Valve Parts — Detailed Guide

This page provides a comprehensive overview of the main parts of industrial valves, their functions, materials, and inspection considerations. Understanding valve parts is essential for design, selection, maintenance, and audit compliance.

Table of Contents

1. Body
2. Bonnet
3. Trim (Disc, Seat, Stem)
4. Disc / Ball / Plug
5. Seat
6. Stem
7. Packing and Gland
8. Actuator / Handwheel
9. Gaskets and Fasteners
10. Yoke and Bearings
11. Accessories (Positioners, Gearboxes)
12. Materials of Construction
13. Inspection and Maintenance Notes

1. Body

The body is the main pressure-retaining shell of the valve. It houses the internal components and provides the flow passage.

• Function: Withstands system pressure and connects to piping via flanged, welded, or threaded ends.
• Materials: Cast iron, ductile iron, carbon steel, stainless steel, alloys.
• Inspection: Check casting quality, wall thickness, flange dimensions, and markings.

2. Bonnet

The bonnet is the cover for the valve body, providing access to internal parts like the stem and packing.

• Function: Houses stem and packing; provides leak-tight closure with the body.
• Types: Bolted, welded, pressure-seal, screwed.
• Inspection: Verify gasket surfaces, fasteners, and alignment with body.

3. Trim (Disc, Seat, Stem)

Trim refers to the internal parts of the valve that come in contact with the fluid and control flow.

• Disc/Ball/Plug: Closure element that regulates flow.
• Seat: Provides sealing surface for the disc/ball/plug.
• Stem: Connects actuator/handwheel to the closure element.

4. Disc / Ball / Plug

The closure element varies by valve type:

• Gate/Globe: Disc or wedge.
• Ball Valve: Spherical ball with bore.
• Plug Valve: Cylindrical or tapered plug.
• Butterfly Valve: Rotating disc.

Inspection: Check seating surface finish, alignment, and wear.

5. Seat

The seat provides the sealing interface between the closure element and the body.

• Types: Integral, renewable, soft-seated, metal-seated.
• Materials: Stainless steel, hard alloys, PTFE, elastomers.
• Inspection: Verify surface finish, hardness, and leakage test results.

6. Stem

The stem transmits motion from the actuator/handwheel to the closure element.

• Types: Rising stem, non-rising stem.
• Materials: Stainless steel, alloy steels with anti-galling treatment.
• Inspection: Check straightness, threads, surface finish, and hardness.

7. Packing and Gland

Packing prevents leakage along the stem. The gland compresses the packing to maintain a seal.

• Materials: Graphite, PTFE, braided fibers.
• Inspection: Verify correct packing rings, gland follower alignment, and leakage test.

8. Actuator / Handwheel

The actuator provides the force to operate the valve.

• Types: Manual (handwheel/lever), gear-operated, pneumatic, hydraulic, electric.
• Inspection: Check torque rating, mounting interface, and fail-safe position.

9. Gaskets and Fasteners

Gaskets provide sealing between body and bonnet. Fasteners hold components together.

• Materials: Spiral wound gaskets, graphite sheets, alloy bolts/nuts.
• Inspection: Verify torque, material certificates, and traceability.

10. Yoke and Bearings

The yoke supports the actuator and stem assembly. Bearings reduce friction during operation.

• Inspection: Check alignment, lubrication, and wear.

11. Accessories (Positioners, Gearboxes)

Accessories enhance valve operation and control.

• Positioners: Ensure accurate control valve positioning.
• Gearboxes: Reduce torque for manual operation.
• Limit switches/solenoids: Provide feedback and automation.

12. Materials of Construction

Material selection depends on fluid, pressure, temperature, and corrosion resistance.

• Metals: Carbon steel, stainless steel, duplex, nickel alloys.
• Non-metals: PTFE, elastomers, composites for seats and packing.

13. Inspection and Maintenance Notes

• Verify material certificates (EN 10204 3.1/3.2).
• Check dimensional tolerances and surface finishes.
• Witness hydrostatic and seat leakage tests.
• Confirm marking per MSS SP-25.
• Ensure proper lubrication, packing adjustment, and preservation before dispatch.

Note: Understanding valve parts and their functions is critical for correct selection, safe operation, and compliance with international standards.