Pressure Control Valve vs Flow Control Valve

[neroverdi41]

Hello friends;

I wanted to investigate the difference between these two valves, but I couldn't find any clear information. is something added on top of a normal control valve? can you inform me about this?

 

[LittleInch]

There is no difference in the valve itself and I've always just called them control valves.

You can use any number of parameters to control the position of the control valve not just flow or pressure, but also level, temperature, hand position, or any variable you can measure.

Many valves have multiple inputs into the same valve, you just run it through a low selector block to choose the parameter which close the valve more than any other.

 

[neroverdi41]

There is no difference in the vane itself and I've always just called them control valves.

You can use any number of parameters to control the position of the control valve not just flow or pressure, but also level, temperature, hand position, or any variable you can measure.

Many valves have multiple inputs into the same valve, you just run it through a low selector block to choose the parameter which close the valve more than any other.

Thank you for your answer.

there is a regulator and positioner in the flow control valve. is there a device other than these in the pressure control valve? what do they adjust the pressure according to? for example, I want to close the valve when the pressure drops to 20 bar. how do I do it?

 

[LittleInch]

The same way, just substitute the signal from the pressure transmitter or sensing line for the flow transmitter.

Depends whether you are wholly electronic or pilot operated.

So electronic, you get a signal from the pressure transmitter in 4-20mA or 1-5V or a digital number. This goes into your PID controller which compares the signal to the set point you've set the valve to. If its higher then it sends a signal to close the valve until the pressure reduces, if less then one to open.

Pilot operated or relay driven works in much the same manner except they use springs and valves to do the same thing. Many water systems are whoilly self contained with no external power source for pressure control. See this e.g. https://www.cla-val.com/wp-content/...orks-How-Automatic-Control-Valves-Operate.pdf

As said, forget about a valve being called a FCV or a PCv or a TCV, it's just a control valve. How you control it is up to you and your instrument engineer.

Many simple controller come with the valve and actuator and all you do is feed it power, sometimes air and a signal from your measing device, then read the manual on how to set it to control what you want.

 

[neroverdi41]

The same way, just substitute the signal from the pressure transmitter or sensing line for the flow transmitter.

Depends whether you are wholly electronic or pilot operated.

So electronic, you get a signal from the pressure transmitter in 4-20mA or 1-5V or a digital number. This goes into your PID controller which compares the signal to the set point you've set the valve to. If its higher then it sends a signal to close the valve until the pressure reduces, if less then one to open.

Pilot operated or relay driven works in much the same manner except they use springs and valves to do the same thing. Many water systems are whoilly self contained with no external power source for pressure control. See this e.g. https://www.cla-val.com/wp-content/...orks-How-Automatic-Control-Valves-Operate.pdf

As said, forget about a valve being called a FCV or a PCv or a TCV, it's just a control valve. How you control it is up to you and your instrument engineer.

Many simple controller come with the valve and actuator and all you do is feed it power, sometimes air and a signal from your measing device, then read the manual on how to set it to control what you want.

I am just a control valve designer and analyst. the customer ordered it as a pcv. i wondered if i should add something other than a regulator and positioner. i will only design and manufacture the control valve. the customer will think for himself what he needs to control pressure, flow, temperature, blah blah blah. Is that right?

And what is mean of discharge presssure?

 

[LittleInch]

I don't think you need to do anything more.

Like I always say, the valve doesn't know what is causing it to open or close so just ignore the letters before CV and you'll be fine.

Depends on your scope of supply. If it includes taking in a signal then find out what form that signal is.

 

[neroverdi41]

I don't think you need to do anything more.

Like I always say, the valve doesn't know what is causing it to open or close so just ignore the letters before CV and you'll be fine.

Depends on your scope of supply. If it includes taking in a signal then find out what form that signal is.

Whatever the customer wants to control, he will set up a system accordingly, but he will do it himself. this is how I understood it. I try to ask questions from the simplest because even if I know the subject, I don't want to miss anything. thank you for your help.

 

[Danlap]

LittleInch already explain very thoroughly.
Do you have like engineering group or something within your company to discuss this thing, assuming you're working for valve manufacturing company.

Discharge is basically downstream side of the valve, and suction is upstream side of the valve. So flow is coming from suction passing through valve towards discharge line.

How to know pressure drop? usually there is pressure transmitter not far located from the valve (discharge side). Let say this set into certain value (of maximum pressure drop). Signal (either in Voltage or current) either feed into control room and some might locally connect to control valve regulator.
Pressure transmitter and to connect it to your regulator is (usually) end user responsibility.

One thing that you may want to ask to customer is what is the output signal would be, so that you can adjust your regulator (brain of the actuating valve) input accordingly. sometimes I/P converter might be required.

 

[neroverdi41]

LittleInch zaten çok detaylı bir şekilde açıklamış.
Şirketinizde bu konuyu tartışmak için bir mühendislik grubu veya benzeri bir şey var mı, tabi eğer bir vana üretim şirketinde çalışıyorsanız.

Deşarj temel olarak vananın aşağı akış tarafındadır ve emme vananın yukarı akış tarafındadır. Yani akış, vanadan geçerek deşarj hattına doğru emişten gelir.

Basınç düşüşü nasıl bilinir? Genellikle vanadan çok uzakta olmayan bir basınç vericisi bulunur (tahliye tarafı). Diyelim ki bu belirli bir değere (maksimum basınç düşüşü) ayarlandı. Sinyal (Voltaj veya akım olarak) kontrol odasına beslenir ve bazıları yerel olarak kontrol vanası regülatörüne bağlanabilir.
Basınç vericisi ve regülatörünüze bağlanması (genellikle) son kullanıcının sorumluluğundadır.

Müşteriye sormak isteyebileceğiniz bir şey, regülatörünüzün (harekete geçiren vananın beyni) girişini buna göre ayarlayabilmeniz için çıkış sinyalinin ne olacağıdır. Bazen I/P dönüştürücü gerekebilir.

Öncelikle Küçükinç'in detaylı anlattığını biliyorum arkadaşım. İngilizce bilgim yetersiz olduğu için çeviri yaparak yazdığım için tüm sorularımı çok basit bir şekilde anlattım. Kontrol vanaları hakkında zaten bilgim var. Deşarj basıncı ne demek emin olmak için sormak istedim.

Diğer cevapların için teşekkür ederim dostum. Rahatladım.

 

[LittleInch]

What's the translation of that?

 

[neroverdi41]

I already know what Kucukinch is talking about. Since I have a poor command of English (B1), I use a translate to answer you, but it translates differently because the phrases in my native language and the phrases in English are different. So I write my questions as simple as possible so that they can be understood. I have detailed information about control valves. Sometimes there is information I do not know. I was confusing discharge pressure with outlet pressure and differential pressure. I wanted to learn this clearly.

Thanks for your other answers my friend. I feel relieved.

 

[Taicho567]

physically no difference, not that I know. Maybe I can learn a thing or two here but not that I know of. PCV and FCV have the same built. Trims, bonnet, stem, positioner, actuators, etc.

The wet parts are the most important as the built are dependent of the fluid characteristics (fluid state, temperature, corrosive, etc) and what parameters (sizing, Cv, etc) it try to achieve. But again, it's not about what it's controlling (pressure, flow, level, temperature) that affecting the built but rather the fluid characteristics and the parameters.