Gate valves are widely used in industrial piping systems and municipal water supply projects due to their reliable opening and closing, low flow resistance, and suitability for large-diameter applications. Their primary function is to serve as a shutoff device in pipelines, allowing fluid to flow through and through by raising and lowering the valve disc. However, during long-term operation or use, some users may encounter a problem where the gate valve fails to rise, meaning it cannot open properly. This situation not only impacts production and water supply stability but can also cause equipment damage or safety hazards. This article will analyze the common causes of gate valve failure and propose corresponding solutions based on the basic principles of gate valves.
A gate valve uses a disc as its opening and closing element. The disc moves perpendicular to the flow direction, opening or closing the pipeline. Based on their structural characteristics, gate valves can be divided into rising-stem gate valves and non-rising-stem gate valves.
Rising-stem gate valves: During operation, the valve stem moves the disc upward and downward, and the valve stem is visible from the outside.
Non-rising-stem gate valves: The valve stem does not raise or lower itself, but rather the valve disc is driven by a threaded drive.
The advantages of gate valves are unobstructed flow and low fluid resistance, making them suitable for applications requiring less frequent opening and closing. However, due to limitations in the valve structure and operating environment, problems such as the disc sticking or the stem becoming immobile may occur during operation, preventing the valve from rising properly.
When a gate valve fails to open smoothly, the problem often lies with the drive components, the disc itself, or the internal valve body environment. We can investigate these issues from the following aspects:
Overtightened or aged packing: The packing in the stem seal is compressed too tightly or hardened over time, generating significant friction and causing the valve stem to “lock.”
Internal jamming: Crystals, impurities, or foreign matter in the pipeline accumulate in the valve cavity, blocking the disc and seat, preventing it from disengaging.
Thread damage: The stem’s drive threads become damaged and “seized” due to wear, corrosion, or poor lubrication, causing the handwheel to spin idly and prevent the disc from lifting.
Bent or Corroded Valve Stem: The valve stem may bend due to external impact or become roughened due to corrosion from the media, causing it to become stuck during movement.
Thermal Expansion and Contraction: Rapid temperature fluctuations in the system cause different expansion or contraction coefficients of components such as the valve body and gate, eliminating clearances and causing the valve to “lock.”
Regularly apply grease to the valve stem threads to reduce wear and corrosion.
Periodically cycle gate valves that have been out of service for extended periods to maintain flexibility.
Install a filter before system commissioning or operation to reduce impurities from entering the valve body.
If stuck due to impurity blockage, disassemble and clean the valve seat and valve cavity after shutdown.
If the valve stem threads are severely worn, replace the valve stem or nut promptly.
Repair or replace any deformed valve disc or body.
Check if the packing is overtightened. Loosen or replace the packing if necessary to reduce frictional resistance on the valve stem.
For large-diameter or high-pressure valves, it’s advisable to equip them with a turbine drive, electric, or pneumatic actuator to prevent valve opening failure due to insufficient manpower.
In highly corrosive or high-temperature environments, corrosion-resistant alloys or specialized valves should be used to reduce the risk of sticking.
In summary, gate valve failure is a common fault caused by a variety of factors, often involving operation, maintenance, model selection, and operating conditions. From overtightened packing and internal sticking to thread damage and stem deformation, negligence at any stage can be the trigger for a valve failure. Therefore, resolving this issue requires not only accurate fault diagnosis and timely action, but also a systematic preventative approach. Only in this way can the long-term stable operation of the gate valve in the system be ensured.
Q: Can a gate valve be forced open if it won’t open?
A: No. Forcing the valve open can break the valve stem, dislodge the valve disc, damage the handwheel or piping, and even cause personal injury. The correct approach is to stop operation and try lubricating, tapping, or slightly turning the valve. If none work, release the pressure and then inspect or replace the valve.
Q: The handwheel turns, but the valve stem does not rise or rotates freely. What’s the cause?
A: This is usually caused by worn or stripped valve stem threads, preventing the handwheel from moving the valve stem. Stop operation immediately, inspect and confirm, then replace the valve stem or internal valve components. In serious cases, the entire valve may need to be replaced.
Q: Can an extension rod be used to force open a stuck gate valve?
A: Not recommended. Forced operation may break the valve stem, damage the valve disc, crack the handwheel, or damage the pipe due to stress. The correct approach is to lubricate, tap, or release the pressure before disassembling and repairing.
Q: Why is a gate valve more likely to become stuck if it’s been closed for a long time?
A: Prolonged inactivity can cause impurities to accumulate, corrode, and stick, and lubrication to fail. It should be opened and closed regularly (e.g., quarterly or semi-annually) to maintain fluidity.
