The basic performance of the pump, usually from six personalized parameters can be. 1, flowrate (capacity, discharge) Pump flow refers to the unit of time out of the pump outlet section of the liquid volume or quality, respectively, referred to as the volume flow (volume capacity) and mass flow (mass capacity). The volume flow is indicated by the symbol Q, and the mass flow is expressed by Qm. Volume flow commonly used units of liters per second (L / s), cubic meters per second (m3 / s) or cubic meters per hour (m3 / h); mass flow commonly used units of kilograms per second (kg / s) or Ton per hour (t / h). By definition, volume flow and mass flow have the following relationship: Qm = ÏQ, where Ï is the density of the liquid being conveyed (kg / m3). Due to the varying flow requirements for a variety of applications, the vane pump has a wide range of design flows of less than 1 liter per second, while large ones reach tens or even hundreds of cubic meters per second. In addition to the pump flow above, the concept of pump theoretical flow QT and leakage flow q is also encountered in the study of the impeller theory. The so-called theoretical capacity refers to the flow through the pump impeller. Leakage capacity (leakage capacity) refers to the theoretical flow out of the impeller, there is a part of the pump rotating components and static components between the gap, such as the impeller inlet port ring and the gap between the pump housing, packing box pump shaft and packing And the gap between the balance hole in the axial force balance device or the balance disc and the housing, etc., flows back to the impeller inlet and out of the pump. It can be seen, the pump flow, the theoretical flow and leakage flow between the following relationship: QT = Q + q. 2, the head head, symbol H, refers to the unit weight of liquid delivered through the pump after the gain of energy, that is, the actual pump to the total weight of the liquid per unit of energy, the unit is m (N · m / N = m). Therefore, by the definition of the pump head, head can also be expressed as the pump inlet and outlet cross-section of the unit energy difference. 3, power (power) Power refers to the pump in the unit of time the size of the work done by the liquid, the unit is watts (W) or kilowatts (kW). Pump power includes shaft power, effective power, power matching power, water power and loss of power within the pump four. (1) Shaft power, input power The P-axis power is the power delivered to the main shaft of the pump after passing through the transmission equipment, that is, the input power of the pump. The power listed on the pump nameplate usually refers to the pump shaft power. (2) Actual power, effective power Pe Effective power refers to the energy obtained from the flow of the pump out of the unit time, that is, the actual effective work done by the pump on the flow of the liquid being delivered. (3) Matching power of motive power machine The power of Pg power machine is the output power of the prime mover matched with the water pump. Considering that overload may occur during the operation of the water pump, the power of the power machine is usually selected to be higher than that of the water pump Shaft power. (4) water power Pw water power is the power remaining after the shaft power of the pump overcomes the mechanical resistance, that is, the power the impeller transmits to the liquid passing through it. (5) lost power within pump The input power (ie, shaft power) of the pump is only partially transferred to the delivered liquid. This part of the power is the effective power and the other part is used to overcome the pump operation Pump within the various losses, that is, loss of power. Power losses within the pump can be divided into three categories, namely mechanical losses, volumetric losses and hydraulic losses. 4, efficiency (efficiency) The effective level of pump delivery of energy is called efficiency. The pump input power (shaft power P), due to mechanical loss, hydraulic loss and volume loss, can not be fully passed to the liquid, the liquid can only be obtained through the pump effective power Pe. Efficiency is a parameter that reflects the amount of power loss in the pump and the degree of effective utilization of the shaft power P, ie, the ratio of the effective power Pe to the shaft power P. 5, speed (pump speed) n is the speed, is the pump shaft or impeller rotation per minute number, usually expressed in N, the unit is r / min. Pump speed and other performance parameters are closely related to a certain speed, resulting in a certain flow, lift, and the corresponding shaft power, when the speed changes, it will cause other performance parameters corresponding changes. The pump is designed according to a certain speed, so the power machine should not only meet the working conditions of the pump, but also the speed of the pump should be consistent with the speed of the pump. 6, allowing suction on the vacuum height [Hs] or required NPSH Δhr allow suction vacuum height (required suction vacuum lift) and the required net positive suction head required is characterized by the water pump in the standard state of the steam Erosion performance (inhalation performance) parameters. Pump work, often due to improper device design or operation, there will be pressure at the inlet of the pump is too low, resulting in cavitation occurs, resulting in decreased performance of the pump or flow intermittent, increased vibration phenomenon. Cavitation occurs in the pump after the pump can not work properly, cavitation serious or even not work. In order to avoid the occurrence of pump cavitation, it is necessary to correctly determine the geometric installation height of the pump and design the pump system through the cavitation performance parameters of the pump.
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