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Regulator Trim
2

Regulator Trim

Regulator Trim

(OP)
Really basic question here: can someone please explain what "trim" refers to with regards to regulators? And, is it the same as the percent capacity?   

RE: Regulator Trim

Its the special little goodies inside that change or somehow modify the pattern of flow through the valve to get a particular desired characteristic, such as low noise, reduced cavitation possibilities, etc.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

RE: Regulator Trim

(OP)
Thanks biginch.

Can you give examples of what these goodies are tho?  & does this mean that it DOES affect the capacity & therefore is also expressed as %capacity (instead of % trim)?

RE: Regulator Trim

The trim pertains to components such as the valve plug, seat, and associated components.  In the case of some "self-contained pressure-regulators, few options exist besides the actual regulator model selection.  For example, perhaps the valve plug in a Fisher 620 or 630 "Big Joe" has a Teflon disc that seats against a nozzle similar to the seat on a pressure safety relief valve.  However, with control valves there are many selections for metals, soft parts and the method that the pressure drop is made.  

RE: Regulator Trim

(OP)
i gotcha. thanks folks.

so how is the capacity determined from using different internals?  that is, how do you determine the trim level (70%,80% or 100%) if you replace a part with a different part??  or how is that trim level number determined in the first place??

RE: Regulator Trim

I don't know what you mean by trim "level?"

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

RE: Regulator Trim

(OP)

trim level = %trim = %capacity

check out this spec sheet for a mooney regulator:

http://www.mooneycontrols.com/pages/valves/29.html

in the bottom right corner are varying Cg's based on the level of trim or %capacity.  does anyone know how this level is determined?  

RE: Regulator Trim

It is not clear to me whether those are trim choices or just properties of THE trim.  This could be more like the tables for percent stem travel with the Cv for that percentage opening.  Email the vendor to confirm such details.

RE: Regulator Trim

Check this,
If you look at the little graph,

http://www.mooneycontrols.com/pages/valves/29-detail.html#graph

you will see that there is one of two springs that you can select.  Since each spring has a different spring constant, the percent open would be different for each spring at the same capacity, therefore (apparently) it made more sense for them to relate Cv to %Capacity rather than to %O.  The typical method of showing Cv to %O would require two graphs, one for each spring.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

RE: Regulator Trim

(OP)
thanks biginch. i didn't even think to look at that graph tho i had looked at a couple of the others. & your explanation does make sense. :)
 

RE: Regulator Trim

Its a pretty small graph.  Didn't make sense until I happened to "click on it".

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

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