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Common problems and solutions for target flow switches
Published Time:
2022-12-23 15:25
Source:
Vane Flow Switch Although its price is low, due to defects in its design principles, it is susceptible to many external factors. Therefore, the service life of a general vane flow switch is relatively short, and the later maintenance costs are relatively high. This is also one of the biggest drawbacks of vane flow switches. For this reason, the editor has compiled some common problems and solutions for vane flow switches for your reference:
I. Vane Fatigue Damage
During normal use, the vane will be subjected to water flow pressure. If it is subjected to excessive flow velocity for a long time, leading to severe bending and deformation of the vane, fatigue damage is likely to occur. Therefore, the installation pipe diameter of the vane flow switch must meet the technical requirements provided by the manufacturer. If the pipe diameter is too small, causing the flow velocity to exceed the specified detection range of the vane flow switch, it will affect the service life of the vane, and when the water flow velocity exceeds 3m/s, its life will be significantly shortened. In such a situation, the water flow velocity can be reduced by increasing the size of the installation pipe to ensure the normal operation of the vane flow switch. Moreover, when using large-diameter long vanes, the individual use of long vanes often cannot meet rigidity requirements, which will lead to vane failure. Therefore, the vanes must be installed overlapped, and the longest vane should be installed at the very front.
Backflow impact of cooling water when the pump stops is also one of the causes of fatigue damage to the vane. At this point, a check valve can be installed downstream of the vane water flow switch, which can ensure unidirectional water flow and avoid generating significant water resistance during operation.
II. Flow Switch Not Actuating
Usually, the reason a flow switch does not actuate and fails to start the equipment is that the impulse received by the vane is too small, and its displacement is insufficient to close the normally closed contact of the switch, especially in situations with large pipe diameters and low flow rates. Increasing the vane area can be used for flow control; this problem often arises because the pipe diameter is large while the vane is relatively small. If it is a unidirectional vane flow switch, care must be taken during installation to ensure its direction is consistent with the water flow. If the vane cannot return, the reason might be that it is too wide or too long and gets stuck. When the installation gap is insufficient, it might work normally at first, but with long-term use, rust or scaling on the inner surface of the pipe can narrow the passage, causing the vane to get stuck inside the pipe and fail to actuate effectively. Therefore, during installation, there must be a distance of no less than 5 mm between the edge of the vane and the inner wall of the pipe. To prevent adverse consequences caused by dirt in the water leading to switch malfunction, in addition to necessary water treatment, a water filter can be installed upstream of the vane flow switch, or directly
select a product with a filtering device.
III. Inaccurate Flow Detection
As a sensing element in contact with fluid, the vane reflects flow by detecting the water flow velocity. Its installation method and position directly affect the flow protection value of the vane water flow switch.
1. The vane flow switch should be installed on a horizontal pipe, with a straight guiding section upstream of 10 times the pipe diameter and a straight pipe section downstream of 5 times the pipe diameter. If installed in a vertical pipe, the vane's own gravity can cause incorrect switch actuation. If installed near local resistance components, due to sudden changes in water flow velocity and direction, the water flow passing through the vane will be uneven, affecting the accuracy of flow detection.
2. During installation, ensure the vane plane is perpendicular to the direction of water flow. Vane water flow switches are usually fixed by threaded connections. It is common for the vane not to be perpendicular to the incoming flow direction after being screwed into the interface, which reduces the impact force of the water flow on the vane and prevents accurate flow detection. Marking the position at the interface before installing the vane can avoid this problem.
3. When used in air compressors, the cooling water system may sometimes contain air. When air bubbles pass through the vane, the impulse weakens, and the instantaneous reset of the vane sends incorrect flow information to the air compressor, leading to an alarm and shutdown of the air compressor. However, a very small amount of air mixed in does not affect the cooling water flow. To prevent such detection errors, the vane flow switch should be used in conjunction with a time delay relay to delay the execution of the air compressor's water cut-off protection.
The above are Vane Flow Switch common problems and solutions. To effectively avoid the above-mentioned issues, please read the installation guide provided by the manufacturer carefully. Alternatively, you can choose to use a thermal conductivity flow switch with no moving parts, which can reduce long-term maintenance costs.
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