【Daily Question】Chemical Engineering Principles 113: Gas Binding Phenomenon (July 18)
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This post was last edited by “Back to Cambridge” on September 22, 2015, at 10:50. Starting today, the Chemical Engineering Theory section is launching the “Question of the Day” activity, aimed at helping everyone reinforce their basic knowledge in chemical engineering. Subsequently, series such as “Fundamentals of Chemical Engineering”, “Mass Transfer and Separation”, “Chemical Thermodynamics”, and “Chemical Process Technology” will also be introduced. We hope for your active participation! For the “Question of the Day” activity, answers can be viewed directly in the replies; however, the thread will be closed after one day ! You get 2 wealth rewards just for participating, and an additional 3 wealth points for correct answers~~~ Short answer question: How to prevent the phenomenon of gas binding? The centrifugal pump should be filled with liquid before starting
The main steps are: filling the pump, venting, and preventing leaks in the suction lines and shaft seals. To avoid air locking, the pump must be filled with the liquid to be transported before it is started up; this process is commonly referred to as filling the pump. In conditions of normal or positive pressure, the inlet valve of the pump is opened along with the outlet vent, and once liquid starts to flow out, that’s sufficient. However, in cases of negative pressure, the outlet vent cannot be opened; otherwise, not only will the pump not be filled properly, but air will also be drawn in, affecting the operation of the entire tower. The vacuum line at the pump outlet should be opened; if there is no return line to the tank connected to the pump, the inlet valve should be opened and vacuuming should be carried out for a few minutes. If that still doesn’t work, manually start the pump at the midpoint (the same procedure applies when starting a canned motor pump as well).
Air binding occurs when a centrifugal pump fails to start properly due to insufficient priming of the pump
Prime the pump before starting the centrifugal pump to remove all air from within it.
Before starting the pump, the pump casing must be filled with liquid to remove the air inside the pump.
The shell must be filled with liquid before startup
How to prevent gas entrapment? When a centrifugal pump is started, if there is air inside the pump, the low density of air results in a weak centrifugal force generated upon rotation; as a result, the low pressure created in the center area of the impeller is not sufficient to draw liquid from the storage tank into the pump, and thus the pump cannot transport liquid even when it is started. This phenomenon is known as gas locking, indicating that the centrifugal pump does not have self-priming capability; therefore, the tank must be filled with liquid before starting.
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The phenomenon in which a centrifugal pump can only spin idle without transferring liquid is known as air locking. To prevent air locking, the centrifugal pump should be filled with liquid before starting.
How to prevent gas entrapment? When a centrifugal pump is started, if there is air inside the pump, the low density of air results in a weak centrifugal force generated upon rotation; as a result, the low pressure created in the center area of the impeller is not sufficient to draw liquid from the storage tank into the pump, and thus the pump cannot transport liquid even when it is started. This phenomenon is known as gas locking, indicating that the centrifugal pump does not have self-priming capability; therefore, the tank must be filled with liquid before starting.
Pre-fill the pump with an external liquid in advance