Creating a homemade compressor is a classic project for the home workshop, which allows you to get a powerful tool for mere pennies. The main components here are a decommissioned fire extinguisher, which acts as a receiver, and a compressor head from an old, but still working household refrigerator. This combination is ideal for airbrushing, inflating tires or working with low-power pneumatic tools.
The main advantage of this design lies in its quiet operation and compactness compared to factory piston counterparts. Refrigeration compressor it is capable of producing pressure up to 6-8 atmospheres, which is quite enough for most garage tasks. In addition, the use of a fire extinguisher guarantees safety, since these containers are initially designed for high pressure and undergo strict quality control during production.
In this article we will analyze in detail the entire assembly process, from the selection of materials to the final setup of the system. You will learn how to properly prepare receiverwhat valves need to be installed and how to avoid common mistakes when installing the electrical part. A properly assembled unit will last for many years, requiring only minimal maintenance.
Selection and preparation of the necessary components
The first step will be to find a suitable donor for the compressor head. Soviet-made refrigerators or modern models with piston compressors, which are easily identified by their characteristic black “barrel,” are ideal. It is important to check the performance of the motor: when plugged in, it should confidently suck in air at the inlet pipe and blow it out with noticeable pressure at the outlet. If the device hums but does not pump, the piston group may be jammed, and such an instance will not work.
It is best to use fire extinguishers with a volume of 10 liters or more as a receiver. The metal body of such cylinders has a significant thickness, which eliminates the risk of rupture when pumping air. Before starting work, you must ensure that there is no through corrosion and mechanical damage. Fire extinguisher You should completely empty the old contents and thoroughly rinse the inside with water to remove any remaining powder or foam that may cause corrosion in the future.
In addition to the main components, you will need a set of fittings, hoses and fasteners. Copper tubes or reinforced hoses that can withstand pressure are often used to connect nodes. You will also need electrical equipment: wiring, plug, switch and, preferably, a thermal relay to protect the engine from overheating. All these components must be selected with a margin of strength and conductivity.
⚠️ Attention: Before drilling or cutting a fire extinguisher, make sure that it is completely empty and there is no residual pressure inside. Even an old cylinder can be fraught with danger if a compressed gas mixture remains in it.
It is also worth thinking about the installation platform in advance. The compressor should be stable and not vibrate excessively. To do this, they often use a sheet of plywood or a metal frame, to which all elements are bolted through rubber gaskets for vibration insulation.
Cleaning and preparing the receiver
The process of preparing a fire extinguisher for the role of a receiver requires care. If there was a powder composition inside the cylinder, it must be washed until it is perfectly clean. Chemical residues can react with the condensate that inevitably forms when air is compressed, which will lead to rapid rotting of the metal from the inside. It is better to wash under pressure, filling the container with water several times and shaking it.
After washing, you need to let the container dry completely. You can speed up the process by using a hairdryer or placing the balloon in warm air. In parallel with drying, you should start drilling holes for fittings. Typically, three holes are required: for the compressor inlet pipe, for the outlet pipe with a tap, and for installing a pressure gauge. In some cases, a fourth hole is made at the lowest point to drain condensate.
Drilling metal a fire extinguisher requires the use of a high-quality metal drill and coolant. Do not press too hard to avoid overheating the drill bit and deforming the threads in the future. After drilling, the edges of the holes must be cleared of burrs and a thread of the appropriate diameter is cut, most often a 1/2 or 1/4 inch thread is used.
The outer surface of the cylinder should also be treated. It is better to clean the old paint, degrease it and cover it with a new layer of heat-resistant enamel. This will not only improve the appearance of the product, but also protect the metal from external corrosion. Choose a bright color so that the unit is clearly visible in the workshop.
Installation of the compressor group and fittings
Installing the compressor on the receiver is a key stage of assembly. The motor from the refrigerator is attached to the base (frame or directly to the cylinder, if the design allows) using rubber dampers. This is necessary to reduce noise and vibration levels. A check valve is installed between the compressor and the receiver, which prevents compressed air from returning back to the compressor head after the engine is stopped.
The system of pipes and connections must be sealed. To seal the threaded connections, use flax tow with sealant or special fum tape for high pressures. Check valve is a critical element: without it, oil from the compressor will be thrown into the receiver in large quantities, and at start the engine may not turn over due to back pressure.
A tee is installed on the output pipe of the receiver. A pressure gauge is connected to one of its outputs for visual monitoring of pressure, and to the other - a ball valve that regulates the air supply to the consumer. The third output can be used to connect reducerif you need to reduce the pressure for delicate work, for example, for airbrushing.
☑️ Installation of fittings
Do not forget that the compressor from the refrigerator requires an oil supply for lubrication rubbing parts, if it is not of the oil-free type. The oil level in the sight glass (if there is one) should be in the middle. In some models, the oil is already filled at the factory, and it just needs to be monitored.
Electrical part connection diagram
The electrical circuit of the refrigerator compressor is quite simple, but requires care. The motor is connected via a start relay, which is usually already installed on the compressor itself. Your task is to correctly supply power to the relay and output control to the switch. For the safety of the entire system, it is highly desirable to include a thermal relay in the circuit, which will break the circuit in case of overcurrent or overheating of the windings.
The wiring must be designed for the current consumption of the motor. This is usually about 1-1.5 Amps, but inrush currents can be higher. Use copper wire with a cross-section of at least 1.5 mm². All connections in the electrical part must be reliably insulated, since the metal housing of the compressor and receiver are conductors and can become live if the insulation breaks down.
For ease of operation, you can assemble a separate control unit, where you place a switch, an indicator lamp and connection terminals. This will allow you to quickly de-energize the device if necessary. Do not forget about grounding: the compressor housing and the metal cylinder must be grounded to protect against electric shock.
Why do you need a thermal relay?
The thermal relay protects the engine from combustion. Since refrigerator compressors are not designed to operate continuously under load, they can overheat. The relay will turn off the power if the temperature of the windings exceeds the permissible limit, saving the motor from an interturn short circuit.
If you plan to automate the process, you can add a pressure switch. This device will automatically turn the compressor on and off when certain pressure thresholds are reached, eliminating the need to constantly monitor the pressure gauge.
Specifications and components table
Understanding the characteristics of the assembled unit will help to properly configure its operation and not demand the impossible from it. Compressors from household refrigerators are low-pressure equipment. They are not designed to create high pressure in large volumes in a short time, like their industrial counterparts, but they are quite sufficient for periodic work.
It is important to consider the productivity, which is usually about 50 liters per minute. This means that filling a 10-liter receiver to 6 atmospheres will take a little more than a minute. However, with active air consumption (for example, when working with a spray gun), the pressure will drop, and the compressor will have to work continuously, which can lead to overheating.
Below is a table with the approximate characteristics of the components of a homemade compressor:
| Component | Parameter | Value | Note |
|---|---|---|---|
| Engine | Power | 100-150 W | Depends on the refrigerator model |
| Receiver | Volume | 10-20 l | Standard fire extinguisher OU-10 |
| System | Max. pressure | 6-8 atm | Limited by head performance |
| Electrics | Voltage | 220 V | Single-phase network |
| Noise | Level | Low | ~40-50 dB at a distance of 1 m |
When assembling, it is important to maintain a balance between the volume of the receiver and the performance of the compressor. A cylinder that is too small will result in frequent engine starts, which will shorten its life. Too large a volume will take a long time to fill, making the work intermittent.
Testing and safety measures
After assembling all the components and connecting the electrics, the testing stage begins. Carry out the first start in a well-ventilated area and wear safety glasses. Turn on the compressor and carefully monitor the pressure gauge readings. The pressure should increase smoothly, without jerking. Check all connections for air leaks. The easiest way is to apply a soap solution to the joints of pipes and fittings; the appearance of bubbles will indicate a leak.
Pay special attention to the temperature regime. Let the compressor run for 10-15 minutes. The motor housing should not heat up to temperatures at which it is impossible to hold your hand (more than 60-70 degrees). If severe overheating is observed, it is necessary to increase the rest time between operating cycles or improve cooling, for example, by installing a fan.
⚠️ Attention: Never leave a home-made compressor running unattended for a long time. The lack of factory automatic safety equipment requires your constant monitoring of the pumping process.
Regular maintenance will extend the life of your device. Periodically drain the condensate from the bottom of the receiver by opening the appropriate tap. Moisture accumulating inside is the main enemy of metal and a source of corrosion. Also check the oil level in the compressor and top it up if necessary.
Frequently asked questions (FAQ)
Is it possible to use compressor from a modern refrigerator?
Yes, you can, but with reservations. Modern compressors often have a shorter operating life in continuous mode compared to old Soviet models. They may also be more sensitive to frequent switching on and off. For a garage compressor, it is better to (look for) models from refrigerators produced in the 80s and 90s.
What kind of oil should be poured into the compressor?
A special compressor oil is usually poured into compressors from refrigerators. If topping up or replacement is required, use only the oil recommended by the compressor manufacturer, or its modern analogues with a viscosity corresponding to the original. It is not recommended to mix different types of oils.
Is it necessary to paint the inside of a fire extinguisher?
Painting the inside of a fire extinguisher is not necessary and is even harmful. Paint can peel off due to vibration and air flow, getting into the air tool and clogging it. The main thing is to ensure the inner surface is dry and clean. If the metal is heavily corroded, it is better to find another cylinder.
Why does the compressor hum but not pump?
This is a sign of a malfunction of the piston group. The piston may have burst or the rings may have worn out. It could also be due to a lack of oil, causing the parts to jam. In some cases, replacing the starting capacitor or relay helps if the engine hums but does not start.
What is the maximum size of the receiver that can be used?
Theoretically, the size of the receiver is not limited, but in practical terms there is only up to a certain volume. If the receiver is too large relative to the compressor capacity, the waiting time for filling will become unacceptably long. The optimal ratio is the filling time to operating pressure is no more than 2-3 minutes.