# Why are double-acting reciproating compressors more efficient than single-acting ones?

On many websites, I read that double-acting reciprocating compressors are more efficient than single-acting compressors. These sources say it's because they complete two compression cycles on each crank shaft turn.

Why should the number of compression cycles per crank shaft turn matter for energy efficiency? That should give me double the amount of compressed fluid at double the energy expense, isn't it?

These sources also mention that a double-acting reciprocating compressor uses a crosshead between the piston and the rod. I could imagine that this crosshead can absorb the typical piston thrust and thus reducing the piston friction. But does it make such a big difference that double-acting pistons are one of the "most efficient ways" to provide a compressed fluid?

Two example websites claiming the above statements:

• Why not analyse both situations and see how the energy requirements change? Oct 10, 2023 at 14:15

You will find losses in a single acting compression such as leakage, even with a seal as the pressure difference is high, any leaked fluid in a dual acting compressor is less of a loss as it leaks into something that will have work done to it. You would also find inertial losses with a single acting compressor but with a dual acting compressor these are two for one assuming they don't change. As for your reasoning you are right if the systems weren't lossy then the single and dual acting compressors should be the same.

• Thanks, wouldn't have thought that these losses make such a big difference. Could you kindly elaborate further what you mean with the inertial losses being "two for one" in dual acting compressors? Oct 11, 2023 at 11:42
• Sorry that was my intuition, maybe minor accelerating and deceleration of the piston with every stroke as the load isn't constant with a single acting compressor, also if you think about frictional losses in the mechanism then you can maybe see that you get two for the price of one. Oct 11, 2023 at 12:40
• I'm assuming compression takes more load than expansion. Oct 11, 2023 at 12:41