Category And Type Selection Of Single Screw Pump

Single Screw Pump Type selection
1. Selection of valve body type for single screw pump The selection of valve body is the most important part in the selection of single screw pump. There are many types of single screw pump valve bodies, and the commonly used ones are straight-through single seat, straight-through double seat, angle, diaphragm, small flow, three-way, eccentric rotation, butterfly, sleeve, ball and other 10 types. Before selecting a valve, it is necessary to carefully analyze the medium, process conditions and parameters of the control process, collect sufficient data, understand the system's requirements for single screw pumps, and determine the type of valve to be used based on the collected data. When making a specific selection, the following aspects can be considered:

(1) The shape and structure of the valve core are mainly based on the selected flow characteristics and unbalanced force and other factors.
(2) Wear resistance When the fluid medium is a suspension containing a high concentration of abrasive particles, the joint surface of the valve core and the valve seat will be severely rubbed every time it is closed. Therefore, the flow path of the valve should be smooth and the internal material of the valve should be hard.
(3) Corrosion resistance Since the medium is corrosive, try to choose a valve with a simple structure if it can meet the regulation function.
(4) Temperature and pressure of the medium When the temperature and pressure of the medium are high and vary greatly, valves with valve core and valve seat materials that are less affected by temperature and pressure changes should be selected.
(5) Prevent flash evaporation and cavitation Flash evaporation and cavitation only occur in liquid media. In the actual production process, flash evaporation and cavitation not only affect the calculation of the flow coefficient, but also cause vibration and noise, shortening the service life of the valve. Therefore, when selecting a valve, the valve should be prevented from flashing and cavitation.

2. Selection of single-screw pump actuator

(1) Consideration of output force
Regardless of the type of actuator, its output force is the effective force used to overcome the load (mainly refers to the unbalanced force and unbalanced torque plus the friction, sealing force, gravity and other related forces). Therefore, in order for the single-screw pump to work normally, the actuator used must be able to generate sufficient output force to overcome various resistances and ensure high sealing and valve opening.

For double-acting pneumatic, hydraulic, and electric actuators, there is generally no return spring. The magnitude of the force has nothing to do with its running direction. Therefore, the key to selecting an actuator is to understand the maximum output force and the torque of the motor. For single-acting pneumatic actuators, the output force is related to the opening of the valve. The force on the single-screw pump will also affect the motion characteristics. Therefore, it is required to establish a force balance in the entire opening range of the single-screw pump.

(2) Determination of the actuator type

After the output force of the actuator is determined, the corresponding actuator is selected according to the process use environment requirements. If there is an explosion-proof requirement on site, a pneumatic actuator should be selected, and the junction box should be explosion-proof. An electric actuator cannot be selected. If there is no explosion-proof requirement, both pneumatic and electric actuators can be selected, but from the perspective of energy saving, electric actuators should be selected as much as possible. Hydraulic actuators are not as widely used as pneumatic and electric actuators, but they have the characteristics of high adjustment accuracy, fast and smooth movement. Therefore, in some cases, in order to achieve better adjustment effects, hydraulic actuators must be used, such as speed adjustment of transparent machines in power plants, temperature control of reactors in catalytic devices in refineries, etc.