Of all the types of air compressors on the market, you can’t beat the single acting reciprocating air compressor for simplicity:
This simplicity is key to a couple of major advantages:
- Price: they can cost 20-40% less than a similar rated (but more efficient) rotary screw model, up to about 5HP sizes. This makes them great choices for home hobbyists and small industrial or commercial settings.
- High pressure: It’s common to see reciprocating compressors that are capable of generating up to 3,000 psig. Because the power is transmitted in the same direction as the fluid flow, they can handle the mechanical stresses necessary for this much better than other types of air compressors, which may need special modifications for that kind of performance.
- Durability: out of necessity, their construction is very robust and rugged. A good regimen of preventive maintenance will keep them running for a good, long time. Speaking of which…
- Maintenance (preventive): if you change your car’s oil and brake pads yourself, you have most of the know-how – and tools – to perform regular upkeep on a reciprocating air compressor. There’s really not that much to them:
The internals of a single acting reciprocating compressor.
Those advantages are buffered, though, by certain drawbacks:
- Efficiency, part 1: The real work (compressing the air) only happens on the upstroke. They’re less efficient than their dual acting counterparts, which compress on the downstroke too.
- Efficiency, part 2: As size increases, efficiency decreases. As stated above, smaller sizes usually cost appreciably less than more efficient (rotary screw, vane, centrifugal, etc.) types, but as you approach 25HP or higher, the cost difference just isn’t there, and the benefits of those other types start to weigh heavier in the decision.
- Maintenance (corrective): Whereas they’re easy to maintain, if/when something does break, the parts (robust and rugged as they are) can get pretty pricey.
- Noise: No way around it; these things are LOUD. Most of the time, you’ll find them in a remote area of the facility, and/or in their own (usually sound-insulated) room.
- High temperature: When air is compressed, the temperature rises due to all the friction of those molecules getting shoved together…that’s going to happen with any air compressor. All the metal moving parts in constant contact with each other, in a reciprocating model, add even more heat.
- Oil in the air: If you’re moving a piston back & forth in a cylinder, you have to keep it lubed properly, which means you have oil adjacent to the air chamber. Which means, no matter how well it’s built, you’re likely going to have oil IN the air chamber.
All that said, the benefits certainly do sell a good number of these compressors, quite often into situations where it just wouldn’t make sense to use any other type. If you’re in the market for an air compressor, you’ll want to find a local reputable air compressor dealer, and discuss your needs with them. If those needs entail the use of engineered compressed air products, though, please feel free to give me a call to discuss. We can make sure you’re going to ask your compressor folks the right questions.
Russ Bowman
Application Engineer
EXAIR Corporation
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Compressor internals image courtesy of h080, Creative Commons License.