Selection of the compressor on the main characteristics

Homeowners or garage owners frequently find themselves in situations where they need to use pneumatic tools for a variety of tasks around the house or for maintaining their cars. Because pneumatic tools rely solely on compressed air for their operation, it is crucial to choose the right compressor for efficient performance.

Purpose and scope of application of compressors

• Performing the task of applying primer, paint or varnish to surfaces of different materials;
• Clearing away debris and dust from various parts in manufacturing or repair procedures;
• Administering anti-corrosion compounds to hard-to-reach areas of automotive vehicles;
• Operating pneumatic polishing and grinding machinery;
• Manipulating pneumatic vises and diverse clamps;
• Utilizing screwdrivers and wrenches.

Characteristics for compressor selection

When beginning the process of choosing a compressor, it is crucial to have a precise understanding of the intended applications it will serve. It is only with this information in mind that one can make an informed decision and select the appropriate unit, considering its key features.

One of the crucial characteristics of this unit is its ability to create compression. The efficiency of pneumatic tools depends on the working pressure indicated.

The compressor’s documentation may express the pressure in the following units:

• Pascals (Pa)
• Bars (bar)
• Atmospheres (atm)
• Millimeters of mercury column (mmHg)
• Kilograms-force per square centimeter (kgf/cm2)
• Pounds per square inch (PSI)

The most commonly used units are Pa and bar (1 bar = 0.1 Pa).

Important! When choosing a unit, take into account the loss of air pressure as it travels to the tool. Pressure may decrease due to a lengthy duct, the presence of numerous bends, flaps, valves, and so on. Consequently, it will be necessary to use a compressor with a sufficient pressure reserve in order to ensure the normal operation of the pneumatic tool.

For instance, the compressor may be capable of compressing air up to a maximum of 10 Pa. However, by the time it reaches the tool through the pipeline, the pressure may decrease to 6 Pa. If the tool can effectively function at this pressure, all is well. However, if the pneumatic equipment is designed for higher working pressure levels, then a more powerful compressor will need to be utilized.

Performance

The productivity of the unit refers to the amount of compressed air it can generate in a given amount of time. The capacity of a compressor is measured in l/min or m3/min and can vary depending on the model and the temperature of the surrounding air.

Tip: To ensure proper functioning of pneumatic tools, it is advisable to select a compressor with a slightly higher capacity than required.

The power of the compressor is stated in the passport in kilowatts (kW) or horsepower (hp) (1 kW = 1.36 hp). In essence, the power of the machine determines its performance. Therefore, the larger the power rating, the greater the engine power of the compressor. The calculation of the capacity will be explained later, so there is no need to compute it.

Operating voltage and frequency

Air compression equipment can be operated from either a three-phase or single-phase power source. While three-phase power is not commonly available in private homes, it is often used in professional settings and is typically designed for industrial production. For residential use, it is recommended to choose a single-phase unit that is compatible with the standard voltage and frequency of the household electrical network, which in Russia is typically 220 V and 50 Hz.

It is important to consider the high starting current of the compressor unit. In areas with lower voltage, the motor of the equipment may have difficulty starting. To ensure proper operation, it is advised to connect the compressor to a dedicated outlet with a sufficient wire gauge.

Receiver capacity

The storage tank, known as the receiver, is where the compressed air from the compressor compression chamber is stored. The receiver’s size determines how often the unit needs to be switched on or off. If the receiver has a larger capacity, the unit will need to be switched on less frequently in order to pump air into it. However, it will take more time to fill a larger receiver. On the other hand, a smaller receiver will fill up quickly, but the pressure will drop rapidly when the tool is in use.

Tip! It is recommended to choose a unit with a large capacity receiver, especially for a garage setting.

A major drawback of compressors is the amount of noise they produce. Reciprocating compressors, in particular, can generate noise levels of up to 85 dB, which is similar to the noise near a railroad. When choosing a compressor, it is important to check if it is equipped with noise insulation and what noise level it produces. Ideally, the noise level should not exceed 68 dB. If the manual does not provide this information, you can ask the seller to test the compressor for noise by turning it on.

Pro tip: If noise level is a critical factor, especially for use in a room with multiple people, a screw compressor is the best choice. Screw compressors are known for being the quietest and most compact type of compressor available.

The GUDEPOL 7.5 kW 500L screw compressor

Manufacturer

There is a thriving market for compressor equipment, with numerous companies involved in its production. This means there is a wide range of options available to consumers. If you are looking to purchase a high-quality unit, it is important to take the brand into consideration. For home and professional craftsmen, it is advisable to choose a compressor from reputable brands such as Metabo, Fini, Fubag, and Abac.

The capacity of the compressor is determined by its design. The most commonly used units for air compression are piston and screw units.

Capacity of a reciprocating unit

To determine the compressor’s capacity, you need to consider the number of pneumatic tools that will be connected to it and its nominal characteristics.

The productivity calculation is done using the following formula:

Q=((Q1*K1)/0.65) + 30%, where:

• Q – total capacity of the compressor;
• Q1 – air consumption of the equipment connected to the compressor;
• K1 – coefficient of instrument utilization;
• 0.65 is an approximate efficiency index of the compression chamber, taking into account pressure losses in the main line;
• 30% – capacity reserve.

For example, let’s say the working air flow rate of a wrench (as indicated in its manual) is 400 liters/min. So, Q1 = 400.

Moreover, while employing this particular instrument, pauses are inevitably encountered, occupying roughly 80% of the overall workflow. This implies that the utilization factor of the instrument will amount to 20%, or rather K1 = 0.2.

By plugging the given values into the equation: Q = ((400 x 0.2)/ 0.65) + 30% = 160, we determine that a compressor with a flow rate of 160 liters per minute is necessary for the optimal functioning of this wrench.

If you have the need to connect multiple tools to the air line, such as a grinder and a drill, you will need to add up their individual air consumption values (200 + 240) and input them into the aforementioned formula. However, it is important to consider the synchronization factor which determines the compressor’s performance when multiple tools are being used simultaneously. Typically, for 2 points of compressed air consumption, the synchronization factor is 0.95. By plugging in the numerical values into the formula, we arrive at: Q = ((200 + 240) x 0.2) x 0.95 / 0.65 + 30% = 167.2 l/min. This represents the quantity of air per minute that the compressor will need to supply to the system in order to maintain the normal operation of two pneumatic tools.

Capacity of the screw compressor

This value can be expressed as the sum of the volumes inside the compression unit that are limited by screws and are delivered to the output from it per unit of time. The capacity is calculated using the formula: Q_t = l * m₁ * n₁ * f₁ + l * m₂ * n₂ * f₂where:

• Q_t – unit capacity, theoretical;
• I – screw length of the compression unit;
• m₁– is an indicator of the number of runs made by the driving propeller;
• n₁ – frequency with which the driving screw rotates, s-1 ;
• f₁ – area of the depression on the driving screw, m 2 ;
• m₂ – indicator of the number of passes made by the slave screw;
• f₂ – the size of the depression on the driven screw is equal to m₂ square meters.

If we consider that m₁ * n₁ = m₂ * n₂ = m * n, the equation can be simplified: Q_т = l * m * n * (f₁ + f₂).

In reality, the actual flow rate is influenced by various internal leakages in the compressor unit and leakages through the seals, as well as various energy losses. Therefore, it is always lower than the theoretical flow rate and is accounted for mathematically by the delivery coefficient.

Based on the information provided, the formula Q_д = Q_т∙η_п — Q_п is used to determine the actual capacity of a system.

• Q_д represents the actual capacity.
• Q_п indicates the value of air leakage through the seals.
• η_п is the feed coefficient.

Required parameters for different pneumatic tools

When choosing an air compressor to ensure the proper functioning of a tool, it is not always necessary to prioritize large indicators of capacity and receiver size. This is because most pneumatic equipment can function well with average characteristics of the unit. It is possible to save money by avoiding overpaying for power and other parameters that won’t be used in the future.

Each pneumatic tool has specific values for pressure and air flow that allow it to perform effectively. The table below displays comparative data for commonly used air tools in conjunction with air compressors.

By referring to this table, you can effortlessly find a suitable pneumatic tool based on the compressor’s specifications, or vice versa – a compatible compressor based on the tool’s requirements. For instance, you can determine which pneumatic tool can operate at a pressure of 7 bar, and which tool necessitates a more robust compressor.

Tips for choosing the type of compressor for work in the garage

1. When it comes to compressors, the most common options are screw and reciprocating units. Screw compressors tend to be more expensive and are better suited for large workshops that have a high demand for compressed air. By using a screw compressor, it’s possible to have multiple points of compressed air consumption, such as for pneumatic tools, tire inflation devices, and tire repair stations.
2. For medium or small car services, as well as garages, it’s recommended to choose a reciprocating compressor. Piston-type compressors are the most popular due to their reasonable prices, ease of use, and reliability. Despite their compact size, these compressors can be connected to multiple independent air ducts. There are two types of piston compressors available.
3. Direct drive compressors have the motor shaft located on the same axis as the crankshaft of the compression unit. These compressors are commonly used in garages and for field work. However, it is important to note that this type of compressor has a limited service life of approximately 6000 motor hours.
4. Belt-driven compressors, on the other hand, have pulleys on both the unit and motor shafts, connected by a belt drive. The service life of a belt-driven compressor is significantly longer because the pulleys on the engine shaft and crankshaft of the unit are of different sizes. This leads to a slight dampening of engine torque, reduced crankshaft speed, and less load on the unit, resulting in less wear on the compression block components.

When making a decision about which compressor model to choose, it is important to inquire with the seller regarding its classification – whether it is a household or professional-grade equipment. Household compressors are typically made with simple and affordable materials, sometimes lacking in quality, and may require occasional breaks during operation. On the other hand, professional compressors are similar to their household counterparts, but are manufactured using high-quality and durable components. Moreover, professional-grade equipment is capable of sustained operation without overheating for extended periods of time.