Guide to the Operation and Maintenance of Manual Valves

Manual valves are the most commonly used fluid control devices in industrial pipeline systems, including ball valves, gate valves, globe valves, butterfly valves, plug valves, and more. These valves are widely used in various working conditions due to their simple structure, ease of use, and low cost. To ensure the safe and stable operation of valves and to extend their service life, proper operation and maintenance are crucial. This article will provide a comprehensive explanation of manual valves from four aspects: operating standards, common issues, special working condition requirements, and maintenance suggestions.

Operating Standards for Manual Valves

The correct operation of manual valves is key to ensuring their performance and service life. Here are the standards to follow when operating manual valves.

1. Use the Appropriate Torque

The handwheel or handle of manual valves is designed for operation by ordinary human force, taking into account the strength of the sealing surface and the torque required for closure.
Prohibit the use of extended levers: Using long levers or wrenches may cause the handle or handwheel to break, or excessive torque may damage the sealing surface.
Apply force smoothly, avoiding impact: When opening or closing the valve, maintain smooth operation to avoid additional damage caused by impact.

2. Correct Operation for Full Open and Full Closed Positions

After fully opening, reverse slightly: After a valve is fully opened, the handwheel should be reversed by about 1/4 turn to tighten the threads and prevent loosening that could damage the equipment. Record the open and closed positions of stem valves: The position of the stem should be recorded when the stem valve is fully open or closed to avoid hitting the dead point when fully open and to facilitate checking whether the fully closed state is normal.

3. Requirements for High-Pressure and Steam Valves

High-pressure valves can be opened and closed with impact: High-pressure valves designed to withstand impact can be operated more quickly when opening and closing, but it is necessary to ensure that the durability of the sealing surface meets the working condition requirements.
Pre-treatment of steam valves: Preheat the valve before opening and remove condensate from the pipeline. The start-up operation should be carried out slowly to avoid damage to the pipeline and equipment from water hammer.

Common Problems and Solutions

During the use of manual valves, various issues may arise. Here are common problems and their solutions.

1. Cleaning the Sealing Surface

When a pipeline is put into use for the first time or after long-term operation, the sealing surface of the valve may have debris attached, affecting the sealing effect.

Cleaning method: Slightly open the valve to use the high-speed flow of the medium to flush away debris. Close and reopen the valve several times until it is completely clean. Especially for valves that are often open, the sealing surface should also be cleaned before closing to ensure reliable sealing when closed.

2. Damage to the Handwheel or Handle

When the handwheel or handle is damaged, it should be replaced with the appropriate parts immediately. The use of adjustable wrenches is prohibited. Adjustable wrenches may cause valve stem damage or failure to open and close properly, which can lead to production accidents.

3. Sealing Surface Gap Caused by Cooling

After some media cool down, the valve components may contract and form gaps.
Solution: After closing the valve, tighten it again within an appropriate time to ensure there are no gaps in the sealing surface and to prevent high-speed fluids from eroding the sealing surface through the gaps.

4. Causes and Handling of Difficult Operation

If the operation of opening and closing is difficult, the possible causes include:

Over-tightened packing: The packing can be loosened appropriately.
Bent or skewed valve stem: Professional repair is required.
Thermal expansion issues: When the closing part swells due to heat and makes operation difficult, the valve cover threads can be loosened by half to one turn to release stress before attempting operation.

Precautions for Valves in Special Working Conditions

In some special working conditions, the operation of manual valves requires special attention to ensure their safety and reliability. Here are suggestions for different special working conditions.

1. Bellows Seal Globe Valves

Bellows seal globe valves usually adopt a stem design with a positioning block, which can avoid the dead point problem when fully open or fully closed. In addition, these valves have stable sealing performance and are suitable for occasions with high temperature, high pressure, or strong corrosive media.

2. High-Pressure Impact Valves

High-pressure impact valves have been designed with impact in mind, and their sealing surfaces and key components have high impact resistance. They can be opened and closed more quickly during operation, but it is still necessary to ensure smooth movement and not to rely too much on impact.

Maintenance and Care Suggestions

Regular maintenance and care of manual valves are important measures to ensure their long-term stable operation. Here are suggestions for the maintenance of manual valves.

1. Cleaning of New Pipelines Before First Use

For new pipelines, it is essential to first flush out any debris inside the pipe before gradually opening the valve to use the fluid to flush out impurities inside the pipeline and valve. The flushing process should be done by lightly opening the valve, avoiding fast opening and sudden closing to prevent debris from damaging the sealing surface.

2. Regular Inspection and Repair

Regularly check the operating condition of the handwheel, handle, and valve stem, and deal with any loosening or damage promptly. For valves that are operated frequently, it is recommended to lubricate the valve stem regularly to ensure smooth opening and closing.

3. Maintenance of Long-Open Valves

Valves that are long-open should have their sealing surfaces cleaned before closing. After closing, residual debris can be removed by opening and closing the valve several times to prevent damage to the sealing surface.

4. Special Maintenance for Valves with Cooling Media

For valves with media that cool down after operation, they should be closed again at an appropriate time to prevent the sealing surface from being eroded by the medium.

Conclusion

In summary, the correct use and regular maintenance of manual valves not only extend their service life but also ensure the safety and efficiency of the pipeline system. During operation, it is important to strictly follow the standards, especially controlling the force, cleaning the sealing surface, and pre-treatment requirements under specific working conditions. With scientific management and reasonable operation, manual valves can perform optimally in various complex working conditions, providing a stable guarantee for industrial production.