Use of old ones household appliances to create new useful equipment is not just a cost savings, but also a great way to understand the principles of operation of equipment. Refrigerator compressor is an ideal candidate for conversion into a vacuum pump, since it was originally designed to work with gases under pressure. Many home craftsmen and professionals are looking for affordable ways to obtain a vacuum for various tasks, from pumping air out of air conditioning systems to conducting experiments.
The main idea of the modification is to change the direction of air flow inside the device. A standard refrigerator works by pumping freon, creating high pressure in the condenser. To obtain a vacuum, we need the device to operate on suction air from a sealed chamber. This requires minimal design changes, but compliance with strict rules of tightness and safety.
In this article we will examine in detail the creation process vacuum installation, starting from choosing a suitable compressor and ending with the final assembly of the system. You will learn about the materials needed, potential risks and how to eliminate them. The finished unit will become an indispensable assistant in the workshop, allowing you to perform tasks that were previously only possible with expensive industrial equipment.
Principle of operation and choice of compressor
Before proceeding with disassembly, it is necessary to understand the physical essence of the process. The piston mechanism used in household refrigerators is capable of creating a vacuum at the inlet and pressure at the outlet. For our purposes, inlet pipe becomes the point of air intake from the vacuum container, and the outlet becomes a channel for release into the atmosphere. It is important to choose a unit that is in good technical condition.
The best choice would be compressors from Soviet refrigerators, such as Atlant or old models ZIL. They are distinguished by high reliability, thick case walls and the ability to work for a long time without overheating. Modern Chinese analogues often have thinner metal and less durable valves, although they are suitable for amateur use subject to operating conditions.
When inspecting the device, pay attention to the integrity of the copper tubes and the absence of traces of oil on the body, which may indicate a leak in the seal. Also check the electrical part: the motor windings should not have visible damage or a burning smell. If the compressor was previously removed from the refrigerator, make sure that no moisture has entered it, which can cause corrosion of internal parts.
⚠️ Attention: It is strictly forbidden to open the sealed compressor housing (with a grinder or a hacksaw) in order to change the oil or lubricate the internals. Inside there is freon and special oil, and when opened under pressure, metal fragments may fly apart. Work only with external pipes.Required tools and materials
To successfully implement the project, you will need to prepare a certain set of tools. The quality of the build directly depends on how thoroughly you prepare for the process. You should not ignore the need to purchase high-quality materials, since saving on little things can lead to loss of vacuum.
The basis of the design will be metal and rubber elements that ensure tight connections. Pay special attention to the choice of hoses: they must withstand atmospheric pressure outside without collapsing when pumping air. An ordinary garden hose will not be suitable for this purpose, since its walls are too soft.
- 🛠️ Tool set: Pliers, wire cutters, screwdrivers, wrenches for working with fittings.
- 🔩 Materials: copper or brass tubes with a diameter of 6-10 mm, epoxy glue or cold welding.
- 🔌 Electrics: cable with plug, switch, capacitor (if required for starting), terminal block.
The issue of lubrication deserves special attention. Vacuum pumps use special oil, but when reworking a refrigeration compressor, we often leave the standard refrigeration oil. It has low volatility, which is critical. If you are planning intensive operation, it makes sense to think about installing oil catcher at the outlet so that oil vapors do not contaminate the pumped-out system.
Preparing the compressor for rework
The first stage of work is dismantling the compressor from the refrigeration frame and cleaning it of excess elements. Carefully cut the copper tubes, leaving “stumps” 3-5 cm long for easy connection of new lines. Try to prevent metal shavings from getting inside the body, as they can jam the piston group.
Next, you need to determine which pipe is the suction pipe and which is the discharge pipe. To do this, briefly plug in the compressor (observing safety precautions!). Place your finger at the ends of the tubes: where the air is blown in, there is input, and where it is blown out with force, there is an exit. Remember their location or mark with a marker.
☑️ Preparing the compressor
Done: 0 / 5An important point is to install the compressor on the base. During operation, it produces vibration, which may cause the device to move. It is best to mount it on a wooden board or metal sheet through rubber shock absorbers. This will reduce the noise level and extend the life of the engine bearings.
Component Purpose Requirements Inlet pipe Air intake from the system Diameter 6-8 mm, tightness Outlet pipe Emission of air into the atmosphere Resistance to pressure, presence of filter Electrical cable Motor power supply Cross section of at least 1.5 mm², double insulation Time relay (optional) Automation of operation To prevent overheating during prolonged periods work Modernization of the pipe system and sealing
Standard copper compressor tubes are often too short or inconvenient for connecting a vacuum chamber. They need to be expanded or replaced with more convenient adapters. To do this, use pieces of copper tube of the appropriate diameter, inserting them inside the standard pipes.
The connection must be absolutely tight. The best method is soft soldering using flux. If there is no soldering equipment, you can use epoxy glue or cold welding, but the reliability of such a connection will be lower. Thoroughly clean the surfaces before applying sealant.
It is recommended to install fine filteron the inlet pipe (suction). This could be a simple car fuel filter or a homemade device with a mesh. The filter will protect the inside of the compressor from dust and moisture that may be contained in the pumped air. It is also useful to install an oil trap filter on the outlet pipe.
How to make a simple oil trap?
Take a transparent glass or plastic container with two holes in the lid. Insert a tube into one hole all the way to the bottom (oil inlet), into the second - a short tube just under the cap (air outlet). Oil vapor will condense on the walls and flow to the bottom, and clean air will come out further.
Pay special attention to soldering and gluing areas. After the sealant has dried, perform a leak test. To do this, you can plug the inlet pipe with your finger and try to create a vacuum. If the finger is firmly sucked in and the compressor stalls or hums with force, the system is sealed. If you feel an air leak, look for a defect using a soap solution.
Electrical circuit and automation
Connecting the compressor to the network requires an understanding of the operation of the starting relay. Most refrigeration compressors use a thermal relay and a start capacitor (or start winding). When remaking, it is important to preserve the original relay connection diagram, as it protects the engine from overloads and ensures correct starting.
Assemble the electrical circuit using a reliable grounded cable. Be sure to include a circuit breaker or a latching button in the power circuit. This will allow you to quickly de-energize the device in an emergency. It is not recommended to leave the compressor turned on unattended for a long time.
- ⚡ Phase and zero: connect to the relay contacts according to the markings on the case (usually L and N).
- 🛡️ Grounding: be sure to connect the grounding wire to the metal body of the compressor.
- 🔋 Capacitor: If the compressor does not start or is humming, the starting capacitor may need to be replaced.
For more advanced operation, you can assemble a simple automation system. For example, connect vacuum sensor (an electrical contact pressure gauge), which will open the power circuit when the desired vacuum level is reached. This will prevent the engine from running idle and save the resource of the device.
⚠️ Attention: The electrical circuit should be assembled only with the power completely disconnected from the network. Errors in the connection of the phase and the starting winding can lead to motor burnout or electric shock. If you are not confident in your knowledge of electrical engineering, contact a specialist.Testing and first launch
Before the first full start, conduct a visual inspection of all connections. Make sure the compressor is on a level surface, the hoses are not kinked, and the electrical cable is not damaged. Plug in the device and listen to the engine.
A smooth, monotonous hum without knocking or grinding indicates the serviceability of the mechanical part. Check the heating of the housing: in normal operation, the compressor can heat up to 60-80 degrees, but should not smoke or smell like burning insulation. If it gets very hot, take a break to cool down.
Perform a performance test. Connect the pump to a vacuum chamber (for example, a glass jar with a lid) and try to pump out the air. If after 1-2 minutes the lid becomes difficult to remove, and air whistles inside the jar when you try to move it, you have succeeded. The system is working correctly.
Possible problems and their solutions
During the operation of a homemade vacuum pump, various malfunctions may occur. Most often they are associated with loss of tightness or overheating. Knowing the typical problems will help you quickly eliminate them without disassembling the entire device.
If the pump has stopped creating a vacuum, but is humming as usual, the tightness of the connections is most likely broken or the piston rings are worn out. Check all joints with soapy water. If the problem is inside the compressor, then, unfortunately, repairing the piston group in a sealed housing is impossible without damaging the integrity, which is not recommended.
- 📉 Decline in performance: Check the cleanliness of the inlet filter, it may be clogged with dust.
- 🔥 Strong heating: Provide additional cooling by installing a fan blowing the case.
- 💧 Moisture ingress: If water gets into the compressor, it must be dried in a warm place disassembled (only the case without electrics), but there are no guarantees of restoration.
Remember that The service life of a household compressor when operating in vacuum pump mode may be lower than when operating in a refrigerator due to the lack of active cooling with freon. Let the device rest every 30-40 minutes of operation so that the oil has time to cool and retain its properties.
Is it possible to use a compressor from an old refrigerator to pump out aggressive gases?
No, absolutely not. The compressor oil system is not designed to handle aggressive chemicals. Vapors from acids or alkalis will destroy the seals, react with the oil and damage the device. For such purposes, special oil-free or membrane vacuum pumps are used.
What is the maximum vacuum that can be obtained in this way?
A single-stage piston compressor from a refrigerator is capable of creating a residual pressure of the order of 0.05–0.1 atmosphere (500-100 mbar). This is enough for most household tasks, but not enough for high-tech processes that require a deep vacuum.
Is it necessary to change the oil in the compressor after refurbishment?
Standard refrigeration oil has low volatility and is well suited for working in a vacuum. Changing it to a regular motor or industrial one is not recommended, as they can begin to actively evaporate, creating oil mist at the outlet and losing their properties. If the oil is contaminated, it is easier to replace the compressor than to try to flush the sealed housing.
Why does the compressor get very hot when operating under vacuum?
When operating under vacuum, the compression ratio is higher than when operating under discharge into the atmosphere, which leads to increased heating. In addition, there is no flow of cold freon, which cools the motor windings in the refrigerator. Therefore, forced air cooling (fan) for a homemade pump is highly desirable.