Increases irregularities (A) I and II (B)I and III (C)II and III (D)II and IV 2. This is the result of a workshop test where the upstream and downstream pressure are held constant and the only variables are the flow rate and opening of the valve. Nm³ : Volume of a medium (liquid or gas) at the standard state 1 bar (abs) 20°U Sm³: -> engl: the American variant of Nm³. Does chemistry workout in job interviews? An alternative to two valves in parallel is to select a valve with a high rangeability such as a vee-ported ball valve. On resetting valves, for example those equipped with a return spring, the —– position is the position assumed by the moving parts of the valve when it … Generally desuperheaters are used in process plants where the steam is used for heating. The pressure reducing valve does so on the downstream side whilst the pressure maintaining valve does so on the upstream side of the valve (UV=backpressure regulator). Multiple Choice Questions Chapter 1 1. Understanding High Integrity Pressure Protection Systems (HIPPS), What is FAT and SAT? This enables the loop to remain tuned at all conditions with the same calibration settings. The Kv value is a reference value for the flow rate of valves: For engineering a necessary KV value is calculated on basis of the given operating conditions. In a standard globe valve the trim would just be the plug and seat. The backpressure regulator only discharges the quantity of the medium needed to attain the nominal value. What Is The Difference Between Rangeability And Turndown? Then we will help you out by providing you with Control Valves Interview Question and Answers on our wisdomjobs site page. The outlet pressure indicates the pressure in the system downstream of the valve. With clean gases there is no problem with choked flow. What is the valve seat? Increases accounting errors III. Interview Questions on Control Valves, Control Valves MCQ, Control Valves Objective Questions, Control Valves Multiple Choice Questions. Multiple Choice Quiz: Multiple Choice Quiz This activity contains 15 questions. regulation of differential pressure, of quantities, or vacuums). In case of type­1 system steady state acceleration is (a) unity (b) infinity (c) zero (d) 10 Ans: b 74. Severe damage can occur inside a valve due to erosion caused by the impact of liquid droplets travelling at high speeds. Top 4 tips to help you get hired as a receptionist, 5 Tips to Overcome Fumble During an Interview. What is the difference between a start-up and continuous bleeding valve? After this point the pressure rises above the vapour pressure again and during this pressure recover stage (recall also the concept of FL) the bubbles collapse, and cavitation takes place. What Is A Desuperheater And How Does It Differ From An Attemporator? H20 exists as a solid (ice), liquid (water), vapour (saturated steam), and a gas (superheated steam) – it depends on the temperature and pressure which phase is current. Feedback. Control Valve Flow Characteristics . This enables the flow direction to be chosen to assist with the fail action, which means that only a small bias spring is necessary inside the actuator to start initial movement in the right direction in the event of air failure. The pressure acting on the control surface closes (pressure reducing valve) or opens (backpressure regulator) the valve against the spring force. The control valve is most often the final control element of the process industries. Three methods exist for treating cavitation in control valves – the first is to ensure that the plug and seat are made of a material that can resist the damage (e.g. The working principle of the extended bonnet (named “cold box”) used in cryogenic service (below -100°C) is based on the principle that portion of LNG which evaporates and stagnates in the upper portion of the bonnet has a function of thermal insulation between the process fluid and the gland packing. Question 7. Are you searching for Control valves jobs? The second is to ensure that the plug and seat are made of a material that can resist the damage (e.g. Question 19. The basic pneumatic valve is a mechanical device consisting of a body and a moving part (poppet or stem), which connects or disconnects passages within the body. Take the quiz, post your results, and challenge your co-workers! What is Nm³ (cubic metre standard), Sm³ (American cubic metre standard) and Bm³ (cubic metre during operation)? Quiz on Chapter 10: Directional Control Valves. There are then two phases flowing (i.e. The higher the velocity the better the material to be used. The higher the Pressure Drop and the greater the flow rate then more energy will be dissipated. Use the choked pressure drop in any equation to calculate Cv or flow rates. Question 12. The term “rangeability” normally refers to a mechanical concept applied to a single throttling device. Settings. During operation they are kept closed by the internal pressure of the vessel. The pressure setting range indicates the range within which a valve can be set or used. Equal Percentage – For equal stem movements the change of flow resulting from the movement is directly proportional to the flow rate immediately before the change took place. This compares with generally accepted line velocities of about 3 m/s, which explains why control valves often are smaller than the line size. Question 5. The third is to control where the bubbles collapse and keep this away from vulnerable components (for instance close to internal surface of valve body or pipe). This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level. F.i. The overflow valve (backpressure regulator) limits the pressure upstream of the valve to the set (but alterable) nominal value. What Is The Trim In A Control Valve? Turndown applies to the application and is the ratio of the calculated Cv at maximum conditions to the calculated Cv at minimum, Rangeability applies to the valve and is the ratio of the Cv of the valve fully open to the minimum Cv at which it can control. What is the trim in a control valve? The sealing face is part of the valve body and so the separable flanges are only there to hold the body in the line – they are not required to seal. A. pulmonic B. bicuspid ... C. television remote control D. magnet. High recovery valves, such as ball and butterfly, will become choked at lower pressure drops than low recovery valves such as globe which offer a more restricted flow path when fully open. The most common is to use the profile on the front of the plug head. The trim consists of the parts of the valve that affect the flow … The reduction ratio indicates the max. Question 30. Question 14. Generally the term rangeability is used to describe the capability of a control valve (i.e. d. Society has little need for any type of social control. To grant this benefit the stem/actuator axis must be in upright position. The rangeability of the selected valve must exceed the turndown requirements of the application. Hard face trim (using hard facing materials such as Stellite, or Tungsten Carbide), Increase size of valve, thus reducing the velocity. All Control valves cause pressure drop in the fluid as it passes through the valve. Thus damages caused by a vacuum will be avoided. For long life on liquid applications the velocity at the exit of the valve body should be less than 10 m/s. It helps keep the process variable close to the desired point. The change in flow resulting from a fixed increment of valve travel is constant throughout the whole stroke. Ideally the inherent valve characteristic should be chosen to give an installed characteristic as close as possible to linear (see inherent vs installed characteristic). We put together a quiz about valves to test your knowledge. A desuperheater is a device that is used to control the addition of water to superheated steam to reduce the temperature to within 10°C of saturation. In pneumatic systems time lags are obtained by. What is the difference between “Rangeability” and “Turn-down” in a steam desuperheating system ? The medium, flow velocity, viscosity and the pressure range to be regulated. 499 different Multiple Choice Quizzes on JetPunk.com. Adaptive gain is used for controlling processes. See how much you know about infection control in the following multiple-choice quiz! 2-way, 3-way and 4-way valves are directional control valves. Valves Objective Questions. How Can Flashing Damage Be Contained? In such a case the differentiation between Bm³ and Nm³ is of particular importance. The actuators for many control valves are either spring-to-open or spring-to-close. Difficulty. Which parameters are important for the selection of the nominal diameter apart from the Kv(s) values)? A diffuser is a plate with a large number of small holes in it that is installed in the downstream pipework. Pneumatic Control System Multiple Choice Questions and Answers; 36. What is the difference between flashing and cavitation? Why Is Live Loading Sometimes Offered On Valves? How to Convert Your Internship into a Full Time Job? 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