The pre-swirl changes the incidence angle of the incoming air as it approaches the inducer section of the impeller, effectively reducing the energy required to produce pressure and flow. As the guide vanes are rotated from full open to partially closed, they cause the drawn-in gas to rotate in the same direction as the impeller. These vanes, in the wide-open position, are parallel to the airflow, and at fully closed are at 90 degrees to airflow. Inlet Guide Vanes or (IGVs): The inlet guide vanes may also be driven electronically or pneumatically, and are a series of radial blades arranged in the intake. Inlet butterfly valve (IBV): The inlet butterfly valve may be driven electronically or pneumatically, and as it closes it creates a pressure drop across the valve, effectively reducing the inlet pressure into the compressor and throttling the compressor's ability to make pressure and subsequently flow. The following are two methods for throttling the inlet: Regulation range is also affected by external factors, such as inlet air conditions (temperature, pressure, and humidity), and coolant temperature. For example, turndown is affected by the number of stages and the impeller design. The regulation range, or turndown, is determined by the design of the machine. The minimum flow is determined when the pressure ratio reaches the pump limit and the machine reaches maximum pressure. The inlet can be throttled on a dynamic compressor to continuously reduce the capacity of the compressor. A centrifugal compressor's flow and pressure are typically controlled by a combination of an inlet control device and an unloading valve (UV).ĬABP: Can you summarize how these devices work in combination to achieve the desired results and share what options might be available?ĬAGI: Well, since a centrifugal compressor’s controls are a bit more complex, we will walk readers through the systems and the options available. Without any control system, the compressor would operate along this natural curve. The members of the Centrifugal Compressor Section of CAGI can provide that assistance.Ĭentrifugal compressors are dynamic, and each has a characteristic curve of rising pressure as capacity decreases. Since the capacity controls on a centrifugal compressor are a bit more complex than positive displacement types of compressors, consulting a factory-trained technician is always recommended. Why have you selected centrifugal compressor capacity controls for this interview, and can you give a brief introduction?ĬAGI: CAGI and our centrifugal customers all share a common interest and goal - to maximize the compressor system efficiency and optimize the system energy usage. Compressed Air Best Practices® (CABP) Magazine recently caught up with Compressed Air and Gas Institute’s (CAGI).ĬABP: Gentlemen, thanks for the series of articles on centrifugal compressors.
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