Globe valves are compact, reliable-sealing valves widely used in steam, oil, water, and chemical pipelines.

During long-term operation or frequent cycling, internal components can experience wear, corrosion, or deformation, with valve stem bending being one of the more common issues.

This article provides a professional overview of the main failure points in globe valves, the causes of valve stem bending, and recommended handling methods, helping users determine the appropriate time for repair or replacement.

 

1. Function and Importance of the Valve Stem

 

The valve stem is the “transmission core” of a globe valve, transferring the force from the handwheel or actuator to the valve disc to enable opening and closing.

It not only performs the mechanical transmission but also provides sealing guidance and positioning.

Therefore, any bending or damage to the valve stem can result in difficult operation at best, or sealing failure and valve jamming at worst.

 

2. Common Causes of Valve Stem Bending

 

Excessive Operation or Forced Opening/Closing

If the operator continues to turn the handwheel before the valve is fully open or closed, uneven stress may occur on the stem, causing slight bending or twisting.

 

Misalignment During Installation

When the valve is not installed coaxially with the pipeline, lateral forces act on the stem during operation. Over time, this can lead to bending.

 

High-Temperature Deformation

In high-temperature steam or hot oil systems, improper material selection or poor heat dissipation can cause the stem to bend due to excessive thermal expansion.

 

Blockage by Debris or Deposits

If particles or scale are present inside the valve body, the valve disc may be obstructed during operation, exerting reverse forces on the stem that lead to deformation.

 

Material Fatigue or Corrosion

Prolonged service can cause metal fatigue or corrosion, reducing stem strength and resulting in slight bending or even breakage.

 

3. Can a Bent Valve Stem Still Be Used?

 

In general, it is not recommended to continue using a bent valve stem. The main reasons are:

 

Misalignment of the valve disc and seat: Bending prevents the disc from properly aligning with the seat, reducing sealing performance and potentially causing internal or external leakage.

 

Uneven friction with the packing: This accelerates packing wear and can lead to seal leakage.

 

Heavier operation: A bent stem increases the load on the actuator or handwheel, reducing operational flexibility.

 

Further component damage: Continued use may damage the guide bush and valve disc, potentially leading to complete valve failure.

 

For slight bending, some manufacturers may perform mechanical straightening or replace the stem. However, this must be verified by professional inspection to ensure the stem axis is restored and its strength uncompromised before returning the valve to service.

 

4. Other Common Damage Points in Globe Valves

 

Valve Disc and Seat

Prolonged exposure to high pressure or erosion can cause wear or pitting.

Minor damage can be repaired by welding or grinding, but severe wear requires replacement.

 

Packing Chamber

Aging packing or insufficient compression can lead to leakage.

Regular adjustment or replacement restores proper sealing.

 

Bonnet-to-Body Connection

Gasket aging or loose bolts may cause leaks.

Periodic retightening or gasket replacement is recommended.

 

Stem Threads

Lack of lubrication or severe wear increases operating torque.

Regular application of grease prolongs service life.

 

5. How to Prevent Stem Bending

 

Proper Installation: Ensure the valve is aligned with the pipeline to avoid uneven loads.

Standard Operation: Avoid excessive force or over-travel when opening or closing.

Regular Maintenance: Periodically lubricate the stem threads and inspect guiding components.

Material Selection: Use stainless steel or alloy steel stems in high-temperature or corrosive environments.

Operational Monitoring: If the valve becomes hard to operate, stop immediately and inspect before continuing.

 

6. Conclusion

 

Although the stem is just one component of a globe valve, its straightness and strength directly affect the valve’s sealing performance and service life.

Using a bent stem can lead to leakage and further damage.

Proper installation, careful operation, and routine maintenance are essential for extending valve longevity.

 

Q&A

 

Q1: Can a slightly bent stem be corrected?

Yes, but it must be inspected and realigned by a professional using specialized equipment. Ensure there are no cracks or stress concentrations before reuse.

 

Q2: Can a bent stem be repaired?

If the bend is minor and the metal has not fatigued, repair is possible. Severe deformation or compromised sealing requires stem replacement.

 

Q3: Will a bent stem cause leakage?

Yes. The valve disc may not fully contact the seat, leading to internal leakage. Uneven friction at the packing can also cause external leakage.

 

Q4: How can stem bending be prevented in the future?

Proper valve alignment, regular stem lubrication, and avoiding excessive torque during operation are effective ways to prevent deformation.