pumps and pumping systems part-1
TRANSCRIPT
Pumps & Pumping Systems
(Part-1)
M.M.Palitha Mahinda Munasinghe
Farm Mechanical Instructor
2
INTRODUCTIONINTRODUCTION
• Domestic, commercial, industrial and agricultural services
• Municipal water and wastewater services
Use of Pumping System
11/08/2007 mmpmm
3
Objective of pumping system
What are Pumping SystemsWhat are Pumping Systems
• Transfer liquid from source to destination
• Circulate liquid around a system
11/08/2007 mmpmm
4
• Components• Pumps
• Prime movers: electric motors, diesel engines, Wind mill
• Piping to carry fluid
• Valves to control flow in system
• Other fittings, control, instrumentation
• End-use equipment• Heat exchangers, tanks, hydraulic machines
What are Pumping SystemsWhat are Pumping Systems
11/08/2007 mmpmm
5
• Head• Resistance of the system
• Two types: static and friction
• Static head• Difference in height between
source and destination
• Independent of flow
Pumping System CharacteristicsPumping System Characteristics
11/08/2007 mmpmm
6
• Static head consists of• Static suction head (hs): lifting liquid relative to pump
center line
• Static discharge head (hd) vertical distance between centerline and liquid surface in destination tank
• Static head at certain pressure
Head (in feet) = Pressure (psi) X 2.31 Specific gravity
11/08/2007 mmpmm
Pumping System CharacteristicsPumping System Characteristics
7
• Friction head• Resistance to flow in pipe and fittings
• Depends on size, pipes, pipe fittings, flow rate, nature of liquid
• Proportional to square of flow rate
• Closed loop system only has friction head(no static head) Friction
head
Flow
11/08/2007 mmpmm
Pumping System CharacteristicsPumping System Characteristics
8
Total head = Static head + friction head
11/08/2007 mmpmm
Pumping System CharacteristicsPumping System Characteristics
9
Pump performance curve
• Relationship between head and flow• Flow increase
• System resistance increases
• Head increases
• Flow decreases to zero
• Zero flow rate• risk of pump burnout
Head
Flow
Performance curve for centrifugal pump
11/08/2007 mmpmm
Pumping System CharacteristicsPumping System Characteristics
10
Pump operating point
• Duty point
Rate of flow at
certain head
• Pump operating point
Intersection of
pump curve and
system curve Flow
Head
Static head
Pump performance curve
System curve
Pump operating point
11/08/2007 mmpmm
Pumping System CharacteristicsPumping System Characteristics
11
Pump suction performance (NPSH)• Cavitations or vaporization: bubbles inside pump
• If vapor bubbles collapse• Erosion of vane surfaces• Increased noise and vibration• Choking of impeller passages
• Net Positive Suction Head• NPSH Available: how much pump suction exceeds liquid
vapor pressure• NPSH Required: pump suction needed to avoid cavitations
11/08/2007 mmpmm
Pumping System CharacteristicsPumping System Characteristics
12
Type of PumpsType of Pumps
Classified by operating principle
11/08/2007 mmpmm
Pumps
Dynamic
Centrifugal Special Effect
Others
(Impulse, Buoyancy)Positive
Displacement
Rotary
Internal Gear External Gear
Lube Slide Vane
Reciprocating
13
Type of PumpsType of PumpsPositive Displacement Pumps
• For each pump revolution• Fixed amount of liquid taken from one end
• Positively discharged at other end
• If pipe blocked• Pressure rises
• Can damage pump
• Used for pumping fluids other than water
11/08/2007 mmpmm
14
Positive Displacement PumpsPositive Displacement Pumps
• Reciprocating pump• Displacement by reciprocation of piston plunger
• Used only for viscous fluids and oil wells
• Rotary pump• Displacement by rotary action of gear, cam or
vanes
• Several sub-types
• Used for special services in industry
11/08/2007 mmpmm
15
Dynamic pumpsDynamic pumps
• Mode of operation• Rotating impeller converts kinetic energy
into pressure or velocity to pump the fluid
• Two types• Centrifugal pumps: pumping water in industry –
75% of pumps installed
• Special effect pumps: specialized conditions
11/08/2007 mmpmm