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 is caused by
- 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
