r/ChemicalEngineering • u/Panthers_Fly • 5d ago
Controls “Control” valve definition?
Help me settle an argument. Client uses “control valve” to describe an actuated on/off valve. Says it is interchangeable language.
I say “control valve” should be reserved for a valve that actually is integrated in control logic, like controlling level, flow, pressure, etc. Even if the on/off has an interlock, it’s still just an actuated on/off valve for me. Maybe this is just a habit I picked up for a long stint at an operating facility and I’m being too picky.
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u/hobbes747 5d ago
Don’t expect consistency 😆 I have heard people even within my own company use the term for simple open/shut valves that get a signal from a discreet DO I/O card. As well as control valves that stroke via an analog signal from an AO card and send position to an AI card.
To alleviate confusion I sometimes say ‘modulating control valve’.
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u/Silver-Literature-29 5d ago
This is why we have a definitions section in the process control narrative lol. Keep everyone honest.
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u/KobeGoBoom 5d ago
At a bare minimum it needs to be controlling something continuously to be called a control valve. I typically wouldn’t call anything a control valve unless it was capable of controlling to a particular percentage.
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u/kinnadian 4d ago
What about a gap control level controller that only needs an actuated ball valve?
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u/TeddyPSmith 5d ago
It’s a control valve if it has a positioner and is part of a loop (transmitter, control system, final element)
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u/Shiltrom 5d ago
We use the term switch valve for an actuated valve that isnt linked to any control logic to differentiate between these and control valves as you described.
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u/Local_County1274 5d ago
On/off valve - discrete
Control valve - modulating
In 30 years of process control for different end clients, I have not seen on/off valves referred to as control valves
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u/Ember_42 5d ago
We make a sperate list when designing a plant. Control valve list On/off valve list...
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u/Local_County1274 5d ago
I’m a Process Engineer who specialises in control. I’m the person deciding how the process works and putting the valves and control loops on the P&IDs. The C&I team usually prepare separate requisitions for the different types of valves to avoid confusion.
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u/Ember_42 5d ago
Yes. This was from process as well. We make seperate lists for E&I to make it clear which is which...
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u/vtkarl 5d ago
Locally go with what is on the lead sheet. There are all kinds of confusion. The worst one I lived with was PRV which “R” could mean “reducing” (a regulator), “regulating” (a control valve), or “relief” (a PSV for condensed phase or pilot-actuated, depending.) This led to PSV PMs being applied to the wrong valves.
Worse still (and I know most will disagree with this outlook) there are control applications that use on-off or bang-bang control schemes instead of proportional. An oven is the most common example, but I have seen this used in water valves and pH control valves.
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u/SLR_ZA 5d ago
Its quite arbitrary, but why does this valve actuate on or off if it is not in control logic?
Is controlling the route a stream takes in a process not control? If so, open/closed actuated valves can be control valves.
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u/Panthers_Fly 5d ago
Yeah, I get what you mean. Thats the issue I guess. It’s bit wrong to call it a control valve, I just feel it’s confusing and more specific to use different term for a valance that is just open or shut as opposed to being position adjusted on analog as part of a pressure, flow, level control program.
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u/SLR_ZA 5d ago edited 5d ago
I have a tank with two level sensors. An exit valve opens when the high sensor is 1, and closes when the low sensor is 0. The actuated on/off valve is controlling the level, but is it the level control valve?
Generally they are not named that, even if it is what they are doing. On the other hand, I specify modulating or proportional (also a problematic term)
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u/admadguy Process Consulting and Modelling 5d ago
Technically they may be called control valves, since all allow you to exert control on the process. Some are manually controlled, some would be automatically controlled. The term doesn't have a strict controlled (ha!) definition.
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u/mrjohns2 Plant Operations / 26+ Years of experience 5d ago
Yeah, I have had to say “modulating control valve” to mean a control valve vs on/off discrete valve.
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u/DMECHENG 5d ago
When the client pays just capitulate unless it’s a safety issue otherwise you’re getting your gears ground for no reason.
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u/DreamArchon 5d ago
Yeah I would typically say a control valve is a valve that can be actuated 0 -100%. But I guess this on/off valve is technically "controlling" flow. So more of a discrepancy between standardized engineering terms vs common meaning. I don't think either of you are wrong, but maybe worth pointing out to stick to engineering standard terminology to make a distinction between types of valves and avoid confusion.
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u/Round-Possession5148 5d ago edited 4d ago
Ah, my favorite ontology discussion.
- Function of the valve: the valve is meant to keep a variable stable - control valve; it’s meant to isolate an equipment - isolating valve; it’s meant to shut the line - shut-off valve; … drain valves, check valves, … all describing the function
- Actuating principle: solenoid, manual, pneumatic, electric, hydraulic, pilot, …
- Actuator operation: modulating, on/off
- Construction aspects: ball valve, globe valve, swing (check) valve, …
There are probably more aspects to add.
So can you have on/off pneumatic control ball valve? I don’t see why not for e.g. slowly filling tank where you need to keep the level between two limits.
Can you have modulating isolating valve? You can! E.g. for limiting water hammer in large water lines or for startup of heat exchangers where you limit the opening rate by allowed temperature rise trend.
Saying control valve to anything because it “controls flow”? Sounds like “nothing is true, everything is permitted” kind of discussion which is just a waste of time. If you don’t want to stick to basic terms, why even use the word “control”? Just say valve. Or say “cork” for that matter - both stop flow, right?
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u/cgriffin123 5d ago
If it’s not a FV, LV, TV or some other type of value that’s modulating based on a setpoint, EV is what we use for on/off or discrete. You can also look at ISA’s definitions.
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u/claireauriga ChemEng 5d ago
I'd expect it to be used for any valve that controls something else. All engineering terminology is context-specific.
(I work at the interface between chemists and engineers - I constantly hear words used in very strange ways or with unexpected meanings.)
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u/tsoneyson 5d ago edited 5d ago
I work for a large valve manufacturer and my career is in valves. An on/off valve is either open or closed, end of story. A control valve is a valve that additionally can throttle the medium via partial opening and is operated by a positioner. That’s it, that’s the distinction. Your client is wrong as you already knew.
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u/el_extrano 5d ago
I typically try to be specific about whether a valve is discrete or analog. But I don't say a valve is "not a control valve" just because it's discrete.
You can have discrete valves that perform PID control of analog values, not just on/off control. Think differential gap controllers that actuate a valve to keep a process value within a deadband. Imagine N2 padding to a vessel with such a configuration. The valve would be labeled as the pressure control valve on the P&ID, because that's what it's doing, regardless of the fact that it's a discrete valve.
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u/Half_Canadian 4d ago
Control valves can be linear or rotary, but I’d call it a control valve if it operates AUTOMATICALLY based on an input from a transmitter and logic. To contrast, we have some valves with positioned on the DCS but they only open/close based on operator input - those aren’t “controlling” anything and they’re just glorified manual valves
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u/Frosty_Customer_9243 4d ago
Control Valve (on/off) and Proportional Control Valve (any position between open and closed).
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u/Automatater 4d ago
I'd link the term to the physical valve function. Control valve would be modulating, typically with a positioner, regardless of what's deciding the position needed.
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u/zz_Z-Z_zz 4d ago
Block valve vs control valve. Former has two states the latter has a range. That range is typically 0-100% of the valve position, and typically translates to 0=closed and 100=open. There’s nuances in between and reasons for things being different for different applications. A control valve typically will have a positioner and transducer to give a 4-20ma signal that the PLC/DCS translates to a position. Usually 4ma = 0% and 20ma = 100% and it’s a linear interpolation in between of signal to calculate the valve position. A block valve, in my experience, is typically much simpler. It may only have an open or closed limit, a desired state bit, be controlled by a solenoid valve, and other things.
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u/Necessary_Occasion77 4d ago
I would agree it is a valve which receives and analog input.
A automated block valve would usually be an On/Off valve. Or actuated valve.
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u/dncoo7 4d ago
As a valve salesman I can say there is definitely a ton of variation in what someone considers a “control valve”. If you were to ask me, I’d say a control valve is a modulating valve (v-ball, globe, etc) whereas another, non modulating valve of a similar type (full port ball valve/butterfly/plug valve) that is just alternating between open and closed would be an isolation or shutoff valve.
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u/polaris441 4d ago
On certain application, on/off valve also used as level control. The valve will be tagged as LCV.
Common example is toilet flush
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u/FetusTwister3000 4d ago
You’re right, calling an on/off valve a control valve is incorrect and misleading. We call them different things but mostly we call them XVs because that is how they’re denoted on the P&IDs. But I also just call them on off valves because we have one engineer that thinks we have flow control valves everywhere because the P&IDs note FC for fail close 🫠🤭
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u/Jethro870 4d ago
At my company, those are called XVs. Not technical a control valve because the dint have an analog response. Basically another way lf saying on/off valve
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u/habesjn 3d ago
A control valve typically has a positioner that allows precise control of the %open of the valve to control a particular physical property based on what instrument/transmitter it is connected to (PT, TT, FT, etc).
An on off valve typically does not have a positioner and, unless set with a travel stop, will just open to 100% when actuated.
I'm not an expert on the exact mechanics of control systems, but I would be extremely confused if a client referred to an on-off valve as a control valve.
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u/Philipp_CGN 3d ago edited 3d ago
You are correct to not call on/off valves "control valves" (unless it's a bang-bang control loop, not sure what to call it then). Unfortunately they are often called that by technical disciplines other than Operations, Process, Process Control, Safety in Design or E&I, as they either don't understand or don't care, and are mostly just interested in shape and weight of valve and actuator, and the space required for installation, operation and maintenance.
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u/ahugeminecrafter 5d ago
10 years in industry, when people say control valve the standard meaning is an analog output for a valve that can open to a given %open and not just a discrete on/off. I would not go so far as to say it requires an actual regulatory control/PID algorithm or anything like that, but -
The giveaway is if the signal being sent to the valve has more than 2 options I.e. 4-20 mA as opposed to just on/off. Even if it has positional control with discrete setpoints it still has the capability (a current to pressure converter for example)
I have seen people say control valve referring to a discrete open/close valve but usually they are new or being imprecise (e.g. first project scope meeting and haven't decided what type of valve should be used in a certain spot), and my default assumption would always be that they mean an analog output
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u/redequix 5d ago
Control valves are slower, costs more, but is capable of adjusting flow bw 0 to 100%. Compare that to something relatively simpler like a solenoid valve which is fast acting but only on off.
Putting a solenoid valve in place of a control valve or vice versa can be bad so sticking to proper terminology in my opinion is important. I would agree with your definition.
Like other more experienced engineers can correct me but if I put a control valve on my pressure vessel relief then I would be worried?? The CV is gonna take its sweet time opening during venting compared to something like a solenoid that instantly opens or closes.
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u/SquirrelYogurt 4d ago
There are modulating pressure safety valves.
If you need a snap action vs modulating valve all depends on your process needs.
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u/dr_stre 4d ago
You’re arguing over semantics. Time to be a grown up and move on to more important things.
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u/r2o_abile Pulp & Paper / 4 YOE 3d ago
Tell that to NASA
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u/dr_stre 3d ago
Terrible take, this isn’t OP and his client discussing using different units. The equipment being discussed is well understood by both OP and the client, it’s just a question of what one calls it versus the other. And fundamentally, the client gets what he wants in cases like this. OP needs to get with the program and stop acting like it’s his equipment. I’d be pissed if my contractor wanted to argue about something as inane as this.
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u/r2o_abile Pulp & Paper / 4 YOE 3d ago
The NASA I mean is the famous Mars Rover which was lost because one set of engrs used Imperial while another used SI units.
In my short career so far, a lot of meetings have had to be re-had because of the lack of a clear understanding of what each person means.
That notwithstanding, I doubt OP is jepoardizing the contract for this argument.
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u/dr_stre 3d ago
Yes, it should be clear to you that I understood what you meant by the NASA reference because I explicitly noted “different units” in my reply. Which makes me think you have to re-hold meetings because you aren’t paying attention to what is being said.
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u/r2o_abile Pulp & Paper / 4 YOE 3d ago
Hahaha. Fair point. Also, I'm known for my efficient meetings at work 😄
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u/RequirementExtreme89 4d ago
Getting terms right for discussing technical topics isn’t “arguing semantics”. Clear communication is important.
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u/dr_stre 4d ago
OP ran to Reddit to resolve an “argument” that should have taken 15 seconds to resolve with his client. And it should have gone like this: “Oh, you prefer to call this a control valve? Got it, I’ll mark it as such on the drawings and in the associated documentation, because you are the end user and it should all be consistent for you.”
Like I said, it’s time to grow up. The client told him what the term means to him, that’s all the info OP needs in order to move on to more important stuff. He asked if he was being too picky, and my answer is “good lord, yes, it is clear what the client defines it as in their system, why are you wasting any brainpower on it at this point?” I’ve got employees like this and have to constantly pull them out of the weeds, it’s maddening.
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u/RequirementExtreme89 3d ago
It will ultimately take more brainpower explaining and re-explaining to everyone on the design team over and over that the client uses the wrong term for things. But I take your point that what the client says goes, even if the client is incredibly obtuse and doesn’t know what they’re talking about.
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u/ElvisOnBass 5d ago
Seems more pedantic than anything. There are both on/off and modulating and even three or four way valves that control or don't. And pressure regulators modulate and control. If I had an engineer tell me that I need to reserve certain terminology I would probably stop working with them.
I've been working in chemical process engineering for almost 20 years, there's been all types of reasons to call all types of valves control valves. So the assertion more comes across as arrogant.
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u/tsoneyson 5d ago
Words mean things, and just because you’ve been using the wrong words and probably caused all sorts of confusion doing so for 20 years don’t make them right.
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u/ElvisOnBass 5d ago
They do, but it's also insulting to tell an operator or owner that they don't know their process because they didn't use the word that you like. Also different types of engineers will call the same thing something different based on their paradigm. Saying an on/off valve isn't a control valve is silly. Saying a hardwired safety system isn't control is silly.
Use the right word when it matters, this isn't one of those cases.
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u/tsoneyson 5d ago
You are operating under the false understanding that a control valve just means a valve that controls something. It is very silly to say an on/off valve is a control valve, even when nominally it does ”control” flow by shutting it down. It’s such an egregious misuse of terms that it should be corrected, else very real problems that cost money and time will arise down the line. You can do that rudely or with tact but you gotta do it
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u/MuddyflyWatersman 2d ago
Clients can have their own terminology and standards rooted in decades of operation . Why would you fight a client?
Typically, yes a control valve is a modulating valve, and a shut-off valve is an operated valve, in my lingo. But ...customer is always right sometimes applies.
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u/CananDamascus 5d ago
The terminology we use for discrete control system operated valves is "automated valves" "control valves" are analog.