Angle Type Globe Valve Versus Globe valve with RO

[Sawsan311]

Dear All,

for high pressure drop liquid throttling applications , we tend to select angle type globe choke valve for fulfilling the same. Alternatively, a normal globe valve of straight pattern can be installed along with an RO.

I evaluated both scenarios and found the below:
1- angle valve installation is limited in size, some vendors stage up to 8'' body size only. can you confirm from your experience.
2- when I looked into sizing the RO , it is very tricky to distribute the pressure drop across the RO and the globe valve. Accordingly, if one takes 20% pressure drop across the upstream RO remaining pressure drop will be compensated by RO.
3- for the case where inlet pressure upstream the globe and RO is varying, I could see that if we size the liquid RO for the low delta P case, will end up with large RO for that constant Q. but in reality if the actual pressure is higher, the RO will give much higher flow which can in fact exceed the hydraulic velocity limit of the downstream piping in case the globe valve was not throttled sufficiently to limit that increased flow.

4- while I did the Cv calcs for the angle valve, in some cases, I saw that I would need a 6'' body size valve however, my main line size is 20'' so would that be fine? I have always came across a typical rule of thumb that globe valve size is typically 2 sizes smaller than the main line, but is 6 sizes less would be practical?

Appreciate your views.

Regards,

 

[casflo]

You don´t give details about flow rates and pressure drops, and it´s difficult to advise which is the best solution. In any case, if the pipe has 20", it´s very big to install an angle valve.
In the case of a globe valve + RO you must take into account the cavitation of both and in general, is better to install the globe valve upstream the RO

 

[Sawsan311]

Hi caslo, my general query is about the size limitations of the angle valve and whether alternatively we can install a 6'' straight pattern globe in a 20'' line i.e. is it practically mechanically possible?

If I can cover by Cv requirement with a special anti cavitation trim, why not have a globe valve since introducing the RO as I explained above will be based on a fixed flow rate and any variation in inlet pressure would varying throttling loads on the globe valve.

 

[LittleInch]

sawsan,

Your terminology is confusing me.

You appear to be referring to angle type choke valve which use a cage and plug mechanism for the high pressure regulation - commonly seen on things like oil and gas wells.

Then you start talking about globe valves which are usually low pressure application with various shaped plugs over a single nozzle / seat.

Which one ?

Also you're talking about a specific case, but don't give us details such as flow rate, fluid, differential pressure accross the valve.

what's a high pressure to you might be a low pressure to someone else.

RO's can be very useful, but if you have a variable flow and pressure drop not so useful. Also you need to think about how to start and stop the flow as their DP depends on flow.

You can have any size valve in any line with enough reducers. The two sizes thing is just a rough guide that, in general, control valves need to be smaller than the main pipe, but if you have a very highdifferential pressure might need to be a lot smaller.



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

 

[crshears]

RO . . .

I'm Assuming this means Restricting Orifice

and not

Reverse Osmosis

or

Regional Operator

or

Regulatory Oversight

or . . .

For the benefit of all readers, define abbreviations, please.

Thank you.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Sawsan311]

Thank you LittleInch, we agree that having the RO will be difficult for varying flow and pressure drop specially that the delta P itself would drive the flow for the fixed RO size.
for the angle type valve, these are special type of globe valves which is a is a modified version of “T”-Pattern Globe valve with inlet and outlet at right angles. It looks like a choke valve only.

 

[horacio Torres]

I don't use angle valve larger than 4 in , as a eng practice