Final Control Element Flashcards
A direct acting actuator does what with air pressure
Extends with increased pressure
A reverse acting actuator does what with increasing air pressure
Retracts with increasing air pressure
A direct acting valve
Is normally open
A reverse acting valve is
Normally closed
Valve F O def
Fails open
A piston actuator is used
When the stroke or thrust of a diaphragm actuator is too short
A valve positioner
Positions the valve stem and plug
2 types of electric actuators
Solenoid and motor
Springs convert from a double acting rack n pinion actuator too :
A single acting, ie the air opens , springs close
Scotch yoke actuators are for
2 position operation. I side energized the other side vented
A current to pressure transducer
Changes a 4 to 20 ma signal to 3 to
15/20 to 100 kPag
Trip valves
Fail/shutdown the system when supply pressure falls below a certain point . Resets when pressure comes up
4 types of actuators
- manual
- pneumatic
- electric
- electro hydraulic
On rotary actuators how often should PMs be done
Every 6 months
Bench set is
Applying low and high pressure to a diaphragm actuator to get rated valvebplug travel
Why is a weaker actuator spring better than reductions actuator control pressure when differential pressure causes issues,?
Because the 20 to 100 kPg signal is often fixed
Hazards associated with servicing controls
- high pressure instrument air
- electrical power sources
- stored spring energy
- pinch points
- hydraulic fluids
Most volume boosters have a gain of
1
A reciprocal control valve is aka
Sliding stem
A segmented ball valve is called
A chatacterised
If a valve won’t stroke at all the issue could be
Excess friction/ packing too tight
Flashing is
Pressure decrease causes the liquid to explode into vapour
Cavitation aka
- increased pressure causes liquid to implode back into the fluid,
- micro jets
Def the point of smallest constriction and fastest velocity / least pressure
Vena contracta
______ damages the trim with a smooth polished appearance
Flashing
_____ damages the trim with erosioncausing pitting
Cavitation
Damage type that causes excessive noise and vibration
Cavication
Anti cavitation trim works how
Many smaller holes separates the pressure drop reducing chances of flashing therefore cavication
Using a whisper cage can reduce noise by _____ db
30 db
Industry standard material for valves
Type 316 stainless
Cro-moly wc9 good for what kind of valve service
Steam n boiler feed water
317 stainless used for valves of what service
Pulp/ paper
Ie : digester
Fail safe mode of an air to open valve
Failed closed
Fail safe mode of an air to close valve
Fails open
Valve symbol with arrow pointed at “head”
Fail open
Valve symbol with arrow pointed away ( down ) from head
Fail closed
Valve symbol with 2 arrows at/away from head
Drift open or drift closed
For general safety what fails closed
Steam / hot oil
For general safety what fails open
Cold/ chilled watee
Flow direction for an unbalanced valve are almost always _____
Because _____
FTO flow to open
Because other way will try to close valve giving poor control
Noise and cavitation control flows are
Opposite
PTFE IS also called
Teflon
