Back pressure valve (BPV) functions 1

[CloudNine1]

Hi guys,

I read on the internet that BPVs not only control the upstream pressure in the system, but can also work as pressure reducers.
How is it possible?
For instance, if I want to hold pressure of 200 bar, I will use a BPV, but from what I understand, if I want to reduce the pressure after the BPV to 100 bar (for instance), I can use the same BPV, at the same location, to do so. But if I do so, won't the overall pressure in the system drop to 100 bar as well?
A bit confused, and would like to get your wise answers

Thanks!

 

[LittleInch]

What you are referring to is actually just a control valve. All it can do is open to a certain percent open and depending on your flow create a certain pressure drop across it or close once the a certain pressure has been reached . That's all.

Now how you control that opening is up to you.

A back pressure control valve controls the pressure upstream of the valve to a set figure. If the pressure is higher than it's set figure it opens up, possibly 100% open. Only when the pressure approaches or falls below its set pressure does it start to close to try and maintain the UPSTREAM pressure to a certain figure.;

Now if you want to control to a downstream pressure then the valve control changes. Now it tries to maintain a certain pressure. If the pressure falls below it set point it starts to open sometimes up to 100%. If the pressure rises above its set point then it starts to close, possibly to 0% open if the flow through the valve stops.

Hence you can use the same valve, sometimes for both purpose, but you need sensing lines upstream and downstream of the valve and then a re-configuration of the control system (electronic, electric or pneumatic) to change the valves purpose in life.

Now if you try to use the same valve for two different purposes, you really need to decide which is more important to you - back pressure control or downstream pressure. Hence whichever is then below (BPV) or above (PRV) its set point the valve will start to close.

Does that make it any clearer?

Try drawing a schematic if you're unclear and post it.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[CloudNine1]

Thank you very much for the elaborated answer.
I'm afraid I'm still confused...
As far as I understand, BPV is not equal to pressure reducer.
A BPV is a device used to accurately control the pressure of a system, through opening just as much as is needed to return to normal pressure levels. The BPV keeps a steady pressure flow and reacts to the levels of the system to keep good stability.
Correct me if I'm wrong, but this device is much more sophisticated than pressure reducer...
But anyways, I still don't understand how a BPV can function as a controlling pressure device and a reducing pressure device simultaneously.
When the BPV wears the hat of a pressure reducer valve, won't it ruin the sole purpose of the pressure controlling valve?
If I reduce the pressure from 200 bar to 20 bar DOWNSTREAM, how can I then go back to be a controlling device that ensures that a constant 200 bar will be upstream?

 

[LittleInch]

ok

As far as I understand, BPV is not equal to pressure reducer.
errr yes it is. A back pressure valve works by creating a pressure drop across a flowing fluid. A pressure regulator does exactly the same thing. The only thing which changes is how you control it.

A BPV is a device used to accurately control the pressure of a system, through opening just as much as is needed to return to normal pressure levels. The BPV keeps a steady pressure flow and reacts to the levels of the system to keep good stability.
Correct me if I'm wrong, but this device is much more sophisticated than pressure reducer...
I'll correct you. A pressure regulator and a back pressure regulator are the same thing sophistication wise.

But anyways, I still don't understand how a BPV can function as a controlling pressure device and a reducing pressure device simultaneously.
Depends on your system requirements. If your back pressure control is a minimum of some pressure, but normally operates higher than that minimum, then it could be used to control the downstream pressure, but maintain your minimum as an "override". If on the other hand you need to maintain back pressure at a fixed level then yes, it can only do one function at a time.

When the BPV wears the hat of a pressure reducer valve, won't it ruin the sole purpose of the pressure controlling valve?
If I reduce the pressure from 200 bar to 20 bar DOWNSTREAM, how can I then go back to be a controlling device that ensures that a constant 200 bar will be upstream?
See my previous answer - you can't control upstream and downstream to fixed values with a single valve.

Does that work?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[CloudNine1]

Yes I think it's more clear now.
Thank you very much!