Introduction of pump head, flow and power

专栏：SERVICE SUPPORT

发布日期：2020-04-21

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Introduction of pump head, flow and power

Head unit weight of liquid through the pump after the effective energy. A part of power must be consumed, so it is impossible for the pump to change the input power of the power machine into the effective power completely, in which there must be power loss, that is to say, the sum of the effective power of the pump and the loss power in the pump is the shaft power of the pump.

Head unit weight of liquid through the pump after the effective energy. It is an important working energy parameter of pump, also known as head. It can be expressed as the increase of pressure head, kinetic head and potential head of fluid, namely

H=(p2-p1)/ρg+(c2^2-c1^2)/2g+z2-z1

Where h -- lift, m;

P1, P2 -- liquid pressure at pump inlet and outlet, PA;

C1, C2 -- flow rate of fluid at the pump inlet and outlet, M / S;

Z1, Z2 -- height of inlet and outlet, m;

ρ - liquid density, kg / m3;

G -- acceleration of gravity, M / S2.

The head, flow and power of water pump are important parameters to inspect the performance of water pump

flow

The flow of water pump is also called water delivery capacity, which refers to the volume of water delivered by the pump in unit time. Expressed in Q, in m3 / h, L / s.

lift

(the lift of the centrifugal pump is different from the lift height (lifting height). The lift height of the pump refers to the vertical height that the pump delivers liquid from the low place to the high place. Only when the inlet and outlet vessels of the pump are at 0.1mp, the inlet and outlet pipe diameters are the same and the pipeline resistance can be ignored, the lift of the pump is equal to the lifting height.)

The head of water pump refers to the height that the water pump can lift, usually expressed as h, and the unit is m. The head of centrifugal pump is based on the center line of impeller, which is composed of two parts. The vertical height from the center line of the pump impeller to the water surface of the water source, i.e. the height that the pump can draw up the water, is called the suction head for short; the vertical height from the center line of the pump impeller to the water surface of the water outlet, i.e. the height that the pump can lift up the water pressure, is called the pressure head, simply called the pressure head. That is, the head of water pump = suction head + pressure water head, it should be pointed out that the head marked on the nameplate refers to the head that can be produced by the water pump itself, which does not include the loss head caused by the friction resistance of pipeline water flow. When selecting water pump, attention shall not be ignored. Otherwise, you will not be able to pump water.

Pump head = net head + head loss net head refers to the height difference between the suction point and the high-level control point of the pump, such as pumping water from the clean water tank to the high-level water tank. Net head refers to the height difference between the suction port of the clean water tank and the high water tank.

power

In unit time, the amount of work done by the machine is called power. It is usually represented by the symbol n. Commonly used units are: kg · M / s, kW, HP. Generally, the power unit of electric motor is expressed in kilowatts; the power unit of diesel engine or gasoline engine is expressed in horsepower. The power transmitted by the power machine to the feed pump shaft is called the shaft power, which can be understood as the input power of the water pump. Generally speaking, the pump power refers to the shaft power.

Because of the friction resistance between the bearing and the packing, the friction between the impeller and the water when it rotates, the vortex of the water flow in the pump, the backflow of the clearance, the impact of the inlet and outlet, etc. A part of power must be consumed, so it is impossible for the pump to change the input power of the power machine into the effective power completely, in which there must be power loss, that is to say, the sum of the effective power of the pump and the loss power in the pump is the shaft power of the pump.

Main parameters of motor: motor power (kw), speed (R / min), rated voltage (V), rated current (a).

1. What is flow? What letter is used? How many units of measurement are used? How to convert? How to convert it into weight and formula?

Answer: the volume of liquid discharged from the pump in unit time is called flow, and the flow is expressed in Q. the unit of measurement is cubic meter / hour (m3 / h), liter / second (L / s),

L / S = 3.6 m3 / h = 0.06 m3 / min = 60L / Ming = q ρ G is weight ρ is specific gravity of liquid

Example: the flow of a pump is 50m3 / h, and the weight per hour is calculated when pumping? The specific gravity of water ρ is 1000 kg / m3.

Solution: g = q ρ = 50 × 1000 (m3 / h · kg / m3) = 50000kg / h = 50t / h

2. What is lift? What letter is used? What unit of measurement is used? And pressure conversion and formula?

Answer: the energy that unit weight liquid obtains through pump is called lift. The head of the pump includes the suction head, which is approximately the pressure difference between the pump outlet and inlet.

The head is expressed in H, and the unit is m.

The pump pressure is expressed in P, in MPa (MPA), H = P / ρ. If P is 1kg / cm2, H = (LKG / cm2) / (1000kg / m3)

H = (1kg / C m2) / (1000kg / m3) = (10000kg / m2) / 1000kg / m3 = 10m1mpa = 10kg / cm2, H = (p2-p1) / ρ

(P2 = outlet pressure P1 = inlet pressure)

3. What is pump efficiency? How about the formula?

Answer: it refers to the ratio of effective power and shaft power of the pump. η = power of PE / P pump generally refers to the input power, that is, the power transmitted from prime mover to pump shaft

Also known as shaft power, expressed in P. The effective power is the product of the lift, mass flow and acceleration of gravity.

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