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Analyzing direct drives and belt drives

Dry Oil Free Air Compressor Pharmacy Industry

In the transmission system of the air compressor, it can generally be divided into direct drive and belt drive. The direct drive of the screw air compressor refers to the fact that the motor shaft drives the rotor through a coupling and a gear box, which is not actually a direct drive in the true sense. Direct drive in the true sense means that the motor is directly connected (coaxial) to the rotor and both speeds are the same. This situation is obviously rare, so the idea that there is no energy loss in direct drive is wrong. Only 1:1 direct connection is the real direct connection! Another transmission method is belt drive, which allows the speed of the rotor to be changed through pulleys of different diameters.

Comparison of gear drive and belt drive:

1. Efficiency.

Excellent gear transmission efficiency can reach 98%-99%, and excellent belt transmission design can also reach 99% efficiency under normal working conditions. The difference between the two does not depend on the choice of transmission mode, but on the design and manufacturing level of the manufacturer.

2. No-load energy consumption.

For gear direct transmission, the no-load pressure is generally maintained above 2.5 bar, and some even as high as 4 bar, to ensure the lubrication of the gearbox. For the belt drive mode, theoretically speaking, the no-load pressure can be zero, because the oil sucked by the rotor is enough to lubricate the rotor and the bearing. Generally, for safety reasons, the pressure is maintained at about 0.5 bar. Take a 160 kw gear-driven air compressor as an example. It works 8,000 hours a year, of which 15% (1,200 hours) is no-load. This machine will consume 28,800 more than a belt-driven air compressor with the same power. The kwh electricity bill (assuming that the no-load pressure difference between the two machines is 2 bar, about 15% difference in energy consumption), in the long run, this will be a big expense.

3. Oil loss.

Experienced practical users know that the gearbox will be the first to suffer in the event of oil loss. Belt drive systems do not have this safety issue at all.

4. Design working pressure according to user requirements.

Usually the working pressure required by the user is not completely consistent with the pressure of the manufacturer’s standard model. For example, the user requires a pressure of 10 bar, depending on the condition of the post-processing equipment, the length of the piping and the degree of sealing, the required working pressure of the air compressor may be 11 or 11.5 bar. In this case, an air compressor with a rated pressure of 13 bar is generally installed and the outlet pressure is set to the required working pressure on site. At this time, the displacement will remain basically unchanged, because the final working pressure has decreased but the speed of the rotor has not increased.   Belt drive design and manufacturer representing modern technology can simply change the diameter of the pulley and design the working pressure to be completely consistent with the user’s requirements, so that the user can obtain more air volume with the same power motor. For gear transmission, it is not so convenient.

5. The pressure of the installed air compressor changes.

Sometimes due to the change of the user’s production process conditions, the design pressure of the originally purchased air compressor may be too high or too low, and I hope to change it, but for the gear-driven air compressor, this work will be very difficult and expensive. But for the belt drive air compressor, it is a breeze, just replace the pulley.

6. Install new bearings.

When the rotor bearing needs to be replaced, for the gear-driven air compressor, the gearbox and the gearbox main shaft bearing need to be overhauled at the same time, and the cost is unacceptable to the user. For belt drive air compressors, there is no such problem at all.

7. Replace the shaft seal.

Any screw air compressor uses an annular shaft seal, which needs to be replaced after a certain lifespan. For gear-driven air compressors, the motor and coupling must be separated before access to the shaft seal, which makes this work time-consuming and labor-intensive, thereby increasing maintenance costs. For belt drive air compressors, it is much easier to just remove the pulley first.

8. The motor or rotor bearing is damaged.

For gear transmission air compressors, when the motor or rotor bearing is damaged, it will often affect the connected important components and cause direct and indirect double damage. This situation does not exist for belt drive air compressors.

9. Structure noise.

For gear transmission air compressors, since the motor is rigidly connected to the rotor, the vibration of the rotor in the compression chamber will be transmitted to the gearbox and motor bearings, which not only increases the wear of the motor bearings, but also increases the noise of the machine.


Sollant Group-Professional Compressed Gas Solutions Provider



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