What is the difference between fixed frequency screw machine and variable frequency screw machine

The core differences between fixed-frequency screw machines and variable-frequency screw machines are reflected in four aspects: operation mode, energy efficiency performance, stability and applicable scenarios. The specific analysis is as follows:

1. operation mode: fixed speed vs dynamic adjustment

• fixed frequency screw machine: The motor speed is constant, and the exhaust volume is controlled by adjusting the opening of the intake valve. When the gas demand changes, the intake valve opening changes, but the motor always runs at a fixed frequency, resulting in fluctuations in exhaust pressure. For example, at low load, the motor still runs at full power, resulting in a waste of energy.
• Frequency conversion screw machine using the stepless speed regulation characteristic of the frequency converter, the gas demand is monitored in real time through the PID regulator, and the motor speed is dynamically adjusted to make the displacement accurately match the load demand. For example, in the 37kW model, pressure fluctuations can be reduced by 27%, enabling on-demand air supply.

2. energy efficiency performance: high energy consumption vs high energy efficiency

• fixed frequency screw machine:
  • high energy consumption: Low load still need to consume electricity similar to full load, frequent start and stop to further increase energy consumption.
  • Large start-up impact: The current impact is obvious at the moment of starting, causing pressure on the power grid, and the mechanical parts are easy to wear due to frequent starting and stopping.
• Frequency conversion screw machine:
  • significant energy saving: By accurately matching the output power, avoid invalid energy consumption, the annual power saving can reach 110000 degrees (take 37kW model as an example).
  • Gentle start: No impact current, prolong the life of the equipment, and the operating efficiency is 2-8 percentage points higher than that of ordinary variable frequency motors of the same specification.

3. stability: pressure fluctuation vs constant pressure output

• fixed frequency screw machine:
  • large pressure fluctuation: Due to the hysteresis of the intake valve adjustment, the exhaust pressure fluctuation range can reach more than 0.5bar, affecting the process stability.
  • Simple maintenance: Simple structure and low maintenance cost, but wearing parts (such as intake valve) need to be replaced regularly.
• Frequency conversion screw machine:
  • constant pressure: By dynamically adjusting the speed, the pressure fluctuation is controlled within ± 0.1bar to meet the high-precision gas demand (such as biopharmaceutical sterile gas delivery).
  • Complex maintenance: The variable frequency drive increases the complexity of the equipment and requires professional maintenance, but the failure rate is lower than that of the fixed frequency machine.

4. applicable scenarios: low cost vs high requirements

• fixed frequency screw machine:
  • applicable Scenarios: Limited budget, stable gas demand (e. g. ordinary factory production lines, construction sites).
  • Case: A factory uses a fixed frequency machine to meet the basic compressed air demand, the initial investment is low, but the annual energy consumption cost is high.
• Frequency conversion screw machine:
  • applicable Scenarios: High requirements for air quality and stability (such as electronic manufacturing, food processing, sandblasting and engraving).
  • Case: An electronic factory adopts a frequency converter to achieve a level 0 dust-free standard, the pressure fluctuation in sandblasting operation is reduced, and the qualified rate of products is increased by 15%.

5. comprehensive comparison table

6. selection recommendations

• selected frequency screw machine: If the budget is limited, the gas demand is stable (e. g. small factories, temporary sites), and the compressed air quality requirements are not high.
• Selection of frequency conversion screw machine: If you need long-term energy saving, high pressure stability (such as continuous production lines, precision processing), or large fluctuations in gas demand (such as multi-station sandblasting, automation equipment).