Atlas Copco ZR 250 VSD (FF VSD⁺) Oil-Free Rotary Screw Air Compressor

Description

Where the ZR 250 VSD Sits in the Oil-Free Range

The ZR 250 VSD holds the middle of the ZR/ZT 200-355 VSD+ platform, the oil-free line that Atlas Copco builds for plants whose compressed air demand has grown past the 110-160 class.

Two 125 kW drive modules give the machine its 250 kW of installed power. The water-cooled machines of the line below this range are covered by the ZR 160 VSD. The VSD+ control turns both of them across a turn-down window that reaches down to 11% of full speed. The platform shares one body design from 200 to 355 kW, so a plant that installs the 250 kW step keeps the same layout, the same service concept and the same spare parts logic as the smaller and larger machines around it.

The VSD+ control of the ZR 250 VSD also reads the demand of the network directly.

The letter Z of the ZR 250 VSD marks the oil-free architecture of the range. The compression elements never inject oil into the air stream, so the delivered air carries no added oil and the ZR 250 VSD fits food, pharmaceutical, electronics and textile processes that audit their air supply. The R marks the water-cooled branch: cooling water takes the heat out of the oil circuit, the compressor elements and the motor jackets, which keeps the package compact and stable in warm plant rooms.

Minimum, Effective and Maximum

The VSD+ concept drives the motor between a minimum, an effective and a maximum pressure setting, and the rated data lists a flow band for each of the three. At the minimum setting of 4 bar(e) the ZR 250 VSD produces 210 to 846 l/s (12.6 to 50.8 m3/min), at the effective setting of 7 bar(e) it produces 210 to 806 l/s (12.6 to 48.4 m3/min), and at the maximum of 10.4 bar(e) it still delivers 208 to 668 l/s (12.5 to 40.1 m3/min).

A plant that sizes its network around the effective point can run quiet, slow and efficient through night shifts, then let the drive climb to full speed when the day load arrives.

These three bands come from one machine. The ZR 250 VSD does not change its gearing between the settings; the drive simply moves the two modules across their speed window, and the rated flow follows.

Technical Specifications of the ZR 250 VSD

The figures below are copied from the official ZR/ZT 200-355 VSD+ technical data. Unit performance is measured according to ISO 1217, Annex E, Edition 4 (2009), with the reference conditions of 0% relative humidity, 1 bar absolute inlet pressure and 20°C intake temperature. Free Air Delivery is measured at the effective working pressure.

Rated Data of the VSD+ Pack

The Pack build carries the compressor, the gear train, the drive system and the controls in one enclosure of 3044 mm length, 1760 mm width and 2150 mm height. The table lists the three pressure bands for the 50 Hz supply.

For plants on a 60 Hz supply the same Pack is rated as follows.

The A-weighted emission sound pressure level at the work station is measured according to ISO 2151:2008 with the sound intensity scanning method of ISO 9614-2, and the published value carries the total uncertainty of +/- 3 dB(A). At 73 dB(A) the ZR 250 VSD stays inside the sound level of a normal industrial hall, so the ZR 250 VSD can stand on the production floor without a dedicated compressor room.

Rated Data of the Full Feature iMD Build

The Full Feature build adds the integrated iMD dryer, the water-based heat-of-compression unit that dries the air inside the compressor package. Because the dryer works with heat the process already produces, the FAD band shifts to the ratings below.

On a 60 Hz supply the Full Feature iMD build reads as follows.

Rated Data of the iMDG Split Package

The iMDG build splits the Full Feature concept into two engineered packages: the compressor Pack and the drum dryer as its own unit on the floor. The rated data of the split concept runs as follows.

For the 60 Hz supply the iMDG data reads as follows.

The drum dryer package of the iMDG build measures 5651 mm in length, 1927 mm in width and 2150 mm in height. Splitting the two packages lets a plant place the dryer where the air network wants it, which shortens the piping between drying and point of use and keeps the compressor room layout free for service access.

Dimensions and Weight

Across the 200-355 platform the Pack body keeps one footprint, and the rated weight of the ZR Pack stands at 5439 kg (11991 lb). The Full Feature iMD package adds the dryer internals inside the same enclosure and reads 6687 kg (14742 lb). A plant planning its floor can reserve one bay for the Pack and, in the iMDG concept, a second bay for the drum dryer package.

Dual NEOS Drives Without Unload Losses

The ZR 250 VSD carries two NEOS drive bodies, each coupled to its own 125 kW permanent magnet motor, and the VSD+ control splits the work between them across the speed window. Between 11% and 100% of speed the machine changes its flow with the demand of the plant, so the blow-off and idle phases that burn energy on fixed-speed machines simply do not appear in the duty cycle. At part load each element runs well inside its rating.

The dual drive layout splits the mechanical load: each element runs at a lower share of its rating, which keeps noise, wear and temperature down at part load.

The motor speed range of the VSD+ concept keeps the oil separation and the drying function inside their working windows while the flow follows the demand. The Elektronikon controller coordinates the two modules, and the drive shafts, gears and bearings of the NEOS bodies are dimensioned for continuous duty in the oil-free cycle.

Water Cooling and the Two-Stage Air Path

Air enters the ZR 250 VSD through the inlet filter and passes the first compression stage, which lifts the pressure to an intermediate level. The pulsation dampener steadies the flow before the intercooler, the automated moisture separation removes the condensate, and the second stage brings the air to its final pressure with the efficiency that two-stage compression gives over a single stage at these ratios.

The cooling water serves three circuits. One circuit feeds the intercooler and aftercooler that condition the compressed air. A second circuit stabilizes the oil temperature for the gears and bearings. The third circuit runs through the jackets of the motors and the elements to hold their operating temperature.

The oil loop of the ZR 250 VSD itself pumps cooled oil through a high efficiency filter to the gear train, and bypass valves protect the filter while keeping the oil pressure stable across the speed range of the drive.

Class 0 Air Purity for Critical Processes

The ZR 250 VSD is certified to ISO 8573-1 Class 0, the strictest oil quality class of the standard, which sets the total oil carry-over limits at the values the certification measured instead of a declared figure. Together with the ISO 1217 performance rating and the ISO 9001 manufacturing certificate, the machine documents what it delivers to processes that must prove their air quality to auditors.

The Integrated Heat-of-Compression Dryer

In the Full Feature builds the drying function uses the heat of compression instead of external energy. In the iMD package the whole drying function lives inside the compressor enclosure. In the iMDG split concept about 60% of the main flow is cooled in the precooler and aftercooler while the remaining flow regenerates the adsorption drum, so the dryer imposes no purge loss on the network and no separate power feed.

Control and Monitoring

The Elektronikon controller of the ZR 250 VSD manages the pressure band, the two drive modules and the dryer, and it logs the operating data that a maintenance team needs. The display shows the state of each module, and the controller communicates with plant systems so a central room can supervise several machines as one supply group. Service planners read the logged hours and the component states directly from the controller, which turns the maintenance plan of the ZR 250 VSD into a schedule instead of a reaction.

Options and Engineered Solutions

The 200-355 platform carries an options list that adapts the machine to the site: energy recovery units that put the cooling heat to work, sound attenuation packages, connection sets for the water circuit, and control accessories that link the machine into a master-supply network. The build of the ZR 250 VSD is selected at order time, and the Pack, iMD and iMDG concepts share the same base design so a later extension of the plant can add machines of the same family without re-engineering the room.

Applications of the ZR 250 VSD

The ZR 250 VSD fits plants that run a continuous oil-free demand around the clock: glass and bottle lines, tire curing, chemical dosing, central medical and laboratory supplies, and textile mills that dry and shape fibers with clean air. The 10.4 bar(e) maximum covers high-pressure networks directly, and the flow band of 208 to 846 l/s follows the batch rhythm of the production day.

Water cooling makes the ZR 250 VSD a natural choice in plants that already operate a cooling water circuit, because the ZR 250 VSD needs no ductwork to the outside and keeps its rated output in hot plant rooms. Where the site wants dry air without extra dryer hardware, the iMD and iMDG builds deliver Class 0 air with the dew point already controlled inside the supply.

Service and Support Around the ZR 250 VSD

Service access on the ZR 250 VSD follows the layout of the platform: one side of the enclosure carries the routine service points, and the fluid, filter and separator service kits of the ZR 250 VSD match the shared design of the 200-355 family. Atlas Copco backs the installed base with a global service organization, and genuine parts for the ZR 250 VSD are specified in the service plan that ships with the machine.

FAQ

What does the ZR 250 VSD deliver at maximum pressure?

At the maximum setting of 10.4 bar(e) the Pack build produces 208 to 668 l/s (12.5 to 40.1 m3/min), and the Full Feature iMD build produces 249 to 664 l/s (14.9 to 39.8 m3/min) from its minimum setting of 6 bar(e).

Is the ZR 250 VSD water-cooled?

Yes. The R in the model name marks the water-cooled branch of the range, and the cooling water serves the intercooler, the aftercooler, the oil circuit and the motor jackets in three separated circuits.

How oil-free is the air?

The machine is certified to ISO 8573-1 Class 0, and the oil-free element design adds no oil to the air stream at any speed of the VSD+ control.

What is the difference between iMD and iMDG?

Both are heat-of-compression dryer concepts. The iMD integrates the dryer inside the compressor package, while the iMDG delivers the drum dryer as a separate engineered package that measures 5651 x 1927 x 2150 mm and places where the air network needs it.

How far down can the machine turn down?

The VSD+ control operates the dual drives down to 11% of full speed, so the flow follows the plant demand between the minimum, effective and maximum pressure bands without unload losses.

How loud is the ZR 250 VSD?

The rated emission sound pressure level at the work station is 73 dB(A) across the Pack, iMD and iMDG builds, measured according to ISO 2151:2008 and ISO 9614-2 with a total uncertainty of +/- 3 dB(A).