4 replies to this topic

[bme]

Hello.
I am a newbie here today. I have gone thru some of the topics and could not find the one I need. I wonder if anyone has information on how to size a throttle valve (butterfly valve) for natural gas application. Please share or direct me to any useful webpage.
Thanks in advance.
bme Gen

[djack77494]

bme,
Sizing any valve is determining an optimum or near optimum size for your application. For a throttling or modulating valve you want to have available convenient valve positions that would achieve the desired results. Let's look at each element separately.

1) Convenient valve position
Effective control is NOT achieved when the valve is operating close to its extremes. What you or I call close to extremes is arbitrary, but I tend to select valves that would operate between about 15% to 85% open. Furthermore, I define open in relation to the distance or the angle that I have available to move the valve's stem. Depending on the valve's characteristics, flow carrying capability is often not linearly related to position. For example, say I move the stem from 0degrees (fully closed) to 45degrees (half open) to 90degrees (fully open). At the 45degree position, the valve may be able to pass 75% of its ultimate capacity. The range I would consider acceptable would be (90*0.15=13.5degrees) to (90*0.85=76.5degrees).
2) Desired results is essentially the desired flowrate, constrained by:
a-Pressure Drop
b-Velocity (e.g. erosion/corrosion and/or saltation/stagnation concerns)
c-Noise/Vibration
Hope this helps. If not what you were looking for, come back with more specifics.
Doug

[bme]

Doug,
Thanks very much for your response. I have been searching the web for the information but I have not been satisfying with what I have found so far.
I am trying to come up with a right size (the throttle bore diameter) for a specific application. I habe seen lots of sites talking about the Cv, obtaining Cv for sizing etc... But how the Cv data related to the bore diameter of the throttle valve.
In summary, if I want to know what the right bore size is for my throttle body, what info do I need and how do I come up with the answer using the provided information. Thanks for your help.
bme Gen

[bme]

Hi Doug,
Will the mass flow rate and pressures information are enough to calculate the Throttle valve bore ID?
How is it accurate with the butterfly open/close? Thanks.

[djack77494]

bme,
I'm afraid that there is no simple & straightforward way of doing this type of calculation. But why do you care about the valve's bore? You're overthinking this problem, unless you work as a valve designer for a valve manufacturer. You only need to know what size valve will satisfy your needs. Refer to the literature obtainable from valve manufacturers for this information. Post back if you still have questions.