Why does only centrifugal compressors experience surge while reciprocating compressors do not?
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As the title suggests: Why do only centrifugal compressors experience surge while reciprocating compressors do not?
First, reciprocating compressors are positive-displacement compressors, while centrifugal compressors are not. Surge* is the phenomenon in which, when the back pressure at the outlet of the network is higher than the pressure at the outlet of the centrifugal compressor, the airflow reverses direction momentarily and impacts the unit. Imagine what the exhaust valve of a reciprocating compressor is, in essence It’s a one-way valve! So the airflow cannot flow back into the cylinder. But the reciprocating pump piston force is determined by the back pressure of the subsequent pipeline network! Once the backpressure in the subsequent pipeline network exceeds the design conditions, it is very likely to cause the relatively weak parts of the unit to break.
Reply to 2# Be careful** Doesn’t that centrifugal compressor have an outlet valve?
Reply to 4# Be careful** Isn’t the outlet valve of that centrifugal compressor a one-way valve?
Reciprocating machines are positive-displacement types, while centrifuges are centrifugal types; check valves cannot prevent surging.
Check valves are available at both the outlets of the reciprocator and the centrifuge
What causes surging? It is vortex separation that occurs in the impeller flow channels, which blocks the flow and leads to a decrease in flow rate. As a result, the pressure in the system pipelines becomes higher than the outlet pressure, causing the gas to flow back. Reciprocating structures are different in this regard; it depends on where such phenomena occur, and these factors affect the pattern of gas flow
Reply to 5# uknow86: The check valve at the outlet of the centrifuge is designed to provide better protection for the unit. When the unit is shut down, liquid and impurities from the process pipelines may flow back; the check valve then serves to protect the unit
Because the stable operating range of the centrifuge is relatively narrow. It is mainly related to the high flow rate characteristic of centrifuges; surge occurs when the inlet flow is insufficient. In contrast, reciprocating machines have a low flow rate, so surge does not occur in them
Air flows back into the compressor, causing eddies and surging. In reciprocating compressors, pistons are used for operation, and check valves serve to prevent air from entering the compressor