Graco Husky 2150e - Page 28

PerformanceCharts
How How
How
to to
to
Calculate Calculate
Calculate
Your Your
Your
System’s System’s
System’s
Net Net
Net
Positive Positive
Positive
Suction Suction
Suction
Head Head
Head
– –
–
Available Available
Available
(NPSHa) (NPSHa)
(NPSHa)
Foragiven󰘱owrate,theremustbeaminimum
󰘱uidheadpressuresuppliedtothepumptoprevent
cavitation.Thisminimumheadisshownonthe
PerformanceCurve,labeledasNPSHr.Theunits
arefeetWC(WaterColumn)absolute.TheNPSHa
ofyoursystemmustbegreaterthantheNPSHrto
preventcavitationandthereforeincreaseef󰘰ciency
andthelifeofyoupump.TocalculatetheNPSHaof
yoursystem,usethefollowingequation:
NPSHa NPSHa
NPSHa
= =
=
H H
H
a a
a
± ±
±
H H
H
z z
z
– –
–
H H
H
f f
f
– –
–
H H
H
v v
v
p p
p
Where: Where:
Where:
H H
H
a a
a
istheabsolutepressureonthesurfaceoftheliquidinthesupplytank.Typically,thisisatmospheric
pressureforaventedsupplytank,e.g.34feetatsealevel.
H H
H
z z
z
istheverticaldistanceinfeetbetweenthesurfaceoftheliquidinthesupplytankandthecenterlineofthe
pumpinlet.Valueshouldbepositiveifthelevelishigherthanthepumpandnegativeifthelevelislower
thanthepump.Alwaysbesuretousethelowestleveltheliquidcanreachinthetank.
H H
H
f f
f
isthetotalofthefrictionlossesinthesuctionpiping.
H H
H
vp vp
vp
istheabsolutevaporpressureoftheliquidatthepumpingtemperature.
283A4068H