Function: According to system requirements, automatically control the start/stop or load/unload of the compressor to maintain the pipeline pressure within a set working range.
Working Principle:
Loading/Starting Pressure: When the system pressure drops to the preset minimum value (e.g. 100 PSI), the switch will activate, commanding the compressor to start pumping or loading.
Unloading/Stop Pressure: When the system pressure rises to the preset maximum value (e.g. 125 PSI), the switch will activate, commanding the compressor to stop pumping (unloading) or completely stop running.
Purpose: To avoid frequent start stop of the compressor, stabilize system pressure, save energy, and prevent excessive equipment wear.
2. Differential pressure switch – maintenance indicator (for filters)
Function: Monitor the blockage of the compressor inlet filter and oil filter, and issue maintenance signals in a timely manner.
Working principle: Connect the inlet and outlet of the filter with a switch, and monitor the pressure drop (pressure difference) at both ends.
The new filter is clean and the pressure difference is very small.
When the filter is clogged with dust or impurities, the fluid resistance increases and the pressure difference increases accordingly.
When the pressure difference exceeds the preset safety limit (such as 10-15 PSI), the switch is triggered, and the “replace filter element” alarm light on the control panel is lit.
Purpose: To achieve predictive maintenance. Avoid insufficient air intake (reducing efficiency) or poor oil circuit (causing equipment lubrication and damage) due to filter blockage.
3. Safety Valve – Ultimate Safety Protection
Function: A pure mechanical device that serves as the last line of defense against pressure control switch failure.
Working principle: When the system pressure rises abnormally due to some malfunction (such as pressure switch failure) and exceeds the set pressure of the safety valve, the valve will be forcibly opened to release excess gas into the atmosphere, preventing the gas storage tank or pipeline from exploding due to high pressure.
Purpose: To protect life and equipment safety, it is a mandatory safety device.
2、 Pressure switch and differential pressure switch on the dryer side
1. Differential pressure switch – core maintenance indicator (for dryer filter)
This is one of the most important switches on the dryer.
Function: Monitor the blockage of the pre filter and post precision filter of the dryer.
Working principle: The principle of the differential pressure switch of the filter on the compressor side is completely the same.
When the pressure difference of the pre filter is too high, it indicates that the filter element is clogged and needs to be replaced. If not replaced, it will increase the overall pressure loss of the system.
When the pressure difference of the rear precision filter (especially the coagulation filter) is too high, it indicates that the filter element is saturated or clogged and needs to be replaced. If not replaced, it will not be possible to effectively remove oil and water, resulting in water and oil mist directly entering downstream precision instruments, causing serious damage or control failure.
Purpose: To ensure dry air quality and protect downstream expensive instruments and equipment.
2. Pressure switch system linkage control
Function: Used for linkage control between dryer and compressor.
Working Principle:
Standby/Start Pressure: When the compressor is detected to be started and the pipeline pressure is established, this switch allows or triggers the dryer to start running to avoid no load.
High/Low Pressure Protection: Monitor the operating pressure of the dryer itself. If the pressure is abnormally high or low, it may indicate pipeline blockage or leakage, and the switch will trigger an alarm or shut down to protect the dryer body (such as the refrigeration system of a refrigerated dryer).
Conclusion:
These switches together constitute the “nervous system” and “immune system” of the instrument’s air system. They not only automate the process, but more importantly, prevent faults by monitoring pressure changes, ensuring that the generated air always has dry, clean, and stable pressure characteristics, thereby ensuring the reliability and safety of the entire industrial process control system. Ignoring the alarm signals of these switches often leads to more serious equipment damage or production interruption.