Stall is when a centrifugal compressor reaches a point of maximum flow and minimum head. The wheel can deliver no more gas. (For a description of the centrifugal wheel and head, see “Centrifugal Refrigeration Compressor Surge”.) Stall is common in aircraft engines, turbo-chargers, and other turbo machinery that operate in an open loop, but much less likely to occur in a closed loop refrigeration machine. A theoretical wheel curve is displayed bellow, the far-right line labeled “stall”, is at the operating conditions the compressor must reach to induce “stall”. For a refrigeration machine to reach the conditions at stall on the graph above, there would need to be almost no head across the compressor, and a flow, far exceeding the design.
Refrigeration machines are closed loop systems, take a vacuum cleaner and stick the suction nozzle into the discharge port, wa-la, closed loop system, if you kept the motor cool, the vacuum would run and run and never see a stall condition. Now, I agree, not a fair comparison, vacuum cleaner and refrigeration machine, but the point is clear, without a mechanism to induce more volume flow into the loop, the flow can’t exceed what the compressor is capable of. It is true, that a great deal of volume can be generated by the boiling of the refrigerant in the evaporator, and it does, but not more than the machine is designed to handle. I guess you could have huge evaporator that, at times, gets overloaded, and is piped up to a compressor that runs forward on the curve, with a ginormous condenser that sits in the arctic; I just have never come across such a design or miss-applied machine to witness this perfect storm. However, if you have I would love to hear about it.
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AuthorI worked for over thirty years in the HVACR industry. I have designed, installed, serviced, and trouble shot units of various types throughout the years. The posts here are information based on that experience, I hope you find them useful. If you have a different experience, please comment. Archives
September 2020
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