Control valve position 1

[kmic]

Hi everybody
I‘d like to make one question about control valve position. My question is that at which position is better to put a control valve before or after a PHE or any devise in order to have better control of flow either hot-water or cooling water and why.
Pl’s advice

 

[willard3]

Probably better posted in piping or HVAC forum.

 

[georgeverghese]

If the pressure drop is small compared to operating pressure, then preference can be for either upstream or downstream.

Usually the selection for the location of the control valve is based on the possible risk of and the HSE consequences resulting from (a) interstream leakage and or (b) leakage to atmosphere.

 

[itdepends]

Sometimes putting it downstream is necessary to ensure sufficient backpressure is applied to prevent flashing of the hot fluid (which you are cooling) in the exchanger, or to prevent siphoning/emptying under low flow conditions if the outlet of one stream goes to a lower level (e.g. cooling water to a sump system).

As the control valve would normally be "placed" on the P+ID, before piping layouts are determined- I'd put it downstream of the HX in most cases to avoid the above issues arising. Note that a lot of our cooling HX's have their cooling stream discharge to a sub surface drainage system.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

 

[kmic]

Thank you guy's

 

[FredRosse]

Fluid flashing downstream of the control valve (this is cavitation) should generally be avoided, and there are so many fluid system variables that would give upstream/downstream preference that much additional specifics would be needed to answer the control valve cavitation question alone. Also flashing of fluids upstream or downstream of the control valve, in the piping or PHE may need consideraton. There are instances that would dictate the control valve be placed either upstream or downstream, frequently independent of the control valve cavitation issues.

Beyond that, there are potentially several other considerations that could prefer the control valve upstream or downstream, for example, downstream might not be a good idea if closing the control valve might overpressurize a component. If the upstream fluid is very hot or very cold, then a special control valve ($$$) if mounted upstream. If the downstream fluid is very hot or very cold, then a special control valve ($$$) if mounted downstream.

These are just a few examples, and illustrate that a general "rule of thumb" is not applicable here.