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Pump parameters, performance and the relationship between each other
Pump parameters and performance (1) Pump parameters and performance (1) The main parameters of the pump Pump parameters is the main technical performance of the pump technical data, including flow, lift, speed, efficiency And the specific number of revolutions. 1, flow (Q) pump flow is the amount of liquid discharged per unit time. The flow rate of the pump is usually calculated by volume and expressed in Q in units of m3 / h (m3 / h), m3 / s and l / s, Expressed in tons / hour (t / h), tons / second (t / s), kg / s (kg / s). The relationship between G and Q: G = r × Q r - heavy liquid (kg / m 3) Since the weight of water is approximately 1000 kg / m 3, 1 liter / second = 3.6 m 3 / hour = 3.6 tons / Head (H) The head of a pump is the amount of energy that a unit weight of liquid increases through the pump. H said that in essence is the height of the pump to pumped water, also known as the total head or full head. Units for the height of the meter liquid column, customary to omit the "liquid column", in meters (m) said. The overall head of the pump consists of two parts, the head of suction and the head of water. Therefore, the total head = head of suction = the head of water, but due to various resistance when the water flows through the pipe, the suction head and the head of the pump are reduced, so the suction head = actual Water head + water absorption head lift head = actual head lift + head loss head loss = head loss + head loss head lift = head head lift + pump lift head as indicated on the pump head is the total head of the pump, it can not Mistakenly believe that the lift on the nameplate is the actual lift value, the actual lift of the pump is smaller than the lift value on the pump nameplate. Therefore, in determining the pump head, this should pay special attention. Otherwise, if you only press the actual lift to determine the head of the pump, ordered the pump head is low, it may reduce the efficiency of the pump, or even hit the water. The loss lift is closely related to the type of water pipes and accessories (low valve, gate valve, check valve, straight pipe and elbow pipe), quantity, inner diameter of pipe, pipe length, roughness of inner wall of water pipe and pump flow, etc. Care should be taken when designing piping and piping and accessories. 3, to allow suction on the vacuum height (Hs) allows suction vacuum height refers to the vacuum gauge reading suction head, which is the pump suction lift (referred to as the pump suction), including the actual suction head and water absorption loss head. In Hs said the unit is meters (m). Suction vacuum level is allowed to install an important parameter of the pump height, the installation of the pump, the pump should be less than the suction head suction height of the vacuum, otherwise the installation is too high, it can not absorb water or cavitation phenomenon. Such as the production of cavitation, not only deterioration of the pump performance, but also may damage the impeller. 4, speed (n) speed is the number of revolutions per minute pump impeller, expressed in n, the unit is rev / min (r / min). Each pump has a certain speed, can not be arbitrarily increased or decreased, the fixed transfer called the rated speed, the pump nameplate rated speed is the rated speed. If the pump runs at more than the rated speed, it will not only cause overloading or turning of the power machine, but also the parts of the pump will be easily damaged. When the speed is reduced, the efficiency of the pump will be reduced and the normal operation of the pump will be affected. 5, than the number of revolutions (ns) In the aforementioned pump models, some models have the ratio of the number of components of this parameter. Than the number of revolutions and speed are two concepts, the pump than the number of revolutions, referred to as speed, common symbol ns. The specific rpm of a pump refers to the number of revolutions of an imaginary so-called standard pump impeller. This hypothetical pump is geometrically similar to parts of a real pump impeller. At a power consumption of 0.735 kW, a head of 1 m and a flow rate of 0.075 m3 M / s with the number of revolutions. The same or similar pump impeller shape than the same number of revolutions, impeller shape is not the same or not similar to the pump is not the same number of revolutions. If the ratio of axial flow pump than the mixed flow pump, mixed flow pump is also a reflection of the characteristics of a comprehensive index. In addition, pay attention to the pump than the number of revolutions, the speed is not necessarily high; less than the number of revolutions, speed is not necessarily low. Large flow, low lift pump, than the large number of revolutions, otherwise small. Generally lower than the number of revolutions centrifugal pump, the flow is small, high lift; and higher than the number of axial flow pump, the flow, lift low. 6, Power Power refers to the unit in the unit of time work size. Pump power can be divided into effective power, shaft power and supporting power of three. (1) Effective Power It is the net power, output power or water horsepower after it is used to remove the power lost from the pump and used solely for pumping water. Commonly used symbols for the N-effective units in kilowatts (or horsepower). Effective power value can be calculated using the pump flow and lift: Flow (kg / s) × total head (m) Effective power rate (kilowatts) = ---------------- 102 ( 2) Shaft Power It is the power transmitted from the power machine to the pump shaft, so it is called shaft power or input power. Common symbols for the N axis. It is the sum of pump effective power and pump loss power. The loss of pump power mainly includes the friction of bearing in pump body, the friction between pump shaft and packing, the friction between water and impeller and pump shell, and the return loss of high pressure water in pump. (3) supporting power It refers to the power pump should be matching the power, so also known as power. The common symbol is N, it is bigger than the shaft power. This is because the motive power transmission pump to the process, there are transmission losses; also consider the pump work, the flow and lift fluctuations may appear power machine overload, so the power need to have a pump power than the large power reserve. Supporting power can be obtained by the following formula: Dynamic safety factor × (kg / s) × head (m) Supporting power (kW) = --------------------- 102 × pump efficiency × transmission efficiency Dynamic safety factor (or reserve factor) can be determined according to the size of the pump shaft power, take a large value when the shaft power is small. Transmission rate depends on the transmission type and transmission method to determine. When using the direct drive coupling, take 0.99. The use of belt drive, open transmission take 0.98, cross drive to take 0.9, semi-cross-drive take 0.92 ~ 0.94; V-belt drive take 0.96. 7, efficiency (n) Efficiency is the ratio of effective power to shaft power, so it is a technical and economic indicator that reflects the degree of power utilization by the pump for power. The common symbol is n, its size expressed as a percentage. It can be expressed as: Effective Efficiency Pump Efficiency = - × 100% Shaft Power Because the effective power is less than the shaft power, the pump efficiency is always less than 1. However, the greater the value of the pump efficiency shows that the greater the effective power, the pump less power loss. When we choose the pump, we should try to choose a high efficiency pump. The efficiency on the nameplate means the highest possible efficiency of the pump. The highest efficiency of agricultural pumps is 60% ~ 80%. Some large pumps exceed 80%. (B) the relationship between pump performance parameters Pump parameters, but they are not isolated but interrelated influence each other. To master the relationship between them, the right to buy and use the pump has a certain significance. 1, the pump speed is constant, the relationship between flow and lift, power, efficiency, that is, its head, power and efficiency changes according to certain changes with the flow. Centrifugal pump and axial pump, for example, their variation is not the same. Although the head of these two pumps with the increase of flow rate decreases, with the increase of flow rate increases, but the axial flow pump change is more significant. And when the flow is zero (equivalent to the outlet gate valve closed), its lift higher than normal. The centrifugal pump lift is not significant. The relationship between the power and flow of two pumps, the changing law is the opposite. Centrifugal pump power decreases with the decrease of flow (or with the increase of head decreases), when the centrifugal pump flow is zero, the power is minimal. Therefore, the centrifugal pump should be closed before starting and stopping the valve to reduce starting power and stable parking. The axial flow pump on the contrary, its power is increased with the flow rate decreases, the flow rate of zero when the maximum power. Therefore, the valve can not be closed to start, it is for this reason, so the axial flow pump outlet pipe is not installed. The relationship between the efficiency of two pumps and the flow, the changing law is not the same. Centrifugal pump efficiency changes in the flow, it changes less, that is, the flow rate changes in a larger range, still maintain a high efficiency. Due to the wide range of high efficiency centrifugal pumps, the pump regulates the head of the flow during operation. However, on the contrary, axial flow pump, flow slightly changed, greater efficiency changes. Therefore, the pump should not adjust the flow and lift in operation. 2, the pump speed changes, the flow and lift, power, efficiency. (Editor: Xiaoxia QQ:) Recommended reading: 2017 exhibition information