Contents
Sequence
In industrial compressed air systems, a compressor sequence refers to the intelligent, programmed order in which multiple air compressors are automatically started, loaded, unloaded and stopped to match a facility’s changing air demand. In a multi-compressor system, the sequencer ensures all compressors work together in harmony, rather than competing or conflicting for control.
Think of the system’s sequencer as the conductor of an orchestra. This “conductor” directs which compressors should operate, when to bring additional machines online and when to turn others off — all to support system efficiency.
A typical logic used in sequencing is the “Lead/Lag” operation. Here, one compressor — the “Lead” — handles most of the regular demand. Additional units — the “Lag” or “Trim” compressors — only join in when the plant’s air demand rises above what the Lead unit can supply. This coordinated mode ensures the system runs as efficiently as possible.
Ultimately, the main goal of compressor sequencing is to maintain stable plant air pressure while minimizing both total energy consumption and the mechanical wear on each compressor.
Modern compressor sequencers are critical for efficiency because they deliver several important benefits over traditional controls:
- Tighter pressure bands: Traditional “cascade” controls require a wide pressure swing, sometimes 15-20 psi, for basic operation. A modern automatic sequencer can keep all compressors operating within a much tighter band, often just 2-5 psi. This means the compressors don’t have to work harder than needed, saving significant energy.
- Wear equalization or automatic rotation: Sequencers can automatically rotate which compressor is the “Lead” on a daily or weekly schedule. This ensures that run hours are balanced across the fleet, preventing uneven wear, maximizing equipment life and simplifying maintenance schedules.
- Eliminating unloaded waste: Without sequencing, compressors often run “unloaded” or idling, burning 25%-30% of their full power yet producing zero air. A sequenced system rapidly shuts unneeded units off, preventing costly waste and reducing operating hours.
FAQs
Cascading uses separately set, progressively lower pressure points for each compressor, such as Compressor A at 100 psi and B at 90 psi. This approach is inefficient and causes the plant to run at unnecessarily high pressures — often resulting in instability and increased energy use.
Sequencing, by contrast, employs a central master controller or automatic sequencer to operate all units together in response to real-time demand data. All compressors are kept within a precise, narrow pressure band, optimizing efficiency and air quality.
Yes, this is often the best approach. The recommended strategy is to designate large, fixed-speed compressors to handle the steady “Base” load, while using a variable speed compressor as the dedicated “Trim” unit. The variable speed drive (VSD) compressor efficiently absorbs demand fluctuations, keeping pressure steady without unnecessary cycling or energy waste.
A master controller like Quincy’s Q-Control provides advanced compressor management, networking all air compressors together, typically via Ethernet or CAN bus. It gives facility managers a systemwide dashboard for instant monitoring, diagnostics and energy optimization — all from a single screen.
As a rule of thumb, any facility with two or more compressors, including backup units, will benefit from sequencing. Even with just two machines — for N+1 redundancy — a sequencer ensures regular running of the backup unit, avoiding seizures from sitting idle, and eliminates the need for manual rotation.
