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Some Questions About Choke Valves

12/27/2011 1:49 AM

Dear all,

I have some confusion regarding the choke valves. I know the very basic working principles. I know what is choked flow but I could not clearly understand the followings;

1-How choke valves can reate choked flow while other valve types can not? What is the key property that allows choke valves to create choke flow?


2-Why do we need chokevalves? Is it like when we have varying downstream pressure but constant upstream pressure? Lets say I have a varying downstream pressure but constant upstream pressure&temperature (exit of a boiler or steam generator) and I used choke valve-What is the main advantage against other type of valves?


3-In which situations the choke valves MUST definitely be used?

I did some search on these topics. I have some understanding but not clear yet. Please share your ideas in as detail as possible.

THANKS.

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#1

Re: Some questions about choke valves

12/27/2011 3:11 AM

This sounds a lot like homework to me. And I doubt that you've actually done any searches. But, since a simple search reveals this

Choke valve - Wikipedia, the free encyclopedia

I'll help you, just this once.In the future at least perform a simple search before coming here for free homework answers.

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#4
In reply to #1

Re: Some questions about choke valves

12/27/2011 4:18 PM

Wikipedia briefly tells what choke valves do, not how they do it-that's what I am trying to understand. In the third paragraph, it tells some about how choke valves work but that is not clear and comprehensive. Briefly go through the information on wikipedia and read my questions again, I think you will understand that the information in wikipedia is not enough to clearly explain my questions.

I am not here for free homework answers, these questions might be very easy to you but I am new to this and I could not find necessary information to understand them even though I surely did some web search.

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#2

Re: Some Questions About Choke Valves

12/27/2011 12:56 PM

Turkish Aggie,

I agree with Lyn, your post sounds like school work and you are trying to take a shortcut to the answer.

however I am also willing to offer help.

A. I do not think you or your instructor in using the correct word (term). Choke Valve is not normally used in the piping engineering and design of pipe lines or process plants such as refineries and chemical plants.

B. The definition of "Choke" is:

Choke - [chohk]

noun

1. The act or sound of choking.

2. A mechanism by which the air supply to the carburetor of an internal-combustion engine can be diminished or stopped.

3. Machinery. any mechanism that, by blocking a passage, regulates the flow of air, gas, etc.

4. Electricity. choke coil.

5. A narrowed part, as in a chokebore.

verb (used with object)

1. to stop the breath of by squeezing or obstructing the windpipe; strangle; stifle.

2. to stop by or as if by strangling or stifling: The sudden wind choked his words.

3. to stop by filling; obstruct; clog: Grease choked the drain.

4. to suppress (a feeling, emotion, etc.) (often followed by back or down ): I managed to choke back my tears.

5. to fill chock-full: The storeroom was choked with furniture.

C. You will notice that the combination of "Choke" and "Valve" is not used here. I think the term (words) you (and your instructor) should be using is "Control Valve". If you check this web site (http://en.wikipedia.org/wiki/Control_valves) you will find an answer that more closely fits what you want.

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#5
In reply to #2

Re: Some Questions About Choke Valves

12/27/2011 4:32 PM

A. I agree that there is a terminological confusion regarding choke valves or control valves that chokes the fluid. As far as I understand, choke valve is a sub-type of control valves or it might be just some people prefers to call it choke valve. Some companies offer products clearly named "choke valve". If you google it, you will see that. So it is clear that at least some people and companies, apart from me, use these terms.

C. I also saw some terms like "needle choke valve" "butterfly choke valve". So I think that it might be a name given to some type of control valves which chokes the flow. I am not sure yet but I will figure it out soon.

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#7
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Re: Some Questions About Choke Valves

12/27/2011 5:00 PM

As I understand it;

"Choke" is more about the function a valve performs in a circuit.

Any type of valve [that can be partially closed] can be used as a choke.

Some are that are made specifically for flow control, like needle valves, are often referred to as 'choke' when their use is more about setting a base flow, than an exact one. A choke valve is generally one of the adjustable orifice designs, rather than a gate type, or washer type, which would wear asymmetrically, or develop channels.

A choke can also just be a plain orifice

Above a choke function in 'accuracy' are "metering valves" and "flow regulators".

You will often find a 'choke' used upstream of these if there is a big pressure, or volume, variation in the supply.

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#3

Re: Some Questions About Choke Valves

12/27/2011 1:08 PM

Or do you mean check-valve?

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#6
In reply to #3

Re: Some Questions About Choke Valves

12/27/2011 4:32 PM

nope, definitely I do not mean check valve.

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#8

Re: Some Questions About Choke Valves

12/27/2011 7:43 PM

The more common term is "throttling" valve, which is meant to operate well at partly open positions, in order to meter fluid flow at a controlled rate. Because of large pressure drop and high velocity through such a valve, the trim may be of hardened material.

Gate valves are generally unsuited to throttling service. Butterfly and ball valves are intermediate in this respect. Needle/cone/characterized-plug types are usually best, along with some sliding slotted-disk types.

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#9

Re: Some Questions About Choke Valves

12/27/2011 10:59 PM

A special kind of angle globe valve is CHOKE VALVE, used for most wellhead applications. Angle valves allow for easy draining, since no pockets exist that allow the fluid to pool. One disadvantage of using an angle valve is that turbulent flow created by the regulating element can channel the turbulence directly into the downstream piping, creating more vibration and noise than would be created using a flow-through body.

For more details search for globe valve (Control Valve), or refer Valve Handbook By Philip Skousen or Emerson's Control valve Handbook.

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#14
In reply to #9

Re: Some Questions About Choke Valves

01/29/2012 12:51 AM

GA

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#10

Re: Some Questions About Choke Valves

12/27/2011 11:16 PM

Per that wikipedia entry in paragraph 3 The main advantage of choke valves is that they can be designed to be totally linear in their flow rate.

They introduce an engineered obstruction with a predictable behavior.

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#11
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Re: Some Questions About Choke Valves

12/28/2011 12:55 AM

It depends upon which type of plug & cage is used, pl refer below images.

As the flow is diverted by 90° due to budy shape & the orifice due to cage, flow will be turbulant.

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#12

Re: Some Questions About Choke Valves

12/28/2011 5:31 AM

try this... however if this is homework, you might not get anyone else to answer your questions again

http://www.fmctechnologies.com/en/FluidControl/Technologies/CompactValves/ThrottleValves.aspx

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#13

Re: Some Questions About Choke Valves

12/28/2011 7:35 PM
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