fundamentals of centrifugal pumps - Master Pumps and Power
fundamentals of centrifugal pumps - Master Pumps and Power
fundamentals of centrifugal pumps - Master Pumps and Power
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PRODUCT TRAINING<br />
FUNDAMENTALS OF<br />
CENTRIFUGAL PUMPS<br />
1
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
A <strong>centrifugal</strong> pump is a mechanical device that<br />
converts energy to hydraulic work<br />
Energy is supplied by a driver such as an electric<br />
motor, turbine, or engine<br />
Hydraulic work is the movement <strong>of</strong> a liquid mass<br />
through a distance<br />
This presentation is limited to <strong>centrifugal</strong> pump<br />
types only<br />
Sundyne <strong>pumps</strong> are a special design that will not be<br />
covered in this presentation<br />
2
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
Just Say NO!!!!!<br />
3
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
The work takes place at an impeller which<br />
accelerates the liquid by whirling it through<br />
the impeller thus adding <strong>centrifugal</strong> force<br />
<strong>and</strong> hence acceleration<br />
4
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
When an object is<br />
spun around in a<br />
circle it is accelerated<br />
outward by<br />
<strong>centrifugal</strong> force<br />
5
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
When liquid is spun<br />
around in a circle, it<br />
accelerates outward<br />
from the center <strong>of</strong> the<br />
circle due to<br />
<strong>centrifugal</strong> force<br />
6
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
An impeller has vanes<br />
which are blades that<br />
push the liquid through<br />
the impeller. The center<br />
<strong>of</strong> the impeller where the<br />
liquid enters the impeller<br />
is called the eye<br />
Vanes<br />
Eye<br />
7
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
To obtain useful<br />
work, the impeller is<br />
contained in a casing<br />
which directs the<br />
accelerated fluid<br />
along a desired path<br />
Discharge<br />
8
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
Pump Impeller <strong>and</strong> Shaft<br />
9
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
Pump Impeller <strong>and</strong> Shaft<br />
with Pressure Casing<br />
10
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
Pump Impeller<br />
<strong>and</strong> Shaft with<br />
Pressure Casing<br />
<strong>and</strong> Cover<br />
11
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong><br />
Process<br />
Fluid<br />
Adjustment<br />
Packing<br />
Stuffingbox<br />
Cover<br />
12
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Impeller Design<br />
The impeller is the most important part <strong>of</strong> the<br />
pump since it is where the work is taking<br />
place. Furthermore, the impeller plays an<br />
important role in the design <strong>of</strong> other pump<br />
components. It has a direct effect on the seal<br />
cavity pressure for example<br />
13
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Many different types <strong>of</strong><br />
impeller styles are used.<br />
Most, but not all, have vanes<br />
that curve away from the<br />
flow path so that the liquid<br />
is in contact with the<br />
impeller longer. These are<br />
referred to as “reverse reverse<br />
curve” curve vane impellers<br />
Vanes<br />
Eye<br />
14
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Impeller vanes may be<br />
enclosed by “shrouds shrouds”. .<br />
In general impellers with<br />
shrouds are slightly less<br />
efficient due to the drag<br />
<strong>of</strong> the liquid on the<br />
shroud<br />
15
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Therefore many<br />
impellers have no<br />
shrouds. They are called<br />
“open open” impellers. Note<br />
that the bottom impeller<br />
is “partially partially shrouded” shrouded<br />
due to a shroud area<br />
around the impeller eye<br />
16
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Some impeller designs<br />
may also have a shroud<br />
only on one side <strong>of</strong> the<br />
impeller. They are also<br />
said to be partially<br />
shrouded or semi-open semi open<br />
or semi-closed semi closed<br />
17
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Shrouds are generally used on larger impellers to<br />
help support the vanes <strong>and</strong> maintain the<br />
impeller shape under extreme pressure <strong>and</strong><br />
temperature conditions. They also have the<br />
disadvantage <strong>of</strong> limiting the particle size that can<br />
pass through the impeller<br />
18
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
There are two different impeller<br />
types used in the process industry.<br />
They differ by the type <strong>of</strong> flow<br />
through the impeller. The most<br />
common type is a “radial radial flow” flow<br />
impeller where the liquid makes a<br />
90 o turn as it passes through the<br />
impeller<br />
19
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
In a turbine type impeller, the liquid<br />
also makes a turn as it passes through<br />
the pump, but less than 90 o . These are<br />
most <strong>of</strong>ten found in “diffuser diffuser” type<br />
<strong>pumps</strong> which relates to the casing<br />
design <strong>and</strong> will be discussed later.<br />
Since the liquid makes less <strong>of</strong> a turn, a<br />
turbine style impeller may be slightly<br />
more efficient than a similar “radial radial<br />
flow” flow impeller<br />
20
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
The impeller has a direct relationship to<br />
pump performance. The design <strong>of</strong> the<br />
impeller is the single most important factor<br />
in determining the flow rate <strong>and</strong> liquid<br />
pressure that a pump can generate<br />
21
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
The <strong>Master</strong> <strong>Pumps</strong> & <strong>Power</strong> catalog is an<br />
excellent reference resource for most<br />
pump application problems. It should be a<br />
part <strong>of</strong> every engineers library. It is free to<br />
all <strong>of</strong> our customers<br />
22
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Flow through an impeller is determined<br />
primarily by three factors<br />
Vane width<br />
Number <strong>of</strong> vanes<br />
Impeller speed<br />
23
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
A wide vane impeller<br />
will move more liquid<br />
per unit time than a<br />
narrow vane impeller.<br />
The flow is directly<br />
proportional to the<br />
vane width<br />
24
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Flow (Q) through an<br />
impeller is also<br />
directly related to the<br />
impeller speed. The<br />
more times an<br />
impeller rotates per<br />
unit time the more<br />
fluid is will move<br />
25
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Finally the flow<br />
through a pump is<br />
somewhat related to<br />
the number <strong>of</strong> vanes<br />
although it is not<br />
directly proportional.<br />
More vanes will move<br />
more fluid<br />
26
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
An impeller creates<br />
“head head” by<br />
accelerating the fluid<br />
to a given velocity.<br />
As it spins, the fluid is<br />
accelerated outward<br />
by <strong>centrifugal</strong> force<br />
27
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
The fluid exits the<br />
impeller at a given<br />
velocity. Therefore it<br />
will rise to a given height<br />
in a column based on the<br />
exit speed regardless <strong>of</strong><br />
the weight <strong>of</strong> the fluid<br />
28
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
Therefore a <strong>centrifugal</strong> pump is said to be a<br />
“constant constant head” head device. At a given speed it will<br />
accelerate a liquid to a given velocity regardless<br />
<strong>of</strong> the weight <strong>of</strong> the liquid.<br />
A heavier liquid would require more<br />
horsepower <strong>and</strong> the discharge pressure would<br />
be higher, but it would rise in a column no<br />
higher than a light liquid<br />
29
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
This phenomenon is based on simple laws <strong>of</strong><br />
physics<br />
(V 2 = 2 AS) where V is the velocity, A is the<br />
acceleration <strong>of</strong> gravity, <strong>and</strong> S is the height<br />
Note that this formula makes no<br />
consideration <strong>of</strong> weight<br />
30
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
If fluids are pushed up a<br />
column to the same<br />
height, the pressure at<br />
the bottom <strong>of</strong> the<br />
column would be<br />
different for fluids <strong>of</strong><br />
different weight.<br />
The formulae for this<br />
relationship are as follows<br />
hd. hd.<br />
ft. =<br />
(psi psi X 2.31) / sp. gr.<br />
psi =<br />
(hd hd ft. / 2.31) x sp. gr.<br />
31
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impellers<br />
<strong>Pumps</strong> <strong>Pumps</strong>-Impellers Impellers<br />
To illustrate, a pressure gauge<br />
at the bottom <strong>of</strong> a 231 ft. high<br />
column filled with water<br />
would read 100 psi. psi.<br />
If the<br />
column was filled with butane<br />
having a specific gravity <strong>of</strong><br />
only .5, the gauge would read<br />
50 psi<br />
231 ft.<br />
32
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
In order for the pump to move fluid, the system<br />
must be able to push fluid into the pump as fast<br />
as the pump can push it out.<br />
Therefore there must be a certain minimum<br />
required suction pressure for each pump based on<br />
the pump flow<br />
This pressure is expressed in head feet <strong>and</strong> is<br />
referred to as NPSH -net net positive suction head<br />
33
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
NPSH is expressed in two ways<br />
NPSHA is the net positive suction head available<br />
from the system<br />
NPSHR is the net positive suction head required by<br />
the pump at a particular flow<br />
NPSHA must always be greater than NPSHR or<br />
damage to the pump will occur due to cavitation<br />
34
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
Cavitation is the flashing <strong>of</strong> the liquid at the<br />
pump impeller eye caused by the pump<br />
lowering the pressure in the eye area as it<br />
accelerates fluid across the impeller<br />
The damage occurs when the flashed gas is<br />
compressed back to a liquid as it gains<br />
pressure while traveling through the impeller<br />
35
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
Cavitation causes pump problems in two areas<br />
Severe cavitation can erode the pump<br />
impeller resulting in decrease performance<br />
<strong>and</strong> vibration due to imbalance<br />
Cavitation normally results in substantially<br />
higher vibration in the entire pump<br />
36
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
NPSH is the total suction head in feet<br />
<strong>of</strong> liquid (absolute at the pump<br />
centerline or impeller eye) less the<br />
absolute vapor pressure (in feet ) <strong>of</strong><br />
the liquid being pumped<br />
37
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
NPSHA is the NPSH available at the pump suction nozzle <strong>and</strong><br />
depends on the suction system design. It must always be equal<br />
to or greater than the NPSHR<br />
NPSHR is the NPSH required by the pump for stable operation.<br />
It is determined by the pump manufacturer <strong>and</strong> is dependent on<br />
many factors including the type <strong>of</strong> impeller inlet, impeller design, design,<br />
pump flow, rotational speed, nature <strong>of</strong> the liquid, etc. It is<br />
usually plotted on the characteristic pump performance curved<br />
supplied by the pump manufacturer<br />
38
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
NPSHA is a difficult calculation. It will require<br />
the help <strong>of</strong> a process engineer from the plant<br />
NPSHA can be determined by direct field<br />
measurement if the vapor pressure is known. A<br />
method for this calculation is presented later<br />
39
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
*Assume vapor pressure<br />
<strong>of</strong> water @ 80 F = .5psia<br />
or 1.2 feet = hvpa *Assume atmospheric<br />
pressure @ sea level<br />
or 34.0 feet = ha Height = hst *Assume pipe losses = 15 feet<br />
3.5 feet = hfs *NPSHA = ha - hvpa - hst - hfs *NPSHA = 34 - 1.2 - 15 - 3.5 =<br />
14.3 feet<br />
NPSHA Example for Suction Lift<br />
Atmospheric<br />
Pressure = h a<br />
40
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
Atmospheric Pressure = h a<br />
Height = h st<br />
15 feet<br />
*Assume vapor pressure<br />
<strong>of</strong> water @ 80 F = .5psia<br />
or 1.2 feet = h vpa<br />
*Assume atmospheric<br />
pressure @ sea level<br />
or 34.0 feet = h a<br />
*Assume pipe losses =<br />
3.5 feet = h fs<br />
*NPSHA = h a - h vpa + h st - h fs<br />
*NPSHA = 34 - 1.2 + 15 - 3.5 =<br />
44.3 feet<br />
NPSHA Example<br />
for Flooded Suction<br />
41
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-NPSH<br />
<strong>Pumps</strong> <strong>Pumps</strong>-NPSH NPSH<br />
Simple Method to Determine NPSHA<br />
NPSHA is the total suction head in feet <strong>of</strong> liquid (absolute at<br />
the pump centerline or impeller eye) less the absolute vapor<br />
pressure (in feet) <strong>of</strong> the liquid being pumped<br />
Measure the suction pressure <strong>and</strong> convert to feet <strong>of</strong> head<br />
(must be absolute not atmospheric)<br />
Determine the vapor pressure <strong>of</strong> the liquid <strong>and</strong> convert to<br />
feet <strong>of</strong> head<br />
Subtract the vapor pressure from the suction pressure<br />
42
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
A pump manufacturer will supply a curve for<br />
every pump purchased which graphically<br />
represents the expected pump performance<br />
For most applications, a copy <strong>of</strong> the pump curve<br />
is required information for properly selecting a<br />
sealing system <strong>and</strong> flush plan<br />
43
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Head<br />
BHP<br />
Flow, GPM<br />
NPSHR<br />
Efficiency<br />
44
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Contents<br />
What pump curves represent<br />
How to read pump curves<br />
45
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Head<br />
BHP<br />
A Pump Curve<br />
Flow, GPM<br />
NPSHR<br />
Efficiency<br />
46
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Summary <strong>of</strong> Pump Curve Info<br />
Graphical representation <strong>of</strong> performance<br />
Head Head<br />
BHP BHP<br />
Efficiency Efficiency<br />
NPSHR NPSHR<br />
47
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Summary <strong>of</strong> Pump Curve Info<br />
Graphical representation <strong>of</strong> performance<br />
Contains more than performance data<br />
speed<br />
stages<br />
may have info about liquid<br />
impeller, case patterns<br />
wear ring clearances<br />
48
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Actual Sample Curve<br />
Pricebook Curve<br />
49
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Actual Sample Curve -Job Curve<br />
50
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
P1<br />
How Pump Curves are Made<br />
Pump<br />
P2<br />
Flow Meter<br />
51
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Test Data<br />
Flow P2 - P1 BHP<br />
0 311 20<br />
400 291 117<br />
800 234 156<br />
960 195 163<br />
Pressure in PSIG<br />
52
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Convert Pressure to Feet <strong>of</strong> Head<br />
Head = 2.31 (P -P 2 1) ) / S.G.<br />
Head is in Feet!<br />
53
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Compute Efficiency<br />
Efficiency = Theoretical Horsepower<br />
divided by Actual Horsepower<br />
Convert to Percent<br />
54
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Test Data<br />
Flow Head BHP Efficiency<br />
0 718 20 ***<br />
400 672 117 58%<br />
800 540 156 70%<br />
960 450 163 67%<br />
Now in feet<br />
55
TDH Head Portion <strong>of</strong> Pump Curve<br />
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
0 200 400 600 800 1000 1200<br />
Flow, GPM<br />
56
BHP<br />
180<br />
160<br />
140<br />
120<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
BHP Portion <strong>of</strong> Pump Curve<br />
0 200 400 600 800 1000 1200<br />
Flow, GPM<br />
57
Eff<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Efficiency Portion <strong>of</strong> Pump Curve<br />
0 200 400 600 800 1000 1200<br />
Flow, GPM<br />
58
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
NPSH<br />
Net Positive Suction Head<br />
NPSHR: Required<br />
NPSHA: Available<br />
59
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
NPSH<br />
Net Positive Suction Head<br />
NPSHR: Required<br />
NPSHA: Available<br />
NPSH = Actual Pressure - Vapor<br />
Pressure, then convert to feet <strong>of</strong> head<br />
60
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
NPSH Required<br />
Determined during pump test<br />
Throttling Throttling suction to pump<br />
Hot Hot water<br />
Based on 3% head loss-reduce loss reduce NPSHA<br />
until 3% loss in produced head is observed<br />
Based on water<br />
61
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Test Data<br />
Flow Full Head 3% Loss<br />
0 718 - 22 = 696<br />
400 672 - 20 = 652<br />
800 540 - 16 = 524<br />
960 450 - 14 = 436<br />
62
NPSHR<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
0<br />
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
NPSHR Portion <strong>of</strong> Pump Curve<br />
0 200 400 600 800 1000 1200<br />
Flow, GPM<br />
63
NPSHR<br />
NPSH<br />
TDH<br />
TDH<br />
EFF<br />
Eff<br />
BHP<br />
BHP<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
0<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
180<br />
160<br />
140<br />
120<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
0 200 400 600 800 1000 1200<br />
0 200 400 600 800 1000 1200<br />
0 200 400 600 800 1000 1200<br />
0 200 400 600 800 1000 1200<br />
FLOW IN GPM<br />
Flow, GPM<br />
64
Head<br />
BHP<br />
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
A Pump Curve<br />
Operating Point<br />
BEP<br />
Flow, GPM<br />
NPSHR<br />
Efficiency<br />
65
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
The pump manufacturer will normally show the<br />
point on the curve where the pump is expected<br />
to operate<br />
BEP is the best efficiency point taken at the<br />
highest point <strong>of</strong> the efficiency curve<br />
At BEP the pump normally operates the most stably<br />
Operation below BEP can result in mechanical <strong>and</strong><br />
hydraulic problems<br />
66
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Performance <strong>Pumps</strong> <strong>Pumps</strong>-Performance Performance Curves<br />
Summary <strong>of</strong> Pump Curve Information<br />
Graphical representation <strong>of</strong><br />
performance<br />
Contains more than performance data<br />
67
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impeller <strong>Pumps</strong> <strong>Pumps</strong>-Impeller Impeller Effect<br />
Balance Holes<br />
68
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impeller <strong>Pumps</strong> <strong>Pumps</strong>-Impeller Impeller Effect<br />
Effect <strong>of</strong> back wear rings<br />
<strong>and</strong> balance holes<br />
Pressure at O.D. <strong>of</strong><br />
impeller breaks down<br />
across back wear ring<br />
Balance holes bleed<br />
pressure back to suction<br />
Seal chamber at same<br />
pressure as balance holes<br />
69
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impeller <strong>Pumps</strong> <strong>Pumps</strong>-Impeller Impeller Effect<br />
Impeller with PumpoutVanes<br />
70
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impeller <strong>Pumps</strong> <strong>Pumps</strong>-Impeller Impeller Effect<br />
Effect <strong>of</strong> pump out<br />
vanes<br />
Vane O.D. is the same as<br />
the impeller O.D. <strong>and</strong> is<br />
turning at the same speed<br />
Therefore vane puts up<br />
same head as impeller<br />
Therefore back <strong>of</strong><br />
impeller at shaft is at same<br />
pressure as front<br />
71
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impeller <strong>Pumps</strong> <strong>Pumps</strong>-Impeller Impeller Effect<br />
Impeller with no back wear<br />
rings or pumpout vanes<br />
72
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Impeller <strong>Pumps</strong> <strong>Pumps</strong>-Impeller Impeller Effect<br />
Effect <strong>of</strong> no back wear<br />
rings or pump out vanes<br />
Pressure at impeller<br />
O.D. is present<br />
behind entire impeller<br />
Seal chamber at<br />
discharge pressure<br />
73
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
If a higher pressure<br />
differential is required<br />
across the pump the<br />
designer has several<br />
options. Two would<br />
be to:<br />
Increase the pump<br />
speed-the speed the flow would<br />
also increase<br />
Increase the impeller<br />
O.D.<br />
74
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
In most cases neither is practical<br />
There is a practical limit to the impeller diameter.<br />
Beyond that limit it would be difficult to control<br />
the tolerances to ensure proper fit <strong>and</strong> balance.<br />
The hardware would be prohibitively expensive<br />
There is also a practical limit to the shaft speed.<br />
Not only would balance be critical, but the<br />
bearing <strong>and</strong> lubrication system would be complex<br />
<strong>and</strong> expensive<br />
75
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
The third option is simpler. To achieve high<br />
differential head without the expense more than one<br />
stage or impeller are used. Multistage <strong>pumps</strong> come<br />
in many varieties<br />
Multistage volute<br />
Split case<br />
Double case<br />
Multistage diffuser<br />
Vertical<br />
Horizontal<br />
76
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
To underst<strong>and</strong> multistage pump design, it is first<br />
essential to know that there are in general two<br />
different ways that the pump case directs the<br />
flow from the impeller to the discharge nozzle<br />
Volute pattern<br />
Diffuser pattern<br />
77
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Volute Pump<br />
One or two passages in<br />
the pump case guide the<br />
fluid from the impeller to<br />
the pump discharge or the<br />
next stage<br />
Single volute <strong>pumps</strong> can<br />
result in excessive<br />
hydraulic load on the<br />
impeller <strong>and</strong> shaft<br />
78
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Single Volute Double Suction Pump<br />
79
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Diffuser Pump<br />
A multipassage “diffuser diffuser”<br />
or “bowl bowl assembly” assembly<br />
surrounds the entire<br />
impeller O.D. <strong>and</strong> guides<br />
the fluid to the discharge<br />
nozzle or next stage<br />
through multiple paths<br />
80
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Diffuser <strong>Pumps</strong><br />
Note that the Byron Jackson design incorporates a<br />
“mixed mixed flow” flow impeller<br />
The fluid does not make a full 90 o turn in the impeller.<br />
Since it is not a radial flow impeller, it is termed a mixed<br />
flow impeller<br />
Not all turbine <strong>pumps</strong> are mixed flow. Some are<br />
furnished with radial flow impellers such as the<br />
horizontal diffuser pump shown previously<br />
81
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Multistage Volute Split Case<br />
82
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Most multistage volute type <strong>pumps</strong> have front <strong>and</strong> back<br />
wear rings.<br />
Therefore the seal cavity pressures would be as<br />
follows:<br />
One end-suction end suction<br />
The other end-discharge end discharge pressure <strong>of</strong> one <strong>of</strong> the stages unless<br />
some measures are taken to reduce the pressure<br />
Most multistage volute <strong>pumps</strong> will have several taps<br />
on the pump case where various pressures are available<br />
for the flush source<br />
83
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Multistage Volute Double Case<br />
84
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Most multistage double case volute type <strong>pumps</strong> have<br />
front <strong>and</strong> back wear rings.<br />
Therefore the seal cavity pressures would be as<br />
follows:<br />
One end-suction end suction<br />
The other end-discharge end discharge pressure <strong>of</strong> one <strong>of</strong> the stages<br />
unless some measures are taken to reduce the pressure<br />
Only pump discharge pressure is available for a flush<br />
source<br />
85
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Many <strong>of</strong> these <strong>pumps</strong> as well as other multistage<br />
designs will have some provision for reducing the<br />
pressure in the seal chamber at the high pressure end<br />
Balance line<br />
Close clearance bushing<br />
86
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
A balance line will typically bleed the high pressure seal<br />
chamber to about suction plus 70% <strong>of</strong> one stage<br />
differential<br />
Depends on the bushing wear<br />
Also depends on the allowable flow in the<br />
balance line which represents pump<br />
inefficiency<br />
87
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Don’t Don t assume<br />
Check to see if the<br />
balance line exists<br />
Measure the seal<br />
cavity pressure<br />
The following slide<br />
illustrates a balance<br />
line-they line they are not<br />
always so visible<br />
Confucius say - “When you<br />
assume you make a donkey<br />
out <strong>of</strong> “u” <strong>and</strong> “me”<br />
88
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Multistage Volute<br />
with Balance Line<br />
89
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Multistage Diffuser Horizontal<br />
90
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Multistage Diffuser Horizontal<br />
Since all the impellers face <strong>and</strong> pump the same<br />
direction the seal cavity pressures are as follows<br />
One end-suction end suction<br />
The other end-full end full discharge unless some measure<br />
is taken<br />
91
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Multistage Diffuser Horizontal<br />
Measure taken to reduce seal cavity pressure on high<br />
pressure end<br />
Balance drum (piston)<br />
Balance disc<br />
Both are similar to balance lines <strong>and</strong> close clearance<br />
bushings<br />
92
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Multistage Diffuser Horizontal<br />
Balance drum (piston)<br />
Balance disc<br />
Both have additional function in that they are<br />
part <strong>of</strong> the mechanism to reduce the load on the<br />
pump thrust bearing<br />
Both are very complex <strong>and</strong> extremely precise<br />
mechanical devices<br />
93
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Multistage Diffuser Vertical<br />
Byron Jackson<br />
Sumpmaster<br />
94
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Multistage Diffuser Vertical<br />
Byron Jackson VLT<br />
(Very Large Turbine)<br />
Process Pump with Case<br />
95
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Vertical Turbine <strong>Pumps</strong><br />
Note that the sumpmaster is shown without a<br />
mechanical seal. This is typical for low pressures<br />
but many <strong>of</strong> these pump styles do have<br />
mechanical seals<br />
Since all the impellers are pumping in the same<br />
direction <strong>and</strong> the seal sits in the discharge head <strong>of</strong><br />
the pump, the seal cavity is at discharge pressure<br />
unless measures are taken<br />
96
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Vertical Turbine <strong>Pumps</strong><br />
Measures taken depend on the pump seal cavity<br />
construction<br />
Internal seal head-the head the seal actually sits in the pump<br />
discharge flow-it flow it can only be at pump discharge pressure<br />
External seal or packing head-a head a close clearance bushing<br />
<strong>and</strong> balance line arrangement are used to reduce the<br />
pressure to suction plus 70% <strong>of</strong> one stage. Again you<br />
must measure to be sure<br />
97
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Vertical Turbine <strong>Pumps</strong><br />
Measures taken depend on the pump seal cavity<br />
construction<br />
Internal packing head-the head the seal chamber is a<br />
separate piece but sits in the discharge flow-<br />
usually some provision is made to reduce the<br />
pressure in the packing or seal area<br />
98
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Internal<br />
Seal Head<br />
99
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
External<br />
Seal Head<br />
100
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Internal<br />
Packing<br />
Head<br />
101
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
There are three typical styles <strong>of</strong> pump<br />
construction<br />
Overhung: an example follows<br />
Double-ended: Double ended: several examples have been given<br />
similar to the previous slides <strong>and</strong> the slide<br />
following the overhung pump<br />
Vertical: many variations exist<br />
Turbine style-an style an example is the previous slide<br />
Process with <strong>and</strong> without a bearing bracket-examples<br />
bracket examples<br />
will follow<br />
102
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Typical end Suction<br />
(Overhung) Process Pump<br />
103
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Many <strong>pumps</strong> use a double suction impeller<br />
design which is a single impeller with two inlets<br />
High flow<br />
Low NPSHA<br />
Since a double suction impeller must be radial<br />
flow, they are all in volute type cases almost<br />
without exception<br />
104
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Double Suction <strong>Pumps</strong><br />
In a single stage double suction pump the seal or<br />
seals sit in the impeller eye<br />
The only pressure they can see is suction<br />
There are limited choices to dealing with<br />
inadequate vapor suppression margin for these<br />
<strong>pumps</strong><br />
Close clearance throat bushing with plan 11 or 32<br />
flush<br />
Cooling<br />
Cooling<br />
105
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Double Suction Radially Split<br />
106
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Double Suction Axially Split<br />
107
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Double Suction Overhung<br />
108
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Vertical Process <strong>Pumps</strong><br />
In addition to those previously shown, there are a<br />
class <strong>of</strong> <strong>pumps</strong> that are process <strong>pumps</strong> mounted in a<br />
vertical configuration. They are almost always volute<br />
single stage <strong>pumps</strong>. There are two styles<br />
Rigid coupling-no coupling no bearing bracket<br />
Flexible coupling with bearing bracket<br />
109
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Vertical Inline<br />
Process Pump with<br />
Rigid coupling-<br />
No bearing bracket<br />
110
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Pump <strong>Pumps</strong> <strong>Pumps</strong>-Pump Pump Case Design<br />
Vertical Inline<br />
Process Pump with<br />
flexible coupling<br />
<strong>and</strong> bearing bracket<br />
111
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Seal <strong>Pumps</strong> <strong>Pumps</strong>-Seal Seal Cavity Pressure<br />
Since these <strong>pumps</strong> are process style <strong>pumps</strong>, the<br />
seal cavity pressure can be at anything between<br />
<strong>and</strong> including suction <strong>and</strong> discharge<br />
The normal rules apply. It is necessary to know<br />
the impeller <strong>and</strong> case construction to estimate<br />
the seal cavity pressure<br />
112
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
Some pump designs have inherent mechanical<br />
problems because <strong>of</strong> their design <strong>and</strong> resultant<br />
impeller <strong>and</strong> shaft loads<br />
Vertical inline rigid coupling no bearing<br />
bracket<br />
Overhung double suction or two stage<br />
Single volute<br />
113
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
Some pump designs have inherent mechanical<br />
problems because <strong>of</strong> their design <strong>and</strong> resultant<br />
impeller <strong>and</strong> shaft loads<br />
Shaft deflection <strong>and</strong> vibration are common to<br />
these designs<br />
Something must be done to address the<br />
mechanical situation<br />
114
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
Cure or eliminate problem pump<br />
constructions<br />
L3 /D 4 < or = 40<br />
Vertical inline with rigid coupling<br />
Two stage or double suction overhung<br />
Internal sealed (gl<strong>and</strong>less) pump designs<br />
Something we haven’t haven t discussed<br />
No seal chamber or stuffingbox-similar stuffingbox similar to internal seal<br />
arrangementfor vertical turbine <strong>pumps</strong><br />
115
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
L3 /D 4 < or = 40<br />
L = distance in inches from center <strong>of</strong> radial<br />
bearing to center <strong>of</strong> impeller<br />
D = diameter <strong>of</strong> shaft in inches under the seal<br />
sleeve<br />
116
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
L3 /D 4 < or = 40 Solutions<br />
Replace bearing bracket <strong>and</strong> stuffingbox with<br />
7th edition upgrade<br />
Modify existing pump with heavier shaft <strong>and</strong><br />
more robust bearings<br />
Close clearance non galling wear rings <strong>and</strong><br />
throat bushing<br />
117
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
Vertical inline with rigid coupling<br />
Fine for low horsepower (
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
Vertical inline with rigid coupling (continued)<br />
Close clearance non galling wear rings <strong>and</strong> throat<br />
bushing<br />
Add external bearing assembly on top <strong>of</strong> seal flange<br />
May require more first obstruction-add obstruction add motor<br />
spacer ring <strong>and</strong> lengthen pump shaft<br />
May be oil mist or grease lubricated<br />
119
Fundamentals <strong>of</strong> Centrifugal<br />
<strong>Pumps</strong>-Problem <strong>Pumps</strong> <strong>Pumps</strong>-Problem Problem Constructions<br />
Two stage or double suction overhung, old API <strong>pumps</strong> with<br />
large calculated shaft deflection, single volute <strong>pumps</strong><br />
Same problem as L 3 /D 4 < or = 40<br />
Replace bearing bracket <strong>and</strong> stuffingbox with 7th<br />
edition upgrade<br />
Modify existing pump with heavier shaft <strong>and</strong> more<br />
robust bearings<br />
Close clearance non galling wear rings <strong>and</strong> throat<br />
bushing<br />
120