PEMA ZRX
Oil-free rotary screw compressors with water injection
How much electricity does your plant use per cubic metre of air? ZRX removes heat during compression. A water film seals clearances in the air end, reducing the amount of air that leaks back and needs recompressing.
ZRX and dry oil-free compression
Both technologies compress air without oil injection. The comparison covers the single-stage ZRX and the two-stage dry twin-screw machine described by the supplier.
| PEMA ZRX | Dry oil-free compressor |
|---|---|
| Heat removal | |
| Water absorbs heat inside the compression chamber. The closer compression is to constant temperature, the less work is needed to reach the target pressure. | There is no coolant in the compression chamber. The air heats up more during compression and passes through an intercooler between stages. |
| Sealing and speed | |
| A water film limits backflow through the working clearances. The air end in this comparison runs at about 3,000 rpm. | Rotors run with a small clearance. High speed helps limit the effect of backflow. The supplier quotes 10,000–20,000 rpm for the dry air ends compared. |
| Drive and maintenance | |
| The motor drives the screw rotor directly through a coupling. No gearbox, timing gears or gearbox oil changes are needed. Service includes the air filter, water treatment and water filtration. | A gearbox increases speed and timing gears maintain rotor alignment. Lubricating oil for the gears is isolated from the air path and requires maintenance. |
How much energy does a cubic metre of air cost?
Divide total electrical input in kW by free air delivery in m³/h. The result is specific energy consumption in kWh/m³. Compare at the same discharge pressure and load.
Example for the 160 kW class
The supplier quotes 26.8 m³/min with water injection and 23.1 m³/min for the dry machine. The working pressure for the water-injected unit is unspecified. Calculating savings requires flow and power input for both units at the same pressure.
How the water-lubricated air end works
Two star wheels mesh with the grooves of one screw rotor. As it turns, the chambers shrink and air pressure rises. Treated water cools the chambers, seals the clearances and forms a lubricating film. It also lubricates the silicon carbide hydrodynamic bearings.
Where air purity matters
Oil can damage products or surfaces when blowing off packaging, conveying ingredients, spray painting or cleaning electronics. ZRX adds no oil during compression. After liquid water separation we specify drying for the required pressure dew point and filtration for the point of use.
PEMA ZRX in operation
Show photosCollapse gallery
Enquire about a PEMA ZRX compressor
For sizing, specify the required pressure, normal and peak demand, air use and purity requirements.