Head, flow and power are important parameters to examine the performance of the pump:

1.Flow rate

The flow rate of the pump is also called the water delivery volume.

It refers to the amount of water delivered by the pump per unit time. Represented by the symbol Q, its unit is liter/second, cubic meter/second, cubic meter/hour.

2.Head

The head of the pump refers to the height at which the pump can pump water, usually represented by the symbol H, and its unit is meter.

The head of the double suction pump is based on the centerline of the impeller and consists of two parts. The vertical height from the centerline of the pump impeller to the water surface of the water source, that is, the height at which the pump can suck water up, is called the suction lift, referred to as the suction lift; the vertical height from the centerline of the pump impeller to the water surface of the outlet pool, that is, the water pump can press the water up The height is called the pressure water head, referred to as the pressure stroke. That is, water pump head = water suction head + water pressure head. It should be pointed out that the head marked on the nameplate refers to the head that the water pump itself can produce, and it does not include the loss head caused by the frictional resistance of the pipeline water flow. When choosing a water pump, be careful not to ignore it. Otherwise, the water will not be pumped.

3.Power

The amount of work done by a machine per unit time is called power.

It is usually represented by the symbol N. Commonly used units are: kilogram m/s, kilowatt, horsepower. Usually the power unit of the electric motor is expressed in kilowatts; the power unit of the diesel engine or gasoline engine is expressed in horsepower. The power transmitted by the power machine to the pump shaft is called shaft power, which can be understood as the input power of the pump. Generally speaking, the pump power refers to the shaft power. Due to the frictional resistance of the bearing and packing; the friction between the impeller and the water when it rotates; the vortex of the water flow in the pump, the gap backflow, the inlet and outlet, and the impact of the mouth, etc. It must consume part of the power, so the pump cannot completely change the input power of the power machine into effective power, and there must be power loss, that is to say, the sum of the effective power of the pump and the power loss in the pump is the shaft power of the pump.

Pump head, flow calculation formula:

What does the head of the pump H=32 mean?

Head H=32 means that this machine can raise the water up to 32 meters

Flow = cross-sectional area * flow velocity The flow velocity needs to be measured by yourself: stopwatch

Pump lift estimate:

The head of the pump has nothing to do with the power, it is related to the diameter of the impeller of the pump and the number of stages of the impeller. A pump with the same power may have a head of hundreds of meters, but the flow rate may be only a few square meters, or the head may be only a few meters, but the flow rate may be up to 100 meters. Hundreds of directions. The general rule is that under the same power, the flow rate of high head is less, and the flow rate of low head is large. There is no standard calculation formula to determine the head, and it depends on your use conditions and the model of the pump from the factory. It can be calculated according to the pump outlet pressure gauge. If the pump outlet is 1MPa (10kg/cm2), the head is about 100 meters, but the influence of suction pressure must also be considered. For a centrifugal pump, it has three heads: the actual suction head, the actual water pressure head and the actual head. If it is not specified, it is generally believed that the head refers to the height difference between the two water surfaces.

What we are talking about here is the resistance composition of the closed air conditioning cold water system, because this system is a commonly used system

Example: Estimating double suction pump head

According to the above, the pressure loss of the air-conditioning water system of a high-rise building about 100m high can be roughly estimated, that is, the lift required by the circulating water pump:

1. Chiller resistance: take 80 kPa (8m water column);

2. Pipeline resistance: Take the resistance of the decontamination device, water collector, water separator and pipeline in the refrigeration room as 50 kPa; take the length of the pipeline on the transmission and distribution side as 300m and the specific frictional resistance of 200 Pa/m, then The friction resistance is 300*200=60000 Pa=60 kPa; if the local resistance on the transmission and distribution side is 50% of the friction resistance, the local resistance is 60 kPa*0.5=30 kPa; the total resistance of the system pipeline is 50 kPa+ 60 kPa+30 kPa=140 kPa (14m water column);

3. The resistance of the air conditioner terminal device: the resistance of the combined air conditioner is generally larger than that of the fan coil unit, so the resistance of the former is 45 kPa (4.5 water column); 4. The resistance of the two-way regulating valve: 40 kPa (0.4 water column) .

5. Therefore, the sum of the resistance of each part of the water system is: 80 kPa+140kPa+45 kPa+40 kPa=305 kPa (30.5m water column)

6. Double suction pump head: Taking a safety factor of 10%, the head H=30.5m*1.1=33.55m.

According to the above estimation results, the pressure loss range of the air-conditioning water system of buildings of similar scale can be basically grasped. In particular, it should be prevented that the pressure loss of the system is too large due to uncalculated and too conservative estimates, and the water pump head is selected too large. Resulting in wastage of energy.