Pump - Firdaus Sabturani Flashcards
What is a pump?
Is an energy converter where it converts mechanical energy
supplied at the pump shaft into mechanical energy of the liquid
flowing into the pump
Purpose of Pump
To enable the liquid to flow through a pipeline or rises to a higher level or pressure.
Centrifugal Pump
– Widely used in process industry
– Most used to transfer huge amount of liquid
– Low operating cost
Positive displacement Pump
– Small size
– More efficient than centrifugal pump
– Used for Chemical injection, dosing pump, etc
Pump Fundamentals
- Fluid is led to the eye or center of the impeller and is set into rotation by the impeller vanes
- Fluid is thrown from the periphery of the impeller with considerable velocity and pressure through centrifugal
force - The casing, which surrounds the impeller, has a volute or diffuser shaped passage of increasing area
- The casing collects the fluid leaving the impeller and converts a portion of its velocity energy into additional
pressure energy - The casing passage leads to the discharge nozzle of the pump where connected piping discharges the fluid to its place of use
Types of Positive Displacement Pump
- Reciprocating pump
- Rotary pump
Reciprocating pump
– Capable of handling of liquids with a high viscosity.
– Capable of handling low flow / high differential head combinations.
– Suitable for dosing/metering applications, including hazardous
Rotary pump
– Capable of handling of liquids with a high viscosity.
– Capable of handling low flow / high differential head combinations.
– Flow is almost independent of the discharge pressure.
Pump Capacity
refers to a rate of flow typically expressed in either m3/hr, barrels per day, or Kg/hr
The total developed head
equal to the discharge head minus the suction head, (TDH = hd–hs), and is typically expressed in either “Meter” or “Kg/cm2”.
Affinity Law
– Flow changes DIRECTLY(linear) with RPM.
– Head changes as a SQUARE of RPM.
– Power is proportional to Flow times Head
-it changes as CUBE of RPM.
Case for Net Positive Suction Head
– Inside a pump, if pressure gets low enough (below vapour pressure), liquid will boil. The lowest pressure zone is usually at the suction area.
If too many bubbles
suction gets blocked by them, and no more pumping…That is where “pump losses its head”
How to Prevent
NPSH Required
- Double suction impeller
- Enlarged eye impeller
- Lower speed
- Suction inducer
How to Prevent
NPSH Available
- Raise suction liquid level ( hs)
- Increase suction pressure ( Ps)
- Booster pump
- Reduce suction friction ( hf)
- Cool liquid ( reduce Pv)
Cavitation
the formation of bubbles or cavities in liquid, developed in areas of relatively low pressure around an impeller.
what happen during
Cavitation
- As bubbles flow from low pressure to higher, they implode against metal surfaces. These micro-hammer-like impacts erode the material, creating cavities –thus “cavitation”
- The collapsing of these bubbles trigger intense shockwaves inside the pump, causing significant damage to the impeller and/or the pump housing.
NPSHR
the suction capability of an impeller
NPSHR determined by:
- Inlet Diameter
- Rotating Speed
- Inlet Blade Angle
- Suction Inlet Approach
Typical low flow situation is normally encountered in the industry due to
- Malfunction of downstream control valve or check valve
- Inadvertent closure of block valve
- Improper line-up
damage of the pump and its component due to
the following reasons:
- Re-circulation at impeller inlet & outlet
- Risk of hydraulic instability
- Increased risk of cavitation damage
- Increased radial & axial thrusts
- Increased vibration levels
- Reduced seal and bearing life
- Temperature rise within pump
Minimum Flow Protection
For centrifugal pump
- Recycling
- Continuous recycle for small pumps
Minimum Flow Protection For positive displacement pumps
- Speed variation
- Recycling
- Stroke variation
Methods for regulating/control Pump Flow
- Discharge throttling
– Reduce flow by throttling discharge valve - By-Pass Control
– Return excess flow back to suction tank - Cyclic Control
– Switch pump off & on to limit total flow - Variable Speed
– Reduce pump speed to reduce flow
