Valve stems may appear to be simple linear shafts, but they play one of the most critical roles in a valve’s functionality and safety. As the central component connecting the actuator or handwheel to the valve’s closure element (disc, plug, or ball), the valve stem enables precise control of fluid flow across pipelines and equipment.

For industries such as marine, oil & gas, chemical processing, power generation, and water treatment, a valve stem failure can lead to catastrophic leakage, production downtime, or environmental hazards. For this reason, understanding the types of valve stems, their mechanisms, materials, and application fit is essential for engineers, maintainers, and procurement teams.

As a trusted Singapore-based marine and industrial valve stockist, Aik Soon Hardware provides deep technical expertise and quality-assured components—including stems and full valve assemblies—to ensure safe and reliable operations across critical industries.

This comprehensive article explores everything you need to know about valve stems.

1. What Is a Valve Stem?

A valve stem is a precision-machined shaft that transfers motion from a handwheel, actuator, or gearbox to the valve disc, ball, plug, or gate.

Key Functions of a Valve Stem

• Transmits torque and linear motion

• Ensures accurate open/close positioning

• Maintains sealing between internal and external environments

• Supports packing integrity to prevent leakage

• Withstands pressure, temperature, and corrosive media

2. Major Types of Valve Stems

2.1 Rising Stem (OS&Y)

OS&Y = Outside Screw & Yoke.

Description

In rising stem valves, the stem moves up and down as the valve opens or closes. The threads are on the outside of the valve body.

Mechanism

• Handwheel rotates the stem.

• The stem physically rises out of the valve when opening.

• Provides visual confirmation of valve position.

Common Applications

• Gate valves

• Globe valves

• High-pressure and high-temperature systems

• Fire protection systems

• Marine engine rooms and pump rooms

Advantages

• Clear open/close position indication

• Reduced internal wear

• Better suited to harsh media

Disadvantages

• Requires vertical clearance

• Exposed threads may require lubrication or protection

2.2 Non-Rising Stem (NRS)

Description

In non-rising stem valves, the stem rotates but does not move vertically.

Mechanism

• The stem threads are inside the valve body.

• The disc travels up/down over the stem.

Applications

• Limited-space installations

• Underground pipelines

• Ballast systems on ships

• Urban water distribution

Advantages

• Compact design

• Protected stem threads

Disadvantages

• Position is not visibly obvious

• Internal thread wear may occur over time

2.3 Rotating Stem

Description

A rotating stem turns without rising. Used in ball and plug valves.

Mechanism

• Torque is transmitted to a rotational closure element (ball/plug).

Applications

• Marine fuel lines

• Chemical plants

• Tanker cargo handling systems

• Oil refinery manifolds

Advantages

• Fast operation

• Minimal linear movement eliminates packing wear

2.4 Non-Rotating Stem

Description

The stem moves linearly but does not rotate during actuation.

Mechanism

• Used in valves with linear actuators

• Rotation is prevented to reduce packing friction

Applications

• Globe control valves

• Cryogenic valves

• Diaphragm valves

Advantages

• Extends seal life

• Excellent for throttling operations

2.5 Stub Stem (Short Stem)

Description

A compact stem designed for small valves or limited installation space.

Applications

• Sampling valves

• Utility lines

• Auxiliary systems on vessels

2.6 Extended Bonnet / Extended Stem

Description

A longer-than-normal stem used to protect packing from extreme temperatures.

Applications

• Cryogenic LNG handling

• Steam systems

• Chemical plants with high heat zones

3. Valve Stem Materials and Their Use Cases

Coatings Sometimes Applied to Valve Stems

• Hard chrome plating

• PTFE coating

• Nitrided surfaces

These coatings enhance wear resistance and reduce friction.

4. Selection Criteria for Choosing the Right Valve Stem

4.1 Operating Pressure & Temperature

High-pressure steam or refinery systems require high-strength materials like alloy steel or stainless steel.

4.2 Fluid Type

• Seawater → Duplex, SS316, Monel

• Acids → Hastelloy

• Hydrocarbons → Carbon steel, stainless steel

4.3 Valve Type

Ball valves = rotating stems
Gate/globe valves = rising or non-rising stems

4.4 Installation Space

Use NRS stems for underground or tight compartments.

4.5 Stem Sealing Requirements

Consider packing requirements such as:

• Graphite

• PTFE

• Elastomers
  depending on temperature and chemical compatibility.

4.6 Maintenance Frequency

Rising stems offer easier inspection and lubrication access.

4.7 Environmental Conditions

Marine salt exposure requires corrosion-resistant alloys.

5. Where Valve Stem Types Are Found Across Industries

Marine Vessels

• Ballast systems (NRS)

• Engine cooling systems (Extended stems)

• Fuel lines (rotating stems)

Tankers

• Cargo pump rooms (rising stems)

• Vapour recovery lines (rotating stems)

Oil Refineries

• High-temp cracking units (alloy steel stems)

• High-pressure gate valves (OS&Y rising stems)

Chemical Plants

• Acid dosing lines (Hastelloy stems)

• High-purity lines (SS316 stems)

Water Treatment Plants

• Sludge lines (NRS)

• Chlorination systems (PVC & stainless stems)

6. Maintenance Considerations for Valve Stems

• Regular lubrication of threads (for rising stems)

• Inspection of packing and seals

• Check for pitting or galling

• Monitor stem travel smoothness

• Evaluate torque consistency during operation

Conclusion

Valve stems may be small components, but they are critical to mechanical integrity and valve reliability. Understanding the differences between rising, non-rising, rotating, non-rotating, extended, and short stems allows operators across marine, industrial, chemical, and water treatment sectors to select components that enhance safety, durability, and performance.

With decades of experience supporting Singapore’s marine and industrial sectors, Aik Soon Hardware provides trusted expertise and high-quality valve components—including various stem types and materials tailored to your operational needs.

For technical support or quotations, our team is ready to assist.