Abstract: In this paper, the use of pump operating curve, the current speed of the water supply system with pump capacity to carry out theoretical analysis. Pump capacity allocation, especially the transfer / fixed speed pump capacity ratio is not appropriate, directly affects the speed of water supply stability and operational efficiency. Speed ​​governing water supply system used in our country, now has two years of history. After many years of practice, I found that it is exactly the capacity of the pump equipped with a direct impact on the stability of the speed control system and operational efficiency. The following, the author on the water supply system speed / constant speed pump capacity allocation issues are discussed. A speed regulating pump operating efficiency analysis Some articles have made a discussion, that the speed regulating pump operation in the regulation process, you can always maintain the operating efficiency unchanged, I think this view is not correct, in Figure 1.1 for qualitative analysis. 1.1 Formulas and applicable conditions Pump head lift H is calculated as follows: H = PR-PV + (V22-V12) / 2g + △ z - formula (1.1) H - pump head, m. PR - pump outlet pressure gauge readings, meters. PV - pump inlet pressure (vacuum) table readings. V2, V1 - pump outlet, the entrance of the flow rate, m / s. △ z - export, entrance meter installation height, m. g - acceleration of gravity, m / s 2. General engineering calculations lift simplified formula as (1.2). H = PR-PV - Eq. (1.2) Equation (1.2) shows the correlation between the pump head and the pressure at the outlet. The working curve of the pump are expressed as the flow Q - lift H curve, and look at the speed control of the pump, the water pump pressure PR as a control parameter, therefore, I use the pump flow Q - PR pressure curve Auxiliary analysis, for the difference, the curve of the curve points are called the condition curve and operating point. 1.2 Speed ​​?? pump operating efficiency Press equation (1.2), the impact of the pump pressure PR of the water there are two main factors, one is caused by changes in water head lift changes; then there is the inlet pressure PV changes, if the water remains the same , PR pressure curve for auxiliary analysis of water pressure, for the difference, the curve and curve points are called the condition curve and operating point. 1.2.1 Speed ​​changes when the water supply pump speed changes in efficiency Changes in water supply, causing the pump head H changes, assuming the inlet pressure PV = O, then PR = H, the use of pump flow Q - water pressure PR Curve (working curve) for analysis, as shown in Figure 1.1. Constant pressure water supply pump speed adjustment mode, when the speed pump running at full speed, the condition curve is SH, the water pressure is PS, the working point is A, when the water supply decreased, the speed governor to adjust to reduce the pump operation Speed, then the pump working condition curve SL, operating conditions point B, the pressure remains unchanged. A, B point of the same pressure (equivalent to the same head), it is clear that they inequality point, according to the pump law, B point in the curve SH equivalent point C, the following relationship holds: QB / QC = n PB / PC = n2 QA ~ QD - A ~ D corresponding to the amount of water, m3. PC, PD - C, D corresponding pressure, m. n - transfer rate. PS - water supply to ensure pressure, meters. According to Eqs. (1.1) and (1.2), point C corresponds to the flow rate (QC) and pressure (PC), flow rate (QS) and pressure (PB) which are greater than point B and located between point A and point B Figure 1.1 shows. If there is no governor, when the water supply drops, the working point of the pump is shown as point D in Figure 1.1. The efficiency points for each point are shown in the efficiency curve in Figure 1.1. Curves ηB, ηL are pump efficiency curves corresponding to curves SB and SL. According to Figure 1.1 analogy, when the water supply decreases, the efficiency of the pump moves to the left; relative to the operating point of the governor, the operating point is located in the right after the governor position, so that the water supply to reduce pump efficiency Decline, there is a governor pump operating efficiency is relatively higher than the governor without a pump. 1.2.2 pump inlet pressure changes on the efficiency of the inlet pressure increases, the outlet pressure remains constant, the pump head that is, at this time do not take into account the changes in water Q, pump working curve shown in Figure 1.2, SH and SL are respectively the working curve of the pump before and after the change. A and B are working points. As shown in Fig. 1.1, the equivalent point of point B is C, and their corresponding efficiencies are shown by the curves ηB and ηL . Qualitative analysis of the results are as follows: With the inlet pressure increases, the pump speed decreases in a certain amount of water supply conditions, the efficiency of the pump gradually move to the right of the efficiency curve. Integrated water supply and inlet pressure of two factors, reducing the water supply pump operating point to the left to move the water pressure to the right to move the pump operating point, the relative speed governor operating point, Speed ​​after the operating point is located in the right curve of the efficiency curve, so that the governor of the pump, the operating efficiency is relatively high without the governor of the pump. At this stage, the capacity ratio and problems of speed-regulating pumps and constant-speed pumps are high. Because the price of speed-regulating devices is high and the maintenance is difficult, most of the water supply systems at this stage are equipped with multiple speed pumps (speed pumps) Almost all of the current design stage, speed pump and fixed-speed pump capacity is not much difference (some capacity ratio or even 1.1), according to my company's experience, such a capacity ratio is not appropriate, the main drawback in The following two aspects: First, resulting in instability in the operation of the water supply system; second, the efficiency of the variable speed pump is very low. To transfer / constant speed pump capacity of 1.1 for example analysis. 2.1 transfer, constant speed pump capacity of 1.1 when the system stability analysis Water supply pump work as shown in Figure (2.1) to speed pump as the main pump
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