Oil-free screw compressor SCR-250 WG 250 kW motor power, FAD 2 700 Nm³/h at 7 bar, water cooling, fixed speed, pressure 7 / 8 / 10 bar

Product detailed description

250 kW · class 0

SCR-250 WG is an oil-free screw compressor with a 250 kW motor, water-cooled and running at fixed speed. It is supplied in three pressure versions: 2 700 Nm³/h at seven bar, 2 520 at eight and 2 280 at ten. The air is compressed by two screw blocks in two stages and the rotors are never lubricated — so the compressed air contains no oil, not filtered out, but none at all. The outlet is DN 100, the noise level 82 dB(A).

What the designation SCR-250 WG means

The number in the designation is the motor power in kilowatts, the letters after it say two things. W at the start means water cooling, and without a V the machine runs at fixed speed. The heat leaves through water-to-air exchangers, not into the room. The machine is quieter and lighter than its air-cooled counterpart, but it needs a cooling water circuit. Once the pressure is reached the machine switches to idle running — the motor keeps turning the block, but no air is produced. With steady demand that does not matter; with a fluctuating one it becomes a significant part of the electricity bill.

What is inside the SCR-250 WG

Two stages, two blocks

The air passes through two screw blocks one after the other. The first stage compresses it to roughly 2 bar, an intercooler cools it down and the second stage pushes it up to the outlet pressure. The rotors are never lubricated — the first stage is carbon steel, the second stainless, both with an MoS₂ based coating. The rotor space is separated from the gearbox by a labyrinth seal and a hermetic stainless one, and the shafts run in SKF bearings.

Why a coating instead of oil

Where a lubricated machine injects oil into the block, here the friction is cut by a molybdenum disulphide coating on the rotors and on the inner wall of the housing. According to the manufacturer this markedly extends the time between overhauls — and replacing the whole block is exactly the most expensive item an oil-free machine can bring.

Three pressure versions, three order numbers

The machine is ordered in one of three pressures and it is set at the factory — it is not a switch on the panel. A higher pressure is always paid for in air: between seven and ten bar it costs 16 % of the output with exactly the same 250 kW motor. So it is worth finding out what pressure the end use really needs instead of buying a reserve blindly.

With fixed speed the control is two-state: the machine is either producing air or running idle.

What the machine will ask of the plant

How much space it takes and how loud it is

The machine measures 3 350 × 2 280 × 2 080 mm (L × W × H) and weighs 5 200 kg, so it takes up 7.64 m² of floor. Neither the dimensions nor the weight differ between the three pressure versions. At 82 dB(A) it belongs in a separate compressor room — this is industrial machinery, not a machine to stand beside a workstation. Besides electricity it needs a cooling water connection; in return it does not heat the room and you do not have to take the heat away with ventilation. The compressed air outlet is DN 100.

What the machine consumes

For every cubic metre of air per minute the seven-bar version draws roughly 5.6 kW of rated motor power (250 kW for 45 000 l/min). At the higher pressures it is worse, because the motor power stays the same and the air output drops. It is a figure worked out from the manufacturer table, so it can be compared directly with the machine you are weighing up alongside it. At partial demand, however, the consumption does not fall nearly as much — the machine goes into idle running and the motor keeps taking energy. If your demand fluctuates, take a look at the version with a drive.

SCR9000 control

A colour seven-inch touch display or eight navigation buttons. It shows the pressure, the temperature, the energy consumption and the hours run, keeps an eye on service intervals and returns to operation by itself after a power failure. Over Modbus RS485 the SCR-250 WG can be built into network control of up to sixteen compressors — with machines this size such sets are built routinely.

Where the air from the SCR-250 WG is used

An oil-free machine is not bought for comfort, but because nothing else will do. The manufacturer names six fields — in every one of them the air touches the product, the packaging or a person.

Equipment and accessories

What the SCR-250 WG does as standard

• Oil-free class 0 air to ISO 8573-1
• Two-stage compression, two screw blocks with an intercooler
• Rotors and housing wall with an MoS₂ based coating, double stainless steel seal
• Radial and axial SKF bearings
• Cooling by water through water-to-air exchangers
• Fixed speed, inlet valve
• A choice of 7, 8 or 10 bar, outlet DN 100
• SCR9000 controller with a colour display
• Energy consumption metering, four pressure bands, weekly run scheduling
• Modbus RS485 and network control of up to sixteen compressors

What can be ordered on top

• Cyclone water separator integrated into the machine
• Heat recovery — a water-to-oil exchanger for heating service water
• HOC preparation for a loss-free heat-regenerated dryer
• PM motor with permanent magnets, IE4 efficiency
• Vibration diagnostics — sensors watching the condition of the bearings

How it differs from neighbouring machines

The weight of 5 200 kg decides how the machine reaches its foundation — plan the crane and the floor capacity before you order. At the same 250 kW input, 300 kg heavier is the frequency-controlled SCR-250 WGV. Lighter, 5 000 kg, is the step below, the SCR-220 WG with 2 268 Nm³/h at seven bar; above 2 700 Nm³/h at seven bar the only choice is the SCR-280 WG.

The FAD output is measured to ISO 1217 and is given for each of the three pressures in which the machine is supplied; figures at other frequencies are available from the manufacturer in technical data sheets on request. The noise level is given at a distance of 1 m from the machine with a tolerance of ± 3 dB(A). The air purity class is defined by ISO 8573-1.