A water pump is a device that converts mechanical energy into fluid energy to achieve fluid transportation. Its core working principle is to drive internal components such as impellers or pistons to rotate or reciprocate through a power device (e.g., an electric motor), changing the pressure in the pump's internal cavity, and using pressure differences to push fluid flow. Below, we will detail the specific working principles starting from common types of water pumps:

I. Centrifugal Pumps (Most Common Type)

Centrifugal pumps are one of the most widely used water pumps, and their working principle is based on "centrifugal force" and "pressure difference":

Start-up Phase:
Before starting, the pump casing and suction pipe must be filled with liquid (called "priming the pump" to avoid cavitation). The motor drives the impeller on the pump shaft to rotate at high speed (usually 1000-3000 rpm).

Effect of Centrifugal Force:
When the impeller rotates, the blades drive the surrounding liquid to perform circular motion. Under the action of centrifugal force, the liquid is thrown toward the edge of the impeller and enters the volute flow channel of the pump casing.

Conversion of Pressure and Velocity:
The cross-sectional area of the volute flow channel gradually expands, reducing the fluid's flow velocity. Kinetic energy is converted into static pressure energy (pressure energy), enabling the liquid to gain sufficient pressure and be discharged from the pump's outlet.

Suction Process:
After the liquid at the center of the impeller is thrown toward the edge, a low-pressure zone (even a vacuum) forms at the impeller's center. At this point, the pressure at the external liquid surface (usually atmospheric pressure) is higher than the pressure at the impeller's center. The liquid is pressed into the impeller's center through the suction pipe under the action of the pressure difference, completing continuous transportation.

II. Positive Displacement Pumps (Taking Piston Pumps as an Example)

Positive displacement pumps transport liquids by changing the volume of the working cavity inside the pump. Common types include piston pumps, gear pumps, and screw pumps. Taking piston pumps as an example:

Suction Process:
The motor drives the crank-connecting rod mechanism, causing the piston to move to the right in the pump cylinder. The volume inside the pump cylinder increases, forming low pressure. At this time, the suction valve opens, the discharge valve closes, and liquid enters the pump cylinder under external pressure (e.g., atmospheric pressure).

Discharge Process:
When the piston moves to the left, the volume inside the pump cylinder decreases, the liquid is compressed, and the pressure rises. The suction valve closes, the discharge valve opens, and the high-pressure liquid is pushed into the outlet pipeline.

Continuous Operation:
As the piston reciprocates, the suction and discharge processes alternate, enabling continuous liquid transportation. It is characterized by high output pressure and stable flow rate (proportional to rotational speed).

III. Principles of Other Types of Pumps

• Gear Pumps: Two intermeshing gears rotate, and the space between the gear teeth forms a low pressure on the suction side to draw in liquid. On the discharge side, the meshing of the gears 擠壓 (squeezes) the liquid to form high pressure for discharge. They are suitable for transporting viscous fluids (e.g., syrup, lubricating oil).

• Screw Pumps: One or more screws mesh with a bushing. When rotating, the sealed cavity formed by the screw grooves moves axially, pushing liquid from the suction end to the discharge end. They feature stable pressure and uniform flow, often used in scenarios with high hygiene requirements such as food and pharmaceuticals.

• Diaphragm Pumps: The volume of the pump cavity is changed through the reciprocating deformation of a diaphragm (e.g., rubber, plastic). One side of the diaphragm contacts the liquid (made of food-grade materials), while the other side is driven by mechanical force or air pressure, avoiding contact between the liquid and power components. They are suitable for transporting corrosive liquids or those with high hygiene requirements (e.g., beverages, chemicals).

Summary of Core Principles

Regardless of the type, the essence of a water pump is to create a pressure difference of "low-pressure suction and high-pressure discharge" by changing the pressure in the space where the liquid is located (using centrifugal force, volume changes, etc.). This overcomes the liquid's gravity, pipe resistance, etc., enabling transportation from low to high positions or from low to high pressure. Due to structural differences, different pumps are suitable for scenarios with varying flow rates, pressures, and liquid properties (e.g., viscosity, corrosiveness). For example, pumps in beverage machines are mostly small diaphragm pumps or gear pumps, emphasizing hygiene and precise flow control.