A homemade compressor is a universal tool for the garage that allows you to perform painting work, inflate tires and use pneumatic tools. Many craftsmen prefer not to buy expensive factory equipment, but make it from available materials. The basis of this design is motor-compressor from an old refrigerator, which is characterized by quiet operation and durability.
Old fire extinguishers are ideal as a receiver, that is, a container for accumulating compressed air. Their robust housing can withstand high pressure, which is critical for operational safety. In this article we will analyze in detail the entire process of creating a device, starting from the preparation of components and ending with the final launch of the system.
Before starting assembly, you need to make sure that all components are in good working order. It is better to dismantle the engine carefully so as not to damage the copper tubes, since their integrity affects the tightness of the circuit. It is also worth preparing all the necessary tools and consumables in advance.
Preparation of necessary materials and tools
The foundation of your future device will be a compressor unit removed from a non-working refrigerator. The most suitable are Soviet-made models or modern analogues with an open motor type, where the engine and compressor part are not sealed into a single casing, although sealed “pots” are also successfully used. It is important that the engine is working and starts without extraneous noise.
For the receiver you will need a metal cylinder with a volume of 10 to 50 liters. Fire extinguishers of the OC (carbon dioxide) or OP (powder) type are best suited due to their thick walls and reliable locking mechanism. Before use, the cylinder must be thoroughly cleaned of any remaining contents and checked for corrosion.
In addition to the main components, you will need components for assembling the pneumatic line. This list includes high pressure hoses, connection fittings, a check valve and a pressure gauge for monitoring pressure. Also do not forget about the electrical part: cable, plug, possibly a pressure switch and a capacitor to start the engine.
⚠️ Attention: Before starting cutting or drilling the fire extinguisher, make sure that it is completely empty and the pressure inside is equal to atmospheric pressure. Residual pressure or chemically active substances can cause serious harm to health.
A reliable foundation is required for installation of the structure. This could be a sheet of plywood, a metal frame or a profile. All elements are fastened using bolts, nuts and clamps. Do not forget about vibration isolation, since even a quiet refrigerator creates vibration during operation.
Dismantling and preparing the compressor unit
The process of removing compressor from the refrigerator requires care. First of all, you need to disconnect the device from the electrical network. Then the copper tubes running from the compressor housing to the condenser radiator are carefully cut or sawed. It is important to step back from the “pot” by 5-10 cm in order to be able to work with the pipes.
After removing the unit, you need to determine the purpose of the pipes. Usually there are three of them: two short and one long. To avoid guessing, turn on the compressor (observing safety precautions) and place your finger near the holes. Where the air is blown out with force, there will be an outlet for injection. The other two holes are used to suck in air.
The tightness of the internal system is a key success factor. If you are using an old Soviet refrigerator, the tubes may be oxidized. They must be cleaned and, if necessary, replaced with new copper tubes of suitable diameter. To connect to the receiver, you will need an adapter, which can be made from a brass tube or purchased a ready-made fitting.
What to do if the compressor hums but does not start?
A frequent reason is the failure of the starting relay or capacitor. In homemade installations, the standard relay is often replaced with a more reliable industrial one or a circuit with a capacitor of selected capacity is used to ensure a reliable start under load.
The engine should be secured to the base using rubber gaskets. This will reduce noise levels and prevent vibration from being transferred to the frame and receiver. Some craftsmen install the motor vertically, which is acceptable for many models, but a horizontal arrangement is considered more classic and safer for the lubrication system.
Upgrading a fire extinguisher into a receiver
A fire extinguisher selected as a receiver requires serious preparation. The first step is to remove the locking and starting device (ZPU). If the cylinder is powder, the remaining powder is blown out with compressed air or washed out with water, followed by thorough drying. For carbon dioxide cylinders, it is enough to check that there is no pressure.
Next, you need to drill holes for connecting the lines. Usually three holes are made: for air inlet from the compressor, for air outlet to the consumer and for installing a pressure gauge. Holes are drilled at the bottom of the cylinder (for condensate) or at the top, depending on the design, but it is better to make the outlet to the consumer from the top so that the oil does not fly into the tool.
Fittings are welded into the holes or screwed into the threads. Threaded connections must be sealed with FUM tape or anaerobic sealant. It must be installed on the inlet pipe from the compressor Check valve. It will prevent the reverse flow of air from the receiver into the compressor after it is turned off, which protects the piston group from overload the next time it starts.
| Component | Function | Installation location | Connection type |
|---|---|---|---|
| Check valve | Reverse current protection | Between compressor and receiver | Threaded |
| Pressure gauge | Pressure control | Upper part of the receiver | Threaded |
| Drain valve | Condensate removal | Lower point of the receiver | Threaded |
| Safety valve | Emergency pressure release | Receiver | Threaded |
Painting a cylinder is not only a matter of aesthetics, but also protection against corrosion. After stripping off the old paint and rust, apply a metal primer, followed by 2-3 coats of heat-resistant paint. This will extend the life of your homemade receiver for many years.
⚠️ Attention: It is strictly forbidden to use propane or freon gas cylinders for receivers without special training and certifications, since their metal may have microcracks or be designed for liquefied gas, not high-pressure compressed air.
Assembling the electrical circuit and control system
The electrical part of the compressor requires special attention, since the refrigerator engine runs on a 220V network. The standard connection diagram includes a starting relay, which comes with the motor. If the relay is missing or faulty, it must be replaced with one with similar parameters.
To automate the operation of the system, it is advisable to install pressure switch (pressostat). This device will automatically turn on the compressor when the pressure in the receiver drops to the lower limit, and turn it off when it reaches the upper limit. This will save you from the need to constantly monitor the pressure gauge.
The connection is made through the terminal box. All connections must be securely insulated. It is recommended to use a cable with copper conductors with a cross-section of at least 1.5 mm². To protect against overloads, an automatic circuit breaker of the appropriate rating is installed in the circuit.
☑️ Electrical check
If you do not have experience working with electricity, it is better to contact a specialist. Incorrect circuit assembly may result in a short circuit or motor failure. It is also worth considering the possibility of an emergency power shutdown at any time.
Installation of a pneumatic system
The connection between the compressor and the receiver is made with a copper tube or a special hose for refrigerators. The tube is more durable and better able to withstand temperatures that can rise at the compressor outlet. The hose must be designed for pressure 1.5-2 times higher than the working pressure.
A moisture-oil trap filter is installed at the outlet of the receiver. When air is compressed, condensate forms in it, which mixes with oil from the compressor. If this emulsion gets into a spray gun or pneumatic tool, it can ruin the coating or damage the mechanism.
To regulate the pressure at the outlet of the tool, a reducer is installed. It allows you to reduce the high pressure in the receiver to the operating pressure of a specific tool (usually 6-8 atm). The pressure gauge on the gearbox will show the current operating pressure.
All connections are checked for leaks. To do this, the system is pumped with air and generously lubricated with soapy water. The appearance of bubbles will indicate the location of the leak. Eliminating leaks is a mandatory step before full operation.
First start-up and testing of equipment
Before the first start, double-check all fastenings and electrical connections. Make sure the drain valve on the receiver is closed and the outlet valve is closed. Plug in the compressor and monitor the process of pressure build-up.
Pay attention to the operating time before shutting down (if a pressure switch is installed) and the heating temperature of the compressor. Motor-compressor The refrigerator is not designed for continuous operation 24/7, it has an on/off cycle. During long-term operation, a pause may be required to cool down.
Check the operation of the safety valve. It should operate when critical pressure is reached, releasing the air. If the valve does not operate, it must be replaced, otherwise there is a risk of rupture of the receiver.
After successful testing, the assembly can be considered complete. Regularly drain the condensate from the receiver through the drain valve to avoid corrosion of the inner surface of the cylinder.
Frequently asked questions (FAQ)
What is the maximum pressure that a compressor from a refrigerator can develop?
Ordinary household refrigeration compressors are capable of creating pressure up to 10-15 atmospheres. However, for stable operation of pneumatic tools, 6-8 atmospheres are sufficient. Excessive pressure can lead to overheating and breakdown of the unit.
Is it necessary to change the oil in the compressor?
Hermetically sealed compressors (“pots”) are filled with oil for their entire service life and do not require replacement. If you use an open compressor, the oil level must be checked regularly and special compressor oil must be added as needed.
Can this compressor be used for airbrushing?
Yes, but it must be done through a fine filter and a moisture-oil separator, as well as a reducer for precise pressure regulation. Refrigeration compressors produce a pulsating flow, so the receiver here is critical for smoothing out the pulsations.
Why does the compressor get very hot?
Heating to 60-80 degrees Celsius is normal for such compressors. If the temperature is higher, check the ventilation, cleanliness of the cooling fins (if equipped) and the duration of continuous operation. The thermal regime may be disturbed.
What volume of the receiver is optimal?
For painting and working with pneumatic tools, the optimal volume is 20-50 liters. A smaller volume will lead to frequent engine starts, which will shorten its life. A larger volume will increase the initial pumping time.