TL;DR — Direct answer: A container terminal is a compressor system spread across kilometres of quay and yard, not a single plant room: ship-to-shore cranes, yard cranes, reefer racks, straddle carriers and workshop bays all need air, and they need it in salt air, in wind, and through vessel-call peaks when every crane works at once. The design answer is rarely one giant compressor. It is a workshop and utility system sized for the terminal's real coincident crane and yard demand at 7 to 8 bar, protected against salt corrosion, backed by standby capacity for crane-critical air, and distributed so a failure in one yard block does not stop the whole terminal.
A vessel call transforms a terminal in an hour. Cranes that stood idle start cycling continuously, reefer technicians work the racks, yard equipment multiplies its movements, and the workshop fills with maintenance jobs that all need air at the same time. A compressor system sized for the average day sags exactly when the terminal earns its money, and a crane that waits for air is a crane that is not moving boxes.
QiAir, a Chinese manufacturer and supplier of screw air compressors, sizes terminal air from the vessel-call schedule and the crane list, because the peak that matters is the one with a ship alongside and every crane working. The sections below follow that peak from the quay to the workshop.
Crane and yard air: distributed demand, coincident peaks
Crane air duties vary by crane type, but the pattern is shared: ship-to-shore and yard cranes use air for brakes, controls, spreader operation and auxiliary systems, while yard equipment — straddle carriers, reach stackers, terminal tractors — needs workshop air for brakes, tyres and maintenance. These loads peak together during vessel operations and fall away sharply between calls, so a fixed-speed machine sized for the peak idles wastefully for hours, and a VFD machine or a staged multi-machine system follows the terminal rhythm far better. The sizing sheet should list crane counts, their air users, and which cranes truly run together during a call, plus workshop demand at the same hour.
Distribution is the harder problem. A terminal covers a large area, and pressure loss across long quay and yard mains is the usual cause of weak crane brakes and slow workshop tools at the far block. A ring main sized for the farthest user at peak demand, with drops sized for the equipment at each block, and pressure checks at the farthest crane during a live vessel call, not at the compressor outlet, are the honest commissioning tests. Where a yard block is remote, a local receiver or a satellite compressor beats a longer main that loses pressure all the way there.
Reefer racks, workshops and salt-air protection
Reefer container racks add a different air story: reefer plugs and monitoring are electrical, but the technicians who service reefers, the workshops that repair them, and the cleaning and handling equipment around the racks all need clean, dry plant air. Reefer service air should be dry and filtered, because moisture in a reefer service tool or test circuit distorts readings and corrodes fittings that live outdoors in salt air. Keep reefer service drops protected from direct spray and fitted with point-of-use filtration, and the service bay stops chasing corrosion faults that started as wet air.
Salt air is the terminal's constant tax. Coolers foul with salt, cabinets corrode, and unprotected steel pipework degrades faster than the same equipment would inland. The compressor room needs a sheltered, ventilated location away from direct sea spray, coolers washed on a coastal schedule, and corrosion-resistant treatment on cabinets and pipework. Plants that treat cooler washing as a coastal routine, rather than waiting for a high-temperature alarm, keep their capacity through the summer vessel season instead of losing it gradually to salt fouling.
- Size crane and yard air on the vessel-call coincident peak.
- Check pressure at the farthest crane during a live vessel call.
- Wash coolers on a coastal schedule and shelter the compressor room from sea spray.
Reliability, standby and the export checklist
A terminal cannot pause for a compressor failure while a vessel is alongside, so crane-critical air needs standby capacity with automatic changeover, and a service arrangement measured in hours. The standby calculation should cover the cranes and yard equipment that must keep moving during a call, not just half the terminal average, and changeover should be tested under load, because a standby machine that has sat through a quiet week may not start cleanly when the next vessel arrives. Spares on site should cover filters, separators, drains and service kits — the items that stop a terminal air system, not a warehouse of parts that never fail.
Before ordering from China, a terminal buyer should document crane and yard equipment counts, vessel-call peak demand, yard layout and main lengths, required pressure at the farthest user, salt and wind exposure, and voltage and frequency. QiAir sizes export terminal orders from that sheet, because a compressor quoted for an inland warehouse will not hold pressure across a quay main or survive coastal service without the right protection. Get the vessel-call peak and the yard distances in writing, and the system that arrives matches the terminal it will serve.
Frequently asked questions
Why size terminal air on vessel calls?
Because crane and yard demand peaks sharply when a ship is alongside, and a system sized on the average day sags exactly when the terminal earns its money.
What does salt air do to terminal compressors?
It fouls coolers, corrodes cabinets and pipework, and slowly cuts capacity. Coastal washing schedules and sheltered siting prevent most of the loss.
How much standby capacity should a terminal hold?
Enough to cover crane-critical air during a vessel call, with automatic changeover tested under load and a service response measured in hours.
Related reading
- Single-Stage vs Two-Stage Screw Compressors: Which One a China Manufacturer Recommends
- Buying Screw Compressors from China: A Ranking Checklist for Choosing a Supplier
QiAir is a Chinese manufacturer and supplier of screw air compressors. If you are sourcing a screw compressor from China — for a factory, a textile mill, a construction site or a new production line — contact QiAir for a sized quotation, documented performance data and export support.