Fisher Fisher - Seven routine maintenance tasks for control valves

Routine maintenance is a planned overhaul before a control valve fails, which can be understood as preventive maintenance and usually includes the following tasks.

1. Stress relief

Pipelines will produce various stresses due to improper combination or installation, such as thermal stress caused by high-temperature medium, stress caused by unbalanced tightening force during installation, stress caused by certain collisions caused by man-made collisions to the regulating valve and its pipeline, etc. These stresses act on the control valve and its pipeline, which can easily affect the performance of the control valve, and in serious cases, it will affect the control system itself, resulting in the deformation of the valve stem and guide parts and the failure to align with the center of the valve seat; For the control valve of the split valve body, it may cause the disengagement of the valve body flange; Stress can also cause leaks in the valve seat, etc. Therefore, it is important to ensure that stress is avoided or relieved at all times and that the stress is directed away from the control valve.

2. Inspection of safe operation

The control valve and related accessories used in explosive hazardous places should be checked for their safe operation, for example, whether the sealing cover is tightened, the operation of the safety barrier, the power supply, etc., to ensure that the control valve and related accessories can operate safely.

3. Check the support

The best position to install the control valve is to make the travel direction of the stem and the actuator above the valve body in a vertical plane. If the control valve must be installed in a position where the valve stem moves horizontally, or when the valve stem moves at a certain angle to the horizontal plane, the actuator should be supported so that the various parts of the control valve are in a natural state. If no support is added or the support is not properly added, it may cause the misalignment of the stem and seat of the control valve, which can easily lead to faults such as differential change or packing leakage. Even if the control valve has fixed and supported measures, it must be inspected regularly, usually once every 2-3 months.

4. Remove rust and dirt

It is necessary to frequently check whether there is rust, welding slag, dirt, etc. in the connecting pipe of the control valve, and remove it in time after it is found. If foreign matter tends to accumulate in the control valve and pipes, consider installing a simple filtration device on the upstream side of the control valve. In the case of hard debris that is easy to penetrate into the process medium, it is necessary to install a first-class filtration device. When the control valve is closed, a small piece of rust or welding slag is enough to destroy the well-ground seat sealing surface, and these dirt can also cause wear and tear on the spool and seat of the control valve, affecting its normal operation.

5. Regular maintenance and refueling

Fillers and oilers need to be readjusted after a short period of use. In dusty occasions, the stuffing box and guide parts should be protected with plastic sleeves or rubber sleeves around the valve stem, and special protective measures should be used for the occasions where corrosive gas or liquid droplets exist, and the regulating valve should be wrapped in an anti-corrosion bag, but care should be taken not to affect its operation. In the case of fire resistance requirements, special refractory coatings, fireproof bags and other methods can be used, and the materials of fireproof bags contain multiple layers of ceramic fiber or glass fiber.

6. Transportation and storage

After the control valve is assembled and painted and the actuator, hand wheel, positioner and other accessories are installed as required, in order to prevent foreign substances from entering the control valve, all the air interfaces connecting the control valve should be blocked, and the connecting flange should be installed with a protective cover, and attention should be paid to the status of each connection part, such as the valve positioner inlet pipe and the actuator interface. Any protruding accessories that are vulnerable to damage, such as pressure gauges for oil injectors and potentiometers, should be removed from the fittings, packed separately from the control valve and shipped together. The control valve should be fixed with a special bracket to prevent loosening, and the overall vertical or horizontal position should be ensured. If it is transported over long distances, it is better to use a strong wooden box for shipment.

When storing the control valve, do not support the control valve on sensitive parts, such as valve positioners, valve stems, etc. The environmental conditions for transportation and storage should meet the requirements of the product manual. It is good not to carry out other operations in the storage area, and when it is unavoidable, you must be careful not to touch the control valve. The place should also avoid being affected by bad conditions such as sand, dust, rain, etc., and if there is no suitable place, the control valve must be packed in a moisture-proof bag or placed in a similar container before storage.

7. Check the air source and power supply regularly

The air supply is one of the key energy sources to drive the control valve. Although the membrane chamber of the pneumatic control valve does not consume air, if the air source system contains impurities such as water and oil, it will cause the valve positioner, relay and other accessories to block and malfunction. Therefore, the air source and power supply must be checked regularly to ensure that the air source is clean and dry, and the power supply is reliable.

Fisher Fisher - Seven routine maintenance tasks for control valves

Fisher Fisher - Seven routine maintenance tasks for control valves

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