UNIT - II
1.
What is the function of a pump in a hydraulic system?
A pump which is the
heart of the hydraulic system converts mechanical energy in to hydraulic
energy. The mechanical energy is delivered to the pump via a prime mover such
as an electric motor.
2.
What is the function of hydraulic actuator?
The fluid discharged by
the pump is directed to the hydraulic actuator. The actuator converts the
pressure energy of the fluid in to mechanical energy.
3.
A pump has a displacement volume of 98.4 cm3
/ rev. It delivers 1.52 litres/sec. at 1000 rpm and 70 bar. If the prime
mover input torque is 120 Nm. What is the over all efficiency of the pump?
(Ap-May-04)
The volumetric displacement is,
VD = 98.4 cm3
/ rev * (1m / 100 cm) 3 = 0.000100 m3 / rev
Now we have,
QT = VD . N = ( 0.000100 m3 / rev) (1000 / 60
rev/sec) = 0.00167 m3/ sec
Now the volumetric efficiency is,
ηV = ( QA/ QT ) * 100 =
((0.00152 m3/ sec) / ( 0.00167)) * 100 = 89.8%
Now the mechanical efficiency is,
(70*105 N/ m2)
(0.00167 m3/ sec)
ηm = ( P.QT / TA . N) *
100 = _____________________________
(120 Nm) (1000 * 2╥ / 60 rad / sec)
ηm = (11,690 / 12570) * 100 = 93.0 %
Therefore the overall efficiency is
,
ηo = (ηv * ηm) / 100 =(89.8 * 93) / 100 = 85.5%
4.
What do you mean by cushioning of Fluid power
actuators?
Due to the inertia force,
the piston will hit cylinder head at full speed. To overcome this, cylinder
cushioning is provided by which the hydraulic cylinder can be slowly retarded
or cushioned.
5.
Define mechanical efficiency.
It indicates the amount
of energy losses that occur due to the reasons other than leakages. This
includes friction in bearings and between other mating parts.
Theoretical
Power required for operating the pump
ηmech = ---------------------------------------------------------
* 100
Actual power delivered to the pump
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