Adjustable Chokes Indicating mechanism - API 6A 2

[Dinu Stan]

Hi Everyone,

In API 6A, for chokes section, there is a clause for "Adjustable chokes indicating mechanism". as per the clause, whenever the chokes supplied with manual hand wheel actuator,

---quote---

chokes should be equipped with visible orifice-area-indicating mechanism to define the orifice area at any adjusted choke setting throughout its operating range. This mechanism shall be calibrated to indicate diameters of circular orifices having areas equivalent to the minimum flow areas at any adjustable choke setting. These markings shall be in diametrical increments of either 0.4 mm {1/64".} or 0.8 mm(1/32".) for choke settings between 0.0 mm (0 in.) and 19.2 mm (3/4".). inclusive. For choke settings above 19.2 mm (3/4"), diametrical increments of 0.4 mm (1/64".), o.8 mm 1/32".), or 1.6 mm (1/16') may be used.

---unquote---

questions:

1. what is the visible orifice indicating mechanism and how it should design?
2. should we indicate the calculated the orifice area or the circular dia. of the orifice area in the travel plate?
3. What is meant by the diametrical incremental?
4. how we can design the indicating mechanism? can anyone suggest to understand more...

Dinu...

There are no secrets to success. It is the result of preparation, hard work, and learning from failure.

 

[LittleInch]

1) I've been trying to find a photo but this is often a simple gauge going from 0 to 64 or 32 showing how much the valve is open. Sometimes it's a bar with a moving arrow and sometimes a set of figures on a stem with a line indicating the equivalent orifice diameter.
2) I believe it is the calculated equivalent orifice diameter
3) It means the diameter of the orifice equivalent to the orifice diameter if you inserted a fixed orifice of that diameter. This tends to go in units as you describe.
4) You design it so that the movement of the stem translates to the movement of a needle, or you show the movement against a fixed bar which has the increments shown on it and use a pointer fixed to the stem which moves in and out. Up to you.

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

 

[Dinu Stan]

Hi LittleInch, Thank you so much.. i have some Cameron's photograph attached here (got it from the google search).
i have understood what you have mentioned and it is gonna help me to further improvement.
for linear plate design i have done. but i need to know how to design the rotary type...
because in the linear plate, i couldn't accommodate all the orifice sizes like 1/64,2/64,3/64......64/64.
it will possible in the rotary design only. but i couldn't get an idea that how i need to calculate the rotations & place the diameter in the bush as per the opening area.
could you help me to know little bit to boost up my thinking knowledge to find the way to design???

Dinu...

There are no secrets to success. It is the result of preparation, hard work, and learning from failure.

 

[SPDL310]

Your marks are based upon a certain amount of linear travel. You will need to transpose those into a coordinate system that follows the rise of the stem, based on the thread pitch of the stem. You can realistically look at the indication as one long line with a constant slope. Then break that line into segments that are the circumference of your indicator, and stack them on top of each other accordingly. Now you have an (X,Y) coordinate system for your indications.

 

[Dinu Stan]

Thanks SPDL310...
Let me try to think to find some way to apply your concept.

suggest me something further please...

For Example, 40mm travel for 64/64 bean size, the indicator bush marking should have diameter of the equal orifice area like 1/64,2/64......64/64.
Here the travel is in rotary way. based on the thread pitch i can calculate the Linear travel and equate the coordinate points of some diameters by percentage travel vs calculated area of opening orifice.

but how can i place all the complete ratio like 1/64,2/64......64/64 in the correct coordination. should i have to use trail and error method by making one bush and install and then marking. else is there any theoretical methods...

apologies to ask more in detail. since i couldn't know where i need to start.. so many questions are raising in my mind if i have about to start then i came back to think again...

Dinu...

There are no secrets to success. It is the result of preparation, hard work, and learning from failure.

 

[SPDL310]

Dinu,

Think of it as that you are wrapping a string around your drum at the same pitch that you stem thread is rising. That string will be X long and rise Y high. You have a drum circumference of C. As you travel along a straight incline from 0 to X you rise Y. The slope of your string m = Y/X. At each height increment for you opening percentage use the formula Y = mX + b with b=0. For any value of X greater than C subtract C now you have the X,Y coordinates of your indication marks.

 

[Dinu Stan]

Thank You SPDL310.

your answer is gonna be helpful further. Let me try and get back you if i have any further doubts...
Thank You So much...

Dinu...

There are no secrets to success. It is the result of preparation, hard work, and learning from failure.