Yes, as soon as a loss of air stops production. There are three solutions: one machine more than you need, a smaller standby compressor that covers only the critical flow, or a rental arranged in advance. The right choice comes down to two figures: the plant's total flow and its critical flow, the one without which the line stops.
What a production site expects from its compressed air is set out on our page on compressors for industry and production. Here we deal with one question only: how to keep air when the main compressor stops, for a breakdown or for maintenance.
1. Sort the consumers
Before talking about machines, classify what uses air in the plant:
- Critical: the machines that stop the line without air, pneumatic clamping and safety functions.
- Reducible: stations that can slow down for a few hours.
- Can be cut: cleaning blow guns, extra blow-off, maintenance points.
Add up the consumption of the critical stations, in l/min or m³/min, from the machines' data sheets or a measurement on site. A compressed air audit gives you this figure on an existing installation. Also ask about cost: what does one hour of stopped line cost?
2. A worked example
A plant uses 3.0 m³/min at 8 bar in production. Its critical flow is 1.5 m³/min.
Option A, one machine more than needed. Two S 220 PM, each delivering 3.6 m³/min at 8 bar. One alone covers the 3.0 m³/min. If one stops, the plant keeps its full flow. This is the safest solution, and the most expensive.
Option B, a smaller standby. An S 220 PM as the main unit and an S 110 as standby, delivering 1.7 m³/min at 8 bar:
- In normal production, both together: 3.6 + 1.7 = 5.3 m³/min, enough to cover peaks.
- If the S 220 PM stops: 1.7 m³/min remains, above the critical flow of 1.5 m³/min.
- You cut the non-essential points, slow the reducible stations, and the line keeps running.
Option C, a single machine and a prepared rental. One S 220 PM alone, and a rental compressor in case of breakdown. Our rental screw compressors range from 5.5 to 132 kW. This option only works if the plant can tolerate a stop while the relief machine arrives and is connected.
Option D, a mobile compressor as backup. The M 220 delivers 2.0 m³/min at 12.5 bar, on a twin receiver totalling 180 L and wheels. It covers the critical flow in the example and is used elsewhere the rest of the time, for example for maintenance work on site.
3. Prepare the connection in advance
A backup you cannot connect is of no use. Whether the machine is permanent or rented:
- A spare valve on the header, with a coupling you can reach from outside the plant room.
- A power supply at 380 V three-phase, sized for the backup machine.
- A location that is flat, ventilated and accessible for delivery. See the compressor room.
4. The compressor is not the only weak point
Doubling the compressor is not enough if all the air then passes through one single unit.
- The dryer: plan a bypass with valves, or one dryer per compressor.
- The filters: two filters in parallel, or a bypass, let you change a cartridge without cutting the air.
- The drains: a blocked drain fills the network with water. See water in compressed air.
5. Keep the backup machine alive
A machine that never runs ends up failing to start on the day you need it.
- Set its pressure a little lower than the main compressor's: it starts by itself if pressure drops.
- Run it regularly, or alternate the roles between machines to share the hours.
- Keep a service kit in stock for each model. Spare parts remain available for 15 years.
If your plant already has several compressors, our article several compressors or one large one compares the layouts on a site running three shifts.
When a backup is not worth it
On a small site, where a stop of a few hours costs little, regular maintenance, a kit in stock and a rental plan are often enough. Our maintenance and inspection services help you avoid the breakdown rather than suffer it.
Send us your total flow, critical flow and number of shifts with a quote request: we will compare the options with you.
For your trade: Compressor for industry and production.