Fans And Blowers Flashcards
(23 cards)
What are the two common fan designs for imparting energy to air/gas
Centrifugal and axial designs
How does airflow differ between centrifugal and axial fans
Airflow though a centrifugal fan fallows a radial path through the fan wheel .
Axial fan is straight , essentially parallel to the fan shaft.
What is used to measure small pressures in airflow systems
A manometer
How many kinds of pressures are developed by fans and what are they
3 kinds
Static, velocity and total pressure
How is static pressure measured useing manometer
By connecting the manometer to the fan discharge ducting at right angle to the ducting wall,with the other end open to atmosphere.
What is the significance of static pressure in airflow systems
It overcomes the resistance of ducts , fuel beds , filters and grates
Describe velocity pressure and how it is measured
Velocity pressure is the pressure over and above static pressure, caused by the impact of air flowing through a duct .
Measured by connecting one end of the manometer at right angles to duct wall, with the other end facing the airflow.
How is total pressure calculated
By adding static and velocity
When might it be necessary to convert static pressure to velocity pressure
Under certain conditions in duct systems
How is the conversation of static pressure to velocity pressure achieved
By gradually decreasing the cross sectional area of duct ( converging)
What causes static electricity generation in duct work
Striping electrons off ductwork surfaces
What are the consequences of underground static charges in airflow systems
Frequent bearing and coupling failure
How can voltage from static charges be managed in fans
By installing a grund brush and holder so that the carbon brush rubs against the shaft allowing the electrical charge to be transferred to the ground.
What is the general behavior of fan curves in relation to air flow
They arc downward from the 0 airflow condition
What is the consequence of a fan operating in a region where it’s curved intersects with the system resistance curve
Unstable operation
What is the cyclic behavior resulting from interaction between a fan and the system called
Hunting or surge
Which types of fans are most susceptible to instability during operation
Axial fans, forward and backward incline centrifugal fans
What is the term to describe the most pronounced instability in fans
Stall
What ate potential consequences of unstable fan operation
Reduced airflow and increased system pressure
Blower components 6x
Impeller (rotor)
End plate (head plate)
Casing (cylinder)
Bearings
Timing gears
Oil reservoir
Oil seal.
If a blower inlet is piped into a vacuum system
There is often no need for a silencer on the inlet side
Blower problem knocking cause.
:Unit out of time
:Distortion due to incorrect mounting or pipe strain
: excessive pressure differential
: worn gears
: worn bearings
: worn bearing housings
Blower problem excessive blower temperature
: to much oil in gear housing or drive cover
: too low operating speed
:blocked intake filter or silencer
: worn impeller clearances
