Compressor for concrete batching plants, quarries and demolition

A ready-mix concrete batching plant with two to four cement silos usually uses somewhere in the region of 0.5 to 1.2 m³/min (about 18 to 42 CFM) of air at 7 or 8 bar. In most cases, a 7.5 kW 4-in-1 screw compressor such as the K 75, which delivers 1.1 m³/min at 8 bar with a built-in dryer and filtration, supplies the whole plant. Beyond four silos, or with a second mixer, move up to the K 110. Demolition is a different calculation altogether: a single concrete breaker needs roughly 1.4 to 1.8 m³/min on its own.

What is compressed air used for in a concrete batching plant?

In a batching plant, compressed air drives almost everything that opens and closes. When the air fails, the batch stays stuck in the mixer and the truck mixers queue at the gate.

• Aggregate bins and hoppers: cylinders open and close the gates that discharge sand and gravel onto the weigh conveyor.
• Cement silos: a pneumatic butterfly valve or slide gate releases cement into the screw conveyor.
• Silo aeration: aeration pads or nozzles blow air into the bottom of the cone so that the cement flows without bridging.
• Filter cleaning: the filter on the roof of each silo, and often the one on the mixer, is cleaned by pulses of compressed air.
• The mixer: the discharge door is worked by a cylinder, and a blow gun is used for cleaning at the end of the day.
• Vibrators: a pneumatic vibrator on a hopper or a silo cone helps sticky materials move down.

A precast concrete works or a quarry has the same uses, plus pulse cleaning of the dust collectors on the crushing plant and the workshop that maintains the plant and loaders. For precast production (moulds, formwork vibrators, release agent spraying), see our page compressor for construction and precast concrete.

How much air does a concrete batching plant use?

Cylinders use little air, and only in short bursts. What really counts are the functions that blow for several minutes at a time: pulse cleaning of a silo filter while a bulk tanker fills it, and aeration while a silo is being discharged. The values below are a rough guide only; the exact consumption is in the manual for each piece of equipment.

Example: a plant with three silos and one mixer. Only one silo is filled at a time, and usually only one or two are discharged at once.

1. Pulse cleaning of the silo being filled: 150 l/min.
2. Pulse cleaning of the mixer filter: 100 l/min.
3. Aeration of the silo being discharged: 150 l/min.
4. Gate, valve and mixer door cylinders: 150 l/min.
5. Blow gun, used intermittently and counted at half: 75 l/min.

Subtotal: 625 l/min. With a 25 % safety margin for leaks and wear: 625 × 1.25 ≈ 780 l/min. With 20 % for expansion, such as a fourth silo: 780 × 1.2 ≈ 940 l/min, or 0.94 m³/min (about 33 CFM). These are the margins our configurator applies. The valve-by-valve breakdown is in our article concrete batching plant compressor, the sizing.

As for pressure, cylinders and filters generally work at around 6 bar. A setting of 7 to 8 bar is enough to cover the losses in the dryer, the filters and the pipes that run up the silos.

Which compressor for a concrete batching plant?

• Plant with two to four silos: the K 75, a 7.5 kW 4-in-1 screw compressor, delivers 1.1 m³/min at 8 bar. Compressor, 420 L air receiver, refrigerated dryer and filtration are combined on a single frame. It covers the example above.
• Large plant, two mixers or precast works: the K 110 goes up to 1.7 m³/min at 8 bar, still as a 4-in-1. If the plant already has its own receiver and dryer, the S 110 offers the same air flow as a compressor only.
• Quarry with crusher dust collectors and a workshop: the S 220 PM, with a permanent magnet motor, delivers 3.6 m³/min at 8 bar. Beyond that, the S series goes up to 132 kW, on quotation.

The S and K series are variable speed. On a batching plant, demand changes with every batch: the compressor follows it instead of switching between load and idle. See variable speed or fixed speed. And since an air failure stops all production, many plants keep a second compressor on standby: see backup compressor and redundancy.

A practical point on the standby machine: it does not need to match the main compressor exactly. If the duty compressor fails, the plant must keep its gates, valves and silo filters working; the blow gun can wait. Size the standby unit on the essential functions only, and connect it so that it can be switched in without a fitter, with an isolating valve on each side.

Which compressor for concrete breakers and demolition?

Demolition works on a different scale. A 25 to 30 kg concrete breaker strikes without pause and has to be counted at 100 % of its air flow. Two breakers at 1,500 l/min already make 3,000 l/min, then 3,750 l/min with a 25 % margin.

The M series mounts the screw compressor on its air receiver and on wheels, for sites with a 380 V three-phase distribution board. The M 220 delivers 2.0 m³/min at 12.5 bar: it keeps up with a heavy breaker. The M 75 delivers 1.0 m³/min at 10 bar, for chipping hammers and the blow gun. For several breakers, our article compressor for concrete breakers and demolition compares two M 220 units with one fixed compressor. For a job lasting a few weeks, screw compressor hire covers 5.5 to 132 kW.

On a batching plant, a hammer is also needed from time to time to break out concrete that has set in the mixer, a hopper or a chute. A chipping hammer at 300 to 500 l/min can run on the plant compressor between batches; a heavy breaker cannot, so bring in a mobile unit for that work.

Why does a concrete batching plant need dry air?

Cement and water do not mix well, even in compressed air. Moisture reaching a filter bag forms a crust that the pulses can no longer shift. In an aeration pad, it creates lumps that block the fabric. In a gate cylinder, it rusts the rod and makes the seal stick.

Winter adds frost. The pipes run up the outside of the silos over 15 to 30 metres. A refrigerated dryer dries the air to a dew point a few degrees above zero: enough indoors, but not in a pipe exposed to −10 °C. There, the remaining water freezes in the solenoid valves. A desiccant dryer solves the problem, either on the full air flow or only on the exposed branch. See our article dry air in winter on a concrete batching plant and the guide on pressure dew point.

For the two most sensitive uses in detail, read cement silo filter pulse cleaning and cement aeration in the silo.

Where should the compressor be installed on a batching plant?

• In an enclosed room. Cement dust is abrasive and quickly clogs the compressor's air filter. Install it in an enclosed, ventilated room, with an air intake well away from the silos and the mixer. See the compressor room.
• Frost-free. The room must stay above zero in winter, otherwise condensate freezes in the drain and the dryer. Conversely, a room that is too hot in summer makes the machine overheat.
• Condensate. Fit an automatic condensate drain on the receiver and at the low points of the network. This condensate contains oil: it must be collected and treated. See water in compressed air.
• A buffer receiver. A receiver at the foot of the silos keeps a reserve close to the filters and valves. The air receiver size calculator gives a starting volume.

A common mistake on older plants is a compressor tucked into a corner of the mixer building, drawing in air full of cement dust every time the mixer discharges. Moving the intake, or the whole compressor, to a separate room usually does more for its service life than any other change.

What maintenance does a batching plant compressor need?

First service at 500 hours, then every 1,500 hours, with a reminder shown on the controller. In a dusty environment, check the air filter more often than the scheduled interval. Service kits group the parts by model, and the screw compressor maintenance guide explains each step. Our compressors are lubricated: the outlet filtration retains carried-over oil. They come with a 2-year warranty and spare parts remain available for 15 years.

Plan the services for the quiet season. Most ready-mix plants slow down over the coldest weeks, which is the right time to change the air filter, check the dryer and test every automatic drain before the frost really sets in.

Further reading

• Concrete batching plant compressor, the valve-by-valve sizing
• Cement silo filter pulse cleaning
• Cement aeration in the silo
• Compressor for concrete breakers and demolition
• Dry air in winter on a concrete batching plant

To size your installation, start from the configurator and choose the concrete batching plant activity, or send us the list of your silos, filters and valves with a quote request. For a business running several plants, a compressed air audit measures actual consumption before you choose.

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