minimum Cv for a masoneilan choke

[Ebbot]

Good morning folks,

I have a choke from Masoneilan (6" x 8"), and I'm asked how low in flow it can be adjusted.

The problem is that it's a pretty old choke, and I don't have any datasheet of it. The only thing I got is a model number: 38-7777-3C, angle choke from Masoneilan.

Does anyone know what valve it is?

Are there any “rule of thumb” on how low you can go in flow rate of this type of choke? I’m also concerned of the temperature, as it will be pretty cold with too big ?P.

The media is gas, normally used for well-injection (oil platform) and is free from sand/particles.

Thanks!

 

[JimCasey]

Masoneilan has been making the 77000 series valve for at least 40 years, and the 38 actuator is an even older spring-diaphragm design (Spring on top, air pushes stem UP)So a 38 actuator will cause the 77000 to fail open. Actuator is mounted off the side a bit, and drives the valve stem though a rocker arm.

The 77000 has a conical, multistage, balanced plug in a reciprocally shaped, very tall, multistage throttling body. All the stages contribute to pressure loss at any valve position. So controlling down to 10 percent or even a bit less won't cause the seatring to be destroyed or other ill effects, such as uncomfortable noise level. It's MADE for high pressure drop, so that's not a problem. Biggest threat would be grit eroding the small clearances between trim pieces at very small openings, but you report that the stream is grit-free.

 

[Ebbot]

Thanks Jim!

I found some datasheets of the 77000 on internet. It's manually operated (wheel) so I guess there has been some modifications but I think the valve is the one you suggested.

 

[Ebbot]

Ok, so it one of these we have:

http://www.corona-control.se/certificates/BP5500e.pdf

The model no is 38-77773-C wich gives us a Size C linear Plug (high capacity single step). It says that the max. allowable pressure drop is 275bar for a air-to-open as well as an air-to-close valve. Is this value the same for a manually operated (wheel)?

It says something about "rated Cv", is this the maximum Cv (100% open)?

It also says "single step". Could anyone explain that term?

Thanx!

 

[sheiko]

yes "rated CV" is "100 % open CV"

"We don't believe things because they are true, things are true because we believe them."

 

[Ebbot]

Ok,

so if the choke have a rangeability 100:1, and a max Cv of 260. This means that it's ok to choke down to Cv 2.6?

 

[JimCasey]

"Single step" is shown in the "dimensions" page of the linked document. Instead of a series of stage rings on the plug, there is only the single plug element that meets the seat ring. All the pressure is dropped in one stage. Noisy.