Interview Questions

Control valve basic interview questions

1. What are the steps in selection of valve?

– Material to be handled – gas, liquid, power. Material by which valve is constructed, disc type, stem type, how to operate, bonnet type, the body ends, cost. 

2. What is the function of a valve?

– Flow regulation, regulation, non-return and special purposes.

3. What are special valves?

– Multi port valve,  flush bottom, float, foot, pressure relief, breather.

4. What is trim?

– Trim is composed of stem, seat surfaces, back seat bushing and other small internal parts that normally contact the surface fluid.

5. Which standard specifies trim numbers for valve ?

 API 600

6. What are the material used in valve construction?

– Cast iron, bronze, gun metal, carbon steel, stainless steel, alloy carbon steel, polypropylene and other plastics, special alloys.

7. What pressure tests are carried out on valves?

– Shell-hydrostatic, seat-hydrostatic, seat-pneumatic. 

8. What are available valve operators?

– Handlever, handwheel, chain operator, gear operator, powered operator likes electric motor, solenoid, pneumatic and hydraulic operators, Quick acting operators for non-rotary valves (handle lift).

9. What is Barstock Valve?

– Any valve having a body machined from solid metal (barstock). Usually needle or globe type.

10. What is Breather Valve?

– A special self acting valve installed on storage tanks etc. to release vapor or gas on slight increase of internal pressure.

11. What is dimensional standard for plug valve?

– API 599

12. Where WYE body globe valve is used ?

– In line ports with stem emerging at 45 degree, for erosive fluids due to smoother flow pattern.

13. What are the types of bonnets?

– Bolted bonnet, bellow sealed bonnet, screwed on bonnet, union bonnets, A U-bolt and clamp type bonnet, breechlock bonnet, pressure seal bonnet.

14. What is Vacuum breaker?

– A special automatic valve or valve nay suitable for the vacuum service, operated manually or automatically, installed to admit gas (usually atmospheric air) in a vacuum or low pressure space. Such valves are installed in high points of pipes or containers to allow drainage and, sometimes, to avoid the siphoning.

15. What are globe valve port types?

Full port: More than 85% of bore size, Reducer port: One size less than the connected pipe.



Instrumentation Engineer

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