quality gearbox with a moisture separator in front of the spray gun.
How often do you need to change the oil in a refrigerator compressor?
In hermetic compressors, the oil is designed for its entire service life and formally does not require replacement. However, if you use the unit intensively (for years), and it begins to drive oil or make noise, you can try to replace it through the technological hole, flushing the system with special oil for refrigeration compressors.
Why does the compressor not turn on at low pressure?
Most likely, the pressure switch is faulty (the contacts are burnt or the setting is lost) or the thermal protection relay has tripped engine. Check the presence of voltage at the relay input and the integrity of the motor windings. Also make sure that the unloader valve is working correctly.
What is the maximum size of the receiver that can be used?
The size of the receiver depends on the performance of the compressor. A tank that is too large will take a very long time to fill. For a standard refrigeration compressor, a receiver with a volume of 20-50 liters is considered optimal. Increasing the volume beyond 100 liters does not make practical sense, since the waiting time for filling will become unreasonably long.