What Are Gate Valves?

Gate valves are linear motion valves that use a flat closure element (gate) which slides perpendicular to the flow direction to either fully open or completely shut off fluid flow. They are primarily designed for on/off service rather than flow regulation.

Primary Function

Gate valves provide a tight seal when fully closed and minimal flow restriction when fully open. They are ideal for applications where low pressure drop and straight-line flow are required.

Working Principle

Gate valves operate through:

• Vertical movement of a wedge-shaped gate
• Rising stem or non-rising stem design
• Manual operation via handwheel or automated actuation
• Parallel or wedge-shaped seating surfaces

Key Components

• Valve body
• Gate (wedge or parallel disc)
• Stem (rising or non-rising)
• Handwheel or actuator
• Seat rings
• Packing gland and flange
• Bonnet

Types of Gate Valves

Solid Wedge Gate Valves

Most common type, suitable for most fluids including turbulent flow

Flexible Wedge Gate Valves

Feature a cut-around perimeter to improve sealing and compensate for temperature changes

Split Wedge Gate Valves

Two-piece design that self-adjusts to seating surfaces

Parallel Slide Gate Valves

Use two parallel discs with a spreading mechanism

Knife Gate Valves

Thin gate designed for thick fluids and slurries

Stem Design Variations

Rising Stem

Stem rises above handwheel when valve opens, providing visual position indication

Non-Rising Stem

Stem rotates without vertical movement, suitable for limited space applications

Common Applications

• Water distribution systems
• Oil and gas pipelines
• Steam services
• Chemical processing
• Power generation plants
• Fire protection systems
• Irrigation systems

Materials of Construction

• Cast iron for water applications
• Bronze for general service
• Carbon steel for high-temperature services
• Stainless steel for corrosive environments
• Alloy materials for specialized applications

Advantages

• Low pressure drop when fully open
• Excellent shut-off capability
• Bi-directional flow
• Simple design and operation
• Suitable for high-pressure applications

Limitations

• Not suitable for throttling
• Slow operation compared to quarter-turn valves
• Prone to erosion of seating surfaces
• Requires large space for installation
• Subject to vibration in partially open position

Selection Considerations

• Pressure class rating
• Temperature requirements
• Fluid characteristics
• Flow direction needs
• Space limitations
• Operation frequency
• Leakage requirements

Installation Guidelines

• Install in horizontal pipelines with stem vertical
• Ensure proper alignment with piping
• Allow sufficient space for operation and maintenance
• Follow specified torque requirements
• Consider thermal expansion in high-temperature applications

Maintenance Requirements

• Regular exercise to prevent sticking
• Stem lubrication as needed
• Packing adjustment or replacement
• Seat and gate inspection
• Leak testing and repair