Vacuum pump selection procedure
1. Confirmation of environmental conditions
Including environmental temperature, relative humidity, atmospheric pressure, air corrosiveness, dangerous area grade, dust and waterproof requirements.
2. Confirmation of operating conditions
It refers to the absolute pressure of the liquid suction side, the pressure of the liquid discharge side, intermittent or continuous work, fixed or mobile position, convenient installation and maintenance.
3. Confirmation of media properties
It includes medium name, temperature, density, viscosity, saturated vapor pressure, solid particle diameter and content, gas content, corrosiveness, volatility, ignition and detonation, toxicity.
4. Selection of Material for Flow Passing Parts of Pumps
According to the physicochemical properties of pumping media, the following aspects are mainly considered:
(1) Corrosivity of medium
The corrosion resistance of the flow passage parts of the pump can meet the requirements of the use, and the excessive corrosion resistance should not be pursued. Otherwise, the purchase cost of the pump will be greatly increased.
(2) Does the medium contain solid particles?
Because the hardness and content of solid particles are directly related to the durability of the pump components.
(3) Temperature (pressure) of medium
The higher the temperature (pressure) of the medium, the higher the material strength of the flow passage parts of the pump. Generally, steel castings or steel castings should be selected when the temperature is higher than 250 C.
(4) Medium with hygienic grade or no pollution requirement
Select the appropriate material of the overflow parts. In addition, the pump structure should be easy to clean.
5. Selection of pump performance parameters
(1) Computing method
A. Flow: It is directly related to the production capacity and conveying capacity of the whole plant. For example, in the process design, the normal, minimum and maximum three flow rates of the pump can be calculated. When choosing a pump, the maximum flow rate should be taken as the basis and the normal flow rate should be taken into account. In the absence of the maximum flow rate, 1.1 times of the normal flow rate should be taken as the maximum flow rate.
B. Head: Generally, the head after enlarging 5%-10% margin is used to select the type. Special attention: centrifugal pump flow, especially the head allowance should not be too large, otherwise, the pump may work cavitation, resulting in flow, head can not meet the requirements. Once this happens, generally, remedial measures can be taken to cut the outer diameter of impeller or close the outlet valve of pump.
C. Power: Generally, the form and size of pump power are selected by the manufacturer and marked in the product sample.
D. Cavitation margin
Check whether the device cavitation allowance of the pump matches or not. When it is unsatisfactory, effective measures should be taken to achieve it.
(2) Analogy and experiment
When the resistance value of the pump pipeline system can not be calculated accurately, the performance parameters such as the flow rate and head of the required pump can be determined by analogy or test method.
7. Selection of Pump Installation Type
Horizontal, direct, vertical and other types (right-angle, variable-angle, rotary, double-connection, easy-to-disassemble) are selected according to pipeline layout and installation site.
8. Determine the number of pumps and the reserve rate
Generally only one pump is used for normal operation, because a large pump is equal to two small pumps in parallel operation, and the efficiency of the large pump is higher than that of the small pump. Therefore, from the point of view of energy saving, it is preferable to choose a large pump instead of two small pumps, but when the following circumstances occur, two pumps can be considered to work together:
(1) The flow rate is very large, a pump can not reach this flow rate.
(2) For pumps requiring 50% reserve rate, they can be equipped with two-purpose equipment and three sets in total.
(3) For some large-scale pumps, the pump with 70% flow requirement can be operated in parallel without backup pump. When one pump is overhauled, the other pump still bears 70% of the production flow.
(4) Pumps that must run continuously for 24 hours should run one, spare one and repair one, totaling three. If necessary, it can be selected with the assistance of the pump supplier.