1, flow is one of the important performance data of the pump selection, which is directly related to the production capacity of the entire device and delivery capacity. If the design institute process design can calculate the pump normal, minimum, maximum three kinds of flow. Selection of pumps, based on the maximum flow, taking into account the normal flow, in the absence of maximum flow, usually 1.1 times the normal flow as the maximum flow.
2, the device system required head is another important performance data to select the pump, generally used to amplify the 5% -10% margin after the head to select.
3, the nature of the liquid, including the name of the liquid medium, physical properties, chemical properties and other properties, physical properties have temperature c density d, viscosity u, the diameter of solid particles in the medium and the content of gases, etc., which relates to the system's head, the effective margin of cavitation calculations and the type of suitable pumps: chemical properties, mainly refers to the chemical corrosiveness and toxicity of the liquid medium is the selection of the pump material and selection of the type of shaft seal. A shaft seal type of important basis.
4, the device system piping arrangement conditions refers to the delivery height of the liquid delivery distance to the liquid delivery direction, suction such as the side of the lowest liquid level, the highest liquid level on the side of the highest discharge and some other data and pipeline specifications and their lengths, materials, fittings, specifications, quantities, etc., in order to carry out the calculation of the system comb head and the verification of the cavitation margin.
5, the operating conditions of the contents of many, such as liquid operation T saturated vapor force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, ambient temperature operation is intermittent or continuous, the pump position is fixed or removable.
Two, the specific operation of the pump selection
Based on the principles of pump selection and selection of the basic conditions, the specific operation is as follows:
1, according to the arrangement of the device, topographic conditions, water level conditions, operating conditions, to determine the selection of horizontal, vertical and other types (pipeline, submersible, submerged, non-clogging, self-priming, gear-type and so on) of the pump. 2, according to the nature of the liquid medium, to determine the clear water pump, hot water pumps or oil pumps, chemical pumps or corrosion-resistant pumps or impurity pumps, or the use of non-clogging pumps.
Installed in the explosive area of the pump, should be based on the level of explosive areas, using the appropriate explosion-proof motor. 3, according to the flow size, to determine the selection of single-suction pumps or double-suction pumps; according to the head height, single-stage pumps or multi-stage pumps, high speed pumps or low speed pumps (air-conditioning pumps), multi-stage pumps than the efficiency of single-stage pumps, such as the selection of single-stage pumps and multi-stage pumps can be used, the first choice of single-stage pumps.
4, to determine the specific model of the pump
To determine what series of pumps, according to the maximum flow, (in the absence of a maximum flow, usually 1.1 times the normal flow as the maximum flow), to take the amplification of 5% -10% margin after the head of the two performance of the main parameters in the spectrogram or a series of characteristic curves to determine the Specific models. The operation is as follows: the use of pump characteristic curve, in the horizontal coordinate to find the required flow value, in the vertical coordinate to find the required head value, from the two values were up and to the right of the vertical line or horizontal line, the intersection of the two lines fall exactly on the characteristic curve, the pump is to choose the pump, but this ideal situation is generally very rare, and usually run into the following two situations: the first: intersection of the characteristics of the curve above, which indicates that the flow rate to meet the requirements, but the head is not enough, at this time, if the pump is to meet the requirements, the head is not enough, but the pump is not enough. But the head is not enough, at this point, if the head difference is not much, or a difference of 5% or so, can still be selected, if the head difference is a lot, then choose a larger head pump. Or try to reduce the pipeline resistance loss.
The second: the intersection point in the characteristic curve below, in the pump characteristic curve fan trapezoidal range, on the initial set of this model, and then according to the head difference, to decide whether to cut the impeller diameter,
If the head difference is very small, do not cut, if the head difference is very large, according to the required Q, H, according to the formula for the ns and cutting, cutting the impeller diameter, if the intersection point does not fall in the fan trapezoidal range, should choose the head, or try to reduce pipeline resistance loss. Trapezoidal range, should be selected head smaller pumps. Selection of pumps, sometimes have to take into account the requirements of the production process, the choice of different shapes Q-H characteristic curve. 5, after the pump model to determine the pump or transport medium of the physical and chemical medium similar to water pump, need to go back to the relevant catalog or sample, according to the model performance table or performance curve for the school to see whether the normal operating point falls in the pump priority work area? Effective NPSH is greater than (NPSH). Can also be reversed to NPSH calibration geometric mounting height?
6, for conveying viscosity greater than 20mm2 / s liquid pump (or density greater than 1000kg / m3), be sure to water test pump characteristic curve converted to the viscosity (or the density of the performance curve), especially for the suction performance and input power to carefully calculate or check.
7, to determine the number of pumps and standby rate:
The normal operation of the pump, generally only one, because a large pump and parallel operation of the two small pumps, (referring to the head, flow rate is the same), the efficiency of the large pump is higher than the small pump, so from the point of view of energy saving would rather choose a large pump, but not use two small pumps, but in the case of the following circumstances, you can consider the two pumps in parallel to work together: flow is very large, a pump can not reach this flow. A pump can not reach this flow. For the need to have 50% standby rate of large pumps, can be changed to two smaller pumps work, two standby (*** three)
For some large pumps, you can choose to 70% of the flow requirements of the pumps operating in parallel, without the standby pumps, a pump overhaul, the other pump is still bearing 70% of the production of the conveyor.
The need for 24-hour continuous operation of the pump, you should spare three pumps, a running, a spare, a maintenance.
8, in general, the customer can submit its "basic conditions for pump selection", the Division I give the selection or recommend better pump products. If the design institute in the design of the device equipment, the pump model has been determined, according to the design institute requirements configuration.
9, to determine the number of pumps and standby rate:
Normal operation of the pump, generally only one, because a large pump and parallel operation of the two small pumps, (referring to the head, flow rate is the same), the efficiency of the large pump is higher than the small pump, so from the point of view of energy-saving would rather choose a large pump, rather than use the two small pumps, but in the case of the following circumstances, you can consider the two pumps in parallel to work together: flow rate is very large, a pump can not reach this flow rate. A pump can not reach this flow.
For the need to have a 50% standby rate of large pumps, can be changed to two smaller pumps work, two standby (*** three lift)
For some large pumps, you can choose to 70% of the flow requirements of the pumps operating in parallel, without standby pumps, in a pump overhaul, the other lift pumps are still bearing the production of 70% of the delivery.
The need for 24 hours of continuous operation of the pump, should spare three pumps, operation, a standby, a maintenance.