Topic 3 : THE BASIC PUMP CLASSIFICATIONS

PUMPS

THE BASIC PUMP CLASSIFICATIONS

CENTRIFUGAL PUMP

Calculate The Power And Efficiency The Characteristic

a. Radial flow b. Axial flow

The Performance Of Pump In Parallel And In Series

Cavitation And Its Effects On A Pump

Calculate Operational Flow Rate, Head Or Efficiency Of A Pump And Plot The Characteristic Curves For The Following

Configuration

1. Single Pump 2. Pumps In Series 3. Pumps In Parallel

TOPIC 3

THE BASIC PUMP

CLASSIFICATIONS

A “stable” curve is important for pump operation, especially for pumps in parallel operation. The higher the energy level and the more critical an installation, the more the pump curve could become an issue. API 610 even states that “…pumps that have stable head/capacity curves (continuous rise to shutoff) are preferred for all applications and are required when parallel operation is specified. When parallel operation is specified, the head rise shall be at least 10 percent of the head at rated capacity.”

If the pump curve is stable, a unique point (A—an intersection of a pump curve and system curve) always exists.

See Figure 3. If the pump curve is unstable, the region between Point B and Point F has two possibilities—at either flow Qb or Qf.

Figure : The stable curve (left) has a single, defined intersection between the pump curve and system curve. The unstable curve (right) has two flows at which a pump can operate at the same head.

The Power And Efficiency Of Centrifugal Pump

Output Power, P

_o

=

• ρ = Density of fluid

• g = Gravitational force

• H= Total head

• Q= Volumetric flow rate or capacity

Efficiency,  =/ x 100

• = Watt (input power)

• N = Pump speed(Rotation/ Min)

• T = Torque

•

N

s

= Specific speed (complex units)

Work example

a) A centrifugal pump operate with 1500 rpm was pumped a water with 0.8 m

³

/s and the head obtained is 6.4m. The torque of pump is 420N. Calculate the pump efficiency.

b)A pump with an inlet power of 1.46 kW has been installed to allow the air to flow at 25 m of head. The density and the air flow rate 1.25 kg/m

³

and 3.1 m

³

/s respectively. Calculate the efficiency of the pump.

c) In an experiment using a pump, it was found that the water flow rate is 0.117 m

³

/s, when the relevant head is 6 meters. If the

efficiency of the pump is at 72%, determine the input power of the

pump.

Work example 1

A centrifugal pump operate with 1500 rpm was pumped a water

with 0.8 m3/s and the head obtained is 6.4m. The torque of pump

is 420N. Calculate the pump efficiency.

Work example 2

A pump with an inlet power of 1.46 kW has been installed to allow the air to flow at 25 m of head. The density and the air flow rate 1.25 kg/m

³

and 3.1 m

³

/s respectively.

Calculate the efficiency of the pump.

P

_o

=  gHQ

= 1.25 X 9.81 X 25 X 3.1

= 950.3 Watt

So, the efficiency of the pump. (),

Work example 3

In an experiment using a pump, it was found that the water flow rate is 0.117 m3/s, when the

relevant head is 6 meters. If the efficiency of the pump is at 72%, determine the input power of the pump.

Solution ;

Po = ρ G H Q

= 1000 (9.81) (6) (0.117) = 6886.62 watt

ŋ = (Po / Pi) x 100

0.72 = (6886.62 / Pi) Pi = (6886.62 / 0.72)

= 9564.75 watt

Characteristic of Pump Curve

Q (m³/s) 0 0.016 0.025 0.03 0.035 0.041

H(m) 10.2 9.6 8.8 7.5 6.2 1

η(%) 0 86 96 90 81 48

H_system(m) 8 8.96 10.34 11.38 12.59 14.24

a) Plot the graph of the pump systems.

b) Determine the flow rate and efficiency for this single pump Q (m³/s) = 0.02

η(%) = 94

c) Find the power of pump at the operating point.

P_o=

d) Find the optimum head and optimum flow rate for this system.

Hopt Qopt

0 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04 0.05

0 10 20 30 40 50 60 70 80 90 100 110

Q vs H, η dan Hsystem

H (m) H system eficiency

Q= 0.02m³/s

H = 9 m

η=94%

Pumps in Parallel and in Series

Pumps in Parallel

Pumps in Parallel and in Series

Pumps in Series

Cavitation

Cavitation means that cavities or bubbles are forming in the liquid that we're pumping. These cavities form at the low pressure or suction side of the pump, causing several things to happen all at once:

• The cavities or bubbles will collapse when they pass into the higher regions of pressure, causing noise, vibration, and damage to many of the components.

• We experience a loss in capacity.

• The pump can no longer build the same head (pressure)

• The pump's efficiency drops.

There two types of cavitation in pump,

(i) Suction Cavitation

Suction Cavitation occurs when the Net Positive Suction Head Available to the pump is less than what is Required.

(ii) Discharge Cavitation

Discharge Cavitation occurs when the pump

discharge head is too high where the pump runs at or near shutoff.

Suction Cavitation

Discharge Cavitation

REFERENCES

1. http://slideplayer.com/slide/8643161/

2. http://dec.alaska.gov/water/OPCert/Docs/Chapter6.pdf 3. http://www.freestudy.co.uk/fluid%20mechanics/t2203.pdf 4. http://www.pumped101.com/efficiency.pdf

5. http://personalpages.manchester.ac.uk/staff/david.d.apsley/lectures/hydraulics2/t4.pdf