Brochure
8080
5. Pump losses
5.2 Mechanical losses
The pump coupling or drive consists of bearings, shaft seals, gear, depending
on pump type. These components all cause mechanical friction loss. The
following deals with losses in the bearings and shaft seals.
5.2.1 Bearing loss and shaft seal loss
Bearing and shaft seal losses - also called parasitic losses - are caused by
friction. They are often modelled as a constant which is added to the power
consumption. The size of the losses can, however, vary with pressure and
rotational speed.
The following model estimates the increased power demand due to losses
in bearings and shaft seal:
(5.1)
(5.2)
(5.3)
(5.4)
(5.5)
(5.6)
(5.7)
(5.8)
(5.9)
(5.10)
(5.11)
(5.12)
(5.13)
(5.14)
(5.15)
constantPPP
loss, shaft sealloss, bearingloss, mechanical
=+=
g2
V
HH
2
dyn, inloss, friktion
⋅ ζ = ⋅ ζ =
g2D
LV
fH
h
2
loss, pipe
=
O
A4
D
h
=
ν
=
h
VD
Re
Re
64
f
laminar
=
0.0047
32mm
0.15mm
k/D Relative roughness:
110500
sm101
0.032m3.45m s
VD
Re
Reynolds number:
sm3.45
m0.032
4
sm(10/3600)
A
Q
VMean velocity:
h
26
h
22
3
==
=
⋅
⋅
=
ν
=
=
π
==
−
sm
sm
gD
LV
f
H
h
loss, pipe
1.2 m
9.8120.032m
)3.45(2m
0.031
2
Pipe loss:
2
2
2
=
⋅⋅
⋅
==
g2
V
HH
2
1
dyn,1loss, expansion
⋅ ζ
=
⋅ ζ =
2
2
1
A
A
1
− = ζ
g2
V
A
A
1H
2
0
2
2
0
loss, contraction
⋅
− =
g2
V
HH
2
2
dyn,2
loss, contraction
⋅ζ=⋅ζ=
g2
ww
g2
w
H
2
1, kanal1
2
s
loss, incidence
⋅
−
ϕ=
⋅
ϕ=
2
2
design1
loss, incidence
k)QQ(kH +−⋅=
m
22
6
4
22
3
2
loss, disk
DU
102
103.7k
)e5D(DUkρ
P
⋅ ν
⋅ =
+ =
−
( ) ( )
( )
( )
B
5
2
3
A
5
2
3
B
loss, disk
A
loss, disk
Dn
Dn
PP =
(5.16)
(5.17)
(5.18)
(5.19)
leakageimpeller
QQQ +=
( )
g8
DD
HH
2
gap
2
2
2
stat, impellerstat, gap
−
ω − =
g2
V
1.0
g2
V
s
L
f
g2
V
0.5H
222
stat, gap
++=
gap
leakage
stat, gap
VA
Q
1.5
s
L
f
2gH
V
=
+
=
where
P
loss, mechanical
= Increased power demand because of mechanical loss [W]
P
loss, bearing
= Power lost in bearings [W]
P
loss, shaft seal
= Power lost in shaft seal [W]
5.3 Hydraulic losses
Hydraulic losses arise on the fluid path through the pump. The losses occur
because of friction or because the fluid must change direction and velocity
on its path through the pump. This is due to cross-section changes and the
passage through the rotating impeller. The following sections describe the
individual hydraulic losses depending on how they arise.