300+ [UPDATED] Mechanical Fitter Interview Questions and Answers

Q1. Define Valve?

Valve is a Mechanical flow control element in the process.

Q2. What Is Ppe?

PPE– Personal Protective Equipment

E.g.) Helmet, Boiler Shout, Safety Goggles, Safety Shoe, Gloves, Dust Mask etc…

Q3. What Is The Use Of Vacuum Breaker?

It is used to remove Vacuum (Air Bubbles) from Water line.

Q4. What Is Steam Trap And Gas Trap?

Steam trap using for removal of Water from Steam.

Gas trap using for removal of water from gas.

Q5. What Is Flange? Types Of Flanges?

Flanges used to connect both lines (Fluid, Gas, Oil, Water….)

  • Thread Type Flange
  • Modified Flange
  • Weld Neck Flange
  • Slip On Flange
  • Goose Neck Flange
  • Socket Weld Flange
  • Stepped Flange
  • Spade Flange
  • Spectacle Flange
  • Blind Flange

Q6. What Are Prv And Psv?

  • PRV (Pressure Relief valve) release excessive more than set point, released fluid re circulated.
  • PSV (Pressure Safety Valve) released pressure more than set point to safe the equipments.

Q7. What Are Types Of Valves?

  • Gate Valve
  • Globe Valve
  • Ball valve
  • Butterfly Valve
  • Needle Valve
  • Plug Valve
  • Diaphragm Valve
  • Non-Return Valve
  • Knife Edge Valve
  • Drain Valve
  • Float Valve
  • Flush Bottom Valve
  • Pinch Valve
  • Pen Stack Valve etc.

Q8. What Are The Testing Mediums Used For Testing?

Water, DM Water, Air, Kerosene, Oil, Soap water.

Q9. What Is The Use Of Ejector?

Ejector is used to create Vacuum for process.

Q10. What Is Work Permit System?

Work Permit is an Authority for doing work in a process plant.


Cold Work Permit– Without Sparking, Without Heat etc.

Hot Work Permit– With heat (Grinding, Cutting, Welding).

Note: Two times only extend the permit after the normal valid of permit.

Q11. What Is Gasket? Where It Is Used?

It is sealing member between two flanges.


  1. Water Line, Gas Line, Air Line used CAF Gasket.
  2. RTJ – High Pressure Line.
  3. Chemical Line – Rubber Gasket and Teflon Gasket.
  4. Steam Line – Semi Metallic, Metallic and Graphite.
  5. Impregnated Gasket – Valve Sealing Gasket.
  6. Spiral Wound – Steam Line.

Q12. What Is The Use Of Spade, Spectacle, And Blind?

SPADE– Give space between two flanges and give flow through the spade.

SPECTACLE – Combination of SPADE and BLIND and both option done in one flange.

BLIND – Used for close the line.

Q13. Explain The Valve Parts?

Gate Valve – Body, Bonnet, Seat, Gate, Stem, Hand Wheel, Gland Bush, Gland Flange, Gland Bolt and Nuts. Hand Wheel lock nut.

Ball Valve – Body , End Piece , Ball , Stem , Seal , Seal Follower , Seat , Lock Nut , Handle Gland Packing , Gland Flange , Gland Stud and nut.

Globe Valve – Body , Bonnet , Seat , Plug , stem ,  Hand Wheel , Lock Nut ,Gland Packing , Gland Flange , Gland Stud and nut.

Butterfly – Body , Disc , Stem , Seat ring , Seat ring holder , Bush , End cover , Hand Wheel  or Gear Box , Gland Bush , Gland Packing , Gland Flange , Gland Stud and nut.

Q14. What Is Strainer?

Strainer is a control element to arrest dust from flowing fluids.

Q15. What Are The Types Of Gaskets?

  • CAF – Compressed Asbestos Fiber Filled Gasket
  • Semi Metallic Gasket 
  • Metallic Gasket
  • Rubber Gasket
  • Teflon Gasket
  • Spiral Wound Gasket
  • RTJ – Ring Type Joint
  • Graphite Gasket
  • Impregnated Gasket
  • Graf oil Gasket

Q16. What Is Gland Packing? Uses Of Gland Packing?

Gland packing is a Sealing member between two moving parts or stationary.

It is used for arrest the leak through shaft various lines.

  1. Teflon Gland packing
  2. Graphite Gland packing
  3. Carbon Gland packing
  4. Virgin PTFE Gland packing
  5. Graf oil Gland packing

Q17. What Is Heat Exchanger? What Are The Types Of Heat Exchanger?

It is an Equipment to use for Exchange the heat(Cooling or Heating purpose)


  • Fixed Tube Heat Exchanger
  • Floating Tube Heat Exchanger
  • U Tube Exchanger
  • Plate Type Exchanger
  • Fin Fan Cooler Heat Exchanger
  • Bridge Lock Exchanger

Q18. Define Non Sparking Tools?

Non Sparking tools used in Gas, Oil and Chemicals.

E.g. Brass hammer, Brass Wedge, Brass Spanner, Copper hammer, Copper rod , Brass rod , Brass chisel  , Rubber hammer , Nylon hammer.

Q19. Explain The Following Valves Shell And Seat Testing?

  • Ball Valve
  • Gate Valve
  • Globe Valve
  • Butterfly valve
  • Plug valve

Shell Test of above valves:- 

             Testing flange to be fixed on both sides. Pressurized one side under the valve partial open condition as per the standard. Check the leakage through body, Bonnet sealing area, Gland packing area.

Seat Test of above valves:-

            Testing flange to be fix on one side of the valve. Pressurized the valve under fully closed condition as per the standard. Check the leakage through Seat in opposite side. Follow the same procedure while checking the another seat except Globe and Butterfly.

Q20. Give The Parts Name Of Psv?

  • Body
  • Bonnet
  • Nozzle
  • Disc
  • Disc Holder
  • Stem
  • Blow down ring
  • Blow down ring lock screw
  • Spring Bottom Plate
  • Spring
  • Spring Top Plate
  • Control Screw
  • Lock Nut
  • Cap
  • Gasket