Q&A of valve type selection (part one)

Industry News

Posted: 04/04/2019 15:05:18 Hits: 35

As indispensable equipment in industrial production, valves may encounter many problems from selection, use to maintenance. Here are some common questions and answers.

What are the three main factors that should be considered when choosing a valve?
(1) The output of the actuator is greater than the load of the valve and is reasonably matched.
(2) When checking the standard combination, it is necessary to consider whether the allowable pressure difference specified by the valve meets the process requirements. When the pressure difference is large, the imbalance force of the valve core should be calculated.
(3) It is necessary to consider whether the response speed of the actuator meets the requirements of the process operation, especially the electric actuator.

Compared with pneumatic actuators, what are the characteristics of electric actuators, and how many output forms are there?
The electric drive source is simple and convenient for electric power, with large thrust and torque, and high rigidity. However, the structure is complicated and the reliability is poor, and it is more expensive than pneumatics in small and medium sizes. It is often used in applications where there is no gas source or no strict explosion-proof or flameproof requirements. The electric actuator has three output forms: angular stroke, linear stroke, and multi-turn.

Why is the cut-off pressure difference of the angular stroke type valve relatively large?
The cut-off pressure difference of the angular stroke type valve is large because the resultant force of the medium on the valve core or the valve plate generates a very small torque to the rotating shaft, and therefore, it can withstand a large pressure difference. Butterfly valves, ball valves are the most common angular stroke valves.

Which valves need to choose the flow direction and how to choose?
Single-sealed regulator valves such as single-seat valves, high-pressure valves, and single-sealed sleeve valves without balance holes require choosing flow direction.

There are advantages and disadvantages to flow-to-open type and flow-to-close type. The flow-to-open valve works stably, but the self-cleaning performance and the sealing performance are poor, and the service life is short. The flow-to-close valve has a long service life, self-cleaning performance and good sealing performance, but the stability is poor when the valve stem diameter is smaller than the spool diameter.

Single-seat valves, small-flow valves, and single-seal sleeve valves are usually selected for flow-to-open. When flushing is strong or self-cleaning is required, flow closure is optional. The two-position quick-opening characteristic regulating valve is selected forflow-to-close type.

What other valves with adjustment function besides single, double seat and sleeve valves?
Diaphragm valve, butterfly valve, O-type ball valve, V-type ball valve, eccentric rotary valve are all regulating valves.

Why is model selection more important than calculation?
Compared with calculation, the selection is much more important and more complicated. Because the calculation is just a simple formula calculation, it is not in itself the accuracy of the formula, but whether the given process parameters are accurate.

There are many contents involved in the selection. Improper selection not only causes waste of manpower, material resources and financial resources, but also has an unsatisfactory effect, which brings about some use problems, such as terrible reliability and longevity, operating quality, etc.

Why can't a double seal valve be used as a shut-off valve?
The advantage of the two-seat valve core is the force-balanced structure, which allows a large differential pressure, and one of its biggest disadvantages is that the two sealing faces cannot be in good contact at the same time, resulting in a large leak. If a double seal valve is artificially and forcibly used to cut off, it is obviously not effective and advisable, even if it has made many improvements (like double-sealed sleeve valve).

Why does the double seat valve easily oscillate when working at a small opening?
For a single core, the valve stability is good when the medium is flow-to-open type, whereas the stability of the valve is poor when the medium is flow-to-close. The double seat valve has two cores, the lower core is in the closed state, and the upper core is open. Thus, when working at a small opening degree, the flow-to-close core tends to cause vibration of the valve, which is why the double seat valve cannot be used for small opening situations.

Next: Q&A of valve type selection (part two)

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Teresa

Teresa is a skilled author specializing in industrial technical articles with over eight years of experience. She has a deep understanding of manufacturing processes, material science, and technological advancements. Her work includes detailed analyses, process optimization techniques, and quality control methods that aim to enhance production efficiency and product quality across various industries. Teresa's articles are well-researched, clear, and informative, making complex industrial concepts accessible to professionals and stakeholders.