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Errata HI ANSI 9.8

Errata HI ANSI 9.8

Errata HI ANSI 9.8

(OP)
Hi All,

Has anyone any knowledge of there being an error in the formula in this standard (9.8.7.3)?

The formula given is S = 1.0D + 2.3(Q/0.785*D^2)/(g*D)^0.5)*D

where Q is in L/s;D in metres;g 9.81m/s

For Q=750 L/s D= 1m I get 702m which is incredibly high?

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

RE: Errata HI ANSI 9.8

Yes there's an error. It should be Q expressed im m^3/s.

If you enter your data in the formula reported in HI ANSI 9.8 but for imperial units:

S = 1.0*D + 2.3((12*0,409*Q/D^2)/(12*g*D)^0.5)*D

with:

S in inches
D in inches
Q in USgpm
g = 32,3 ft/s^2

you'll get S = 67 inch = 1.7 m (which is what you'd get entering Q in m^3/s in the formula for metric system

RE: Errata HI ANSI 9.8

(OP)
ione,

Thanks for that. I wonder if ANSI/HI know? The second formula in 9.8.7.3 works with Q in L/s.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

RE: Errata HI ANSI 9.8

The first formula they've provided is not correct from a dimensional point of view. A simple dimensional analysis of the units involved shows that Q must be expressed in m^3/s.

The second formula on the other hand works with Q in l/s, because if you take a look at it you'll notice that the term 1/1069 at denominator is given by:

2.3/(785*(9,81)^0.5)

While in the first formula they've reported 0.785, which clearly exhibits a shift of a 10^3 factor (from l/s to m^3/s).

Said that I sincerely don't know whether at the HI are aware of this.
 

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