Pump Basics

1. What is a pump?

A pump is a machine that converts the mechanical energy of the prime mover into the energy of pumping liquid.

2. What is power?

The work done per unit time is called power.

3. What is effective power?

In addition to the energy loss and consumption of the machine itself, the actual power obtained by the liquid through the pump per unit time is called effective power.

4. What is shaft power?

The power delivered by the motor to the pump shaft is called shaft power

5. Why is it said that the power delivered by the motor to the pump is always greater than the effective power of the pump?

1) When the centrifugal pump is in operation, part of the high-pressure liquid in the pump will flow back to the pump inlet, or even leak out of the pump, so that part of the energy must be lost;

2) When the liquid flows through the impeller and the pump casing, the change of the flow direction and speed, and the collision between the fluids also consume part of the energy;

3) The mechanical friction between the pump shaft and the bearing and the shaft seal also consumes some energy; therefore, the power transmitted by the motor to the shaft is always greater than the effective power of the shaft.

6. What is the total efficiency of the pump?

The ratio of the effective power of the pump to the shaft power is the total efficiency of the pump.

7. What is the flow rate of the pump? What symbol is used to represent it?

Flow refers to the amount of liquid (volume or mass) flowing through a certain section of a pipe per unit time. The flow rate of the pump is indicated by “Q”.

8. What is the head of the pump? What symbol is used to represent it?

Head refers to the increment of energy obtained by a unit weight of fluid. The head of the pump is represented by “H”.

9. Commonly used mechanical pumps are divided into several categories according to their working principles.

1) Vane pump.

When the pump shaft rotates, it drives various impeller blades to give the liquid centrifugal force or axial force, and transport the liquid to the pipeline or container, such as centrifugal pump, vortex pump, mixed flow pump, and axial flow pump.

2) Positive displacement pump.

Pumps that use continuous changes in the internal volume of the pump cylinder to transport liquids, such as reciprocating pumps, piston pumps, gear pumps, and screw pumps;

3) Other types of pumps.

Such as electromagnetic pumps that use electromagnetic to transport liquid electrical conductors; pumps that use fluid energy to transport liquids, such as jet pumps, air lifters, etc.

10. What are the general mechanical disassembly principles?

Under normal circumstances, it should be disassembled in turn from the outside to the inside, first up and then down, and try to disassemble the whole parts as a whole.

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