Diaphragm pump is composed of actuators and valves.Diaphragm pump actuator with pneumatic actuator and electric actuator, models, respectively, the ADD series air diaphragm pump and EDD type electric diaphragm pump.Diaphragm pump body (body) there are four kinds of material: plastic, aluminum, cast iron, stainless steel, choose according to the requirement of the liquid or gas medium respectively.The inside of the diaphragm pump diaphragm is according to different liquid medium with NBR, chloroprene rubber, fluorine rubber, poly (vinylidene fluoride, poly ethylene materials, the so in order to illustrate the medium type.
Diaphragm pump, the mode of selection:
1, the role of the diaphragm pump mode selection:
The role of the diaphragm pump way only when choosing pneumatic actuators, the role of way through positive and negative effect and positive effect of the valve actuator portfolio formation.There are four kinds of combinations are (closed type), positive and negative (gas) type, anyway (gas) type, reflect (gas close type), formed by the four combinations of diaphragm pump have spirit way on and off two.For the choice of the ways of diaphragm pump function, mainly from three aspects to consider:
A, process safety;
B, the characteristics of medium;
C, guarantee product quality, the economic loss is minimal.
2, the diaphragm pump flow characteristic of options:
Flow characteristics of the diaphragm pump is refers to the relative flow and displacement of medium flow through the valve (relative opening degree of valves), the connection between the ideal flow characteristic mainly has straight lines, such as percentage (log), parabolic and quick opening, etc. 4.Commonly used ideal flow characteristic only in a straight line, such as percentage (log), quick opening three.Parabolic flow characteristic between straight line and equal percentage, the percentage of properties such as generally available to replace, and quick opening feature is mainly used for two control and program control, so the choice of diaphragm pump characteristic is, in fact, the choice of straight lines and equal percentage flow characteristics.
The choices for the diaphragm pump flow characteristic through theoretical calculation, but the method and equation are very complicated.Currently use experience more criterion, considering concrete from the aspects:
(1) from the control system regulation quality analysis and choice;
(2) from the process piping is considered;
(3) from the change of the load analysis.
Choose good diaphragm pump flow characteristic, can according to the traffic characteristics determine the shape and structure of the valve core, but for like a diaphragm valve, butterfly valve, etc., due to their structural characteristics, can not change the surface shape of valve core to achieve the required flow characteristic, at this time, but by changing the feedback of the valve positioner CAM contour.
3, the choice of the diaphragm pump diameter:
The choice of diaphragm pump diameter and determine the main basis of valve flow capacity is CV.In all kinds of engineering instrument design and type selection, CV for the diaphragm pump is calculated, and provide the diaphragm pump design specification.From the CV of diaphragm pump to valve diameter calculation method and general subject to the following steps:
A, the determination of calculation flow.The existing production capacity, equipment load and the condition of the medium, decided to calculate flow rate qmax and qmin.
B, the determination of pressure difference before and after the valve.According to the selected valve flow characteristic and system characteristics of the selected s (drag coefficient), and then determine the differential calculation.
C, calculate the CV.According to the regulation of media to choose the appropriate formula and chart, cmax and cmin is obtained.
D, selects the CV.According to the cmax, the selected standard series of the products in select > cmax and with its most close to the level of c.
E, the opening of the diaphragm pump checking.General requirements at the time of maximum calculation flow opening degree 90%, 10% minimum calculation flow when opening.
F, diaphragm pump actual adjustable ratio calculation.General requirements than actual adjustable 10.
G, the determination of the seat diameter and nominal diameter.Verify right after, according to the c.
4, the diaphragm pump type selection
(1) the diaphragm pump valve type selection
The choice of the body is the most important link in diaphragm pump selection.Diaphragm pump valve body is a lot of more phyletic, the commonly used is through single-seat, pass-through two-seater, angular, diaphragm, small flow rate, tee, eccentric rotating, butterfly, sleeve, spherical, etc. 10.Before you choose the valve, the control process of medium, the careful analysis of process conditions and parameters, collect enough data, understand the requirement of system of diaphragm pump, according to the collected data to determine the valve type to be used.In specific choices, can consider from the following aspects:
A and the wear resistance when the fluid is suspending liquid containing high concentrations of wear particles, the valve core and valve seat joint friction surface every time shut down severely.So the valve flow to smooth, internal material is hard.
B, corrosion resistance due to the corrosive medium, in the case of can satisfy regulating function, try to choose structure simple valves.
C, the structure of the valve core shape mainly based on the selected flow characteristic and factors such as unbalanced force.
D, medium temperature, pressure, when the medium temperature, high pressure and large, should choose the valve core and valve seat materials by temperature, pressure changes small valves.
E, prevent flash flash and cavitation and cavitation in liquid medium.In the process of practical production, flash and cavitation effect not only the calculation of flow coefficient, still can form the vibration and noise, make the valve life is short, so when choosing the valve should prevent the valve from flash and cavitation.
(2) the diaphragm pump selection of the actuator
A, output force
Actuator regardless of type, the output power is used to overcome the effective of load (mainly refers to the unbalanced force and unbalanced torque and friction, sealing force, gravity and so on) the action of forces.Therefore, in order to make the normal work of the diaphragm pump, with the implementation of the mechanism to produce enough output force to overcome all kinds of resistance, ensure high seal and valve opening.
For double-acting pneumatic, hydraulic, electric actuators, are generally not reset spring.The size of the force has nothing to do with its direction, therefore, the selection of the actuator is the key to find out the biggest output force and rotational torque of the motor.For single acting pneumatic actuators, the output power is associated with the opening of the valve, the force on the diaphragm pump will also affect the movement characteristics, therefore needs to be established throughout the opening scope of diaphragm pump force balance.
Determination of b, type of actuator
On the actuator output force is determined, according to the process using the environment requirements, choose the corresponding actuator.For the scene with explosion-proof requirements, should choose pneumatic actuators, and junction box for explosion-proof type, cannot choose electric actuators.If there is no explosion-proof requirements, pneumatic, electric actuators are optional, but consider from the aspects of energy saving, should try to choose electric actuators.For hydraulic actuator, the as pneumatic, electric actuators are widely used, but have the characteristics of high precision, fast action and smooth, therefore, in some cases, in order to achieve better control effect, must choose hydraulic actuators, such as power plants transparent machine speed regulation, the refinery catalytic device reactor temperature regulation control and so on.
Diaphragm pump selection in specific choices, can consider from the following aspects:
1, the shape of the valve core structure mainly based on the selected flow characteristic and factors such as unbalanced force.
2, the wear resistance when fluid medium is suspending liquid containing high concentrations of wear particles, the valve core and valve seat joint friction surface every time shut down severely.So the valve flow to smooth, internal material is hard.
3, corrosion resistance due to the corrosive medium, in the case of can satisfy regulating function, try to choose structure simple valves.
4, medium temperature, pressure, when the medium temperature, high pressure and large, should choose the valve core and valve seat materials by temperature, pressure changes small valves.
5, prevent flash flash and cavitation and cavitation in liquid medium.In the process of practical production, flash and cavitation effect not only the calculation of flow coefficient, still can form the vibration and noise, make the valve life is short, so when choosing the valve should prevent the valve from flash and cavitation.