Piping Engineering Essentials: Types of Valves and Their Functions
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Piping Engineering Essentials: Types of Valves and Their Functions
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Introduction to Valves
Overview of Valves
1. What is a Valve?
A valve is a mechanical device that regulates, directs, or controls the flow of a fluid (gases, liquids, fluidized solids) by opening, closing, or partially obstructing various passageways.
2. Functions of a Valve
Stopping and starting fluid flow
Varying (throttling) the amount of fluid flow
Controlling the direction of fluid flow
Regulating downstream system or process pressure
Relieving component or piping overpressure
3. Types of Valves
(Detailed listing covered under classification section below)
4. Cost of Valves in Piping Systems
Valves represent a significant portion of the total cost in piping systems, influenced by their size, type, materials, and complexity.
5. Importance of Valve Selection
Proper valve selection is crucial for system safety, performance, maintenance, and cost-effectiveness.
6. Methods of Controlling Flow Through a Valve
Moving a disc or plug into or against an orifice
Sliding a flat, cylindrical, or spherical surface across an orifice
Rotating a disc or ellipse about a shaft extending across the diameter of an orifice
Moving a flexible material into the flow passage
7. Characteristics of Flow Control Methods
Valve Body or Shell
Main pressure retaining part
Accommodates valve trim
Provides passage for fluid flow
Manufacturing: cast, forged, fabricated, or combination
Materials: various metals and alloys
Connection Ends:
Butt welded
Socket welded
Threaded
Flanged
Wafer
Lug
Types of Body Passages:
Reduced bore
Full bore
Crossflow or Split section
Bonnet or Cover
Encloses internal parts
Designs:
Simple cover (e.g., swing check valve)
Supporting internals/accessories
Valve stem opening
Includes stuffing box
Bonnet-less design available
Connection to body: bolted, threaded, or welded
Bonnet joint often a leakage point
Same material as valve body
8. Valve Trim
Definition: Internal parts in contact with fluid, removable & replaceable
Components: Disc, seat, stem
Additional Parts: Back seat, glands, spacers, guides, bushings, pins, springs
Function: Controls flow by disc movement
9. Valve Disk
Function: Allows, throttles, or stops flow
Defines valve type (globe, gate, etc.)
Manufacturing: cast, forged, fabricated
Features:
Hard-faced for wear
Smooth finish for friction reduction
Pressure retaining part (when closed)
Movement:
By stem
By fluid (in check/safety-relief valves)
10. Valve Seat
Provides sealing surface for disc
Number varies by valve type
Good seal critical to prevent leakage
Types: integral or replaceable
Attachments: screwed, welded, cast/forged
Hardening: heat treatment, Stellite facing
Surface finish crucial for sealing
Seat Types:
Metallic
Non-metallic (for non-critical service)
Combination seats (metal + elastomer)
11. Back Seat
Parts: Stem shoulder + Bonnet surface
Functions:
Seals when valve is fully open
Prevents leakage to packing
Allows in-service gland packing replacement
12. Stem
Connects actuator to disk
Types of motion:
Linear (gate, globe)
Rotary (plug, ball, butterfly)
Typical Material: Forged stainless steel
Connection to disc: Threaded/Welded
13. Bonnet Bolt & Gland Eyebolt
Bonnet Bolt: Seals bonnet and body
Gland Eyebolt:
Connects gland flange and bonnet
Pushes gland bush to retain packing
14. Yoke, Yoke Bushing, Yoke Nut
Yoke: Connects bonnet to actuator
May be one-piece
Must be strong
Yoke Nut: Converts rotary motion to linear
Yoke Bushing: Threaded, softer than stem
May have anti-freeze sleeve bearings
15. Non-Pressure Retaining Parts
Gland Flange
Gland Sleeve/Bush
Gland Packing:
Graphite, PTFE
Prevents leaks/fugitive emissions
Needs proper compression & maintenance
16. Valve Trim Chart
Trim Number: Standard material combination
Standards: API 600, API 602
Common Grades: A410, A316, Alloy 20, Monel
Usage: Simplifies ordering and specification
17. Classification of Valves
By Function
Isolation
Control
Pressure/Vacuum Relief
Non-return
Special Purpose
By End Connection
Threaded
Flanged
Butt Welded
Socket Welded
Wafer & Lug Ends
By Motion
Linear
Rotary
Quarter-turn
By Actuator Type
Manual
Pneumatic
Electric
Hydraulic
