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Know and Understand Centrifugal Pumps Episode 2

Tham khảo tài liệu 'know and understand centrifugal pumps episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Know and Understand Centrifugal Pumps and pressure is added to the liquid again Bernoulli s Principle . The liquid leaves the pump at discharge pressure prepared to overcome the resistance in the system. The flow from a centrifugal pump is mostly governed by the speed of the driver and the height of the impeller blades. The pressure or head that the pump can generate is mostly governed by the speed of the motor and the diameter of the impeller. Other factors play a lesser role in the pump s flow and pressure like the number pitch and thickness of the impeller blades the internal clearances and the presence and condition of the wear bands. In simple terms we could say that PD pumps perform work by manipulating the available space inside the pump. Centrifugal pumps perform work by manipulating the velocity of the fluid as it moves through the pump. There is more on this in Chapter 6. Pressure measurement Force F is equal to Pressure P multiplied by the Area A F p X A. Pressure is equal to the Force divided by the Area p A If we apply pressure to the surface of a liquid the pressure is transmitted uniformly in all directions across the surface and even through the liquid to the walls and bottom of the vessel containing the liquid Pascal s Law . This is expressed as pounds per square inch lbs in2 or psi or kilograms per square centimeter k cm2 . Atmospheric pressure ATM Atmospheric pressure ATM is the force exerted by the weight of the atmosphere on a unit of area. ATM 14.7 psia at sea level. As elevation rises above sea level the atmospheric pressure is less. Absolute pressure psia Absolute pressure is the pressure measured from a zero pressure reference. Absolute pressure is 14.7 psia at sea level. Compound pressure gauges record absolute pressure. 4 Basic Pump Principles Gauge pressure psig Gauge pressure is the pressure indicated on a simple pressure gauge. Simple pressure gauges establish an artificial zero reference at atmospheric pressure. The formula is psig .