What is meant by Pressure is floating on something...?

[JamesCorrobro1232]

What is meaning when Process Engineers say the a pressure of an equipment is floating on something?
For example if there is no pressure control on a vessel , is it meaning that its pressure is floating on some other equipment pressure? How is this terminology used in attached sketch situation? Is pressure of vessel floating on compressor?

 

[MortenA]

Hi James,

The terminology "floating" implies, as you yourself suggest, that the pressure is not controlled directly at the point your are referring to but will vary based on some upstream or downstream condition. In you example i would say that the pressure in the separator AND compressor suction "floats" on the upstream plant pressure assuming there is no pressure/flow control between compressor suction and plant.

Best regards,

--- Best regards, Morten Andersen

 

[LittleInch]

What it usually means is that the pressure can "float" between tow extremes which are sometimes instrumented alarm or safety systems so you set a low pressure ( could be 0 bar ) and a high or high high level and there is nothing actively controlling it.

In your case there is something actively controlling it which is the compressor suction control. Also you state the inlet as 50 psig, not a range so is that controlled as well?

The term float would be if the inlet has say a pressure range of 40 to 70 psig and the compressor control only reacts if the pressure goes above 70 (speeds up a bit) or goes below 40 (slows down). Then you can say that the separator "floats" on the compressor inlet pressure. As drawn I would say that the inlet pressure is fixed at 50 psi and is being actively controlled to that fixed pressure by the compressor.

You've explained exactly ZERO about any of this so you can't say if the pressure floats or not.

Does that make sense?

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

 

[JamesCorrobro1232]

@Little Inch - yes, makes sense. In this case the 50 psig is the battery limit pressure. Compressor suction is controlled by compressor PLC at 40 psig, meaning that if pressure is > or equal to 40 psig, the compressor is moving the flow corresponding to whatever pressure it has. If pressure start to decrease below setpoint compressor capacity control method will come into action and try to maintain 40 psig (VFD, clearance, recycle etc.)