PMVF-II Water-Cooled Two-Stage PM VSD Screw Compressor

The PMVF-II is Kaishan’s two-stage, permanent-magnet, variable-speed rotary screw compressor, and this page covers its water-cooled build, the W and WH models. The range runs from 75 kW to 200 kW in seven ratings, and each rating comes in two pressure classes: the standard PMVF-W-II for 0.6-0.9 MPa, and the PMVF-WH-II (H) for 1.0-1.3 MPa. That gives a buyer a machine tuned to the header pressure the plant actually runs, rather than one oversized compromise, and it puts the whole family on a single platform so spares, service routines and operating habits stay consistent.

The permanent-magnet variable-speed drive is what turns that efficient air end into efficient operation across the load range. The control scheme uses a patented sensorless open-loop design for the PM motor, with torque compensation through a full 360 degrees and bus voltage utilization above 93 percent. A PID algorithm holds the discharge pressure steady, and constant-power control lets the drive raise motor speed to make more air whenever the set pressure sits below the maximum the unit can reach. Kaishan rates the unit as beating the national grade-1 efficiency standard across 60 to 100 percent of its speed range, with the largest energy saving falling in the 40 to 90 percent load band where most plants actually run.

The motor itself is a high-efficiency permanent-magnet synchronous machine. Because the field is provided by permanent magnets, the rotor draws no excitation current, so it saves energy at every speed and especially at low speed. The efficiency and power factor curves stay close to flat, and even at 20 percent load the motor still holds more than 80 percent of its full-load performance, which matters on a machine that spends much of its life part-loaded. The magnets are rated to 180°C, temperature rise is kept low to protect them, and the soft start pulls less than twice rated current instead of the surge a direct-on-line motor produces.

Supporting hardware follows the same standard across the range. The inlet valve is a patented design cycle-tested to five million operations, with a large bore for low pressure drop and a check valve that closes quickly to keep oil and air from blowing back out of the air end. The dedicated motor runs on SKF bearings and carries an oil-filling device that lets the machine be topped up without a shutdown. A custom touchscreen controller with an intuitive menu shows running parameters and history, and the cooling circuit is built for low power draw and low noise with intake and exhaust silencing.

Choosing within the water-cooled PMVF-II range comes down to two numbers. First, read the required free air delivery off the table at the actual header pressure, remembering that the H version is a lower-flow, higher-pressure machine: the 200 kW unit makes 40.5-47.9 m³/min at 0.6-0.9 MPa but 31.4-36.4 m³/min at 1.0-1.3 MPa. Pick the H version only when the plant genuinely needs above 10 bar. Second, size on measured air demand with a modest margin.

Typical Installations

General manufacturing, textile and dyeing, chemical and pharmaceutical processing, steel and metalworking, electronics and any plant with a variable air demand and an existing cooling-water circuit. Kaishan is the brand of Zhejiang Kaishan Compressor Co., Ltd., a compressor manufacturer with 70 years of history, more than 300 patents, a national enterprise technology center, and equipment installed in over 90 countries.

The W models are standard pressure (0.6-0.9 MPa); the WH models are the high-pressure H version (1.0-1.3 MPa). Air delivery varies with set pressure within the drive range.

* Specifications subject to change without prior notice.