Questions discussed which is frequently asked in Interview
1. What is the valve cone?
2. What is the valve seat?
3. How to define seat leak class for control valves?
4. What is the difference between flashing and cavitation?
5. Why a control valve on refrigerant Service can not be mounted with actuator in horizontal position?
6. 7. 8. 9. 10.
11. What is the distinction between a start-up and continuous bleeding valve?
12. What is Nm³ (cubic metre standard), Sm³ (American kiloliter standard) and Bm³ (cubic metre throughout operation)?
13. What is the distinction between a pressure reducing valve and a pressure maintaining valve?
14. What will control unit mean?
15. Why is it better to increase the pipeline in some cases?
16. 17. 18. 19. 20.
21. What is a released valve?
22. What will exhausting facing mean?
23. Why is that the flow velocity thus ?
24. 25. 26. 27. 28.
1. What is the valve cone?
The valve cone may be a movable component inside the valve that bears on the valve seat.
By means that of the cone stroke the valve is opened, throttled or closed.
2. What is the valve seat?
The valve seat is that the apron for an outlined flow through opening within the valve through that the medium to be regulated needs to flow.
3. How to define seat leak class for control valves?
A control valve’s ability to shut off must do with several factors. Seat material, actuator thrust, pressure drop, and also the kind plug (balanced or unbalanced) will all play a section in however well a specific control valve shuts off.
Seat leak Classifications There is literally six completely different seat leak classifications as outlined by IEC 60534-4 std or ANSI/FCI seventy.2.
They normally range from class IV to class Vl class IV is additionally referred to as metal to metal.
It’s the type of leak rate you’ll expect from a valve with a metal plug and metal seat. Class Vl is understood as a soft seat classification.
Soft Seat Valves area unit those wherever either the plug or seat or each area unit made of some reasonably composition material like Teflon or similar.
4. What is the difference between flashing and cavitation?
Cavitation may be a condition that happens in liquid flow wherever the inner pressure of the liquid, at some Location falls below the vapour pressure and vapour bubbles formation takes place.
After this time the pressure rises higher than the vapour pressure once more and through this pressure recover stage (recall additionally the conception of FL) the bubbles collapse, and cavitation takes place.
Flashing may be a condition that happens with liquid flow wherever the pressure falls below the vapour pressure (same as cavitation) and remains below it.
There are a unit then 2 phases flowing (i.e. liquid and vapour) downstream and no collapsing of bubbles takes place.
5. Why a control valve on refrigerant Service can not be mounted with actuator in horizontal position?
The working rule of the extended bonnet (named “cold box”) employed in refrigerant service (below -100°C) is predicated on the principle that portion of LNG that evaporates and stagnates within the higher portion of the bonnet contains a operate of thermal insulation between the process fluid and also the gland packing.
In this manner ice formation on valve stem is avoided. To grant this profit the stem/actuator axis should be in upright position. so valves put in on a vertical pipe (with the actuator in horizontal position) cannot work properly.
11. What is the distinction between a start-up and continuous bleeding valve?
The start-up bleeding valves bleed plants with low internal pressure throughout start-up or filling.
The float acts directly onto the cone. Such valves have an oversized seat diameter to make sure quick bleeding at a pressure below 0.1 bar.
During operation they’re unbroken closed by the inner pressure of the vessel.
Just in case of a suddenly occurring vacuum the valves open and compensate the pressure. so damages caused by a vacuum are going to be avoided.
The continuous bleeding valves area unit accustomed evacuate the air accumulating throughout operation.
They’re supplied with a lever transmission so they additionally operate at terribly low or terribly high pressures.
If air intake is to be avoided the outlet is to be supplied with a non-return valve. In such a case they’re going to act as bleeding valves while not venting operate.
12. What is Nm³ (cubic metre standard), Sm³ (American kiloliter standard) and Bm³ (cubic metre throughout operation)?
Nm³ : Volume of a medium (liquid or gas) at the standard state one bar (abs) 20°U Sm³: -> engl: the american variant of Nm³
Bm³ : Volume of the medium (liquid or gas) within the operative mode. i.e. at operative pressure and operative temperature.
Attention: Bm³ and Nm³ could usually differ from one another owing to the compressibility of the medium. In such a case the differentiation between Bm³ and Nm³ is of specific importance.
13. What is the distinction between a pressure reducing valve and a pressure maintaining valve?
Both valves keep the chosen set pressure constant. The pressure reducing valve will thus on the downstream facet while the pressure maintaining valve will thus on the upstream facet of the valve (UV=backpressure regulator).
Which parameters area unit necessary for the choice of the nominal diameter except the Kv(s) values)?
The medium, flow rate, viscosity and also the pressure range to be regulated.
14. What will control unit mean?
The pressure to be regulated is transferred to the pressure control valve mechanism via the control unit.
The pressure functioning on the control surface closes (pressure reducing valve) or opens (backpressure regulator) the valve against the spring force.
Three construction varieties are distinguished:
1. diaphragm
2. piston with O-ring and different seals
3. bellow
15. Why is it better to increase the pipeline in some cases?
In several cases the valve is sufficiently dimensioned for an exact application with regards to the Kv(s) value, however it would be too little in respect of nominal diameter and also the resulting flow velocities.
Too high flow velocities lead to noise, pressure rise and wear and tear.
On alittle scale the flow velocity may be reduced to a permissible value because of the extended pipeline.
The pipeline extension is to be disbursed by the client.
16.
21. What is a released valve?
On a released valve the forces working on the cone area unit compensated on an equally sized release surface because of the I/L and outlet pressure. so the valve features significantly higher control properties.
22. What will exhausting facing mean?
It is suggested that the cone for pressure control valves for liquids and with a pressure drop of abt. > twenty five bar be designed with a tough facing layer.
This may prevent early wear and tear because of cavitation.
23. Why is that the flow velocity thus ?
Iimportantn pipelines bound flow velocities area unit allowable depending on the medium. additionally to the KV(s) value the flow velocity may be a decisive value for valve orienting .
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