conflict resolution: pump & system interaction - · pdf fileapi 610 and ansi/hi 9.6.3-2017...

Conflict Resolution: Pump & System Interaction
April 13, 2017

What is a system curve and what is it good for?
Friction vs. static head dominated systems
Effects of manual vs. control valves
Affinity laws Parallel composite curves
When will parallel pumps give more flow vs. when they wont - and why
Effects of dissimilar pumps Series composite curves
Complex curves Multiple branch points Different liquid level elevations System curves that change
over time Effect of control features Multiple system curves for a
single system Problems creating system
curves API 610 and ANSI/HI 9.6.3-
2017 best practices
Pump & System Interaction 2
Agenda
April 13, 2017

Pumps and Systems
A pump must overcome two fundamental system-related aspects Friction Static
Liquid elevation differences between supply and discharge Pressure differences between supply and discharge*
E.g., when tanks are pressurized
Since the effects of supply and discharge pressure differences are the same as liquid elevationdifferences, we will simplify things and only discuss elevation differences in this course, with the understanding that pressure differences can cause the same effects
*
3
Elevation Changes, Same Pressure in Tanks
Supply Discharge
Elevation Same, Different Pressure in Tanks
Supply Discharge
P1 P2
Pump & System InteractionApril 13, 2017

A system curve represents the head required to move fluid through a system at various flowrates
In the absence of control features, the system will operate where the pump and system intersect
What Is a System Curve?
4Pump & System InteractionApril 13, 2017

Flowrate
Hea
d
Pump Curve
System Curve
What Is a System Curve? (2)
Total Dynamic Head (TDH)
Operating Flowrate
Static Hs
Friction Hf

System curves help demonstrate pumping system behavior in a graphical manner
If a system curve can be determined, it can help identify the effects of pump and/or system modifications
As systems get more complex, system curves lose usefulness and in fact it is not possible in some cases to determine a unique system curve
What Are System Curves Good For?

Friction occurs in pump systems due to irrecoverable hydraulic losses in: Piping Valving Fittings (e.g., elbows, tees) Equipment (e.g., heat exchangers)
Friction is also used to control flow or pressure Automated flow and pressure control valves Orifices Manual throttling valves
Friction in Pump Systems

It is often convenient to think of pump systems in terms of head rather than pressure
Head loss and pressure loss are related
Frictional head loss typically depends on the square of velocity and flow rate
Friction Characteristics
HgP =
2
2
2
2
2
2
RQH
gAQ
DfLH
gV
DfLH
=
=
=

For systems with pure friction the system curve head goes to zero at zero flow
Closed systems are always purely frictional
Any pump can produce flow (no elevation to overcome)
Pure Friction System Curve
Example: No Elevation Changes
Supply Discharge
Flowrate
Hea
d
Pump Curve
System Curve Hf

When the supply or discharge liquid elevation is changed, the system curve shifts up and down
When there is a liquid elevation increase, no flow can occur unless the pump generates at least enough head to over come the elevation increase
Effect of Elevation Differences
Elevation Changes
Supply Discharge
Example:
Flowrate
Hea
d
Pump Curve System Curve

Effects of Elevation Differences (2)
Flowrate
Hea
d
Pump Curve Old System Curve
New FlowOld Flow
Old TDH
Hs
Hf
Old
IncreasedStatic Head
* In this case, friction head Hf decreases because the flow rate is reduced11
New System Curve (With Increased Static Head)
New TDH
Hs
Hf*
New

A system that is static head dominated is one where the primary effect of the pump is to overcome static head (i.e., gravity, or liquid elevation)
Static Head Dominated Systems
Flowrate
Hea
d
Pump Curve
System Curve
Hs
Hf
12
Large Elevation Change
Supply Discharge

Effect of Control Valves
Control valves (CV) are a form of frictional head loss
13
Flowrate
Hea
d
Pump Curve System Curve
Flow w/o CV
Head Loss Across CV
Flow with CV
w/o CV
Hs
Hf
with CV
Hs
Hf
Hcv

Effect of Manual Throttling Valves
Manual valve throttling increases the friction head loss
14
Flowrate
Hea
d
Pump Curve System Curve Valve Open
Flow Valve Open
Flow Valve Throttled
System Curve Valve Throttled
Valve Open
Hs
Hf
Valve Throttled
Hs
Hf

The pump affinity laws (also known as homologous pump laws) are based on dimensional analysis and allow prediction of pump performance for other impeller sizes and speeds
Pump Affinity Laws
21
QQ
21
HH
21
PP
=
21
DD
=
21
NN
2
21
=
DD
2
21
=
NN
3
21
=
DD
3
21
=
NN
Where:
Q = FlowrateD = (Impeller) DiameterN = SpeedH = HeadP = Power

Using the affinity laws the pump head curve can be adjusted for a different diameter impeller
Impeller Size Changes
Flowrate
Hea
d
Pump Curve 100% Impeller Diameter
System CurvePump Curve 90% Impeller Diameter

Similar to impeller diameter, using the affinity laws the pump head curve can be adjusted for a different speed
Pump Speed Changes
Flowrate
Hea
d
Pump Curve 100% Speed
System CurvePump Curve 90% Speed

Pump Efficiency Effects
Flowrate
Hea
d
Effic
ienc
y
Pump Head Curve
System Curve
Pump Efficiency Curve
Operating Flowrate
Best Efficiency Point
Chart9
100200
10020.906250
9923.6250
9828.156250
9634.50
9442.6562585
9052.6250
8564.406250
78780
7093.406250
60110.62574.76
Efficiency
Flowrate
Head
Sheet1
580.00009062520impeller262.30.85
frictionmixturePowerPower ActualEfficiency
QHHHHLinear
01000.020.08120.040000.0
1001000.920.981.021.862300.0
200993.623.680.927.31233.5400.0
300988.228.279.736.31831.6200.0
4009614.534.577.449.02392.3200.0
5009422.742.774.065.32928.13444.823529411885.0
6009032.652.669.585.33364.200.0
7008544.464.464.0108.83706.8500.0
8007858.078.057.3136.03887.5200.0
9007073.493.449.5166.83924.900.0
10006090.6110.640.6201.33738500074.8
Pump Jct (Time)NameVol. Flow (gal/min)Mass Flow (lbm/sec)dP (psid)dH (feet)Overall Efficiency (Percent)Speed (Percent)Overall Power (hp)BEP (gal/min)% of BEP (Percent)NPSHA (feet)NPSHR (feet)
2 (0)Pump10013.8835.0781.041001002.045N/AN/A43.07N/A
2 (1)Pump20027.7635.0280.931001004.085N/AN/A42.9N/A
2 (2)Pump30041.6534.4979.721001006.035N/AN/A42.65N/A
2 (3)Pump40055.5333.577.421001007.815N/AN/A42.29N/A
2 (4)Pump50069.4132.0374.021001009.34N/AN/A41.84N/A
2 (5)Pump60083.2930.0969.5310010010.53N/AN/A41.29N/A
2 (6)Pump70097.1827.6763.9510010011.3N/AN/A40.65N/A
2 (7)Pump800111.124.7857.2710010011.56N/AN/A39.91N/A
2 (8)Pump900124.921.4249.5110010011.24N/AN/A39.07N/A
2 (9)Pump1,000138.817.5940.6410010010.26N/AN/A38.14N/A
2 (10)Pump1,000138.817.5940.6410010010.26N/AN/A38.14N/A
Sheet1
Flowrate
Head
Efficiency
Flowrate
Head

The efficiency of a pump does not change significantly with speed
Similarly, but to a lesser degree, the same is true for impeller changes
Pump Efficiency Effects (2)
13
12
2
21
21
12
21
21
21 =
=
=
NN
NN
NN
PP
HH
QQ

Iso-efficiency lines on a head/flow diagram follow the behavior of head (quadratic) and flow (linear)
Pump Efficiency Effects (3)
Flowrate
Hea
d
100% Speed
90% Speed
80% Speed
70% Speed
60% Speed82
%
80%8
0%70%50
%
60%
40% Efficiency
Pum
p H
ead
Cur
ves

Friction dominated system curve parallels iso-e

conflict resolution: pump & system interaction - · pdf fileapi 610 and ansi/hi 9.6.3-2017...

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