Pumps (centrifugal) Flashcards
What are the two types of pumps?
Dynamic pump
Positive displacement pump
What are the different types of dynamic pumps?
Radial flow
Axial flow
Mixed flow
Peripheral flow
How is flow created in a dynamic pump?
By using centrifugal force to spin the fluid outwards.
What is pump head?
The pressure the pump has to overcome to be able to move liquid through the system.
Psi
kPa
Bars
What is head?
Pressure converted to a height of a column in which the pumped liquid can maintain.
What is vapour binding?
When pressure on the suction side of the pump drops below the pressure of the liquid, vapour forms.
Can be caused by:
Insufficient suction head
High suction lift
Excessive friction head
High liquid temperature
What is cavitation?
If pressure inside a centrifugal pump drops below the vapour pressure, vapour bubbles form. The bubbles flow with liquid to the high pressure area and collapse, producing a shock wave.
What is net positive suction head?
The required pressure at pump section.
How is the pumps capacity determined?
By the volume of liquid it can deliver per unit of time.
USgpm
L/min
What is the most common radial flow pump?
Volute pump
What’s the difference between radial and axial flow pumps?
Radial pump moves the liquid out radially from the shafts axis.
Axial-flow pump the liquid moves through the casing parallel to the shaft.
Mixed flow pumps use?
A combination of radial and axial pumps
Where do you find regenerative turbine pumps?
Used in compact areas and are suited for high pressure low capacity service
Where are mixed flow pumps used?
Low head, high capacity applications
What are the two types of pump casings?
Split casings:
Horizontally
Diagonally
Radial
Barrel casings
What casing material is best suiting for water, gasoline and other chemically neutral liquids?
Cast iron with bronze fittings
What are the different impeller designs? 7 of them
Open impeller
Semi open
Closed single inlet
Closed double inlet
Screw style
Axial flow
Open mixed flow
How is internal leakage prevented between the discharge and suction side of the pump?
Seals
What happens when the wear rings in a pump wear out?
Re surfaced or replaced when wear exceeds three times the initial clearance.
How are wear rings held into position?
Shrink fit
Spigot, groove, or pins
Screw threads
How are wear rings lubricated?
The pumped liquid
What is a wearing cheek plate?
Easily replaced plates which front and back of the casings
How is hydraulic axial thrust controlled
Using opposing impellers
Holes in impellers
Balancing drum/discs
How do you control leaking through the casing and the shaft?
Mechanical seals
Or
Compression packing
What is a mechanical seal?
Two lapped faces contacting each other to make a seal.
Best suited for high pressure
Describe sealing with compression packing and lanterns?
Usually rings of packing separated by a lantern (lantern ring separates layers of packing and allows a passage for lubrication.) the glad is either tightened or loosened to properly hold rings in place.
How is shaft wear and corrosion at the pumps stuffing box controlled?
Shafts are made of corrosion and wear resistant material.
Larger shaft usually have replaceable sleeves
What is the purpose of the centrifugal pump bearings?
Supports the shaft carrying one or more impellers
Allows shaft to move with limited friction
Keep the rotating shaft and impeller into position.
What are the two basic types of bearing used in pumps?
Friction
Anti friction
Where are axial and radial rolling elements located in axial split and radially split pumps?
On axial split pumps bearings are located at both ends of the shaft.
On radially split pumps radial load bearings are placed at the impeller end and combination bearings are placed at the drive end.
What is a suitable base to mount a pump and drive source?
Must be mounted to a secure base of cast iron or steel. And bolted to a solid foundation.
Compare base mounted pumps to centreline mounting pumps?
Base mounted pumps have mounting lugs on the bottom of the pump casting. Any Change in temp can cause pump to lift and become misaligned.
Centreline mounting pumps are carried on lugs from the centre of the casting which rest on the base. Casting can move in both directions with out changing alignment.
What is a close coupled pump?
Pump casing is directly mounted on the motor casing.
Motor shaft extends through the casing and the impeller is mounted onto it.
What checks should be made prior to starting the pump?
The unit will turn over freely by hand
The pump is driven the the direction shown on the casing.
The bearings are properly lubricated
The pump is primed
All air from seal housing is vented
Plenty of quenching liquid is flowing to the seals
What safety precautions should be followed when working on a pump?
Lock out
Shut off, lock and tag all main valves to and from the pump. Including seal fluid supply
Drain the pump
Flush the pump if it had been pumping acids or anything else that could harm workers
List the preventative maintenance procedures for centrifugal pumps?
Inspect:
Volume and temperature of liquid leaking past the packing.
Oil level
Bearing temperature and noise
Joints and seals for leaks
Flow rates at operating conditions.
What does a pump overhaul consist of?
Inspecting/replacing the impeller
Inspecting/replacing wear rings or plates
Inspecting/replacing shaft or sleeve
Inspecting stuffing box and replacing compression packing or mechanical seal
Replacing all bearings and seals
What symptoms would occur if the impeller where running in the wrong direction?
Failure to deliver liquid
What symptoms would occur if air were leaking past the stuffing box?
Reduced capacity or pressure
What are the possible reasons for the pump driver to be overloaded?
Speed is to high
Viscosity of liquid different then what is recommended for the pump.
Mechanical resistance in the pump.
What are the causes of pump vibration?
Misaligned coupling
Insecure foundation
Unbalanced impeller due to excessive cavitation.
Bent shaft
Worn bearings
What corrections are required if the pump casing wears?
Repair casing by welding or installing an insert.
Or
Replace the pump casing with a more suitable material for the pumped liquid.
What corrections are needed if there is excessive packing wear due to overheating?
Ensure cooling supply to the stuffing box is operational
Ensure gland nuts are not to tight.
What are the usual causes of casing damage?
Impact
Uneven base
Freezing
What are some other names for dynamic pumps?
Continuous flow, kinetic, centrifugal, or non displacement pump.
What is the equation to get Psi from the pump?
Psi = ft x .433 x sg
Specific gravity (SG) of water is 1
One foot head of water has a head pressure of .433