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Unformatted text preview: 1 JHYDRAULIC TRANSIENTS
 Any unsteady state flow condition  Water hammer
 velocity changes pressure changes — included in the analysis
 commasebum e.‘ water
 e‘astmr,‘ ‘5’ pp?  the larger the change andlor the faster the change the greater the transient pressure
change. 2 JWater Hammer  t= : tune of closure  ‘lnstant‘ valve closure
t: < ZUa
were a = Nave $9930 ' I ’
\H = a V59 ‘1 .  I  “Very stout“ valve closure in ’=' 20 Lra ' "
._\H = L wig t.)  ‘Slcw valve closure’
20 Lr'a >t,_ :2 Lia 3 JControlting Transients  increase time of verve closure use caution ﬁlling pipes 1 increase pressure class of pipe limit pipe velocrty Reduce wave speed
 we of pipe — inlect air a Pressure relief
— vane
—— surge tanks 1 j] HYDRAULIC TRANSIENTS
« Any unsteady state flow condition o Water hammer
) l. _
— velocity changes pressure changes " — included in the analysis
 compressbll'rty 0! water
 elasticity of pipe  the larger the change andlor the faster the change the greats
change.
2 jWater Hammer 0 It 2 time of closure  'lnstant‘ valve closure .4 I I 9 x
l‘ : 4.1.  Ly), . r ,' E. ' '"‘ c “. ~ i ‘
1G < 2Ua ’
x , ’1
where a = wave speed " (7 1" 'j " 3' "~
1 ‘l I' v— r
 “Very slow“ valve closure \_ a 3,. I? E a 1 l “ ‘r
t: = 20 U3 g I  “3.. '1
AH = L we u  'Slow valve closure'
20 Ua MC :2 Ua 3 JControlling Transients
 increase time of valve closure  use caution ﬁlling pipes  increase pressure class of pipe Ii HYDIAUIIC HANDIOOK HYDRAL less than the time, required for the induced grueure wave to trevei c t tin f th
from the point a! valve closure to the inlet end of the. line and the 323;.333; ch;
return. Th1. time h, 3‘3th 3': water We: pressing!
_ ~ velocity oi water stopp t =g. 39° 9" N CL” U R t investigations by the p. 1 pressure caused by an where: obtained by the correct
. ' constants of the liquid t m tune. in seconds. for pressure wave to travel the length 0! bun; modulus of elastit the pipe and return.
L =length, in feet, at the pipe line. I=veiocity. in feet per secoud. of pressure wave. ' ‘_
.glggl
. . HIE!!!
One form oi the iormula. developed to determine the velar“, '.iqi
of the pressure wave. is !=#!
12 :E..=
= ' .ﬁ
.‘ , ' :legg.
v i + “E: i .332“
Where: a: velocity of pressure wave, fps. g = acceleration caused by gravity = 32.2 feet per sec. per sec. Iliii w = weight of one ctr. it. of water. lbs. d = inside dismeter of pipe. in. e = thickness oi pipe wall. in. k = bulk modulus of compressibility of water: approximately
300,000 psi. E=modulus of elasticity of pipe material. psi: for steel—
approximately 30,000,000. For cast iron— approximately 15,000,000. Maximum Water Hammer Pressure. The formula that eval
uates the maximum pressure caused by water hammer is: P! 0.433 a V
g \Vhea'e: y = maximum pressure, psig. e = velocity oi pressure wave, fps. ‘5' = velocity of water stopped, fps. 3: acceleration caused by gravity .:. 32.2 it. per sec. per sec. HG. 3. Maximum “,0
i163 = a constant used to convert feet of head to psi. on instantaneous closl M “VDIAUUC HANDBOOK Example :  What is the maximum pressure caused by water hammer in an
' 8inch steel pipe has (0.322inches wall thickness) transporting
water at s steady velocity at 3 fps? Procedure in Using Chart: . . d __ insidedilofpipe. in. __ 7.98! _
Denim” u“ "m" 'e' _ wall thickness at pipe, in. _ 0.322 “ 2”“ Enter the chart at g = 24.8 and project upward to the intersec tion with the line for steel pipe. Note that the value of the velocity oi the pressure wsve. . _.
4225 fps. ' Project horizontally to the right, to an intersection with the 3
fps. velocity line and then down to the base line, where shock pres
sure of 170 psi is chiauct‘. SPECIFIC GRAVITY AND HEAD The head develo by a centrifugal pump depends upon the
peripheral velocity the impeller. It is expressed thus: 11'
H=E
Where ; H = Total Head at zero capacity developed by the pump in feet
of liquid
:1 = Velocity at periphery of impeller in feet per second Notice that the head developed by the pump is independent 0‘.
the weight of the liquid pumped. Therefore in Fig. 4 the head if I_ muss» no. la .9 = 0.70 FIG. 4. Pressure—head relationship identical pumps handling liquids of
diﬂering speciﬁc gravitios. HYD! in feet would he the
with a speciﬁc gravi
3 s3. of 1.2 or a Rain
reading on the get:
peller diameter and The gauge readin Refer to Fig. 5. 1
at 50 psi. Because
liquids each pump t
ii the speed of all thr:
have the largest dist: FIG. 5. Pl’ﬂ'ﬁE; ~
handling liquid: r: Standard perform“
total head in feet 3.5!
Water is the liquid :r.
in feet developed by a
gravity. if the head i:
the desired head and
curves without correr
same as that of wate
will applyo.r11x_t_°_!i:
liquids multiply the
being pumped. J
POWER, EFFICIE The Horse Powc
ured from the follov. IOOK l pr 1 wave to travel
ilet of the line and e to travel the length oi '55“ re wave. 1 determine the velocity ‘h—uIII 32.2 feet per sec. per see. if i ; approximately aterial. psi: for steel—
ist iron—appr0ximately Fhe formula that eval
ater hammer is: 32.2 it. per sec. per sec.
head to psi. HYDRAULIC FUNDAMEN1ALS 13
mm Computations of the preceding formulae permit the layout of
the accompanying chart, Fig. 3. which discloses the maximum
water hammer pressure for various pipe sizes, thickness. and the
velocity of water stopped. This chart is for water only. but recent
investigations by the petroleum industry. disclosed that the shock
pressure caused by any relatively incompressible liquid can be
obtained by the correct substitution of the formula .f the physical
constants of the liquid: namely, those of weight p cu. ft. and
boil modulus of elasticity. Ilaggﬂglmnlnlnl
I arariyﬂnmlm
' gotten2:2!!!lllﬂl
' ‘55::!=:;%:=%=E==!"'
I i==='—:::==::§==§=t"' raineennes'"
I. Eggleeegaﬁeﬂagﬂl
l Egggtggsgggsrsseglll
II Elssssssuiissseeii nunm I IIIIlli'lllll
Ilillllﬂ=l=IIIIIIII=  llllll llllllllllllllll
llllllllllllllll lI “in: II Ir .irie Diorr ., inches
\Jall Thickness, Inches o:Velocily o! Fretsare Ware FI. Set. FIG. 3. Minimum shock pressure caused by wore! hamme' {based
on instantaneous closure of valves}. ...
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 Spring '08
 Heaney

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