SECTION
2
SECTION 2
SYSTEM
HYDRAULICS
PAGE 1
SYSTEM HYDRAULICS
OR SYSTEM HEAD CURVE
A system head curve shows
the parameters that a
particular system will allow a
specific pump to perform within.
SECTION 2
PAGE 2
TERMS
STATIC SUCTION HEAD: Is the vertical distance in feet from the
centerline of the pump suction to the liquid level when the source
of liquid supply is above the centerline of pump suction.
STATIC SUCTION LIFT: Is the vertical distance in feet from the
centerline of the pump suction to the liquid level when the source
of liquid supply is below the centerline of pump suction.
STATIC DISCHARGE HEAD: Is the vertical distance in feet from
the centerline of pump suction to the point of free discharge level
at the highest point in the piping system.
SECTION 2
PAGE 3-A
TERMS (continued)
SYSTEM FRICTION LOSS: Is the equivalent pressure expressed
in feet of liquid required to overcome the resistance to flow
through the piping system (pipe, valves, fittings, etc.).
TOTAL EQUIVALENT LENGTH OF PIPE: Is the equivalent length
of pipe for valves & fittings.
GALLONS PER MINUTE (G.P.M.): Quantity of flow.
TOTAL DYNAMIC HEAD (T.D.H.): Is the vertical distance
between source of supply and point of discharge plus friction
losses, when pumping at required capacity.
SECTION 2
PAGE 3-B
HOW IS A SYSTEM
HEAD CURVE CALCULATED ?
Follow the same
procedures as used for
calculating T.D.H. in
Section 1. Do it for
several flow rates, plot
results on pump curve.
Static suction lift.
(Unchanged)
Static discharge head.
(Unchanged)
System friction loss.
(varies with flow)
Total Dynamic Head
At Flow Rate.
SECTION 2
PAGE 4
90 Deg.
Elbow S.R.
341.5'
15.0'
20.0 Ft.
Discharge
Gate Valve
90 Deg.
Elbow S.R.
3.0'
Swing Check
Valve
12.0 Ft.
Suction
15.0'
Design Condition
400 G.P.M
All Pipe & Pipe Fittings Are
4 Inch, Ductile Iron.
Pump Off
SECTION 2
PAGE 5
2 - 90 Deg. Elbows (10.2 x 2) . . . . . . 20.4 Ft.
1 - Gate Valve . . . . . . . . . . . . . . . . . .
2.1 Ft.
1 - Swing Check Valve . . . . . . . . . . . 26.0 Ft.
Total Equivalent Length of Pipe . . .
48.5 Ft.
Actual Length of Straight Pipe . . . . 374.5 Ft.
Total Length
(Actual and Equivalent)
of Pipe . . . . . . . . . . . . . . . . . . . . . . . . 423.0 Ft.
SECTION 2
PAGE 6
16
423 x
= 67.68 Ft. x .71(C=120) = 48 Ft.
100
F.L.
Static Suction Lift
Static Discharge Head
12.0 Ft.
20.0 Ft.
Total Static Head
F.L. at 400 G.P.M.
32.0 Ft.
48.0 Ft.
T.D.H. AT 400 G.P.M.
SECTION 2
PAGE 7
80.0 Ft.
G.P.M.
TOTAL
PIPE
ACTUAL &
EQUIVALENT
FRICTION
LOSS
PER/100
PIPE
FRICTION
HEAD
C=120
x .71
TOTAL
STATIC
HEAD
T.D.H.
100
423
1.22'
5'
4'
32'
36'
200
423
4.40'
18'
13'
32'
45'
300
423
9.30'
39'
28'
32'
60'
400
423
16.00'
67'
48'
32'
80'
500
423
24.00'
101'
72'
32'
104'
600
423
33.70'
142'
101'
32'
133'
SECTION 2
PAGE 8-A
G.P.M.
TOTAL
PIPE
ACTUAL &
EQUIVALENT
FRICTION
LOSS
PER/100
PIPE
FRICTION
HEAD
C=120
x .71
TOTAL
STATIC
HEAD
T.D.H.
100
423
1.22'
5'
4'
32'
36'
200
423
4.40'
18'
13'
32'
45'
300
423
9.30'
39'
28'
32'
60'
400
423
16.00'
67'
48'
32'
80'
500
423
24.00'
101'
72'
32'
104'
600
423
33.70'
142'
101'
32'
133'
423 x 1.22 = 5' x .71 = 4' + 32' = 36'
100
SECTION 2
PAGE 8-B
G.P.M.
TOTAL
PIPE
ACTUAL &
EQUIVALENT
FRICTION
LOSS
PER/100
PIPE
FRICTION
HEAD
C=120
x .71
TOTAL
STATIC
HEAD
T.D.H.
100
423
1.22'
5'
4'
32'
36'
200
423
4.40'
18'
13'
32'
45'
300
423
9.30'
39'
28'
32'
60'
400
423
16.00'
67'
48'
32'
80'
500
423
24.00'
101'
72'
32'
104'
600
423
33.70'
142'
101'
32'
133'
SECTION 2
PAGE 8-C
G.P.M.
TOTAL
PIPE
ACTUAL &
EQUIVALENT
FRICTION
LOSS
PER/100
PIPE
FRICTION
HEAD
C=120
x .71
TOTAL
STATIC
HEAD
T.D.H.
100
423
1.22'
5'
4'
32'
36'
200
423
4.40'
18'
13'
32'
45'
300
423
9.30'
39'
28'
32'
60'
400
423
16.00'
67'
48'
32'
80'
500
423
24.00'
101'
72'
32'
104'
600
423
33.70'
142'
101'
32'
133'
423 x 9.30 = 39' x .71 = 28' + 32' = 60'
100
SECTION 2
PAGE 8-D
G.P.M.
TOTAL
PIPE
ACTUAL &
EQUIVALENT
FRICTION
LOSS
PER/100
PIPE
FRICTION
HEAD
C=120
x .71
TOTAL
STATIC
HEAD
T.D.H.
100
423
1.22'
5'
4'
32'
36'
200
423
4.40'
18'
13'
32'
45'
300
423
9.30'
39'
28'
32'
60'
400
423
16.00'
67'
48'
32'
80'
500
423
24.00'
101'
72'
32'
104'
600
423
33.70'
142'
101'
32'
133'
SECTION 2
PAGE 8-E
G.P.M.
TOTAL
PIPE
ACTUAL &
EQUIVALENT
FRICTION
LOSS
PER/100
PIPE
FRICTION
HEAD
C=120
x .71
TOTAL
STATIC
HEAD
T.D.H.
100
423
1.22'
5'
4'
32'
36'
200
423
4.40'
18'
13'
32'
45'
300
423
9.30'
39'
28'
32'
60'
400
423
16.00'
67'
48'
32'
80'
500
423
24.00'
101'
72'
32'
104'
600
423
33.70'
142'
101'
32'
133'
423 x 24.0 = 101' x .71 = 72' + 32' = 104'
100
SECTION 2
PAGE 8-F
SYSTEM HEAD CURVES
For a specified impeller diameter and speed, a centrifugal pump has
a fixed and predicable performance curve. The point where the pump
will operates on its curve is dependent upon the characteristics of
the system in which it is operating, commonly called the System
Head Curve.... the relationship between flow and friction losses in a
system. The two things that make up a system head curve are static
head and friction losses. Static head, is the difference between the
liquid level on the suction side of the pump and to the point of free
discharge. If levels vary appreciably the extremes should be checked.
Friction losses, are determined by;
1. Rate of flow.
2. Size of pipe, valves and fittings on the suction and discharge.
3. Type of pipe, valves and fittings on the suction and discharge.
4. Length of actual pipe and equivalent length of valves and
fittings on the suction and discharge,
SECTION 2
PAGE 10-A
SYSTEM HEAD CURVES (continued)
By plotting the system head curve and pump performance curve
together, it can be determined:
1. Where the pump will operate on its curve.
2. What the pump efficiency will be.
3. What the horsepower required will be.
4. What changes will occur if the system head curve or the
pump performance curve changes.
SECTION 2
PAGE 10-B
SYSTEM HEAD CURVES (continued)
The pump performance curve can change by changing the pump
r.p.m. or by trimming the impeller. The system head curve can
change by:
1. Adding other pumps to the existing force main.
2. Changing or adding piping to the existing force main.
3. Changing the static head.
4. Changing size of pipe, valves and fittings on the suction
and discharge.
5. Changing type of pipe, valves and fittings on the suction
and discharge.
6. Changing length of actual pipe and equivalent length
of valves and fittings on the suction and discharge.
SECTION 2
PAGE 10-C
SYSTEM HEAD CURVES (continued)
See figure 1, there are four different system head curves.
Curve "A" is 4" suction piping and 4" discharge piping,
using a C factor of C=120.
Curve "B" is 4" suction piping and 4" discharge piping,
using a C factor of C=140.
Curve "C" is 4" suction piping and 6" discharge piping,
using a C factor of C=120.
Curve "D" is 4" suction piping and 6" discharge piping,
using a C factor of C=140.
The table illustrates the different requirements to get 400 g.p.m.
with the four system curves.
SECTION 2
PAGE 10-D
SYSTEM HEAD CURVES (continued)
The table illustrates the different requirements to get 400 g.p.m.
with the four system curves.
REQUIRED
SPEED
REQUIRED
HORSEPOWER
EFFICIENCY
A (C = 120)
1735
20
49%
B (C = 140)
1610
15
51%
C (C = 120)
1300
10
54%
D (C = 140)
1250
10
55%
CURVE
SECTION 2
PAGE 10-E
SYSTEM HEAD CURVES
See figure 2, if curve "C" was selected, based upon C=120 the
required pump speed would be 1300 r.p.m. If the actual condition
was C=140, at 1300 r.p.m. the pump performance would move to the
right and where the pump performance curve intersect curve "D" the
flow would increase by approximately 50 g.p.m. NOTE: Check the
N.P.S.H. to make sure if you get the 50 g.p.m. increase that your
N.P.S.H.A. is a positive number.
60
1300
C C=120
D C=140
50
30
FIGURE 2
40
50
GPM
20
SECTION 2
PAGE 12-A
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
0
10
SYSTEM HEAD CURVES (continued)
See figure 3, if curve "D" was selected, based upon C=140 the
required pump speed would be 1250 r.p.m. If the actual condition
was C=120, at 1250 r.p.m. the pump performance would move to the
left and where the pump performance curve intersect curve "C" the
flow would decrease by approximately 50 g.p.m.
60 1
250
50
C C=120
D C=140
30
FIGURE 3
40
50
GPM
20
SECTION 2
PAGE 12-B
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
0
10
SYSTEM HEAD CURVES
When upgrading an existing system and you're not sure of the
condition of the pipe, you would want to use several C factors i.e.
C=100, C=120 etc. when laying out the system head curve. By using
several C factors, you will see the worst condition and the best. The
motors and controls should be sized to handle the worst system.
Size the pumps for the worst condition. If the system is actually
better, make sure the pumps will operate satisfactory hydraulically, if
need be make adjustments by slowing the pumps down.
FORCE MAIN VELOCITIES: Velocity criteria for force mains are
derived from observations that solids do not settle out at a velocity
of 2.0 ft/s or greater. Solids do settle at lower velocity or when the
pump is stopped, and a velocity of 3.5 ft/s or greater is required to
resuspend the deposited solids. If the solids don't resuspend it will
effect the I.D. of the pipe which will change your system head curve.
SECTION 2
PAGE 13
PARALLEL PUMPING SYSTEM
SECTION 2
PAGE 14
PARALLEL PUMPING
When operating two identical pumps in parallel, that are the same
size, same speed and impeller diameter, people tend to assume that
if one pump is pumping 400 gallons per minute, if they turn on the
second pump they will get 800 gpm.
The first exercise will show us how to figure the total capacity of two
identical pumps pumping into the same header in parallel. The
second exercise will show us how to figure the total capacity of two
different size pumps pumping into the same header in parallel.
SECTION 2
PAGE 16-A
PARALLEL PUMPING (continued)
Figure 1 represents a duplex pumping station with two 4" pumps
operating at 1750 rpm with a full diameter impeller of 9 3/4 in.
First you must have the station or system head curve for your
particular station. "A" is the system head curve and "B" is the
pump performance curve at 1750 rpm. With one pump operating
alone the capacity will be 400 gpm at 80.0 ft. total dynamic head.
Since we must find what capacity the pumps will deliver with both
pumps operating, it becomes necessary to draw the head capacity
curve for parallel operation of the second pump. The combine
delivery for a given head is equal to the sum of the individual
capacities of the two pumps at the same head. Example: At 102.0 ft.
T.D.H. pump #1 will deliver 50 G.P.M., so the combine deliver for
pumps #1 and #2 will be 100 G.P.M. at 102.0 ft. T.D.H.. See figure 2,
the table illustrates the requirements to plot two pumps in parallel.
SECTION 2
PAGE 16-B
PARALLEL PUMPING (continued)
T.D.H. Ft.
1 PUMP
G.P.M.
1 PUMP
T.D.H. Ft.
2 PUMPS
COMBINE G.P.M.
2 PUMPS
102.0 ft.
50
102.0 ft.
100
98.0 ft.
100
98.0 ft.
200
95.0 ft.
150
95.0 ft.
300
92.0 ft.
200
92.0 ft.
400
88.5 ft.
250
88.5 ft.
500
To avoid over heating, pumps should never run at a flow of less than
5% of the BEP capacity. For instance, if best BEP is 100 G.P.M. flow
should not be less than 5 G.P.M.
SECTION 2
PAGE 16-C
PARALLEL PUMPING (continued)
Figure 2 shows the plot of the performance of two pumps in parallel.
The operating condition is at the head where the combine curve
intersects the system curve or 450 g.p.m. Note the addition of the
second pump only increases the
capacity by 50 g.p.m.
See figure 3, our total capacity is 450 gpm. At the point where pump
#2 intersects your system head curve, draw a line straight back to
pump #1 performance curve then straight down. That will be the
capacity of each pump, approx. 225 and the total dynamic head will
be 90.0 ft.
SECTION 2
PAGE16-D
PARALLEL PUMPING (continued)
When two or more pumps are operating in parallel, you must verify
that the pumps are not operating outside of the pump operating
range. As you can see from this example, we are inside of the pump
operating range indicated by the solid pump performance line. The
dotted line indicates an unacceptable pump operating area.
If you are in the field and want to determine the capacity of two
pumps in parallel (see Fig. 3a) it can be done as follows: Figure 3
indicated the T.D.H. should be 90.0 ft. with both pumps running. To
check pumps in the field, compute the T.D.H. from measured gauges
readings of the pump. Follow the pressure over to the pump H/Q
curve and then down to the actual G.P.M. (Figure 3a) It should be
noted this method of determining capacity is only good for pumps
that match the curve. Worn or poorly adjusted pumps will produce a
reduced curve so capacities will actually be less then the curve
shows at the same head.
SECTION 2
PAGE 20
PARALLEL PUMPING (continued)
The second example of pumps operating in parallel, would be two
different pumps pumping into the same header. It could be two
identical 4 in. pumps operating at the same speed with different size
impellers, with the same impeller diameter but at different speeds, or
it could be a 3 in. and 4 in. pump or a 4 in. & 6 in. pump. It could be
any type of combination. When you are plotting a performance of
two unlike pumps, it is done a little differently.
Figure 4 represents individual curves of a 3 in. and 4 in. pump
performance at 1750 rpm. The system head curve is the same
system head curve that was used in the first example. As you can
see the capacity of the 3 in. pump would be 295 gpm at 61.0 ft. total
dynamic head when operating alone and the capacity of the 4 in.
pump would be 400 gpm at 80.0 ft. total dynamic head when
operating alone.
SECTION 2
PAGE 22-A
PARALLEL PUMPING (continued)
There is a duplex pumping station with a 4 in. pump with a 9 3/4 in.
diameter impeller and a 3 in. pump is added with a 8 3/4 in. diameter
impeller. We must find what will happen if a 4 in. pump would come
on line while the 3 in. pump is operating, or if a 4 in. pump is
operating and a 3 in. pump turns on. It is necessary to draw the
head capacity curve for parallel operation of the two pumps. See
figure 5, the 3 in. pump will not start to deliver until the discharge
pressure of the 4 in. pump falls below that of the shut-off head of the
3 in. pump (88.0 ft.) The combined delivery for a given head is equal
to the sum of the individual capacities of the two pumps at the same
head. Example: At 88.0 ft. T.D.H. the 3 in. pump will not deliver, the 4
in. pump will deliver 255 G.P.M. so the combine capacity for the 3 in.
and 4 in. pump will be 255 G.P.M. at 88.0 ft. T.D.H. See figure 5, the
table illustrates the requirements to plot two different pumps
operating in parallel:
SECTION 2
PAGE 22-B
PARALLEL PUMPING (continued)
T.D.H. Ft.
3 in. PUMP
G.P.M.
3 in. PUMP
D.H. Ft.
4 in. PUMP
G.P.M.
4 in. PUMP
COMBINE G.P.M.
3 in. & 4 in.PUMPS
88.0'
0
88.0'
255
255
84.0'
35
84.0'
330
365
80.0'
70
80.0'
410
480
See figure 6, what we have just plotted is the performance of the 3 in. pump
operating in parallel with the 4 in. pump. The new combined curve intersects
the system head curve at the combine capacity of the 3 in. and 4 in. pump
operating in parallel, approx. 415 gpm, at 82.5 ft. total dynamic head. Follow
that point at the head where the combine curve crosses the system head
curve (82.5 ft.), back to the 4 in. pump curve (point A) and that will be the
capacity of the 4 in. pump approx. 365 gpm. Continue the line back to the 3
in. pump curve (point B) and that will be the capacity of the 3 in. pump
approx. 50 gpm.
SECTION 2
PAGE 22-C
PARALLEL PUMPING (continued)
As you can see from this example, we are outside of the pump
operating range. If the pump was allowed to operate at that
condition point, discharge cavitation, broken shafts and
premature bearing & seal failure could occur.
SECTION 2
PAGE 22-D
PARALLEL PUMPING (continued)
This description of mechanics of pumps operating in parallel is only
intended to show the basic calculations. It also shows foregoing
would not be a good selection of pump capacities or pumps for
parallel operation. This example shows it is possible to get
undesirable results so all applications should be checked.
If you are in the field & want to determine the capacity of a 4 in.
pump in parallel (see Fig. 6a) WITH a 3 in. pump it can be done as
follows: Figure 6 indicated the T.D.H. should be 82.0 ft. with both
pumps running. To check pumps in the field compute the T.D.H. from
measured gauge readings of the pump. Follow the pressure over to
the pump curve and then down to the actual G.P.M. Starting at 82.5
ft. T.D.H. on your pump performance curve, follow that point across
the curve to your 3 in. pump curve, where it intersects your pump
performance curve (1750 R.P.M.) read down.
SECTION 2
PAGE 26-A
PARALLEL PUMPING (continued)
That should be your capacity for the 3 in. pump approx. 50 G.P.M.
Continue across the curve until you intersect the pump curve for the
4 in. pump. Read down. Your capacity for the 4 in. pump would be
approx. 365 G.P.M. Your total capacity with the 3 in. & 4 in. pump
operating in parallel would be approx. 415 G.P.M. (Figure 6a) It
should be noted this method of determining capacity is only good
for pumps that match the curve. Worn or poorly adjusted pumps will
produce a reduced curve so capacities will actually be less than the
curve shows at the same head.
SECTION 2
PAGE 26-B
SERIES PUMPING
Station S/N:
91 - 357 - AXH
Location:
Genessee Water
& Sanitation District
Golden, Co.
Job Name:
Pine Drop Lift Station
Engineer:
Genessee Water
& Sanitation District
Golden, Co.
STAGED DUPLEX / SIMPLEX
AUTO-START
Owner:
Genessee Water
& Sanitation District
Golden, Co.
Design:
250 G.P.M. @ 160' T.D.H.
SECTION 2
PAGE 28
SERIES PUMPING
Double the head at the same flow condition point.
Series pumping is nothing more than a pump station with a booster
pump station at the same location.
Series pumping is usually used to overcome a high static discharge
head or an extremely long force main with high friction losses.
In some applications a project engineer will place a station at the
bottom of a hill. Then half way up the hill another station will be
placed with the wet well. The same is true on extremely long force
mains. The engineer uses this "leap frogging" to over come high
discharge heads.
We, at Gorman-Rupp, feel that series pumping is a more cost
effective and practical method to overcome high discharge heads.
Also, the installation costs are lower due to the fact that there is only
one station installation with one wet well.
SECTION 2
PAGE 29-A
SERIES PUMPING (continued)
ADVANTAGES of SERIES PUMPING:
1) Utilization of the highly reliable and easy to maintain "T" Series
pumps.
2) One pump station installation with one wet well.
3) The "T" series pumps usually require less combined horsepower
than one pump to meet the same condition point.
4) More times than not, the condition point is at the highest
efficiency point on the pump curve.
5) Series pumping provides for a soft hydraulic start/stop. The first
stage pump starts, then after a slight delay, .2 to 60 seconds, the
second stage pump starts. Conversely, on stopping the second stage
pump stops first then after the delay the first stage pump stops.This
helps in relieving water hammer on starting and stopping.
SECTION 2
PAGE 29-B
SERIES PUMPING (continued)
6) The start/stop delay between staged pumps, also provides for
electrical soft start/stops. Only half the required horsepower
starts at a time.
7) Pumps will reprime in about half the time.
8) Series pumping allows the pumps to operate at lower speeds
thereby reducing wear.
9) Equipment is usually smaller, easier to maintain and more
manageable - vs - one large submersible or centrifugal pump.
SECTION 2
PAGE 29-C
SERIES PUMPING
DISADVANTAGES of SERIES PUMPING:
1) Total equipment is doubled
a) (4) Pumps
b) (4) Motors
c) (4) Motor starters and circuit breakers
d) (4) Drives
2) Size or area the pump station takes up.
SECTION 2
PAGE 30-A
SERIES PUMPING (continued)
DESIGN FACTORS OF SERIES PUMPING STATION:
1) The suction flap valve is removed from all four pumps.
2) Dual discharge check valves for each pump discharge. The
primary check valve is an M & H or Gorman-Rupp - depending on the
type of station. This check valve maintains the water column in the
force main. The secondary check valve, Gorman-Rupp, functions as a
suction check valve and maintains a full pump case and suction leg.
3) The automatic air release valve is installed between the two check
valves.
4) Electrically:
a) One elapsed time meter is provided for each set of pumps.
b) One high temperature shutdown indicator is provided for
each set of pumps.
d) One hand-off automatic switch for each set of pumps.
SECTION 2
PAGE 30-B
SERIES PUMPING (continued)
LIMITING FACTORS OF SERIES PUMPS:
1) Maximum operating pressure the second stage pump will
handle.
2) Area the station is to be placed.
SECTION 2
PAGE 30-C
STAGED DUPLEX / SIMPLEX
AUTO-START
"T" SERIES
SECTION 2
PAGE 32
SERIES PUMPING SYSTEM
SECTION 2
PAGE 33
To Section 3