Valves and Pipe Fittings
Overview
Valves and pipe fittings are essential components in plumbing, hydraulic, and pneumatic systems studied in ITI Fitter Semester 3. Valves control the flow, pressure, and direction of fluids in pipelines, while pipe fittings connect, extend, or change the direction of pipes. Understanding their types, materials, applications, and selection criteria is critical for trade practical work and NCVT theory papers.
Typed Notes
Types of Valves and Their Functions
Valves are mechanical devices that control fluid flow in pipelines. Gate valve: used for full open/close, low pressure drop, not for throttling. Globe valve: used for flow regulation, has a disc and seat, higher resistance. Ball valve: quarter-turn operation, quick shut-off, used in gas lines. Butterfly valve: lightweight, used for large-diameter pipes, quarter-turn. Check valve (NRV): allows unidirectional flow, prevents backflow — swing type and lift type are common. Safety/relief valve: automatically releases excess pressure to protect the system.
Pipe Fittings — Types and Uses
Pipe fittings connect, redirect, or terminate pipelines. Elbow: changes flow direction — 90° elbow for right-angle turn, 45° elbow for gradual turn. Tee: splits flow into two branches (equal tee) or joins two lines. Reducer: connects pipes of different diameters — concentric and eccentric types. Union: allows easy dismantling of pipes without cutting. Nipple: short threaded pipe piece used to extend length. Socket (coupling): joins two pipes of same diameter. Flange: bolted joint for high-pressure systems. Cap and plug: used to close pipe ends.
Pipe Materials and Joining Methods
Common pipe materials in fitting trade: GI (Galvanised Iron) — used for water supply; CI (Cast Iron) — used for drainage; MS (Mild Steel) — used in hydraulic and steam lines; Copper — used in refrigeration and medical gas lines; PVC/CPVC — used for cold/hot water supply. Joining methods: Threaded (screwed) joints use BSP taper threads for GI pipes up to 50 mm; Flanged joints for high-pressure steam/water lines; Welded joints for permanent MS pipe connections; Soldered joints for copper pipes; Solvent-cement joints for PVC pipes.
Valve and Fitting Selection, Standards and Maintenance
Selection of valves depends on: fluid type (water, steam, gas, oil), operating pressure and temperature, frequency of operation, and need for flow regulation. Valves are rated by pressure class (PN rating) — e.g., PN 16 means 16 bar working pressure. BSP (British Standard Pipe) threads are used for pipe fittings in India. Leaking valves are repacked using gland packing material (graphite/PTFE). Valve seats are lapped using valve-grinding paste for a leak-proof seal. Pipe threads are sealed with PTFE tape or hemp and jointing compound to prevent leakage.
Topics & Sub-topics
Har topic ke saath sub-topics aur example — chapter ka complete coverage.
01Valves — Types and Applications
- Gate valve: full-bore, on/off duty only
- Globe valve: throttling and flow regulation
- Ball and Butterfly valves: quick-acting, quarter-turn
- Check valve (NRV) and Safety/Relief valve
A globe valve is fitted on the discharge side of a water pump in a workshop to regulate flow rate from 0 to full capacity — a gate valve would be damaged if used for the same throttling duty.
02Pipe Fittings — Types and Functions
- Directional fittings: 90° elbow, 45° elbow, tee
- Size-change fittings: concentric and eccentric reducer
- Joining/dismantling fittings: union, socket, nipple
- Termination and pressure fittings: cap, plug, flange
A 25 mm × 20 mm concentric reducer is used where a 25 mm GI main supply line branches to a 20 mm sub-line feeding a washbasin tap.
03Pipe Materials and Joining Methods
- GI pipes: threaded BSP joints for water supply
- MS pipes: welded joints for hydraulic/steam lines
- Copper pipes: soldered joints for refrigeration
- PVC/CPVC pipes: solvent-cement joints for domestic water
In a 15 mm copper refrigerant pipe joint, a silver-solder (brazing) process at approximately 600 °C is used instead of soft solder to withstand high refrigerant pressure.
04Valve Standards, Ratings and Sealing
- PN rating: PN 16 = 16 bar working pressure
- BSP thread standard used for pipe fittings in India
- PTFE tape and hemp compound for thread sealing
- Gland packing and valve-seat lapping for maintenance
A gate valve marked PN 16 on a steam line means it is rated for a maximum working pressure of 16 bar; using it beyond this rating risks catastrophic failure.
05Pipe Layout and Fitting Assembly Practices
- Pipe cutting: hacksaw, pipe cutter, and die-stock for threading
- Pipe bending: cold bending up to 25 mm, hot bending above 25 mm
- Assembly sequence: cut → ream → thread → fit → test
- Pressure testing: hydraulic test at 1.5× working pressure
A 20 mm GI pipe is threaded using a BSP die-stock with 14 TPI (threads per inch) and then hydraulic-pressure-tested at 1.5 × 10 bar = 15 bar before commissioning.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Gate valve is a full-bore valve used for fully open or fully closed operation — NOT for throttling.
- 02Globe valve is used for throttling/regulating flow; it has higher pressure drop than a gate valve.
- 03Check valve (non-return valve) allows flow in ONE direction only — prevents backflow.
- 04Pipe fittings include elbow (90°/45°), tee, reducer, union, nipple, socket, and flange.
- 05Pipes are joined by screwed (threaded), flanged, welded, or socket-and-spigot methods depending on material and pressure.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What is the main difference between a gate valve and a globe valve? When should each be used?
What is a check valve (NRV) and what are its two common types?
Name any four pipe fittings and state the purpose of each.
What is PN rating of a valve? What does PN 16 mean?
Why is PTFE tape used in pipe fitting, and how is it applied correctly?
Valves (gate, globe, ball, butterfly, check, safety) control fluid flow and pressure in pipelines. Pipe fittings (elbow, tee, reducer, union, flange, socket) connect and route pipes. Material selection (GI, CI, MS, copper, PVC) and joining method (threaded, flanged, welded, solvent-cement) depend on application and pressure. Maintenance involves repacking glands, lapping seats, and sealing threads with PTFE tape.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Which valve is BEST suited for throttling (regulating) fluid flow in a pipeline?
Q2.A check valve is also known as:
Q3.Which pipe fitting is used to connect two pipes of DIFFERENT diameters?
Q4.BSP threads used in pipe fittings in India stand for:
Mark karo — dashboard par progress dikhega.