principle of operation, repair, oil change


The air compressor is a versatile and economical device, without which the operation of various pneumatic equipment used in production and at home is impossible. Compressors can be both stationary and mobile, thereby expanding the scope of use of these units.

Scope of air compressors

Air compressors are widely used in many areas of human activity. These devices are indispensable for assembly, carpentry, construction and repair work. Also, air vehicles are successfully used and at home. For example, a household unit can be used for tire inflation, painting, airbrushing, etc. As a rule, this is a compressor with an electric motor operating from a 220 V network. For professional use a rotary oil unit is better suited, which has an increased service life and is not demanding for frequent maintenance.

High demand for air compressors and in the industrial fieldin industries where the use of compressed air is required.

There are devices with a high degree of air purification. They are used in «clean» industries, for example, in the chemical, pharmaceutical and food industries, as well as in the electronics industry.

In addition, air compressors have found application in the oil and gas industries, in the mining industry, in the extraction of coal and stone.

Air compressor

How an air compressor works

The device of the air compression unit is determined by the type of construction. Compressors are reciprocating, rotary and diaphragm. The most widely used piston air units, in which air is compressed in the cylinder due to the reciprocating movements of the piston inside it.

Device diagram

The device of an air piston compressor is quite simple. Its main element is compressor head. In its design, it is similar to the cylinder of an internal combustion engine (ICE). Below is a diagram of a piston unit, which clearly shows the device of the latter.

Device diagram

The composition of the compressor unit includes the following elements.

  1. Cylinder. This is the volume in which the air is compressed.
  2. Piston. Reciprocating motion sucks air into the cylinder or compresses it.
  3. Piston rings. Mounted on the piston and designed to increase compression.
  4. connecting rod. It connects the piston to the crankshaft, transmitting reciprocating movements to it.
  5. Crankshaft. Thanks to its design, it allows the connecting rod to move up and down.
  6. Inlet and outlet valves. Designed for intake and exhaust of air from the cylinder. But compressor valves are different from internal combustion engine valves. They are made in the form of plates pressed by a spring. The opening of the valves is not forced, as in the internal combustion engine, but due to the pressure drop in the cylinder.

To reduce the friction force between the piston rings and the cylinder in the compressor head oil enters. But in this case, at the outlet of the compressor, the air has lubricant impurities. To eliminate them on the piston apparatus install separatorwhere the mixture is separated into oil and air.

If special purity of compressed air is required, for example, in medicine or in the production of electronics, then the design of the piston unit does not involve the use of oil. In such devices, piston rings are made of polymers, and graphite grease is used to reduce friction.

Piston units may have 2 or more cylinders arranged in a V-shape. This improves the performance of the equipment.

The crankshaft is driven by an electric motor through belt or direct drive. With a belt drive, the design of the apparatus includes 2 pulleys, one of which is mounted on the motor shaft, and the second — on the shaft of the piston block. The second pulley is equipped with blades for cooling the unit. In the case of direct drive, the shafts of the motor and the piston unit are connected directly and are on the same axis.

Also, the design of a piston compressor includes another very important element — receiver, which is a metal container. It is designed to eliminate pulsations of air leaving the piston block, and works as a storage tank.

Compressor device

Thanks to the receiver, you can maintain the pressure at the same level and evenly consume air. For safety, the receiver is set emergency relief valvetriggered when the pressure in the tank rises to critical values.

In order for the compressor to work in automatic mode, it is equipped with pressure switch (pressostat). When the pressure in the receiver reaches the required values, the relay opens the contact and the engine stops. And vice versa, when the pressure in the receiver drops to the set lower limit, the pressure switch closes the contacts, and the unit resumes operation.

Operating principle

The principle of operation of a reciprocating compressor can be described as follows.

  1. When the engine starts, the crankshaft begins to rotate, transmitting reciprocating movements through the connecting rod to the piston.
  2. The piston, moving down, creates a vacuum in the cylinder, under the influence of which the intake valve opens. Due to the difference in air pressure, it begins to be sucked into the cylinder. But before entering the compression chamber, the air passes through the cleaning filter.
    The principle of operation of the compressor
  3. Next, the piston starts moving up. In this case, both valves are in the closed state. At the moment of compression, the pressure in the cylinder begins to rise, and when it reaches a certain level, the exhaust valve opens.
  4. After opening the exhaust valve, compressed air is directed to the receiver.
  5. When a certain pressure is reached in the receiver, the pressure switch is activated, and the air compression stops.
  6. When the pressure in the receiver drops to the set values, the pressure switch starts the engine again.

Common malfunctions and their elimination

Consider the main malfunctions in the operation of the air compressor, which can be fixed by hand.

Unit engine does not start

First of all, if the engine of the unit fails, make sure that there is voltage in the network. It’s also a good idea to check the power cable for damage. Next, the fuses are checked, which can blow during a power surge in the network. If the cable or fuses are found to be defective, they must be replaced.

It also affects engine starting. pressure switch. If it is set incorrectly, the unit will stop turning on. To check the operation of the relay, it is necessary to release air from the receiver and turn on the device again. If the engine has started, then carry out the correct (according to the instructions) adjustment of the pressure switch.

In some cases, the engine may not start due to thermal relay operation. This usually happens if the unit is running in intensive mode, almost non-stop. In order for the equipment to start working again, it is necessary to give it a little time to cool down.

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Engine hums but won’t start

The buzzing of the engine without rotating its rotor may be due to low voltage in the network, fromWhy doesn’t it have enough power to run? In this case, the problem can be solved by installing a voltage stabilizer.

Advice! If the network “sags” due to the operation of any apparatus, for example, a welding machine, then it should be turned off for the duration of the use of the compressor.

Also, the engine is unable to turn the crankshaft if receiver pressure too high, and injection resistance occurs. If this is the case, then it is necessary to bleed air from the receiver a little, and then adjust or replace the pressure switch. Increased pressure in the receiver can also occur with a faulty relief valve. It must be removed and cleaned, and if it is destroyed, it must be replaced.

Outlet air has water particles

If the air leaving the receiver contains moisture, then it will not be possible to qualitatively paint any surface. Water particles may be present in compressed air in the following cases.

  1. In the room where the unit is operating, high humidity. The room must be well ventilated or a dehumidifier must be installed on the compressor (see figure below).
    water separator
  2. Water has accumulated in the receiver. It is required to regularly drain the water from the receiver through the drain valve.
  3. Defective water separator. The problem is solved by replacing this element.

Unit performance drop

The performance of the machine may decrease if burnt or worn piston rings. As a result, the compression level decreases and the unit cannot operate in the standard mode. If this fact is confirmed during disassembly of the cylinder, then the worn rings should be replaced.

Performance degradation can be caused by valve platesif they are broken or stuck. Defective plates should be replaced, and clogged ones should be washed. But the most common reason for the loss of power of the unit is clogged air filterwhich should be washed regularly.

Head overheating

The piston head may overheat when untimely oil change or when using a lubricant that does not correspond to that specified in the passport. In both cases, the oil should be replaced with a special compressor oil, with a viscosity, the value of which is indicated in the passport for the unit.

Also, overheating of the piston head can be caused overtightening the connecting rod bolts, because of which the oil does not flow well to the liners. The malfunction is eliminated by loosening the connecting rod bolts.

Unit overheating

Normally, the unit may overheat when operating in intensive mode or when the ambient temperature in the room is high. If, during normal operation and normal room temperature, the unit still overheats, then the cause of the malfunction may be clogged air filter. It should be removed and washed, then dried well.

Advice! This procedure is recommended to be carried out regularly. If the unit is used intensively, the filter should be washed daily.

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Cylinder knock

called broken or worn piston rings due to the formation of soot. It usually appears if you use low-quality oil.

Also, knocking in the cylinder can be caused wear of the connecting rod head bushing or piston pin. To fix the problem, these parts should be replaced with new ones. When the cylinder and piston are worn, the repair of the air compressor consists in boring the cylinder and replacing the piston.

Knocking in the crankcase

The appearance of a knock in the crankcase during operation of the unit is caused by the following breakdowns.

  1. Loose connecting rod bolts. It is necessary to tighten the bolts with the required force.
  2. Failed crankshaft bearings. Bearings need to be changed.
  3. Worn connecting rod journals of the crankshaft and connecting rod bearings. The elimination of these malfunctions consists in processing the connecting rod journals to the repair size. The liners are also changed to similar parts of the repair size.

Reducing the pressure in the system when the power is turned off

The problem occurs most often due to leaks in one or several elements of the system at once.. First of all, it is worth checking the outlet valve with a piston valve, as well as inspecting the entire line where pressure is pumped and held.air compressor tap with valve

You can use the old proven method: lubricate problem areas soapy water. Air leakage will immediately make itself felt by the appearance of bubbles. The cracks that appear are sealed with any sealing material: preferably in a jelly-like consistency to prevent delamination.

The outlet valve is checked in the same way. If, when fixing in the off state, the solution bubbles, then the part must be replaced. At the same time, special attention must be paid to sealing: when installing a new crane, we must wind it onto the thread plumbing fum tape.

Important! Before carrying out repair work on the air line, it is necessary to bleed all the air in the system. Otherwise, you can not only get serious burns, but also damage the hoses with valves.

Sometimes, to normalize the pressure, it is enough to clean all the moving elements — taps and dampers from accumulated dirt.

Periodic operation of thermal protection sensors

The obvious reason for this effect is a very high temperature in the room or the operation of the device in direct sunlight. If everything is in order with the climatic conditions, then the matter may be in insufficient voltage in the network.

air compressor cooling

Air cooled compressor

A multimeter will help to identify malfunctions of such a plan. When the indicators during ringing are significantly lower than the standards established by the manufacturer of the equipment (indicated in the instructions for the device), then we supplement the circuit with a voltage stabilizer.

The motors in classic compressors have air cooling. If the room is poorly ventilated, the device will quickly heat up, and as a result, the thermal protection sensors will work. In this case, it is necessary to move the equipment to a place with sufficient ventilation. It would also be useful to check the air filter: clean it from accumulated dirt or replace it altogether.

Unstable engine operation

The problem may manifest itself due to too intense air return or a malfunction of the pressure control sensor. If the power consumed by construction equipment does not match the compressor capacity, then a significant difference will always affect the operation of the engine.

Therefore, it is imperative to take into account the characteristics of a pneumatic tool, namely, the volume of air consumed per unit of time, and correlate them with the capabilities of the unit. The air flow for the equipment must not exceed 70% of the compressor output.

pressure switch

Compressor pressure switch

If the technical characteristics of both devices comply with the standards, then it means that the matter is pressure switch. The sensor can be repaired, but it is more practical to replace it: fortunately, it is inexpensive and is sold in almost every specialized store.

Increased air flow

First of all, you need check air filter: Clean or replace if necessary. The next reason is a gas leak in the system. We check every centimeter of the highway, and especially the joints and connections. We process the latter with sealing material and fum-tape.

Some users, after cleaning the receiver from condensate, forget fix the outlet valve. Sometimes, as a result of increased pressure, he himself comes off a couple of millimeters: we tighten it all the way and check the pressure in the system.

Compressor maintenance

Periodic preventive maintenance and following the simple rules that are indicated in the operating instructions for the device will significantly increase the life of the equipment. At the time of purchase of the compressor, you must make sure that you have a passport, a warranty card and a factory inventory of components. Otherwise, the service center may refuse service.

General recommendations of equipment manufacturers and service center specialists sound like this.

  1. When starting the unit for the first time, it is mandatory to check the oil using a dipstick. Lubrication (technical composition) is selected with an eye to the instruction manual. After starting, let the engine idle for 10-15 minutes.
  2. The oil is changed to a new one after 500 hours of operation (we keep a book of records). After draining the mining, the tank is cleaned of accumulated dirt.
  3. Before using the tool, it is necessary to lower the pressure to normal if it is too high.
  4. The air filter should be cleaned at least once a week. Many manufacturers recommend changing it every quarter, especially when the equipment is actively used.
  5. At the end of each working day, it is necessary to drain the accumulated water from the receiver.
  6. At the end of the work, the air is vented, and the equipment is completely de-energized.
  7. When the compressor is idle for a long time, the platform and moving parts of the air valve must be lubricated.
  8. Keep the device clean. The ingress of dirt into the system is fraught not only with a loss of pressure, but also with the failure of the main elements of the compressor.

Particular attention should be paid to equipment grounding for all non-current-carrying metal parts. In a good half of the cases, manufacturers bring the corresponding conductor to the plug. It remains only to ground the outlet itself, where the device will be connected.

How to change the oil in an air compressor

It is quite difficult to calculate the hours worked by the unit. But it is still recommended, at least approximately, to keep a record of them, since the timely replacement of the oil in the apparatus significantly extends its service life. On average, for a new device, the first oil change should be no later than 50 hours. The next maintenance of the compressor to change the lubricant is already carried out after the number of hours specified in the instructions for the compressor. In each case, depending on the device model, this indicator will differ.

Air compressor oil is better use brandedspecifically designed for this equipment. If branded oil is difficult to find, then you can replace it with any compressor oil of the required viscosity.

Important! Plain engine oil must not be poured into the unit!

Compressor oil

So, changing the oil in the air compressor is as follows.

  1. First of all, you need to disconnect the device from the mains, and completely bleed the air from the receiver. The arrows on all pressure gauges must be at zero.
  2. Make a container from a plastic bottle into which the lubricant will drain.
    Plastic bottle
  3. Place a container under the grease drain hole and unscrew the plug nut that closes it. Fine, the lubricant should not be too light or dark. Light grease indicates that moisture gets into it. Too dark oil is the result of overheating of the unit.
    Draining grease
  4. After the grease stops flowing out of the crankcase, tighten the nut back.
  5. Next, unscrew and remove the breather from the crankcase filler hole.
  6. Pour lubricant into the crankcase. It is more convenient to pour oil through a watering can to prevent it from spilling. Pour in just enough grease to reached the control mark in the viewing window.
    Grease inletcontrol window

In the future, you should constantly monitor the oil level in the crankcase, and, if necessary, add it.

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