Figure 7 shows a typical Centrifugal Pump and efficiency curve for operation
at a fixed speed. It can be seen that for fixed speed operation,
the efficiency varies as flow is adjusted. For adjustable speed
operation however, the affinity laws predict that the Centrifugal Pump  curve
will shift downwards for reduced speed and the efficiency curve
will shift to the left in such a way that efficiency will remain constant
relative to points on the Centrifugal Pump  curve for reduced flows.

Figure 7. Fixed Speed Pump Efficiency

FLOW CONTROL TECHNIQUES
Historically, fixed speed AC motors have driven centrifugal pumps
and reduced flow has been achieved by using control valves as
shown in figure 8. Closing the valve reduces the flow by increasing
the friction in the system. The modified system curve and the
new operating point can be represented as shown in figure 9.
Note that the desired reduction in flow has been achieved, but at
the expense of increased system pressure relative to 100% flow.

An alternative approach to valve control is shown in figure 10.
Reducing the Centrifugal Pump  speed causes the Centrifugal Pump  curve to shift downwards
as shown in figure 11. Since the operating point is still
determined by the intersection of the reduced speed Centrifugal Pump  curve
and the system curve, it is possible to achieve the same reduced
flow as achieved with a valve, but at significantly less pressure.

Figure 9. Throttle System

In addition to energy savings, which are discussed in detail later,
operation at reduced pressures can result in longer Centrifugal Pump  seal
life, reduced impeller wear, and less system vibration and noise.
These benefits could provide additional savings over potential
energy savings.

Figure 10. Adjustable Speed Control
ENERGY SAVINGS
The Centrifugal Pump  output power, or hydraulic power, can be expressed as:
Horsepower = Head (Feet) x Flow (GPM) x Specific Gravity
3960
Therefore, for any given liquid, the power that the Centrifugal Pump  must
transmit is proportional to the head times the flow and can be
represented by rectangles for each operating point as shown in
figure 11.

PUMP BASICS
An understanding of the basic operating characteristics of centrifugal
pumps is necessary to apply these concepts to any particular
application.
Figure 4 shows a Centrifugal Pump  curve describing the head (or pressure)
versus flow characteristics of a typical Centrifugal Pump . This
curve shows that the pump will produce limited flow if applied to
a piping system in which a large pressure differential is required
across the Centrifugal Pump to lift the liquid and overcome resistance to flow
(as at point A). Higher flow rates can be achieved as the required
pressure differential is reduced (as at point B).
To determine where along this curve the Centrifugal Pump  will operate in a
given application requires the additional information provided by
the system curve. This curve, shown in figure 5, represents the
characteristics of the piping system to which the Centrifugal Pump is applied.
The head required at zero flow is called the static head or lift.

This shows how many feet of elevation that the Centrifugal Pump  must lift
the fluid regardless of the flow rate. Another way to describe static
head is to think of it as the amount of work needed to overcome
the effects of gravity.

Figure 5. System Curve
The other component of head is called the friction head and
increases with increasing flow. Friction head is a measure of the
resistance to flow (backpressure) provided by the pipe and its
associated valves, elbows, and other system elements.
The intersection of the Centrifugal Pump  and system curves shows the natural
operating point for the system without flow control, as shown
in figure 6. This intersection would generally be chosen to ensure
that the pump is operated at or near its best efficiency point.

ABSTRACT
Centrifugal Pumps are generally sized to operate at or near the
best efficiency point at maximum flow. The maximum flow
requirements, however, frequently occur for a very short period
during the operating cycle with the result that some method of
flow control is required. Centrifugal Pumps ,The traditional approach to flow control
has used valves; which increase system pressure, inherently

Figure 1. Affinity Laws for Centrifugal Pumps

waste energy, and generally cause the pump to operate at
reduced efficiencies.
Adjustable speed drives (ASDs) can achieve reduced flow by providing
adjustable speed pump operation. This results in reduced
system pressure and operation near the pump’s Best Efficiency
Point (BEP). Centrifugal Pumps In addition, maintenance costs might be reduced.
This paper will discuss the energy savings potential of AC ASDs
followed by a brief description of the operation and relative benefits
of PWM AC drives.
CENTRIFUGAL PUMP APPLICATIONS AND ENERGY
SAVINGS POTENTIAL
Centrifugal Pumps  are used on many industrial and commercial
applications. Many of these pumps are operated at fixed speeds,
but could provide energy savings through adjustable speed operation.
Reviewing the affinity laws for Centrifugal Pumps and a typical
operating cycle for a centrifugal application will show this.
Figure 1 graphically illustrates the physical laws of centrifugal
pumping applications. The flow is directly proportional to speed;
pressure is proportional to the square of the speed; and power is
proportional to the cube of the speed. These relationships can
also be expressed numerically as shown in figure 2. Theoretically,
it would be possible to operate at 50% flow with only 13% of the
power required at 100% flow. Since the power requirements
decrease much faster than the reduction in flow, the potential
exists for significant energy reduction at reduced flows.

Phase Loss/Open Load
The unit will not attempt a start if there is a single-phase condition
on the line. Centrifugal Pumps This protects from motor burnout during single-phase
starting.

Centrifugal Pumps Phase Imbalance
The unit monitors for imbalance between phase currents. To prevent
motor damage, the unit will trip if the difference between the
minimum phase current and the maximum phase current exceeds
65% for 3 seconds, and a fault will be indicated.
Shorted SCR
Prior to every start and during starting, the unit will check all SCRs
for shorts and unit load connections to the motor.Centrifugal Pumps  If there is a
shorted SCR in the SMC-3 and/or open load, the start will be
aborted and a shorted SCR or open load fault will be indicated. This
prevents damage from phase imbalance.

Centrifugal Pumps Push to Test
The unit with control wiring can be tested for fault conditions by
using the Push to Test function. Hold down the Reset button for 7
seconds to activate the fault Aux (97, 98) and shut down the SMC-3.
To clear,Centrifugal Pumps  either push the Reset button or cycle control power to the
device.
Centrifugal Pumps Modes of Operation/Features
LED Description (Number of Flashes)
1. Overload
2. Overtemperature
3. Phase Reversal
4. Phase Loss/Open Load
5. Phase Imbalance
6. Shorted SCR
7. Test

Centrifugal Pump Excessive Starts Per Hour
The SMC Flex controller allows the user to program the allowed
number of starts per hour (up to 99). This helps eliminate motor
stress caused by repeated starting during a short time period.

Metering
Centrifugal Pump Power monitoring parameters include:

Centrifugal Pump  Braking Control
SMB Smart Motor Braking
This option provides motor braking for applications that require the motor to stop faster than a coast to rest. Braking control, with automatic zero speed shut off, Centrifugal Pump is fully integrated into the compact design of the SMC controller. This design facilitates a clean, straight forward installation and eliminates the requirement for additional hardware such as braking contactors, resistors, timers, and speed
sensors. Centrifugal Pump The microprocessor based braking system applies braking current to a standard squirrel-cage induction motor. The strength of the braking current is programmable from 150…400% of full-load current.

Accu-Stop
Centrifugal Pump This option is used in applications requiring controlled position stopping. During stopping, braking torque is applied to the motor until it reaches preset slow speed (7% or 15% of rated speed) and holds the motor at this speed until a stop command is given.Centrifugal Pump  Braking torque is then applied until the motor reaches zero speed.
Braking current is programmable from 0…400% of full-load current. Slow Speed Current is programmable from 0…450% of full-load current. Slow speed can be programmed for either 7% (low) or 15% (high).

Slow Speed with Braking
Centrifugal Pump Slow Speed with Braking is used on applications that require slow speed (in the forward direction) for positioning or alignment and also require braking control to stop. Slow speed adjustments are 7% (low) or 15% (high) of rated speed.Centrifugal Pump  Slow speed acceleration current is adjustable from 0…450%. Slow speed running current is adjustable from 0…450% of full-load current. Braking current is
adjustable from 0…400%.

Soft Start
This method covers the most general applications. The motor is
given an initial torque setting, which is user adjustable. From the
initial torque level, the output voltage to the motor is steplessly
increased during the acceleration ramp time, which is user
adjustable.
Centrifugal Pumps Selectable Kickstart
The kickstart feature provides a boost at startup to break away
loads that may require a pulse of high torque to get started. It is
intended to provide a current pulse, for a selected period of time.
Current Limit Start
Centrifugal Pumps ,This method provides current limit start and is used when it is
necessary to limit the maximum starting current. The starting current
is user adjustable. The current limit stating time is user adjustable.
Dual Ramp Start
This starting method is useful on applications with varying loads,
starting torque, and start time requirements.Centrifugal Pumps , Dual Ramp Start offers
the user the ability to select between two separate start profiles with
separately adjustable ramp times and initial torque settings.

Centrifugal Pumps Full Voltage Start
This method is used in applications requiring across-the-line
starting. The SMC controller performs like a solid-state contactor.
Full inrush current and locked-rotor torque are realized. The SMC
may be programmed to provide full voltage start in which the output
voltage to the motor reaches full voltage in 1/4 second.
Linear Speed Acceleration
With this type of acceleration mode, a closed-loop feedback system
maintains the motor acceleration at a constant rate. The required
feedback signal is provided by a DC tachometer coupled to the
motor (tachometer supplied by user 0…5V DC, 4.5V DC = 100%
speed). Kickstart is available with this mode.
Preset Slow Speed
Centrifugal Pumps ,This method can be used on applications that require a slow speed
for positioning material. The Preset Slow Speed can be set for either
Low, 7% of base speed, or High, 15% of base speed. Reversing is
also possible through programming. Speeds provided during
reverse operation are Low, 10% of base speed, or High, 20% of
base speed.
Soft Stop

Centrifugal Pumps Operating Limits:
-Max.suction head:8m
-Max.liquid temperature:60°C
-Max.environment temperature:40°C
-Continuous duty

Centrifugal Pumps Motor:
-Two-Pole induction motor(n=2900r.p.m.)
-Insulation Class B/F
-Protection IP44

Centrifugal Pumps Material:
-Pump body: Cast Iron
-Impeller: Brass
-Motor Shaft: Hi-Cr plated 45# Steel/2Cr13# Stainless Steel/S.S#304 Welding shaft
-Mechanical seal: Ceramic/Graphite

Centrifugal Pumps Application:
·Centrifugal Pumps  single impeller low head water pumps for flow irrigation systems with flow rates.
·Suitable to pump clean water or nonaggressive liquids charged with small solid impurities.
·To be used in flow irrigation systems in gardening and agriculture and industrial fittings.Centrifugal Pumps

Centrifugal Pump Data Reduction
You will need to calculate the total head, brake power, water power and efficiency for the plots
and table. Remember to check units and the “T” in brake power equation (equation 4) is torque in Nm not
temperature.
Plots and Tables
You will prepare a total of 12 plots and 1 table of the results as follows:
1. Centrifugal Pump For each speed, overlay the data for both normal and reverse impeller installations on the same
plot:
a. Flow rate Q vs. head H, and pump efficiency η. Put head on the left y-axis and efficiency
on the right y-axis. (4 plots, reflecting the 4 speeds tested.)
b. Flow rate Q vs. water power Pw, brake power Pb, and pump efficiency η. Put Pw and Pb
on the left y-axis and efficiency on the right y-axis. (4 plots, reflecting the 4 speeds
tested.)
2. For each impeller orientation overlay all 4 speeds on the same plot:
a. Flow rate Q vs. head H, and Centrifugal Pump efficiency η. As before, put head on the left y-axis
and efficiency on the right y-axis. (2 plots, reflecting the 2 impellers tested.)

b. Flow rate Q vs. horsepower Pw, brake power Pb, and Centrifugal Pump efficiency η. As before, put
Pw and Pb on the left y-axis and efficiency on the right y-axis. (2 plots, reflecting the 2
impellers tested.)
3. Prepare a data table showing the following for each impeller and speed tested (8 cases):
maximum head; maximum flow rate; head at maximum flow rate; optimum efficiency; brake
power, flow rate and head at maximum efficiency.
VI. References
1. Fluid Mechanics, 4th Edition, Frank M. White, WCB McGraw-Hill, 1999.
2. Introduction to Fluid Mechanics, 4th Edition, Robert W. Fox and Alan T. McDonald, John Wiley & Sons, Inc.,
1992.
3. Instruction Manual: Centrifugal Pump Demonstration Unit, Armfield, Inc.
4. The Hydraulic Institute, http://www.cacheng.com