Can a control valve perform more than one function?
Can a control valve perform more than one function?
(OP)
Hi All-
Is it possible to have a control valve which can do more than one thing at a same time like control flow (flow control valve)and also control temperature (temperature control valve) at the same time?
Thanks in advance for all your help.
HP
Is it possible to have a control valve which can do more than one thing at a same time like control flow (flow control valve)and also control temperature (temperature control valve) at the same time?
Thanks in advance for all your help.
HP





RE: Can a control valve perform more than one function?
I will try to be diplomatic.
Yes! a Control Valve does do more than one thing at the same time.
It, a TCV (Temperature Control Valve) controls both the temperature and the flow at the same time. It controls the Temperature BY controlling the flow.
All control valves control something (Temperature, Level, Pressure, etc.) by controlling the flow through the line.
That is basic.
RE: Can a control valve perform more than one function?
It dosnt know if it controls "flow" or "temperature" - its just open in a certain positions.
Its the controller, the measurement and logic that "knows".
If you need two dependant variables at the same time - then you need to free - but if you need sometime to control flow and sometime temperature then one is fine.
You dont clearly describe your situation but say that you control the temperature of a process stream using a HX with an outlet control valve on the utility side (common set-up).
In this case you cannot control the flow of utility - because you want a stable temperature of your process medium - the controlled variable.
If you installed a bypass on the utility side and added a control valve here - then you could maintain a steady utility side flow and a steady process temperature.
But say that you need a minimum utility flow rate - and that this is MORE important than the process medium temperature - then you could make a controil logic that would normally control the temperature - but IF flow rate dropped below the treshhold value then it would choose valve position based on utility flow rate.
Best regards
Morten
RE: Can a control valve perform more than one function?
The measured variable can be temperature with a temperature setpoint and an output to the control valve to control temperature. However, temperature control can be slow. An example might be controlling the fuel gas to a furnace. The heat of the fluid flowing through the tubes is directly affected by the fuel gas rate but the response can be slow. OTOH, reflux in a distillation column can be faster using a sub-cooled reflux stream like a shower that cools the upper trays.
Cascade
You could measure the outlet tubes from the furnace and the fuel gas flow and include a controller for each measurement. You can use the output of the slow temperature controller as a remote setpoint for the fast responding fuel gas flow controller.
Other possibilities exist too.
RE: Can a control valve perform more than one function?
FOR EXAMPLE, we have a flow control taking gas from a point going to a compressor. Put if 1 out of 4 compresors goes down, the pressure will rise and overload the engine, so we use a low select relay that sends the output from a pressure controller to the valve. As the pressure is rising, the pressure controller sends a lower signal to shut the valve, the relay selects the lowest signal which is pressure control. The flow controller wants more gas, and sends a higher signal to try to open the valve.
So a high or low select can can have multiple set points. On liquid meters we have a 3 way system, Inlet to the meter pressure that can not be too low, outlet from the meter run, that won't let the outlet presure get to high, and flow control set point. all threen varibles met, one control valve.
RE: Can a control valve perform more than one function?
That wthat i tried to describe
Best regards
Morten
RE: Can a control valve perform more than one function?
RE: Can a control valve perform more than one function?
e.g. if it is to feed a reactor, the valve will control the flow, the flow will effect the kinematics of the reaction.
Same with temperature. the valve controls the floe, the flow will effect the heat transfer.
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RE: Can a control valve perform more than one function?
RE: Can a control valve perform more than one function?