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Mechanical Preliminary Test
RETURN TO KNOWLEDGE TEST SELECTION
If ambient pressure decreases:
GT useful power decreases and GT HR increases
GT useful power decreases and GT HR remains approximately constant
Both GT useful power and GT HR remain approximately constant
When a mechanical system is in "resonance"?
When system vibration amplitude become minimum
When system vibration amplitude become maximum
When the frequency of a periodic force applied to the system is the same of its natural frequency
What can be the cause of decrease of the wheel chamber pressure?
Fouling on high pressure buckets.
Increase of the labyrinth seals clearance.
The shrouds are items used for?
Bearings' oil sealing purpose
Compressed air sealing purpose
Hot gas path sealing purpose
Select the TRUE statement about the thrust bearing shims:
the active side shim sets the axial position of the rotor
the active side shim sets the thrust bearing clearance
the non-active side shim sets the axial position of the rotor
Select the TRUE statement about steam turbine impulse stage:
An impulse stage is usually more efficient than a reaction stage
An impulse stage needs higher peripheral speed than a reaction stage
The optimum value of ψ for an impulse stage is around 2.3
What is the possible cause of flow decrease in tandem dry gas seals system's primary vent?
the gap between the two secondary seal rings increased
the gap between the two secondary seal rings decreased
the gap between the two primary seal rings increased
Regarding the fuel gas system, which of the following sentences is TRUE?
The SRV valve is used to cut the fuel gas supply out while the GCV controls the mass flow rate of the gas fuel to feed the GT.
SRV and GCV are used together to control the fuel gas mass flow rate
The SRV is used to cut the fuel gas out in case of trip and to keep the inter-valve pressure constant during the operation of the GT, to ensure an easier control of the fuel mass flow rate through the GCV.
What is the pressure of the sealing steam?
1.1 ÷ 1.3 bara.
Which is the criterion used to define the maintenance intervals?
Number of running hours
Number of equivalent running hours and equivalent number of starts-stop sequences
Number of equivalent running hours
In case journal bearing's clearance is out of tolerance, what is the correct action to be taken?
insert shims under the lower pads to lift up the rotor in the centered position
replace the lower pads to restore the design clearance
replace all pads
"SALE" and "SALA" are controlled using:
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