Centrifugal pumps are mainly composed of impellers, shafts, pump casings, shaft seals, and sealing rings. Before starting a centrifugal pump, the pump casing should be filled with liquid. When the prime mover drives the pump shaft and impeller to rotate, the liquid moves in a circular motion with the impeller rotation, and is ejected from the center of the impeller to the outer circumference under the action of centrifugal force. The liquid obtains static and dynamic pressure energy from the impeller. When the liquid flows through the volute to the discharge port, some of the dynamic pressure energy is converted into static pressure energy. When the liquid is ejected from the impeller, a low-pressure zone is created in the center of the impeller, which creates a pressure difference with the suction liquid surface. As a result, the liquid is continuously sucked in and discharged at a certain pressure.
The main components of a centrifugal pump are:
impeller; The impeller is a key component of a centrifugal pump.
According to its mechanical structure, it can be divided into three types: closed, semi closed, and open. Closed impellers are suitable for conveying clean liquids; Semi closed and open impellers are suitable for conveying suspensions containing solid particles, but their efficiency is low.
According to different suction methods, impellers can be divided into single suction and double suction types. The structure of a single suction impeller is simple, and liquid can only be sucked in from one side. The double suction impeller can symmetrically suck in liquid from both sides of the impeller at the same time. It not only has a large suction capacity, but also basically eliminates axial thrust.
According to the geometric shape of the blades on the impeller, the blades can be divided into three types: backward bending, radial bending, and forward bending. Due to its advantage in converting the kinetic energy of liquids into static pressure energy, rear curved blades are widely used; Radial blades are mainly used in partial flow pumps and unobstructed pumps; Forward curved blades are rarely used in centrifugal pumps.
Guide vanes and pump body; In order to reduce energy loss caused by impact when the liquid leaving the impeller directly enters the pump casing, a fixed guide wheel with blades is sometimes installed between the impeller and the pump casing. The blades in the introduction gradually redirect the liquid entering the pump casing and continuously expand the flow channel, effectively converting some kinetic energy into static pressure energy. Multi stage centrifugal pumps are usually equipped with guide wheels.
The snail shaped pump casing, the rear curved blades on the impeller, and the guide wheel can all improve the conversion rate of kinetic energy to static pressure energy, so they can all be regarded as energy conversion devices.
Shaft sealing device; Due to the rotation of the pump shaft while the pump casing remains fixed, there must be a certain gap at the contact between the shaft and the pump casing. To prevent high-pressure liquid from leaking out along the gap in the pump or to prevent external air from entering the pump from the opposite direction, a shaft seal device must be installed. The shaft seal device of a centrifugal pump includes a packing box and a mechanical (end face) seal. Packing box is a sealing ring made by passing the pump shaft through the annular gap of the pump casing, and inserting soft packing (such as asbestos rope soaked in oil or coated with graphite) into it. A mechanical seal is composed of a moving ring mounted on a rotating shaft and another stationary ring fixed on a clam shell. The end faces of the two rings are tightly pressed against each other by the spring force and move relative to each other, playing a sealing role. Mechanical seals are suitable for applications with high requirements, such as conveying acids, alkalis, flammable, explosive, and toxic liquids. Mechanical seal, also known as end face seal, mainly relies on the friction between the end faces of the stationary and moving rings to seal. Mechanical seals have better sealing performance, less leakage, longer lifespan, and lower power consumption than packing seals. However, the manufacturing of mechanical seals is complex, requires high precision, is expensive, and requires high installation technology.