Control Valve TCV vs PCV

[C26M13]

Hello,

I am looking for some good reference to get better understanding in the use of Temperature Control Valve and Pressure Control Valve.

I am not really sure how is the function of the TCV and PCV in controlling the flow through a pipe.

I want to ask any help from you to give me some feedback regarding the concept of control valve maximum flow. My question is, if there is a trip upstream of the control valve and the control valve are in fully open position (see attached sketch).
Can TCV limit the flow to PCV (in other words the max flow to PCV depends on the valve Cv of TCV or not) i.e. the max flow through TCV when fully open (Valve Cv: Wide Open) is 500 kg/h.

Is the max flow to PCV also 500 kg/h or the max flow of PCV should be different (Fluid type: Gas)?

In this case, as per "API 521 4.4.8.3 Inlet Control Devices and Bypass Valves" how to determine the flowrate of the control valves?

Many Thanks,

 

[pennpiper]

C26M13,
Let's start out with some basic Control Valve Training.
"Control Valve Training - 101"
- Lots of Companies make Control Valves
- Companies make lots of different types of Control Valves
- Control Valves perform only one function, they "regulate flow"
- You can buy two of the same Control Valves (same type, size, etc)
- You can label each of them with different Tag names i.e. PCV and TCV
- It is not the Tag (Label) that makes them work
- What makes them work is what they are connected to
- The TCV would be connected to a Control System that includes Thermowells
- The PCV would be connected to a Control System that includes Pressure Sensors
- You could also connect this same Control Valve to perform Level or Flow functions
- The FCV would be connected to a Control System that includes Flow Meters
- The LCV would be connected to a Control System that includes Level Sensors

Your sketch does not show any Controls so it will not work.

Sometimes its possible to do all the right things and still get bad results

 

[LittleInch]

There is no reason in your sketch for two control valves. You only need one, but how you control it is up to your control system.

In steady state there is conservation of mass

Can TCV limit the flow to PCV (in other words the max flow to PCV depends on the valve Cv of TCV or not)
Yes it can if the max flow through your TCV is < max flow through PCV

i.e. the max flow through TCV when fully open (Valve Cv: Wide Open) is 500 kg/h.
You tell me

Is the max flow to PCV also 500 kg/h - Yes but only if max flow through PCV> 500 kg/hr fully open
or the max flow of PCV should be different (Fluid type: Gas)? Not in a steady state.

The only reason for your design is someone has not understood how a control system works.


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