That is a large early 20th century horizontal double-acting airor gas compressor with a direct drive synchronous motor. Theoldest machine of it's type that I worked on was a 1917 IngersollRand vacuum pump with a 22 inch piston at the Diamond Almondplant in Orange County California. Frick was an old refrigeration pump company back at a time whenAmmonia was used as a refrigerant. Given the quality of this image, it could still be in use no matter what it is pumping.
A hundred years ago I could probably tell you exactly how that thing worked. Now, decades later, it's just an artful jumble of metal and moving parts. :)
Okay, I'm impressed. I guessed it was a stationary steam engine.
The left side is the crankcase. The connecting rod is attached tosomething called a crosshead. It is sort of a piston but the cylinderis two semi-circles. Turn these two characters ( ) 90 degrees to seewhat I mean. The purpose of the crosshead is to translate the pistonrod to straight back and forth linear motion.The actual piston rod is round and precision ground. The inboardcylinder in this case has a packing box to prevent leakage of airor gas to the atmosphere. Most modern double actingcompressors use mechanical seals. This allows the air or gas toto be compress on both the inboard and outboard strokes. The thingssticking out of the distance piece and the outboard end are valveassemblies. There will be four more on the far side for a total of4 suction and 4 discharge valves. Double acting compressors do notuse a single horsepower more to compress twice the volume.Here is an example of a crosshead. What is not shown is threadedhole where the piston is rod is attached. I hated the job of handling a 100+ pound wrench and beating the crosshead nut 20times with a 20 pound sledge hammer (especially when dealing witha 4 or 6 cylinder compressor:)https://4.imimg.com/data4/NH/EC/MY-2955146/air-compressor-crosshead-500x500.jpg