How to see the pump parameters
How to see the pump parameters
(1) The main parameters of the
water pump water pump parameters refer to the main technical data of the pump performance, including flow rate, head, speed, efficiency and specific rotation number.
1. Flow rate (Q)
The flow rate of the pump refers to the amount of liquid discharged per unit time. The flow rate of the pump is usually calculated by volume, expressed by Q, the unit is m3 / h (m3 / h), m3 / s (m3 / s), liters / sec (1 / s), and can also be used in weight, G Indicate that the unit is ton / hour (t / h), ton / second (t / s), kilogram / second (kg / s).
The relationship between G and Q:
G = r × Q ?? r-liquid weight (kg / m3)
because the weight of water is approximately 1000 kg / m3, so
1 liter / sec = 3.6 m3 / h = 3.6 tons / h
2. Head (H) The
pump head refers to the energy added by the unit weight of liquid through the pump. Expressed by H, it is actually the height that the pump can lift water, also called total head or full head. The unit is the height of the liquid column in meters. It is customary to omit the "liquid column" and express it in meters (m).
The total head of the pump is composed of two parts: the suction head and the discharge head, so
total head = suction head = outlet head
However, due to various resistances when the water flows through the pipeline, the suction head and outlet head of the pump are reduced, so the
suction head = actual Water-absorption head + Water-absorption loss head
Water-out head = actual water-out head + water-out loss head
Loss-up head = water-absorption-loss head + water-out loss head
Total head = actual head + loss head
Since the head indicated on the nameplate of the pump is the total head of the above pump, the head on the nameplate cannot be mistaken for the actual head value. The actual head of the pump is smaller than the head value on the nameplate of the pump. Therefore, when determining the pump head, pay special attention to this point. Otherwise, if you only determine the pump head according to the actual head, the pump head ordered will be lower, which may reduce the efficiency of the pump, or even hit the water. The loss head is closely related to the types of water pipes and accessories on the pipeline (low valve, gate valve, check valve, straight pipe, bent pipe), quantity, water pipe inner diameter, pipe length, water pipe inner wall roughness and pump flow rate, etc. Attention should also be paid to piping design and selection of water pipes and accessories.
3. Allowable vacuum height (Hs) The
allowable vacuum height refers to the suction head of the vacuum meter reading, that is, the suction head of the pump (referred to as the suction head of the pump), including the sum of the actual suction head and the suction loss head. Expressed by Hs, the unit is meter (m).
Allowable vacuum height is an important parameter for the height of the installed pump. When installing the pump, the suction head of the pump should be less than the allowable vacuum height. Otherwise, the installation will be too high and it will not absorb water or produce cavitation. Such as cavitation production, not only deteriorate the performance of the pump, but also may damage the impeller.
4. Rotation speed (n)
Rotation speed refers to the revolution of the pump impeller per minute, expressed by n, and the unit is revolution / minute (r / min). Each pump has a certain speed, which cannot be increased or decreased at will. This fixed speed is called the rated speed, and the speed marked on the pump nameplate is the rated speed. If the pump runs more than the rated speed, it will not only cause the power machine to overload or fail to move, but also the pump parts are easily damaged; if the speed is reduced, the efficiency of the pump will be reduced, affecting the normal operation of the pump.
5. Specific speed (ns)
Among the aforementioned water pump models, some models have a specific revolution parameter. Specific speed and speed are two concepts. The specific speed of water pump, referred to as specific speed, is often referred to as ns. The specific rotation speed of the pump refers to the rotation speed of a hypothetical so-called standard pump impeller. This hypothetical pump is geometrically similar to the impeller of a real pump, with a power consumption of 0.735 kW, a head of 1 m, and a flow of 0.075 cubic The number of revolutions in meters per second. The pumps with the same or similar impeller shape have the same specific rotation speed, and the pumps with the impeller different shape or similar are not the same. If the axial flow pump has a larger rotation speed than the mixed flow pump, the mixed flow pump specific rotation speed is also a comprehensive index reflecting the characteristics of the pump. In addition, it should be noted that the speed of a water pump with a larger number of revolutions is not necessarily higher; the speed of a smaller pump is not necessarily lower. The pump with large flow rate and low head is larger than the rotation speed, and vice versa. Generally, the centrifugal pump with a lower specific speed has a small flow rate and a higher head; while the axial flow pump with a higher specific speed has a larger flow rate and a lower head.
power refers to the amount of work done by the unit in unit time. Pump power can be divided into three types: effective power, shaft power and supporting power.
(1) Effective power ?? It is the power consumed purely for lifting water after removing some of the power lost in the pump, so it is also called net power, output power or water horsepower. The commonly used symbol is N effect, and the unit is kilowatt (or horsepower). The effective power value can be calculated from the flow rate and head of the pump:
flow rate (kg / sec) × total head (m)
effective power rate (kW) = ————————————————
( 2) Shaft power ?? It is the power transmitted by the power machine to the pump shaft, so it is called shaft power or input power. The common symbol is the N axis. It is the sum of the effective power of the pump and the power lost by the pump. The power loss of the pump mainly includes the power consumed by the friction of the bearing in the pump body, the friction between the pump shaft and the filler, the friction between the water and the impeller, the pump casing, and the back leakage of the high-pressure water in the pump.
(3) Supporting power ?? It refers to the power of the power machine that the pump should be matched, so it is also called the power. The common symbol is N, which is larger than the shaft power. This is because there is a transmission loss in the process of the power machine transmitting power to the pump; at the same time, it is also necessary to consider that when the pump is working, the flow rate and head have fluctuations and the power machine may be overloaded, so the power machine needs to have a larger power reserve than the power of the pump shaft. The matching power can be obtained by the following formula:
dynamic safety factor × (kg / sec) × head (m)
supporting power (kW) = ———————————————————————
102 × pump efficiency × transmission efficiency
Power safety factor (or standby factor) can be determined according to the power of the pump shaft, and the larger value is taken when the shaft power is small.
The transmission rate should be determined according to the transmission type and transmission mode. When coupling is used for direct transmission, 0.99 is adopted. When belt transmission is adopted, 0.98 for open transmission, 0.9 for cross transmission, 0.92 to 0.94 for semi-cross transmission, and 0.96 for triangle belt transmission.
7. Efficiency (n)
Efficiency refers to the ratio of effective power to shaft power, so it is a technical and economic indicator that reflects the degree of power utilization given by the pump to the power. The common symbol is n, and its size is expressed as a percentage. It can be expressed by the following formula:
Pump efficiency = —————— × 100%
Since the effective power is less than the shaft power, the pump efficiency is always less than 1. However, the larger the pump efficiency value, the greater the effective power and the smaller the power loss in the pump. When we choose a pump, we should try to choose a pump with high efficiency. The efficiency on the nameplate refers to the highest efficiency that the water pump can achieve. The maximum efficiency of the general agricultural water pump is 60% to 80%, and some large pumps exceed 80%.