What is "turndown ratio" ?
What is "turndown ratio" ?
(OP)
I understand that it's the range of flow ? for example max flowrate (100%open) = 25 ft3/min and has turndown ratio = 150:1 .It means the accurate minimum flow of this valve = 25/150 = 0.167 ft3/min, right ?
Thanks
Nong
Thanks
Nong





RE: What is "turndown ratio" ?
RE: What is "turndown ratio" ?
maximum controllable flow
Rangeability R=-------------------------------
minimum controllable flow
normal maximum flow
Turndown ratio T=----------------------------------
minimum controllable flow
Genrellay valves are designed so that T=0.7*R where R is between 20 and 50.
Best Regards
Morten
RE: What is "turndown ratio" ?
You can actually not say much based on your numbers above, because the flow when the valve is 100% open is NOT controllable and you can therefore not calculate your minimum controllable flowrate.
Best Regards
Morten
RE: What is "turndown ratio" ?
Thank you, but I'm quite not clear from your answer, you mean T = 14 to 35 or 2.5:1 ? (because I always see that turndown = Numbers : Numbers
Rdgs,
nong
RE: What is "turndown ratio" ?
My second positing simply tells you a connection between R and T. But this connection is emperical and not true for all valves.
Best Regards
Morten
RE: What is "turndown ratio" ?
Mostly turn down ratio will indicate the flow parameters . but it is not a neccesity sometime pressure could be a critical turn dowm parameter for which we would be asked to give the gaurantee .
regards
kumar
kum@epc.ltindia.com
RE: What is "turndown ratio" ?
If Max flow is 100 GPM and Min FLow is 10 GPM
Turndown is 10:1 (100/10)
Some times turndown is incorrectly applied to valves, which is actually rangeability.
Rangeability is the range overwhich the valve can control - Ratio between the maximum and minimum flow coefficients. So if a valve provides good control between 2% and 98% of the flow capacity the rangeability is 49:1 (98/2).
Naturally this is a simple explaination and there can be other factors that may affect the outcomes, such as pressures.
But in general, these definitions should get you started.
RE: What is "turndown ratio" ?
Perry's disagree with you. What you have stated is what they term "rangeability" whereas turndown (as i previously posted) is defined as:
Normal max. flow
T= ---------------------------
min. controllable flow
and
Max. controllable flow
R= _____________________________
min. controllable flow
Note that "normal max flow" is not the same as "max. controllable flow". Anyway since this post is more than 1 month old we better hope Nong already got it sorted out
Best Regards
Morten
RE: What is "turndown ratio" ?
I have gone by those definitions for years, although I know that they were often used interchangably. But I checked the ISA standards this AM and it seems that I was wrong, "turndown"is obsoleted and rangability is stated as you say.
Thanks for the heads up.