Selection of metering pumps and common issues

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This post was last edited by 2887848 on 2011-8-22 at 11:52. What information is needed to choose a metering pump appropriately? 1. The flow rate of the liquid to be measured. 2. The main properties of the liquid to be measured, such as chemical corrosivity, viscosity, and specific gravity. 3. The back pressure of the system. 4. Appropriate suction lift height. 5. Other options required, such as analog control, pulse control, flow monitoring, and timers. What are the main advantages of electromagnetic-driven metering pumps? An electromagnetic-driven metering pump has only one moving part—the armature shaft. Generally speaking, the fewer moving parts there are, the more reliable the metering pump will be in operation. Metering pumps are highly suitable for applications with low flow rates and low pressures, and they provide good compensation in the event of fluctuations in supply voltage. Compared to metering pumps with a fixed frequency and varying stroke length, what are the advantages of metering pumps with a fixed stroke length and varying frequency? Through calibration, the amount delivered per stroke is known. Therefore, the total dosage can be calculated (Dosage = Dosage per stroke * Frequency). The total dosage is linearly related to the frequency (50% frequency = 50% dosage). Through external pulse or analog control, the dosage can be adjusted from minimum to maximum within one second. Additionally, its cost for adjusting the stroke length is much lower than that of motor-driven systems. How to use the performance curve diagram of a metering pump? 1. Locate the performance curve diagram corresponding to the metering pump being used. 2. Indicate the current back pressure in the chart below. 3. Determine the correction factor by taking the backpressure value in bars, extending it upward along the curve, and reading the correction factor value vertically to the left at the intersection point. 4. Divide the required dosage value by the correction factor to obtain a value in ml/min or L/h. 5. Place the calculation result in the middle of the dosage scale. 6. When this value is placed on the dosage scale, a ruler can be used to determine the stroke length setting and the stroke frequency setting. Applications: What are the important considerations when operating a dosing system? When running a dosing system, the following aspects should be given special attention: A. Pressure at the injection point B. Stroke frequency C. Suction height D. Altitude E. Corrosivity of the chemicals. What methods can be used to improve the repeatability of dosing by a metering pump when its outlet is at atmospheric pressure? Installing a valve spring on the discharge valve of the metering pump can help improve repeatability, but the most effective solution is to install a backpressure valve at the end of the pipeline. How to adjust the back pressure valve? 1. Never exceed the maximum operating pressure of the metering pump. 2. When there is pressure at the suction side of the metering pump, the pressure at the discharge side of the pump must be at least 1 bar higher than the pressure at the suction side. How to determine the appropriate volume for a pulse damper? By multiplying the metering capacity per stroke of the metering pump (in ml) by 26, it is possible to determine the minimum volume (in ml) of the pulse damper required to reduce pulsation by 90%. How to set the pressure of the safety valve? The pressure of the safety valve can be adjusted within the rated operating pressure range of the metering pump, and it must not exceed the maximum operating pressure of the metering pump. The safety valve is designed to prevent the metering pump from operating under excessive pressure. For example, if the maximum operating pressure of the metering pump is 3 bar, the pressure of the safety valve should be set at 3 bar, or even lower, to ensure the proper operation of the metering pump. Operating under overpressure is one of the main causes of damage to metering pumps. What is the maximum positive pressure allowed when using ProMinent® metering pumps? The Alpha metering pump can operate properly when the positive pressure is more than 1 bar less than the pump’s discharge pressure. If the pressure exceeds the allowable value, the metering pump cannot function properly. If the liquid being pumped is not water, how is the suction lift calculated? Divide the rated suction lift of the metering pump by the specific gravity of the liquid being metered. Under what circumstances is self-priming liquid suction used? Self-priming liquid suction can be applied in the following situations: 1. The liquid to be measured is prone to volatilization ； 2. Measured liquids have a high specific gravity ； 3. When a higher stroke frequency is required ； 4. When a metering pump is operating at high altitudes ； 5. When used in the field, larger storage tanks are required, and self-priming by a metering pump is not feasible. Could you provide some advice on selecting the pump head for metering pumps? What problems typically arise regarding the corrosion of pump heads/seals by chemicals, and how can such issues be avoided? When it comes to metering pump heads, common problems arise when metering acids, chlorine, fluorides, and hydrogen peroxide. Due to differences in drug concentration and operating temperature, it is difficult to determine the specific material of the pump head. When measuring fluorides, we recommend using a PVC pump head with Viton® sealing. For most chlorination applications, it is best to use an NP (acrylic) pump head with EPDM sealing. For metering hydrogen peroxide mixtures, only PTFE-sealed PTFE pump heads or stainless steel pump heads can be used. For handling concentrated hydrochloric acid, acrylic pump heads with Viton® seals are typically used. For concentrated sulfuric acid, a PTFE-sealed PTFE pump head can be chosen for metering. Manufacturers of chemical agents will provide relevant recommendations, or one can refer to the ProMinent® chemical compatibility chart to determine the compatibility between the chemical agent and the materials in contact with it. What factors must be considered when measuring liquids with a pump head? The main factors to consider are the viscosity, specific gravity, vapor pressure, and temperature of the liquid. Attachments/Options: How can I find out what other options are available for each metering pump? For each metering pump and its identification code, detailed information is provided in the ProMinent® product catalog. By querying the identification code, corresponding options can be selected for a specific metering pump. What are the basic components of an attachment kit? The kit includes a foot valve, an injection valve, a 2-meter suction tube, and a 5-meter discharge pipeline. What components are included in a complete metering pump head? A complete hydraulic end consists of the following components: the pump head, diaphragm, valve, backplate, and mounting bolts. What is the main purpose of a foot valve? The bottom valve itself has a certain weight that helps keep the suction pipeline straight and vertical with respect to the chemical tank. It also acts as a check valve, ensuring the forward flow of the chemical solution. The foot valve also helps improve the repeatability of the pump and its proper liquid suction. The bottom valve is equipped with a filter screen to prevent solid particles from being drawn into the liquid suction line; the ingestion of small solid particles can cause damage to the diaphragm of the metering pump. The foot valve also includes a connecting piece used to connect the suction tube. The bottom valve should be installed vertically, and kept at a certain distance from the bottom of the medication tank. It is highly necessary to select the bottom valve for most metering pumps that operate by self-priming. What is the main purpose of an injection valve? Injection valves are used to connect the drainage pipeline and the injection point. Injection valves cannot be used as isolation devices or as protection against siphoning. In applications where the requirements are not too high, the injection valve can generate a back pressure of 0.5 bar. What is the main purpose of rinsing equipment? The flushing equipment is used to clean the metering pump head and discharge lines. It is mainly used in cases where the chemicals used for measurement tend to solidify, or when the metering pump needs to remain idle frequently. What is a float switch and what is its main function? A float switch is a very important device for controlling the liquid level in the medication storage tank. When the liquid level drops, the float sinks and the internal contacts in the switch close. These contacts can be used to control the metering pumps – for example, to stop metering pump 1 and start metering pump 2 – or they can be used to activate an alarm/light to indicate that the medication tank is empty. Through the reverse movement of the float, a float switch can be used in collection tanks to indicate that the tank is full and simultaneously stop the metering pump. What is the difference between a single-stage float switch and a two-stage float switch? When the switch activates, a single-stage float switch stops the metering pump directly. For a two-stage float switch, activating the first stage can be used to give an alarm indication of low liquid level in the medication tank. When the second-stage switch is activated, the metering pump stops. What is a multi-functional valve? A multi-functional valve is a highly versatile product that can generate a constant back pressure to ensure repeatable metering accuracy. The device incorporates a check valve function that prevents chemicals from being drawn into the vacuum pipeline, thus avoiding the formation of a Venturi effect or negative pressure head in the water circuit. The device incorporates a pressure relief valve function, which can protect the metering pump, pipelines, and other system components from operating under excessive pressure in case the system pipelines become blocked. The multi-functional valve also incorporates a priming valve function, which can release pressure from the discharge pipeline to assist the metering pump in priming. The multi-functional valve allows the discharged liquid to flow back safely into the medication storage tank. What is the main function of a flow monitor? Flow monitoring makes use of proximity switches, which are activated whenever a flow pulse occurs. The metering pump compares the discharge stroke with the number of pulses detected by the flow meter. If the pump fails to detect the corresponding pulse signal after 8 consecutive strokes, or after the specified number of strokes, the metering pump stops and issues a fault indication. In cases such as an empty, blocked, or leaking suction line, a blocked discharge line, or a damaged diaphragm, the flow monitor can issue an alarm signal by failing to detect pulse signals. If the measured flow rate decreases by 20% or falls below the set value, the proportional flow monitor can detect it. What are the main uses of fault alarm relays and step relays? The alarm relay opens (NC) or closes (NO) when a fault occurs in the metering pump. When a metering pump fails, the synchronization relay closes; typically, the synchronization relay is connected to the metering pump so that it operates at the same frequency as the main metering pump. What is the main purpose of pulse dampers? Choosing an appropriately sized pulse damper can reduce pulsations by 90% or more, resulting in a flow that is nearly laminar. Pulse dampers reduce the acceleration of the measured medium and lower the head loss. What is the difference in function between a buffer and a pulse damper? Buffers can reduce pulsations in the pipeline, as well as decrease the acceleration of the medium and lower head losses. The liquid and gas inside the buffer are not separated. The interior of the buffer will eventually be filled with liquid, and it is necessary to drain this liquid. What is a diaphragm rupture monitor, and how does it work? There is a leak discharge hole on the backplate between the drive side and the pump head, and a conduit connects the leak discharge hole to a small cylindrical tube. If the diaphragm ruptures, the liquid is discharged into the small cylindrical tube through the leakage outlet. There is a float switch inside the small cylinder; as long as there is 10 ml of liquid in the cylinder, the float switch can be activated. The switch contacts can be set to normally open or normally closed. Regarding electrical aspects, what types of wires will we use in the control cables? 1. There are 5 wires in a general control cable: blue, black, brown, gray, and white. For analog signal control, tie the brown and black wires together and connect them to the negative signal terminal, while connecting the blue wire to the positive signal terminal. The white and gray wires were not used. Note: If the remote pause function is used, the brown wire and the black wire should be connected through an intermediate relay or switch. 2. For contact signal control, tie the brown and black wires together and connect them to one end of the signal, while connecting the white wire to the other end of the signal. (For contact signal control, connecting water meters is a typical application.) For general-purpose control cables, what are the functions of wires of different colors? Black – public terminal; Brown – remote on/off (+). The pump will operate only when black and brown are connected together. A control switch is required for the remote control function. White: Pulse control; Blue: Analog control (the analog control option must be selected); Gray: Auxiliary frequency control. How to connect a metering pump to a water meter? 1. Plug the universal control cable connector into the front slot of the metering pump. A. 2-core control cable: Connect the brown wire and the white wire to the terminals of the water meter. 2. 5-core control cable: Connect the white wire to one of the terminals, and tie the brown and black wires together to connect to the other terminal. Note: If the remote pause function is used, the brown wire and the black wire should be connected through an intermediate relay or switch. Can multiple metering pumps be connected to one water meter? We do not recommend connecting multiple metering pumps directly to a single water meter. The safest way to connect multiple metering pumps to a single water meter is to use the synchronous relay function. The metering pumps should be connected in series. Another common method for connecting multiple metering pumps is to use a ProMinent® 4-pole transmitter. How many metering pumps can be connected using a 4 - 20 mA control signal? The best way to answer this question is by considering the devices within the system as well. First, it is necessary to know the load impedance of the device that supplies a signal to the pump. Generally, the load impedance is 750Ω, or it may be even lower, within the range of 300Ω. The load impedance of our controller is 750Ω. When a 4-20mA signal is used, the impedance of the Gamma metering pump is 70Ω. Approximately 10 metering pumps can be connected in series to the system. The impedance of the wire (wire length and diameter) must be taken into account within the total impedance. Longer wires and smaller wire diameters can significantly increase impedance. Maintenance and troubleshooting: How to replace the diaphragm of a metering pump? 1. Remove the 4 screws that hold the pump head in place. The screw is located on the back of the metering pump. 2. After the pump head becomes loose, but before removing it, adjust the stroke length to 0% position. It ensures that the electromagnetic shaft has sufficient pressure to maintain a secure connection, thereby allowing the diaphragm to be removed. 3. Pull the hydraulic end outward to disengage the screw from the socket. Grab the liquid end and rotate counterclockwise. With a little resistance, the diaphragm can be unscrewed. 4. Once the diaphragm has been removed, check the safety diaphragm of the metering pump to ensure it is intact and free from any damage. Install the new diaphragm; rotate the backplate and diaphragm clockwise until they fit tightly. Adjust the backplate so that the liquid leakage outlet is located at the very bottom of the pump. 5. After the diaphragm has been installed and the leak drainage holes on the backplate are in a vertical position, install the pump head. Ensure that the suction valve is aligned with the liquid leakage outlet, and that the screws on the hydraulic side are aligned with the corresponding 4 holes. 6. Rotate to the 100% stroke length position. This allows the entire assembly to rotate so that the leak outlet on the backplate aligns with the lowest point of the pump. Adjust the hydraulic end and diaphragm to the appropriate positions during pump operation. 7. Once the hydraulic end along with the backplate are in the correct position, the 4 bolts are tightened diagonally until they are properly secured. Apply even pressure when completing this task. I received a spare parts kit, but I had trouble removing the old diaphragm. Could you provide some additional advice on how to remove the old diaphragm? Move the hydraulic end by loosening the 4 pump head screws. Set the rotation stroke length to 0% and grasp the hydraulic end, then slide it out of the screw hole; in this way, the screws do not come into contact with it, but they still hold the backplate and diaphragm in place. Then rotate this component counterclockwise; with a slight amount of resistance, the diaphragm will loosen from the electromagnetic shaft. If the diaphragm is not yet loose, apply some lubricant to the contact surface between the diaphragm and the electromagnetic shaft. After placing it for a few minutes, gently tap the diaphragm with a small plastic hammer. Then proceed again as described above. When measuring hydrogen peroxide using the self-priming method, cavitation occurs in the system. How to solve this problem? The metering pump is equipped with a self-venting pump head, enabling self-priming liquid suction. Keep the suction line as short as possible. Does the metering pump not measure the liquid medication after installation and operation? 1. Is an exhaust pipe installed and is the exhaust valve closed? During the priming stage of the metering pump, the discharge valve needs to be opened. Note: Not all metering pumps have a drain valve. 2. There may be a gas leak at the suction side of the metering pump. The suction side connector on the hydraulic end may be missing an O-ring or the suction valve connection may be loose. 3. The bottom valve of the metering pump may be blocked, preventing the measured medication from passing through. 4. The stroke length setting of the metering pump is inappropriate. 5. The measured chemical substances may crystallize at the hydraulic end, causing the check valve ball and seat to fail to function properly. I am using flow monitoring to measure a high-viscosity medium, and I received a flow error signal during the liquid introduction process. What can be done to resolve this issue? The pulse duration might not be long enough in terms of reaction time. Relative to the standard pulse width of 80 msec, the flow monitor pulse width extension can be activated to increase the pulse width to 300 msec. Activate the smart transfer switch, remove the cover fixing the circuit board, and take away the jumper X-1. This activates the extended function, allowing more time before a fault is indicated. How to prevent the stroke positioning motor from burning out? When adjusting the stroke position, make sure that the motor of the metering pump is always running. If the metering pump motor is not running, the stroke length adjustment rod has to resist the tension of the compression spring, which can lead to premature damage of the stroke positioning motor. Original address: http://www.prominent.com.cn/service.htm.