How to use two air compressors in parallel

Parallel operation of two air compressors can significantly improve the flexibility and reliability of the air supply system, especially for scenarios where gas consumption fluctuates greatly or redundant backup is required. The following are the key steps, technical points and precautions for parallel operation:

core objectives of 1. parallel operation

1. expansion of gas supply capacity: The two air compressors share the gas demand to meet the gas consumption during peak hours.
2. Implement redundant backup: When one equipment fails or is overhauled, the other can operate independently to ensure the continuity of production.
3. Optimize energy efficiency management: Dynamically adjust the number of operating units according to the gas demand to avoid long-term low-load operation of a single device and reduce energy consumption.

Prerequisites for 2. parallel operation

1. device compatibility
   • model and performance matching: The exhaust volume, exhaust pressure, power and other parameters of the two air compressors should be close to avoid uneven load distribution due to performance differences. For example, if one displacement is 10m & sup3;/min, the other is 5m & sup3;/min, although the total displacement after parallel connection is 15m & sup3;/min, but small power equipment may be overloaded for a long time.
   • Consistent control the air compressor with intelligent control system (such as frequency conversion control) is preferred to facilitate unified and coordinated operation. If one is a power frequency machine and the other is a frequency converter, linkage shall be realized through an external controller.
2. Piping System Design
   • main pipe diameter matching: After parallel connection, the total exhaust volume increases, and the diameter of the main pipe needs to be large enough to reduce the pressure loss. For example, a single 10m & sup3;/min air compressor needs DN80 pipe, and it is recommended to upgrade to DN100 when two air compressors are connected in parallel.
   • Symmetrical layout of branch pipes: The outlet pipes of the two air compressors should have the same length and the number of elbows to ensure the balance of airflow resistance and avoid the low load of one equipment due to the large pipe resistance.
   • Install check valve: A check valve is installed at the outlet of each air compressor to prevent the compressed air from flowing back to the shutdown equipment and protect the screw rotor from reverse impact.
3. Gas tank and dryer configuration
   • capacity expansion of gas storage tank: After parallel connection, the fluctuation range of gas consumption increases, and the capacity of gas storage tank needs to be increased accordingly (it is recommended to be 1.5-2 times of the gas storage capacity of a single equipment). For example, a single equipment is equipped with 1m & sup3; Gas storage tank, 2-3m & sup3 is recommended when two are connected in parallel;.
   • Dryer processing capacity matching: Refrigerated dryers need to be selected according to the total exhaust volume (e.g. treatment volume ≥ 15m & sup3;/min), and adsorption dryers need to consider the matching of regeneration cycle and gas demand.

Control Mode of 3. Parallel Operation

1. manual control
   • applicable Scenarios: occasions with stable gas consumption and no frequent start and stop.
   • Method of operation: Manually observe the pressure gauge and manually start and stop the air compressor. For example, when the pressure of the gas tank drops to the lower limit (such as 0.6MPa), start a device, and stop when the pressure rises to the upper limit (such as 0.8MPa).
   • Disadvantages: Slow response speed, easy to cause pressure fluctuations, and can not achieve load balancing.

2. Automatic control (recommended)

• pressure switch linkage: Install a pressure switch on the air storage tank and set the start and stop pressure range (such as 0.6-0.8MPa). When the pressure is lower than the lower limit, the two devices start at the same time; when the pressure is higher than the upper limit, the two devices stop at the same time.
• PLC control system: Realize finer control through programmable logic controller (PLC):
  • load balancing: Dynamically adjust the running time of the two equipment according to the gas demand. For example, when the gas consumption is 12m & sup3;/min, one runs 100 load and the other runs 20% load to avoid single overload.
  • Rotation run: Set the equipment rotation cycle (such as switching between main and standby machines every 24 hours) to extend the service life of the equipment.
  • Failover: When one device fails, the other device is automatically started and an alarm signal is issued.
• frequency conversion control: If both equipment are variable frequency air compressors, the rotating speed can be adjusted in real time through the frequency converter to accurately match the total displacement with the gas consumption, and the pressure fluctuation is ≤ 0.02MPa.

Maintenance Points of 4. Parallel Operation

1. regular inspection of piping and valves
   • check whether the check valve and stop valve are well sealed to prevent air leakage.
   • Clean the carbon and moisture deposits in the pipeline to avoid blockage or corrosion.
2. Simultaneous maintenance of two devices
   • replace the lubricating oil, air filter element and oil filter element in the same cycle to ensure that the performance of the two devices is consistent.
   • Regularly check the screw clearance. If the clearance of a piece of equipment is too large, adjust or replace the rotor in time to avoid uneven load due to differences in leakage.
3. Monitoring operation data
   • record the running time, exhaust temperature, pressure and other parameters of the two equipment, and analyze whether the load distribution is reasonable.
   • If it is found that the long-term load of one equipment is too low (for example, the running time is less than 50% of the other equipment), it is necessary to check whether the pipeline resistance or control logic is abnormal.

Common Problems and Solutions of 5. Parallel Operation

1. large pressure fluctuation
   • reason: Unreasonable pipeline design, defective control logic or slow equipment response speed.
   • Solution: Optimize the pipeline layout, upgrade to PLC + frequency conversion control, increase the capacity of gas storage tank.
2. Overload of single equipment
   • reason: The performance of the two devices is different, the pipeline resistance is uneven, or the control logic does not achieve load balancing.
   • Solution: Select equipment with matching performance, adjust pipeline layout, and optimize control logic.
3. Frequent start and stop of equipment
   • reason: Insufficient capacity of gas tank or narrow setting range of pressure switch.
   • Solution: Increase the capacity of the gas storage tank and adjust the setting range of the pressure switch (e.g. from 0.6-0.8MPa to 0.55-0.85MPa).