When selecting an industrial rotary compressor, plant managers have a choice between two different types of technology: screw or vane.
While each came on the scene about the same time, vane is often regarded as an older technology and even outdated at times. Screw units are frequently chosen over vane due to cost rather than superior technology. Screw compressors make up much of the market, but a rotary vane compressor offers significant advantages in terms of energy use, performance, and reliability.
Here is a rundown of what gives a vane compressor the edge over a screw compressor.
Around 10 percent of the energy used in a plant is for generating compressed air, so air compressors that operate efficiently become an important cost-saving measure.
A rotary screw compressor runs at high speed to compensate for leakage paths that are inherent to the design and worsen with age. The design of a vane unit doesn’t have that issue, so it can run at lower speeds, which leads to better energy efficiency and reduces power use.
The efficiency of a vane compressor actually improves over the first thousand hours or so of use, while the rotary type will become less efficient as the bearings wear.
The rotors in a screw unit tend to use steel in an easily machinable grade. This steel type is prone to wear when there is marginal lubrication. Metal-to-metal contact in every start-up results in this type of wear because the unit doesn’t retain oil there.
A vane unit tends to use quality cast iron for the rotor, stator, and end covers. Using this material for the bearings is important because it retains oil. As long as the blades that contact them are made of a different metal, wear is reduced over time compared to a screw type.
Some vane compressors have run for more than 200,000 hours without changing out the white-metal brushes normally used. By contrast, you have to change out roller bearings every 30,000-40,000 hours of operation.
The extra components of vane and screw machines are pretty similar, such as the oil tank, thermal bypass, and some capacity controllers. This means the maintenance labor and cost of these items would be the same.
But for repairs to the compressor itself, screw types are more expensive and harder and often involve a factory exchange. Vane units can be serviced in the field. The most common repair is blade replacement, which can take no more than a couple of hours depending on size.
Parts for a screw air-end can also involve a wait to get as they are costly and not carried by most dealers. Vane compressor parts are often kept in stock and are less expensive, especially if you go with one of the bigger brands. For example, finding the best price on Gast compressors and parts is far easier than for screw models.
Choose a Rotary Vane Compressor
If you’re shopping for a compressor for your plant, keep in mind that a rotary vane compressor can be a good investment thanks to their energy efficiency. You should also find a vane unit to be a better choice long-term thanks to its construction and reliability, not to mention easier maintenance.