The selection principle and basis of gear pump
To determine the use and performance of the gear pump and to select the collapse type, first of all, choose the type and form of the gear pump, so what principles should be used to select the gear pump? What is the basis for that?
1. Understand the selection principle of gear pump
1. Make the type and performance of the selected pump conform to the requirements of equipment flow, lift, pressure, temperature, cavitation flow and suction process parameters.
2. The requirement of medium characteristics must be satisfied.
The pump that delivers inflammable, explosive and toxic or valuable medium requires that the shaft seal be reliable or be used without leakage pump, such as gear pump, magnetic drive pump, diaphragm pump, shielding pump.
For the pumps that deliver corrosive medium, the convection parts are required to adopt corrosion-resistant materials such as fluorine-resistant and corrosion-resistant pumps, CQF engineering plastic magnetic drive pumps.
The pump containing solid particle medium is used to require the convection parts to adopt the wear-resisting material, and the shaft seal should be washed with clean liquid when necessary.
3. High reliability, low noise and low vibration in mechanical aspect.
4. The overall cost of equipment, operation, maintenance and management fees shall be taken into account.
Therefore, in addition to the following situations, the centrifugal pump should be selected as far as possible:
A, when measuring requirements, use metering pump
B, the lift requirement is very high, the flow is very small and there is no suitable small flow of high lift centrifugal pump optional, can choose reciprocating pump, if the cavitation requirement is not high, also can choose the vortex pump.
C, the lift is very low, the flow is very large, can choose axial flow pump and mixed flow pump.
D. When the viscosity of the medium is large (greater than 650~1000mm2/ s), the rotor pump or reciprocating pump (gear pump, and screw pump) can be considered.
E, the medium contains 75% gas, the flow is small and the viscosity is less than 37.4mm2/ s, the vortex pump can be selected.
F, for the occasion of frequent or inconvenienced, the pump with self-absorption performance should be selected, such as self-priming centrifugal pump, self-priming vortex pump, pneumatic (electric) diaphragm pump.
Ii. The basic basis of the selection of gear pump
Gear pump selection basis, according to the technological process, water supply and drainage requirements, from five aspects into consideration, both liquid throughput, gear head, nature, piping layout and operation conditions of operation.
1. Flow is one of the important performance data of the pump. It is directly related to the production capacity and throughput of the whole device. If the design institute process design can calculate the pump normal, the smallest, the maximum three kinds of traffic. When selecting the pump, the maximum flow rate is the basis, and the normal flow is considered as the maximum flow rate of 1.1 times the normal flow rate.
2. The required lift of the device system is another important performance data of the selected pump, which is generally used to select the type of the pump with a yield of 5% to 10%.
3, fluid properties, including the name of the liquid medium, physical properties, chemical properties and other properties, physical properties with temperature density d, c u viscosity, solid particle diameter and gas content in the medium, etc., this is related to the system of the head, effective computing cavitation allowance and appropriate pump type: chemical properties, mainly refers to the chemical corrosion resistance and toxicity of liquid medium, is what kind of shaft seal material selection and the selection of pump type of important basis.
Number 4, the content of the operating conditions, such as the operation of the liquid saturated steam force T P, suction side pressure PS (absolute), discharge side pressure container PZ, altitude, the environment temperature is clearance or continuous operation, the position of the pump is fixed or movable
5, device and system piping layout condition refers to send liquid height conveying liquid from liquid to, such as absorption side the lowest level, such as the highest level of discharge side length, some data and piping specifications and materials, pipe specification, quantity, etc., comb for department head and NPSH checking calculation.
Use of pump characteristic curve, find the flow on abscissa values, find the head on the ordinate, upward from the two values, respectively, and lead to the right vertical or horizontal line, two line intersection point lies squarely on the characteristic curve, it is to choose the pump, but this ideal rarely, often meet with the following two conditions:
First: the intersection point above the curve, it shows that flow meet the requirements, but the head is not enough, at this point, if the head was similar, or about 5% difference, still can choose, if the head differs a lot, had chosen pump head is bigger. Or try to reduce the loss of pipe resistance.
The second kind: the intersection is under the characteristic curve, in the shape of the pump characteristic curve, the model is initially determined. Then, according to the difference of the lift, whether to cut the diameter of the impeller,
If head difference is very small, not cutting, if the difference in lift, as the required Q, H, and according to the formula, ns and cutting cutting impeller diameter, if point does not fall within the scope of the fan trapezoidal, elected head of the smaller pump. When selecting the pump, it is sometimes necessary to consider the production process requirement and choose the different shape q-h characteristic curve.
5, pump type is determined, the water pump or medium physical and chemical medium almost like water pump, need to related product catalogue or sample, according to the type of table or curve to carry on the work performance, whether normal working point falls on the pump priority workspace? Whether the effective NPSH is greater than (NPSH). Can you reverse the geometric installation height of NPSH?
6, to handle liquid viscosity was greater than 20 / s pump (or density is greater than 1000 kg/m3), be sure to put in water experiment pump characteristic curve converted to the viscosity (or density) of performance curve, especially to inhaled or able to seriously and input power calculation.
7. Determine the number and standby rate of gear pumps:
For normal operation of pump, usually only one, because a large pump and parallel operation of two small pump, (the head and flow rate is the same), big pump efficiency is higher than the small pump, therefore, from energy saving point of view would rather choose a large pump, instead of two small pump, but in case any of the following circumstances, can consider two pump parallel cooperation:
The flow is very high, and a pump can't reach this flow.
For a large pump with a 50% spare rate, two smaller pumps can be changed, two spare (three).
For some large gear pumps, you can select the pump parallel operation of 70% flow requirement, without the spare pump, and the other pump will still be responsible for 70% of the production of the pump during the maintenance of one pump.