The Steamboating Forum

I'm trying to better characterize a steam ball valve for a little project.

1) What is A?
2) What is B?
3) Is the line in area C linear?
4) Should the Y axis be 'Flow' rather then 'Percent Open' to see the quirkiness of the ball valve?

It's a standard 1/4 turn steam rated Apollo Ball Valve (Shouldn't really matter).
-CB

A few moments with Google yields...

http://files.engineering.com/download.a ... le=343.pdf


- Bart

The way you have it is what appears to be common practice with the stem position on the bottom.

That said, a ball valve is a little under 20% open at 45deg and is not 50% open until around 67.5deg

Good steaming

Dave

Thanks guys!

-CB

FYI: When I say percent open that is percent of the fully open valve area not neccessarily the flow which may vary some depending on the characteristics of the fluid in being moved.

Dave

In case some translation is needed: Valve flow is typically described by Cv in US units; in the graph above
the X axis means either Kv or Cv as a percentage of their maximum
values.

Here's a discussion of how to use Cv in calculations:

http://www.engineeringtoolbox.com/flow- ... d_277.html

- Bart

The chart of ball valve flow coefficient vs valve opening is only half the story. The fluid system to which the valve is connected has a strong influence on the flow rate, and the charts presented show only the valve characteristic.

As an extreme example, say you have a pressurized tank with just the valve connected, and compare this to the same condition, except there is 1mile of pipe added to the circuit. In the first case the valve opening governs the flow, and from zero opening to full opening flow will generally increase continuously.

In the second case, the friction in the one mile of pipe dominates the flow, and limits the flow to a small percentage of the first case. As the valve is opened to, say 10%, most of the flow is established, and limited by the one mile pipe friction. Further opening of the valve results in no increase of flow. While this is an extreme example, I have seen many instances where line friction, in the form of a clogged strainer, or an undersized pipe, or other restriction within the circuit is the relevant parameter of the flow rate. In all fluid systems the circuit has an influence that reduced the influence of the valve, except for full shutoff.

fredrosse wrote:The chart of ball valve flow coefficient vs valve opening is only half the story.

I don't especially like black boxes myself.

For my application, as it exists.
Boiler Nozzel -> 1/2" Schedule 80 seamless steel pipe -> Ballvalve(Used Isolation on/off) -> 1/2" Steam King Hose -> same kind of pipe -> Ballvalve(Flow - ie one I'm characterizing) -> same kind of pipe -> 1902 Toledo Engine(1/2" NPT inlet).

It's 8-10FT length including the hose.

So no strainers, and despite a restriction in the steam King Hose ID the max flow is sufficient for my project.

-CB

My experience w/ ball valves as throttle was not great, but that was on a boiler w superheater, so the steam temps could have been high for Teflon.

- Bart

I get by with a ball valve for my throttle but it is a bit sudden when opening. I haven't researched it but is there any off the shelf 1/4 to 1/2 turn alternative? And I don't mean some wonderful machining project with castings.