(A) the choice of diaphragm pump type
1, diaphragm pump valve body type selection The choice of diaphragm pump is the most important part of the selection. Diaphragm valve body types, commonly used through a single seat, through two-seater, angular, diaphragm, small flow, tee, eccentric rotation, butterfly, sleeve, spherical and other 10 species. Before choosing a valve, carefully analyze the medium, process conditions, and parameters of the control process, gather enough data to understand the system requirements for the diaphragm pump, and determine the type of valve to be used based on the data collected. In the specific choice, from the following aspects:
(1) The shape of the spool is mainly based on the selected flow characteristics and unbalanced forces and other factors to consider.
(2) Wear resistance When the fluid medium is a suspension containing high concentration of abrasive particles, the valve core, the valve seat joint surface will be severely rubbed each time it is closed. Therefore, the flow of the valve should be smooth, the valve's internal material to be hard.
(3) Corrosion resistance Due to the corrosive medium, try to choose a simple structure of the valve in the case of regulatory function.
(4) Medium temperature, pressure When the medium temperature, high pressure and changes, should use the valve core and valve seat material by temperature, pressure changes in small valves.
(5) to prevent flash and cavitation flash and cavitation only produce liquid medium. In the actual production process, flash and cavitation not only affect the calculation of flow coefficient, but also the formation of vibration and noise, so that the valve life is shorter, so the valve should be selected to prevent flash and cavitation.
2, diaphragm pump actuator choice
(1) output power considerations
Regardless of the type of actuator, the output force is used to overcome the effective load (mainly unbalanced and unbalanced torque plus friction, sealing force, gravity and other related forces). Therefore, in order for the diaphragm pump to work properly, the associated actuator must be capable of producing enough output force to overcome various resistances and ensure a high degree of sealing and valve opening.
For double-acting pneumatic, hydraulic, electric actuator, there is usually no return spring. The size of the force has nothing to do with its direction of operation, so the key to choosing an actuator lies in knowing 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 appearing on the diaphragm pump will also affect the kinematics and therefore a force balance across the opening of the diaphragm pump is required.
(2) the type of implementing agencies to determine
After determining the output force of the implementing agency, select the appropriate implementing agency according to the process environment requirements. For on-site explosion-proof requirements, pneumatic actuators should be used, and the junction box for the explosion-proof, you can not choose the electric actuator. If there is no explosion-proof requirements, the pneumatic and electric actuators can be used, but from the energy-saving aspects, should try to use electric actuators. For the hydraulic actuator, its use is not as good as the pneumatic, electric actuators a wide range, but with high precision, fast speed and smooth characteristics, therefore, in some cases, in order to achieve better regulation effect, you must use hydraulic actuator Institutions, such as power plant transparent speed control, refinery catalytic reactor temperature control and so on.
(B) the role of diaphragm pump options
Membrane pump mode of action is only used in the selection of pneumatic actuators, and its role in the positive and negative through the implementing agencies and the positive and negative valve action combination. There are four types of combination that is positive (air-off type), positive and negative (air-type), anyway (air-type), anti-anti (anti-off type) Open and Qi off two. For the diaphragm pump mode of action, mainly from three aspects: a) process safety; b) the characteristics of the media; c) to ensure product quality, economic loss is minimal. (C) diaphragm pump flow characteristics of choice
The flow characteristics of the diaphragm pump refer to the relationship between the relative flow of the medium flowing through the valve and the displacement (the relative opening of the valve). The ideal flow characteristics are mainly straight line, equal percentage (logarithm), parabola and quick opening. The only commonly used ideal flow characteristics, such as straight line, such as the percentage (logarithm), quickly open three. Parabolic flow characteristics between the straight line and equal percentage, the general percentage of the characteristics can be used instead of the other, while the fast opening characteristics are mainly used for two-bit adjustment and program control, so the selection of diaphragm pump is actually a straight line and equal percentage flow characteristics s Choice.
The choice of diaphragm pump flow characteristics can be calculated theoretically, but the methods and equations used are complicated. At present, the use of more experience guidelines, specifically from the following aspects: â‘ from the regulatory system to adjust the quality of analysis and selection; â‘¡ from process piping considerations; â‘¢ from the load changes.
Select the flow characteristics of the diaphragm pump, you can determine the valve spool according to its flow characteristics of the shape and structure, but for such as diaphragm valves, butterfly valves, due to their structural characteristics, it is impossible to change the shape of the valve spool to achieve The required flow characteristics can be achieved by changing the feedback cam profile of the valve positioner fitted.
(D) diaphragm pump caliber choice
The selection and determination of diaphragm pump caliber is mainly based on the valve flow capacity Cv. In a variety of engineering design and selection of instruments, should be on the diaphragm Cv calculations, diaphragm pumps and provide design specifications. Calculated from the diaphragm pump Cv to determine the diameter of the valve, generally required by the following steps:
1, to determine the flow of calculation. The existing production capacity, equipment load and the condition of the medium determine the Qmax and Qmin of the flow rate.
2, before and after the valve to determine the pressure. According to the selected valve flow characteristics and system characteristics selected S (resistance coefficient), and then determine the calculation of pressure.
3, calculate Cv. According to the adjusted medium to choose the appropriate formula and chart Cmax and Cmin.
4, choose Cv. According to Cmax, choose Cmax and the closest level C in the selected product standard series.
5, diaphragm pump checking. The general requirements of the maximum flow when the calculation of the opening ≯ 90%, the minimum calculation of flow when the opening ≮ 10%.
6, the actual adjustable diaphragm pump checking. Generally require the actual adjustable ratio ≮10.
7, Seat diameter and nominal diameter of the determination. After verification, according to C to determine.
Operational Notes:
1) diaphragm pump open parking load operation
Diaphragm pump is driven by the variable frequency motor, if the open parking load is too large or too small, short run Juan brake ǘ washing 蟆 â’Š ã¦ è° è¯˜ through the Han Yi slightly on the order of mechanical parameters of Gan Guang 饔 apricot postscript? To avoid the above Occurrence of the situation, the mandatory provisions of the open parking load is controlled at about 30%, and set in the instrument to increase or decrease the load must be completed within a period of time, effectively from the craft done on the inverter maintenance.
2) diaphragm pump instrument air and oil pressure system operation
Diaphragm pump instrument air and oil pressure are interlocked with the main motor, the liquid injection of oil, oil drain valve for the air valve, to always maintain a certain air pressure, the minimum operating pressure of the two valves is not less than 0.4MPa , So the instrument air pressure is generally maintained at above 015MPa, stop the meter air even after stopping the pump, so as not to promote the liquid in the liquid chamber is not enough or excessive, the air supply valve is filtered, oil atomized.
Diaphragm pump in operation, the lubricating oil pressure should not be less than the pressure interlock value (0115MPa), and the oil outlet filter pressure can not be too large, lubricating oil flow within the mirror ball should be in the upper limit position, adjust the flow When the adjustment range can not be too large, so as to avoid the transient flow Ambassador too much pressure drop caused by interlocking jump.
Through the above process improvement and mastering the operation essentials, the diaphragm pump always has a stable process environment. After more than a year of operation, it can run in a long cycle and run safely and efficiently only once due to electrical reasons.
Diaphragm pump applications
Because of the above characteristics of pneumatic diaphragm pumps, diaphragm pumps in the world have been gradually invaded and occupied some of the other pump markets since their inception. Such as: paint, diaphragm pumps in the ceramic industry has occupied an absolute dominance, while in other industries, such as environmental protection, wastewater treatment, construction, sewage, fine chemicals is expanding its market share, and has other pumps irreplaceable Position. The advantages of pneumatic diaphragm pumps are:
1, due to the use of air as the power, so the flow rate with the back pressure (outlet resistance) changes and automatically adjust, suitable for medium and high viscosity fluid. Centrifugal pump operating point is set on the basis of water, if used for slightly higher viscosity fluid, you need to support reducer or inverter, the cost has greatly improved, for the same is true.
2, in a flammable and explosive environment with pneumatic pump reliable and low cost, such as fuel, gunpowder, explosives, because: First, the ground is not likely to spark; second, no heat during work, the machine is not Will overheat; thirdly, the fluid will not overheat because the diaphragm pump agitates the fluid to a minimum.
3, poor construction sites, such as construction sites, industrial and mining wastewater discharge, due to the impurities in the sewage and complex composition, easy to plug the pipeline, so the formation of the pump on the load is too high, the motor heat vulnerable. Pneumatic diaphragm pump through the particles and the flow rate can be adjusted, the pipeline automatically stop blocked to patency.
4, the other diaphragm pump is small and easy to move, do not need the foundation, accounting for the ground is extremely small, easy and economical installation. Can be used as mobile material transfer pump.
5, in a hazardous, corrosive material handling, diaphragm pump can be completely separated from the outside world.
6, or some experiments to ensure that no impurities pollute the raw materials.
7, can be used to transport the chemical properties of relatively unstable fluids, such as: photographic materials, flocculation and so on. This is because diaphragm pumps have low shear forces and little physical impact on the material.
Pneumatic diaphragm pump features:
1, compressed air as power.
2, is a volumetric displacement pump caused by the reciprocating deformation of the diaphragm, its working principle is similar to the piston pump, the diaphragm pump has the following characteristics due to the working principle of the diaphragm pump:
(1) the pump will not overheat: compressed air as a driving force, when the exhaust is an expansion heat absorption process, pneumatic pump temperature is reduced, no harmful gas emissions.
(2) does not produce sparks: pneumatic diaphragm pump without electricity as a motive force, grounding and then prevent the static spark
(3) can contain particles of liquid: Because of the volume of work and imports for the ball valve, so it is not easy to be blocked.
(4) Extremely low shear force on the material: how to suck in and how to spit out when working, so the material agitation is minimal, which is suitable for the transportation of unstable materials
(5) flow rate can be adjusted at the exit of the material to install a throttle to regulate the flow.
(6) Self-priming function.
(7) Can be air operated without danger.
(8) can dive work.
(9) The fluids that can be delivered are extremely wide, ranging from low viscosity to high viscosity, from corrosive to viscous.
(10) There is no complicated control system, no cables, fuses and so on.
(11) small size, light weight, easy to move.
(12) Maintenance is easy without lubrication, and will not pollute the work environment due to drip.
(13) The pump is always efficient and will not be reduced by wear.
(14) One hundred percent energy utilization, when shutting down the outlet, the pump stops automatically, the equipment is moving, worn, overloaded, feverish
(15) There is no dynamic seal, easy maintenance to avoid leakage. No dead spots at work.
Electric diaphragm pump features:
1, without filling the water, self-priming capacity of more than 7 meters.
2, through the good performance, the diameter of 10 mm below the particles, mud, etc. can easily through.
3, as the diaphragm will be transported media and transmission machinery separate, so the media will not leak to the outside. And the pump itself without shaft seal, greatly extend the service life. According to different media, the diaphragm is divided into neoprene, fluorine rubber, nitrile rubber, etc., fully meet the requirements of different users.
4, small size and light weight: As a result of the planetary cycloidal transmission structure, so the pump to get a small size, as compared with the same type of pump, the volume and weight are down about half.
5, the pump medium flow through the part, according to user requirements, is divided into cast iron, stainless steel, rubber lining, the motor is divided into ordinary type, explosion-proof, speed regulation, the pump is being used in the following occasions.
Diaphragm pump troubleshooting work
Diaphragm Pump Troubleshooting Guide This information can be used as a guide to help you develop your service when one or more of the following conditions apply.
The following are some of the irregularities described in this guide: A) Fast cycle / low flow B) No cycle / slow cycle / irregular cycle C) Leakage D) Noise E) Component breakage
In the pump application process, these situations are likely to encounter. Each case can be divided into a variety of possible reasons. This guide lists the cause of the malfunction and gives the correct corrective measures. The meaning of all the specific terms in the guide is listed later.
Air Valve - A brass or stainless steel valve housing is bolted to the center of the pump by four bolts.
Piston - Aluminum cylinder enclosed in air valve to control air flow.
Cavitation - The amount of pump discharge is below the rated amount due to the reduced or lack of fluid supplied to the pump inlet. In fact, the liquid chamber is filled with fluid before it is drained.
Static Displacement Head - Vertical distance (in feet) from pump centerline to free transfer point Inlet Pressure - Inlet is measured in points, including the specific gravity and flow rate of the fluid.
Proportion - The ratio of flow to water weight at 68F. The specific gravity of 68F water is 1.0
Static Suction Lift - The vertical distance between the supply level and the center line of the pump. The pump should be above the liquid level.
Vapor pressure - All liquid creates pressure on the steam on its free surface. In any pump operating system, the operating pressure can not be lower than the vapor pressure, otherwise the steam formed will partially or completely cut off the fluid into the pump. Viscosity - Due to the internal friction of the fluid, the viscosity causes the fluid to flow resistance.
Water Hammer Effect - A higher inlet creates a static head that acts on the pump to create internal pressure.
Diaphragm pump selection and classification
Abstract: This paper mainly elaborates the composition and classification of diaphragm pumps as well as the selection principle and method of adjusting type, actuator, mode of action, flow characteristics and so on, and analyzes the methods and principles of regulating Yan selection.
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