Reasonable selection of metered dose pump parts: metering pump parts include metering pump head, metering pump check valve, check valve ball and sealing ball seat, metering pump diaphragm and metering pump hose joint.
The article mainly answers the questions which should be considered when selecting these parts. Since everyone pays attention to the selection requirements of metering pumps, some knowledge does include some of the main points; some ignore the importance of details to determine the success or failure of the selection.
1. Pump head of metered dose pump:
It is important to consider its material. Generally, the material of the pump head of the general metering pump is selected: PP, PVC, PVDF, PTFE and SS316.
①PP: It is easy to form and low in cost. It has acid and alkali resistance and certain high temperature resistance; but it is not suitable for organic solvents, strong acids and alkalis, and liquids containing hypochlorite, and its concentration is limited.
②PVC: It is easy to form, low cost, acid and alkali resistant. However, it is not suitable for the measurement of organic solvents, strong acids and bases and liquids above 40°C. It is also not suitable for the food and drinking water industries. Because of its toxicity, PVC bags are no longer used in food packaging bags.
③PVDF: It is suitable for most media. It is not resistant to high temperatures. Its price is in the middle to high position.
④PTFE: It is suitable for various media. It is resistant to strong acids and alkalis and high temperature. Its cost is relatively high.
⑤SS316: It is suitable for organic solvents and high temperature liquids, but it is not resistant to strong acids.
2. Diaphragm selection of metered dose pump
Commonly used diaphragms: composite diaphragms and pure PTFE diaphragms;
①Composite diaphragm: A layer of PTFE film is applied to the surface of the NBR rubber diaphragm inlaid with bolts to form a composite diaphragm. Some rubber diaphragms are embedded with steel wire mesh to increase its strength.
The cost of this diaphragm is low. Its elasticity can make the shape larger, and can generate a larger flow rate from a smaller plane size, so that the power of the electromagnet is reduced, and the production cost is reduced. However, when it is operated for a long time, the heat of the electromagnet will accumulate on its rubber surface through radiation and the conduction of its inlaid bolts. With deformation, the diaphragm will quickly deteriorate and break. Therefore, this type of diaphragm metering pump has a diaphragm breakage indicator hole.
②Pure PTFE diaphragm: It is integrally processed by modified PTFE, and the cost is relatively high. The deformation of the diaphragm is also relatively small, but this makes it never damaged.
3. Check valve of metered dose pump
Taking into account the internal structure; the check structure of the one-way valve: gravity check and elastic check.
① Gravity check: The valve ball returns to the sealing surface by its own weight to form a one-way check structure with good sealing effect and high-pressure resistance.
② Elastic non-return: refers to restoring the non-return state by the elasticity of the rubber itself. Its cost is low, and it is not resistant to high pressure. After long-term operation, the rubber will age, which will make the anti-return effect worse. In addition, the corrosion of acid and alkali will deform the structure and deteriorate the anti-return effect.
Most of the metered dose pumps made in Italy on the market are of elastic non-return structure. The metered dose pumps of our company's NEWDOSE, the metering pumps made in the United States, Germany and Japan all have a gravity check structure.
The ball and sealing ball seat of the one-way valve with the gravity check structure. There are two general ball materials: glass ball and ceramic ball.
① Glass ball: its cost is low, but some ions in acid and alkali will cause corrosion to it;
② Ceramic ball: its high cost, but suitable for all kinds of acid and alkali; general sealed ball seat: ordinary plastic ball seat, rubber ball seat and PTFE ball seat.
③ Ordinary plastic ball seat: its cost is low. Part of the medium will corrode it, and the non-return effect will become worse after long-term operation.
④ Rubber ball seat: its cost is low. Prolonged acid-base corrosion will change its shape, worsen the anti-return effect or block the flow channel. (The phenomenon that the normal metering pump can't produce liquid medicine after running for a period of time is usually found in the market is caused by it)
⑤ PTFE ball seat: its cost is high. It is suitable for all kinds of liquids and will never deform.
In summary, considering the comprehensive elements of the metered dose pump, two parameters should be paid attention to when selecting the type: flow and pressure. The pressure on the label is the highest normal working pressure of the metering pump, and the flow is the maximum flow under this pressure.
The metered dose pump is a one-way positive displacement pump. The metered dose pump can only pump out liquid when the pressure in the pump cavity is greater than the external pressure. When the external pressure is higher than the pressure on the label, the metered dose pump works in an overload state. If it is a solenoid diaphragm metering pump, its flow will drop a lot, and even no liquid can be pumped out; If it is a motor-driven metering pump, the motor may be overheated and damaged. All of the above are collected by us. Welcome to view NEWDOSE metering pump products.
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