Published: 06 July, 2018
Although screw air compressors account for a large share of the market, vane technology should not be underestimated when it comes to reliability and its ability to deliver in harsh environments. Andy Jones, managing director at Mattei, looks at how the design of vane air compressors improves energy efficiency without compromising on performance.
In today’s market, there are two main types of industrial rotary compressor – vane and screw. Although both are designed to produce the same output, it is important to know how they work, as these differences affect the maintenance costs, energy efficiency and levels of reliability associated with each technology.
Efficient by design
A rotary-vane compressor comprises a rotor, with slots along its sides which house individual sliding vanes. This assembly is offset within a cylinder, or ‘stator’, and rotates on white-metal bushes. As the rotor turns on its axis, the vanes are pushed against the stator wall by centrifugal force and the air is compressed.
Oil is injected into the stator to seal clearances between the rotor, stator and end covers. The oil also serves to lubricate the moving parts and cool the air during compression. Lubrication also keeps the freely moving vanes in constant contact with the stator’s internal surface, so the air seal is near perfect.
The design of rotary vane compressors eliminates ‘blowholes’ where air under high pressure can be driven to areas of low pressure, which is inherent in screw compressors. This means that vane compressors don’t need to run at high speeds to compensate for air leakage. They can operate at low speeds, from a direct drive coupling, which in turn leads to lower power consumption.
The efficiency of the system also depends on the layout and design of the pipework, and the joints and connections. The distance between the compressor and where the compressed air is used can have important implications in terms of system efficiency. Excessive lengths and bends lower efficiency, so pipe runs need to be suitably laid out. For systems where the point of use and the compressor are relatively close then a single line could be chosen, whereas larger systems with many points of use would benefit from a ring main.
On top of that, the compressor must be sited and installed correctly. Air flow into the compressor needs to be unrestricted, cool, reasonably clean and free from solid and gaseous impurities. The distance between the compressor and where the compressed air is actually used can have important implications too.
Wear and maintenance
The lubricating oil forms a film on which the vanes slide. With no direct metal-to-metal contact between the vanes and the internal stator wall there’s no negative wear. In fact, rather than experiencing damaging wear, the blades of a rotary vane compressor undergo a polishing process during use, which results in less friction, and consequently, better operation and reduced energy requirement.
The absence of roller bearings in a vane compressor means lower maintenance costs and a reduced risk of component failure. In fact, some vane compressors have been known to run for over 200,000 hours without the need to replace the white-metal bushes used in this type of compressor. This poses a serious contrast with roller bearings, which are typically required to be changed out at every 30,000-40,000 hours.
Due to the integrated nature of the airend most vane compressors have fewer hydraulic hoses, further minimising the risk of leakage and breakdowns. All of this means vane compressors offer greater reliability and guaranteed lifetime performance.
It's important never to neglect compressor maintenance. Keep your compressor running to the optimal standard by undertaking regular maintenance in accordance with the manufacturers’ guideline. Not only will this ensure minimum energy wastage, but it will make sure your equipment remains reliable and safe.
Equally, it may seem obvious, but it’s important to regularly check for leaks. In many companies, 30% of the air generated is wasted through leaks, which can prove costly over time. Check for leaks at initial installation, re-check frequently, and carry out an annual leak detection survey.
The polishing effect within a vane compressor’s airend means that its efficiency actually improves for the first thousand hours or so and then stays constant throughout the rest of its operating life, whereas typically a screw compressor's efficiency falls away over time as its bearings wear.
If a rotary vane compressor is looked after in accordance with manufacturer’s instructions (which often only require compliance to a standard and a less than onerous servicing regime) the operating life of its airend can easily extend to over 100,000 hours without wear, even in dusty operating conditions.
Energy efficiency is a serious priority for the industry, and air compressors play a major role in reducing consumption. With its energy efficient design, vane air compression technology can help businesses minimise their energy use whilst lowering the cost of ownership throughout a unit’s lifespan.
For further information please visit: www.mattei.co.uk