Chemicals such as hydrochloric acid, sodium hydroxide, sodium hypochlorite, and sulfuric acid are used in many industries. In the event of a pump failure, the interruption of these chemical additions can disrupt the production process.
When selecting a mechanical pump for the core of the production process for the measurement of corrosive chemicals, engineers need to find pumps that meet the following three requirements:
â—† A pump that can withstand chemical corrosion and is stable in operation.
â—† Pumps that can be accurately metered to achieve maximum yield with minimal chemicals.
â—† Pumps that can be quickly and easily maintained and operated.
Process engineers are increasingly using peristaltic pumps to solve these three problems while reducing life cycle costs and increasing process efficiency.
Peristaltic pump working principle
The peristaltic pump is said to be one of the fastest growing technologies in the world, replacing other positive displacement pumps that are complex and frequently maintained in chemical metering. Acids, bases, and solvents erode the valves, seals, rotors, and moving parts of diaphragm pumps and single-screw pumps (the two most commonly used positive displacement pumps), causing pump damage, downtime, and increased life cycle costs.
Conversely, the working principle of a peristaltic pump can reduce these costs. The peristaltic pump has no valves and does not leak. There are no mechanical parts on the product line. The fluid only contacts the inner wall of the hose or the pipe, and the cost of the pipe is very low, and it is less maintenance and very durable.
In physiology, "peristalsis" refers to the alternating contraction and relaxation of muscles around tubular organs (such as the larynx and esophagus), thereby propelling the flow of internal fluids. The principle of operation of a peristaltic pump is very simple. A length of hose or tube is placed along the fixed pump casing and compressed from the outside by a roller or a bump (hose pump) (see Figure 4). As the roller or tab moves along the outside of the tube, the fluid is pushed toward the outlet; when the hose or tube behind the tab returns to its original shape, more fluid is drawn into the pump.
The heart of the pump is a hose or tube that can be made of different elastomeric materials, has a long service life, and is resistant to corrosion by concentrated acids, concentrated alkalis and solvents. The simplicity of the “wet end†of a peristaltic pump is the opposite of the complexity of a diaphragm pump. The pump casing, diaphragm, ball valve and sealing material of the diaphragm pump must be carefully selected to prevent the pump from malfunctioning under corrosive liquids.
Precise measurement
Positive displacement pumps are often used to meter or add a precise amount of chemicals. For peristaltic pumps, the flow rate is proportional to the rotational speed, and the hose or tube that has been completely sealed allows the pump to continuously perform positive displacement movements to prevent flow reduction caused by backflow. The peristaltic pump has no check valve, which eliminates the source of inaccurate metering, so there is no steam lock.
There are valves in the diaphragm pump, which may cause jamming or blockage (because of corrosion of the ball or seat), causing flow changes, which may damage the consistency of the final product or cause differences in product quality. In addition, chemicals capable of generating gases (such as sodium hypochlorite) may cause the diaphragm pump to lock and completely block the passage of fluid.
The peristaltic pump's adjustment ratio (maximum flow/minimum flow) or flow range is unmatched by other pumps. By simply controlling the rotor speed, the adjustment ratio of the high quality peristaltic pump can reach 2000:1. With different sizes of tubes, the adjustment ratio can be expanded to 1 million. Diaphragm pumps typically only achieve a 20:1 speed ratio under the control of a conventional controller. Although the stroke length of the diaphragm can be adjusted to increase the adjustment ratio, the metering accuracy is greatly reduced in the case of a short stroke. When a large flow range is required, two or three or more diaphragm pumps are usually used to control the flow, which can be solved by a peristaltic pump.
Life cycle cost
The initial investment cost of a peristaltic pump may be slightly higher than other positive displacement pumps, but the associated auxiliary equipment, installation, maintenance, and spare parts costs of other pumps may be very large, and the peristaltic pump is superior in terms of life cycle cost.
In a peristaltic pump, the tube or hose is the only wet part that requires little maintenance, no expensive seals to replace, no check valves that can clog, and no rotor or stator that can wear out. Of course, hoses or tubes need to be replaced regularly. Even so, industrial grade peristaltic pumps can achieve thousands of hours of reliable operation before hose fatigue failure. The process of replacing the hose takes less than an hour, and in some cases it takes only a few minutes. In addition, the hose can be quickly and safely replaced without any special tools.
This is much less than the 4-6 hour repair time required for a diaphragm or single screw pump, not including the extra time they take when moving, transferring and reinstalling. The cost of the hose is very low compared to the repair of a diaphragm pump or a single screw pump, and the latter's wet end replacement components (such as ball valves, rotors and stators) can account for 75% of the initial purchase cost of the pump.
The peristaltic pump does not require the installation of ancillary equipment. The diaphragm pump requires a back pressure valve and an exhaust valve to ensure proper operation of the internal check valve. Single screw pumps typically require dual mechanical seals, flushing systems, dry run protection and built-in check valves. With a peristaltic pump, the cost of these auxiliary components can be eliminated.
The need for process control and chemical compatibility often make the cost of a peristaltic pump lower than other positive displacement pumps. For example, when a single screw pump can only use expensive metals to meet corrosion resistance requirements, its price may increase exponentially.
Many positive displacement pumps require an additional purchase of a separate control board or frequency converter for variable flow metering. If you need to increase the flow range, the cost and complexity will increase. However, the peristaltic pump itself has a high flow range, closed loop speed control capability and a scalable I/O interface that can be connected to DCS, SCADA and PROFIBUS systems.
The peristaltic pump has a self-priming function (up to approximately 10 meters) which increases the safety of the operator as it reduces the handling of hazardous chemicals. The pump also has a dry running function, making it ideal for tank emptying or other unmanned applications. The peristaltic pump can also be reversed and can be used to drain the pipe or to remove the blockage by simply changing the direction of rotation.
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