Precise PLC control of a ball valve?

mnevans93

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Hello everyone. I'm currently trying to make an automated test bench for my company. What it needs to do is burnish friction material, and as part of our burnishing process, we need to turn on a ball valve which allows air to pass through a cold air gun to cool the part. The goal is for the valve to be adjustable, so a PLC can open it just enough for the part to maintain a specific temperature. Right now on our manual test bench, we have a quarter-turn ball valve that we open to different amounts for different parts to achieve the proper cooling.

However, I can't seem to find any valves that have this kind of functionality. The electric valves I've seen are simply open/closed, not partial turn, but then again, I'm not sure what kind of PLC output/language they use. I've only ever used digital before, so what kind of PLC output/language could perform this operation, and what would a valve need to use it? I'm very new to PLCs, so forgive me if my terminology isn't correct.
 
Okay, great! This is precisely what I was looking for.

As far as the PLC goes, what language would I need to use to operate one of these? Analog, PWM, etc.?

Edit: I should add that I want the valve to increase or decrease flow dynamically based on a thermocouple's temperature reading.
 
Last edited:
What widelto linked to is probably a bit large for what you are looking for. I would recommend something like this:
http://xdki.festo.com/xdki/data/doc_ENUS/PDF/US/MPYE_ENUS.PDF

It is a Festo MPYE variable flow directional valve. You don't need the directional control but it would work. I think Festo makes a single direction flow only version of this but I can't find it right now.

You simply set your flow rate using an analog output from the plc. This is a fairly simple valve. It has no flow feedback or even spool position feedback. What you are really setting is a spool displacement force and you are hoping that force produces the displacement, and subsequently flow, you hope to have. Keep in mind that the actual flow rate for a given command is proportional to the input pressure and output restriction.

Keith
 
Okay, thanks so much for all of your responses. One last thing, would analog output allow for that dynamic adjustment based on the thermocouple's reading, i.e. temperature gets too hot, increase air flow, gets too cold, decrease air flow?
 
Yes, and there are several ways to write the logic to control. Start searching for PID (here and youtube). RonBeaufort has some great posts about PID as well.
 
Precise PLC control of a ball valve?
If you really need "precise" control of the volume of air, a ball valve is not the correct tool, you need a 'needle' valve style device.



mnevans93 said:
Hello everyone. I'm currently trying to make an automated test bench for my company. What it needs to do is burnish friction material, and as part of our burnishing process, we need to turn on a ball valve which allows air to pass through a cold air gun to cool the part. The goal is for the valve to be adjustable, so a PLC can open it just enough for the part to maintain a specific temperature. Right now on our manual test bench, we have a quarter-turn ball valve that we open to different amounts for different parts to achieve the proper cooling.

However, I can't seem to find any valves that have this kind of functionality. The electric valves I've seen are simply open/closed, not partial turn, but then again, I'm not sure what kind of PLC output/language they use. I've only ever used digital before, so what kind of PLC output/language could perform this operation, and what would a valve need to use it? I'm very new to PLCs, so forgive me if my terminology isn't correct.
Click to expand...
 
Regardless of the type of valve my experience is that I can get more precise control by eliminating the 4-20 mA positioners. They all have some deadband and that limits the accuracy and incremental movement. I use an electric operator with a long operating time, say 60 to 90 seconds per 90 degrees travel for a ball or butterfly valve. Then I use a timed output from my PLC, with increments a small as one quarter or one half a second. That gives you an increment of movement much smaller than most 4-20 mA positioners can provide.
 
Well, I should probably clarify that I don't need extreme precision. I need precision in the order of plus or minus 10 degrees Fahrenheit in the temperature. For the burnish, we would like to maintain a certain temperature. One of the units uses a Tripco friction material which the customer requests we burnish at a specific temperature, say 380 degrees F.
The friction material needs to be allowed to heat up sufficiently to reach that temperature, but the air needs to turn on in such a fashion that it doesn't exceed 390 or 400, but instead floats around 380. Currently in our manual setup, this is easy to do because we just turn the ball valve to about 45 degrees open out of 90, and adjust slightly to get the temperature where we want it. Replicating that in a PLC seems much more difficult. 60 to 90 seconds would be far too long, seeing as how in about 1-2 minutes the friction material has already hit its threshold temperature.
 
mnevans93 said:
Well, I should probably clarify that I don't need extreme precision. I need precision in the order of plus or minus 10 degrees Fahrenheit in the temperature. For the burnish, we would like to maintain a certain temperature. One of the units uses a Tripco friction material which the customer requests we burnish at a specific temperature, say 380 degrees F.
The friction material needs to be allowed to heat up sufficiently to reach that temperature, but the air needs to turn on in such a fashion that it doesn't exceed 390 or 400, but instead floats around 380. Currently in our manual setup, this is easy to do because we just turn the ball valve to about 45 degrees open out of 90, and adjust slightly to get the temperature where we want it. Replicating that in a PLC seems much more difficult. 60 to 90 seconds would be far too long, seeing as how in about 1-2 minutes the friction material has already hit its threshold temperature.
Click to expand...

A PID will do precisely that, and with more accuracy and consistency than you are doing now. Once setup you'll just need to "tune" it.
 
mnevans93 said:
Well, I should probably clarify that I don't need extreme precision. ..... Currently in our manual setup, this is easy to do because we just turn the ball valve to about 45 degrees open out of 90, and adjust slightly to get the temperature where we want it. Replicating that in a PLC seems much more difficult. 60 to 90 seconds would be far too long, seeing as how in about 1-2 minutes the friction material has already hit its threshold temperature.
Click to expand...

You can always open your flow control valve to a preset position (for example, leave it in the last operating position or move it to 45 degrees) and use a separate solenoid valve in series with the control valve to control off/on operation of the air.
 
Okay, I will definitely look into tutorials for PID. So if I were to go with a model like kamenges suggested above, how quickly could the PLC adjust the opening? I've seen numbers online for various units ranging between 1-5 seconds to do turns. Within 5 seconds, the temperature of the unit can climb 20 degrees, easily. My only concern is if the PID controller could respond quickly enough to maintain the desired temperature without going too far over the threshold temperature.
 

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