Using old refrigeration equipment to create vacuum pumps is a classic technique in the arsenal of a home craftsman. Sealed housing and the reliable design allows you to reuse the unit for tasks far from cooling. There is often a need to evacuate air from the system, evacuate epoxy resin, or create conditions for drying wood.
However, simple modifications require an understanding of the physical processes. Refrigeration compressor Initially designed to work in a closed circuit with a refrigerant, and not to create a deep vacuum in an open system. Without modifications and adherence to technology, such a pump can quickly fail or not give the desired result.
In this article we will analyze all the nuances of the process. You will learn how to properly prepare the unit, what materials will be required for modernization and what are the limitations of home-made installations. The maximum vacuum achievable by a household compressor is about 0.9 atmospheres (residual pressure 0.1 atm), which is sufficient for most DIY tasks, but not for industrial vacuuming.
Operating principle and choice donor
The basis of your future installation will be piston compressorremoved from the refrigerator. The principle of its operation is based on the reciprocating movement of the piston, which sucks in gas (or air) through the inlet pipe and pumps it under pressure through the outlet. For vacuuming, we need to use the inlet pipe.
When choosing a donor, it is critically important to pay attention to its technical condition. Older models that have been in operation for decades may have worn out piston rings or coked oil. The ideal option would be a unit from a modern refrigerator, which failed due to a freon leak or electronics failure, but the motor itself remained serviceable.
There are several types of compressors, but for our purposes only linear piston models are suitable. Rotary or inverter options require complex electronics to start and are difficult to convert into vacuum pumps. It is also worth checking the presence of oil inside: if you hear a strong splash when shaking, it may need to be replaced or topped up.
⚠️ Attention: Never try to start the compressor if liquid with a strong odor is leaking from its tubes or if traces of severe corrosion are visible. This may indicate a breakdown of the internal windings or chemical contamination, which is dangerous to health.
Necessary tools and materials
To successfully implement the project, you will need to assemble a certain set of components. The compressor itself is only the heart of the system, but without the correct piping it will not be able to work effectively. The main difficulty is sealing the connections, since even microscopic gaps will reduce the effectiveness of vacuuming to zero.
You will need copper tubes or high-pressure hoses that can withstand vacuum without collapsing. Regular PVC tubing can collapse under vacuum, cutting off flow. Also necessary oil separator or a filter, since the compressor will emit oil mist along with the pumped-out air.
- 🛠️ Compressor from the refrigerator (power from 1/8 to 1/4 hp)
- 🔧 Set of wrenches and pipe cutter for copper
- ⚙️ Vacuum pressure gauge (range -1...0 bar)
- 🧪 Oil collecting container (oil separator)
- 🔌 Pressure switch or trigger device (if the original is not saved)
Pay special attention to the electrical part. The original compressor start relay should be in good working order. If you plan to automate the process, you will need a pressure switch set to open the circuit when a certain vacuum level is reached. This will prevent the motor from overheating when operating in extreme conditions.
Where to find the starting relay?
The starting relay is usually mounted on the side of the compressor in a black plastic or metal casing. When dismantling, be careful with the wires - they may be fragile. If the relay burns out, it can be replaced with an analogue with the same parameters indicated on the case.
Process of preparation and modification
The first step is to carefully saw off the copper tubes. Do not use a hacksaw with large teeth, as metal shavings may get inside the mechanism and cause jamming. It is best to use a special pipe cutter that gives an even cut without burrs.
After cutting the tubes, it is necessary to determine which of them is suction and which is discharge. To do this, briefly apply power (literally for a second) and place your finger near the holes. Where air is drawn in is the inlet (vacuum), where it blows is the outlet (pressure). Usually the inlet tube has a larger diameter, but you should not rely on this.
⚠️ Attention: When working with open compressor tubes, dust and moisture can get inside. Before assembly, be sure to blow out the system with compressed air or briefly turn on the compressor “to blow out”, closing the inlet with your finger to remove possible condensation.
The installation stage follows oil trap. Since the compressor is lubricated by splashing oil, when operating in vacuum mode, some of the oil will evaporate along with the pumped air. If this is not prevented, oil will enter your vacuum chamber or simply pollute the surrounding space.
To create a simple oil separator, you can use a transparent container with two fittings (inlet and outlet). Air from the compressor is supplied to the container, where the flow slows down, and the oil settles on the walls, and the purified air comes out further. It is important that the container is designed for pressure, at least minimal.
Assembling a vacuum system
Assembling the system requires consistency and accuracy. All connections must be made using sealant or O-rings. It is best to coat threaded connections with anaerobic sealant or use FUM tape, although for vacuum, conical threads or end seals are preferable.
The connection diagram is as follows: Compressor -> Oil separator -> Vacuum chamber (or hose to the object). It is advisable to install a tap between the oil separator and the chamber in order to be able to isolate the system. Also, do not forget about the pressure gauge, which will allow you to control the pumping process.
☑️ Checklist for assembling a vacuum sealer
It is best to mount the compressor itself on vibration isolators. During operation, the piston group creates noticeable vibration, which can be transmitted to the table or shelf, causing noise and rattling. Use rubber gaskets or special anti-vibration feet.
| Component | Function | Material | Criticality |
|---|---|---|---|
| Compressor | Creating a vacuum | Steel, copper, aluminum | High |
| Oil separator | Cleaning air from oil | Glass, plastic, metal | High |
| Hoses | Gas transportation | Copper, reinforced PVC | Medium |
| Pressure gauge | Pressure control | Brass, glass | Average |
Launch and testing of equipment
The first launch is a stress test for your designs. Make sure all connections are securely tightened and electrical contacts are insulated. Plug in the compressor and listen to its operation. There should be no extraneous knocking, clanging or whistling.
The easiest way to check tightness is to use a soap solution. Apply foam to all joints and joints. If bubbles appear, it means there is an air leak that will not allow you to create a high-quality vacuum. Especially carefully check the places where the fittings are inserted into the compressor tubes.
The operating time of the compressor in vacuum mode should not be infinite. Let it cool down after 15-20 minutes of continuous operation. Although refrigeration compressors are designed for long-term operation, in deep vacuum mode they can heat up more than usual due to the lack of freon flow, which normally cools the windings.
Typical errors and safety measures
One of the most common mistakes is ignoring air humidity. When pumping large volumes of air, water vapor condenses inside the compressor, mixing with oil. This leads to the formation of an emulsion that loses its lubricating properties and can cause scuffing in the cylinders.
To avoid this, use air dryer (silica gel or calcium chloride) at the compressor inlet if you are working in a humid environment. Also check the oil level and color regularly. If it has become milky in color, water has entered it and must be replaced.
⚠️ Attention: It is strictly forbidden to vacuum flammable liquids or gases using a conventional refrigeration compressor. Sparking in the starting relay or overheating can lead to an explosion of the mixture inside the housing.
Another mistake is trying to reach a vacuum deeper than the design allows. Piston compressors have what is called "dead space". An attempt to force the process can lead to overloading the motor and burning out the windings. If you need a deeper vacuum, consider a two-stage system or use specialized rotary vane pumps.
Maintenance and durability
A homemade vacuum cleaner requires maintenance no less than industrial equipment. Periodically (every 3-6 months depending on the intensity of use) it is necessary to change the oil. To do this, turn the compressor over or unscrew the bottom plug (if it is structurally provided) to drain the waste.
Keep the air filters clean. If you work in a dusty room, dust will quickly clog the piston group. Installing a simple fine filter at the inlet will extend the life of the unit significantly. Also check the tension and condition of the electrical contacts of the relay.
In general, converting a refrigeration compressor into a vacuum pump is an economical and effective solution for the workshop. With the right approach, such a unit will last for many years, providing the necessary conditions for your experiments and work.
What kind of oil to fill in?
Ideally, use a special vacuum oil, but for domestic needs, synthetic oil for refrigeration compressors (POE) or high-quality spindle oil is excellent. Do not use regular motor oil - it is too viscous and forms a lot of carbon deposits.
Frequently asked questions (FAQ)
Is it possible to use a compressor without an oil separator?
Technically, it is possible to start it, but this will lead to the release of oil into the atmosphere and contamination of the object being vacuumized. In addition, the oil level in the crankcase will constantly drop, which will lead to breakdown. Installation of an oil separator is required.
What is the maximum vacuum that can be obtained?
A single-stage piston compressor from a refrigerator is capable of creating a residual pressure of about 0.05 - 0.1 atmosphere (50-100 mbar). For most tasks of impregnating wood or molding, this is enough, but working with epoxy may require more powerful pumps.
Why does the compressor get very hot during operation?
When pumping air, there is no freon, which cools the motor in normal mode. In addition, in deep vacuum, efficiency drops and energy turns into heat. Be sure to ensure good cooling of the case, for example, by installing a blower fan.
How often should the oil be changed?
The frequency of replacement depends on the volume of air pumped out and its humidity. On average, with active use in the workshop, the oil is changed once every 3-4 months or when it changes color to dark/cloudy.
Is it safe for a beginner?
If you follow safety precautions when working with electrical appliances and do not try to vacuum hazardous substances, then the process is safe. The main thing is to securely fasten all structural elements and monitor the temperature.