Globe vlave vs Plug and cage choke valve

[Erkamal]

HI frds,

i am working in valve company & studying more on valve application .
Few questions are in my mind.

Plug type globe valve & Plug type choke valve both are used.

In both product, plug and cage type trim has been used. so what is the difference between them.
Why we called globe valve not plug type valve.

asn what is the diffrence between plug type globe valve and plug type choke valve? only related pressure ?

why plug type globe valve is not inclued in API 6A?

Choke valve is used only higher pressure rating ?

 

[Danlap]

Hi Erkamal,

Obturator is the more appropriate/scientific term for closure member. It consist of process's main sealing element that are in contact (by mean of pushed) against the Seat. Which covers but not limited to Gate(single/double), Wedge , Globe, Disc (for Swing Check as well as Gate), Ball (V-ball, full ball, etc.) and Plug (Globe, Choke, Plug valve, Diaphragm valve).
Plug is a more convenient term to pronounce since most of the time we refer it to a conical (male) shape of the sealing element, as for the seat inner diameter profile is also conical (however female) shape. Bathtub and toilet plug also refer to this profile.

Not really sure where it came from originally, but I think Globe is referring to the Plug shape that is normally (full) half moon/globe. While choke valve's Plug shape is not necessarily designed that way.

API 6A is Specification for Wellhead and Christmas Tree Equipment which covers maximum rated working pressure of 2000;3000;5000;10000 and 15000 Psi
API 6D is Specification for Pipeline Valves which covers Rating pressure of 150, 300 up to 2500 Psig
Cage is an additional component that surrounds the Plug with function to "re-shape" upstream process flow into desirable profile prior "hitting" the Plug. let say more streamline, reduce risk of cavity and others. Om which if not treated may reduce the lifetime of the Plug or generate vibration, and so on.

Both Globe and Choke valve have the same function which is de-pressuring the flow and or regulating the flow capacity.
Flow de-pressuring is considered high rate if more than 35 bar (circa 500 Psig) pressure drop desired. And considered as low shall below 35 bar.
A single choke valve can easily do high rate de-pressuring, but it is not suggested for a single Globe valve to handle that. Some old refineries/Plants use single Globe valve to de-rate the line from 900 Psig to 600 Psig; 600 to even 150 Psig and so on. Or even regulating the flow under same pressure rating regime Form 900 to 150 suggested to use two Globe valves.
While Choke valve(s) function is mainly to choke the flow from API 6A rating to API 6D rating.

Hopes that answer. Maybe others have a better explanation.

Regards,
MR

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

 

[SPDL310]

I believe that globe valves are called that because of the shape of the body in older designs which was spherical.

It is my understanding that globe valves are generally used in lower pressure drop service. As Danlap stated choke are capable of taking higher pressure drops.

6A doe not mention globe valves as they are rarely if ever installed on Christmas trees or wellheads, which is the scope of 6A equipment.

 

[Erkamal]

Hi Frds.

Thanks lot. Your answer will help me.
i am trying to get more information that why it is not include in API 6A.

Same plug design in choke valve and globe valve so .

Or need to different Plug design consideration for API 6A choke valve and globe valve?

 

[georgeverghese]

There may also be differences in materials of construction / surface hardening for the trim materials between regular globe valves and choke valves.

 

[Danlap]

Now I am puzzled.
What was the question anyway? first asking about vocabularies of globe, plug, choke and 6A, and now the question goes to whether Globe valve might be incorporated into 6A? CMIIW.
Suggest to read the API 6A requirement, since whatever valve you are referring to should pass quite strict requirement (PR1 or PR2 test, etc.).

And also google might help, try write "Globe trim or Choke trim". They have reason why they are different:
a. Trim of Globe is more like a a full cast/forged mug shape;as for Choke is like a big needle with or without a sharp tip
b. Inlet and outlet port of Globe valve center-line is liner whilst for Choke valve is perpendicular (90 deg angle)
etc.



All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

 

[LittleInch]

Erkamel

Further to the excellent answers above

Plug type globe valve & Plug type choke valve both are used.

Both valves are simply control valves, the terminology is just something which has grown up over time.

In both product, plug and cage type trim has been used. so what is the difference between them.
Why we called globe valve not plug type valve.
Globe valves are in a basic sense a disc or contoured plug which moves off a hole and creates a variable pressure drop as the plug moves up and down. As the pressure drop increases, this can result in a cage and plug, but the flow comes from underneath the plug. simple diagram below. Below that is a more complex plug and cage, but again flow is from under the valve to outside

asn what is the diffrence between plug type globe valve and plug type choke valve? only related pressure ?

"Choke" valves are normally used in high pressure drop environments on the outlet of wellheads where there is multi-phase flashing liquid and gas. The wear on the elements and the desire to reduce noise, erosion and fluid velocity within the valve requires special cages and plugs. Also the valves are designed such that the force on the plug movement is not affected by the pressure on the upstream side. Hence choke valves usually have flow from outside the cage to inside to reduce impinging flow on the valve casing. The "plug" is sometimes on the inside, sometimes on the outside, but because it is at 90 degrees to flow velocity, can move up and down easily compared to a globe valve.

why plug type globe valve is not inclued in API 6A?
As noted above, pressure drops required are at a minimum 2 or 3,000 psig rated ( might not be that in practice, but need to be capable of it). Globe valves would require too much force to close under that pressure and would wear excessively, especially at low opening percentages.

Choke valve is used only higher pressure rating ?
Usually yes - Most other pressure drops under say 100 bar are usually some sort of globe valve, maybe with a plug and cage. More than 100 bar and the control valve type moves more into a choke valve type.

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

 

[Erkamal]

HI Littleinch,
Thanks a lot for your fully informative reply.