7. LAW OF CONSERVATION OF ENERGY
MOVING THE SMALL PISTON
10 Cm DISPLACES
1 Cm2 x 10 Cm = 10 Cm3 OF LIQUID
10 Cm
100 kg
10 Cm2
1Cm2
1 Cm
Q=Axh
10
kg
10 Cm OF LIQUID WILL
MOVE LARGER PISTON
ONLY 1Cm.
10 Cm2 x 1 Cm = 10 Cm3
WORK DONE = FORCE x DISTANCE MOVED
W=Fxd
W=Fxd
W=Fxd
= 10 Kg x 10 Cm
= 100 Kg x 1 Cm
= 100 Kg-Cm
= 100 Kg-Cm
ENERGY CAN NEITHER BE CREATED NOR DESTROYED.
WHAT IS GAINED BY FORCE IS SACRIFICED IN THE
DISTANCE MOVED.
8. www.nfiautomation.org
Typical Units of Pressure
The SI unit for pressure is the Pascal (Pa), equal to one newton per
square meter (N/m2 or kg·m−1·s−2).
1 Bar = 14.69 psi = 100 kilo pascal
17. www.nfiautomation.org
Example: Motor Reversing System
b. Motor-Reversing System. A power-driven pump operating a reversible rotary motor. A
reversing valve directs fluid to either side of the motor and back to the reservoir. A relief valve
protects the system against excess pressure and can bypass pump output to the reservoir, if
pressure rises too high.
21. www.nfiautomation.org
Hydraulic Pumps
Hydraulic pumps convert mechanical energy from a prime mover (engine or electric
motor) into hydraulic (pressure) energy. The pressure energy is used then to operate an
actuator. Pumps push on a hydraulic fluid and create flow.
1.
2.
3.
4.
Single Stage Centrifugal Pump
Lobe Pump
Internal/External Gear Pump
Axial Piston Pump
24. Pump
www.nfiautomation.org
Converts mechanical energy into Hydraulic energy
1. External Gear Pump
For constant flow/pressure application
4000 psi = 275 bar
Low Cost & Dirt Tolerance
Used to charged pump to pressurize
the lnlet of vane & axial pump
28. www.nfiautomation.org
Pump Ratings
Typical factors determining nature of Pumps
Displaced Volume or Displacement = Q (l /min) or (l/rev)
Nominal Speed = in rpm
Maximum Pressure = in Bar or psi
Tank Capacity = in litres
Maximum Flow = l/min or l/sec
Fixed Type
Variable Type
29. www.nfiautomation.org
Comparing Pumps
Typical factors determining nature of Pumps
Parameter
Piston/ Axial
Pump
Vane Pump
Gear Pump
Pressure
10000 psi
4000 psi
4000 psi
Power Density
Highest
medium
Lowest
Efficiency
Highest
medium
Lowest
Dirt Tolerance
Lowest
medium
Highest
Noise & Vibration
Moderate
behaviour
Quietest &
vibration free
Noisy & high
vibration
Size & weight
Very Heavy
Heavy
Lightest
Life Expectancy
Long life &
repairable
Long life &
repairable
Short life
42. www.nfiautomation.org
Hydraulic Actuation System
Actuators – Hydraulic Cylinders
Used to produce linear motion
Double Acting Double Rod Cylinder
Double-Acting Double-Rod Cylinder
A double ended piston rod makes a cylinder stronger against side
load, as it has two bearings at the widest distance possible. This type
of cylinder is often mounted with rods fixed and the cylinder itself
moving to displace a part.
44. www.nfiautomation.org
Piston Force
Dependent on the air pressure, the cylinder diameter, and the frictional
resistance of the sealing components.
Single Acting Cyl.
Fn = A. p – (FR+FF)
Double Acting Cyl.
Fn = A. p – FR
Fth = A . p
Fth
=
A
=
p
=
Fn
=
FR
=
Theoretical piston force in N.
Useful piston area in cm².
Operation pressure in kPa.
Effective piston force in Newton
(N)
frictional force (3-20%) in Newton (N)
47. www.nfiautomation.org
Hydraulic Actuation System
Pres sure Re lief Valve
Pressure Relief Valve
Simple, direct-acting relief valve has no
adjusting screw and therefore opens at
a fixed, pre-set pressure as controlled
by setting of compression spring.
Adjustable, direct-acting relief valve blocks
flow through the valve until force of system
pressure on the poppet overcomes the
adjustable spring force and downstream
pressure.
52. www.nfiautomation.org
Valves – Directional Control Valves (DCV)
1. Allowing the passage of fluid and directing it to particular
lines
2. Canceling fluid as required by blocking their passage and
/ or
3. Relieving the fluid back to reservoir
57. www.nfiautomation.org
Flow Control Valves: Check Valve
The check valve allows oil flow in one direction and blocks it
in the opposite direction.
Check Valve
Spring Loaded
Check Valve
Pilot to Open
Check Valve
Pilot to Close
Check Valve
59. www.nfiautomation.org
2/2– Directional Control Valves (DCV)
er w ith Spring Return
2/2 Spring return
Valve with Lever
2/2 Spring return
Valve with Lever
Detent
2/2 Pilot Operated
Valve
63. www.nfiautomation.org
Hydraulics Exercises
1) Draw a hydraulic circuit to actuate two Single Acting Spring Return
cylinder with one 3/2 Valve
2) Draw a hydraulic circuit to actuate Double acting Cylinder with 4/2 Valve
?
?
67. www.nfiautomation.org
Hydraulics Exercises
1) Draw an Electro- pneumatic circuit to actuate Single acting cylinder with
3/2 solenoid valve actuated by Toggle switch
2) Draw a pneumatic circuit to actuate & latch Double acting Cylinder with
4/3 Spring return Solenoid Valve
4/3-Way NC - Double Electrical Control
S1
?
S2
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