Introduction to basic knowledge of water pump

Significance of pump model: such as 40LG12-15 40- inlet and outlet diameter (mm) LG- high-rise building feed water pump (high speed)

12-Flow (m3/h) 15-Single-stage head (M)

200QJ20-108/8 200—indicating frame number 200 QJ—submersible electric pump 20–flow rate 20m3/h 108—head 108M 8—level 8

The basic composition of the water pump: motor, coupling, pump head (body) and frame (horizontal).

The main parameters of the water pump are: flow, expressed by Q, the unit is M3/H, L/S. The head is expressed by H, and the unit is M.

For the clean water pump, the required NPSH (M) parameter is very important, especially when it is used for suction water supply equipment.

For submersible pumps, the rated current parameter (A) is very important, especially when used in variable frequency water supply equipment. To

The main parameters of the motor: motor power (KW), speed (r/min), rated voltage (V), and rated current (A).

Coupling Pump head (body_) Horizontal frame

What is traffic? What letter is used to express? How many units of measurement are used? How to convert? How to convert to weight and formula?

Answer: The volume of the liquid discharged by the pump per unit time is called the flow rate, and the flow rate is expressed by Q. The unit of measurement: cubic meter/hour (m3/h), liter/second (l/s), L/s=3.6 m3/h=0.06 m3/min=60L/min

G=Qρ G is the weight ρ is the specific gravity of the liquid

Example: A pump has a flow rate of 50 m3/h, what is the hourly weight when pumping water? The specific gravity ρ of water is 1000 kg/m3.

Solution: G=Qρ=50×1000(m3/h·kg/ m3)=50000kg / h=50t/h

What is the lift? What letter is used to express? What unit of measurement is used? And pressure conversion and formula?

Answer: The energy obtained by the unit weight of the liquid through the pump is called the head. The head of the pump, including the suction stroke, is approximately equal to the pressure difference between the outlet and inlet of the pump. The head is represented by H, and the unit is meter (m). The pressure of the pump is expressed by P, the unit is Mpa (megapascals), H=P/ρ. If P is 1kg/cm2, then H=(lkg/ cm2)/(1000kg/ m3) H=(1kg/ cm2)/ (1000kg/m3)=(10000kg/m2)/1000kg/m3=10m

1Mpa=10kg/c m2, H=(P2-P1)/ρ (P2=outlet pressure P1=inlet pressure)

What is the efficiency of the pump? How is the formula?

Answer: Refers to the ratio of the effective power of the pump to the shaft power. η=Pe/P

The pump power usually refers to the input power, that is, the power transmitted from the prime mover to the pump shaft, so it is also called shaft power, denoted by P.

The effective power is: the product of the pump’s head, mass flow and gravitational acceleration.

Pe=ρg QH (W) or Pe=γQH/1000 (KW)

Ρ: The density of the liquid delivered by the pump (kg/m3)

Γ: The gravity of the liquid delivered by the pump γ=ρg (N/ m3)

G: acceleration of gravity (m/s)

Mass flow Qm=ρQ (t/h or kg/s)

What is the rated flow, rated speed, and rated head?

Answer: The pump is designed according to the working performance parameters of the set pump, and the best performance is determined as the rated performance parameters of the pump, which usually refers to the parameter values ​​specified in the product catalog or sample.

For example: 50-125 flow rate of 12.5 m3/h is the rated flow, head of 20m is the rated head, and the speed of 2900 rpm is the rated speed

What is cavitation margin? What is suction range? The respective unit of measurement represents the letter?

Answer: When the pump is working, the liquid will generate vapor at the inlet of the impeller due to a certain vacuum pressure. The vaporized bubbles will degrade the impeller and other metal surfaces under the impact movement of the liquid particles, thereby destroying the impeller and other metals. At this time, the vacuum The pressure is called the vaporization pressure, and the cavitation margin refers to the excess energy that exceeds the vaporization pressure per unit weight of the liquid at the suction port of the pump. The unit is marked in meters and (NPSH)r is used. The suction stroke is the necessary NPSH Δh: the vacuum degree of the pump allowed to suck liquid, that is, the installation height allowed by the pump, in meters. To

Suction distance = standard atmospheric pressure (10.33 meters)-cavitation margin-safety amount (0.5 meters)

The vacuum height of the standard atmospheric pressure energy pressure pipeline is 10.33 meters.

For example: a pump must have a NPSH of 4.0 meters, what is the suction range Δh?

Solution: Δh=10.33-4.0-0.5=5.83 meters

What is the characteristic curve of the pump? How many aspects does it include? What’s the effect?

Answer: The curve showing the relationship between the main performance parameters is usually called the performance curve or characteristic curve of the centrifugal pump. In essence, the performance curve of the centrifugal pump is the external manifestation of the liquid movement in the pump, which is obtained through actual measurement. The characteristic curves include: flow-head curve (QH), flow-efficiency curve (Q-η), flow-power curve (QN), flow-cavitation margin curve (Q-(NPSH)r), the function of the performance curve is For any flow point of the pump, a set of relative head, power, efficiency and NPSH values ​​can be found on the curve. This set of parameters is called working state, referred to as working condition or working point, centrifugal pump The operating condition at the highest efficiency point is called the optimal operating point, and the optimal operating point is generally the design operating point. Generally, the rated parameters of centrifugal pumps are the design operating point and the optimal operating point coincide or very close to each other. It is very important to understand the performance parameters of the pump to run in the practical efficiency range, which saves energy and can ensure the normal operation of the pump.

What is the full performance test bench of the pump?

Answer: The equipment that can accurately test all the performance parameters of the pump through precision instruments is the full performance test bench. The national standard accuracy is Class B. The flow rate is measured with a precision worm gear flowmeter, and the head is measured with a precision pressure gauge. The suction range is measured with a precision vacuum gauge. The power is measured with a precision shaft power machine. The speed is measured with a tachometer. The efficiency is calculated according to the measured value: n=rQ102.