Chapter 2-Pressure pump and regualtion.pptx

Chapter-Two
Hydraulic and Pneumatic Pressurization and
Regulation
By: Semahagn Yematawu (MSc)
2024
Liquids: Pump
Gas: Compressor
ኮምቦልቻ ቴክኖሎጂ ኢንስቲትዩት
Kombolcha Institute of Technology
Pressurization
Pressurizing of

Contents
Hydraulic Pumps and regulators
Hydraulic Pumps
Hydraulic Pump Types and working Principle.
Hydraulic Pressure Regulation.
Pneumatic Compressors and regulators
Pneumatic Compressor Types and working Principle.
Pneumatics Pressure Regulation.
Compressor Control

The heart of any hydraulic system, because it generates the
force necessary to move (pull and pushes) the hydraulic fluid from
the storage tank and delivers it to the rest of the system.
Hydraulic pump is the combined pumping and driving motor unit.
Converts Mechanical Energy to Hydraulic Energy
Its working principle:
Mechanical energy is delivered to the pump using a prime mover
such as an electric motor.
Partial vacuum is created at the inlet due to the mechanical
rotation of pump shaft.
Vacuum permits atmospheric pressure to force the fluid through
the inlet line and into the pump.
The pump then pushes the fluid mechanically into the fluid power
actuated devices such as a motor or a cylinder.
PUMP

Classifications of pumps
Fig.2.1 Diagram of Classifications of pumps

Conti…
The two broad classifications are:
 Non-positive displacement(Dynamic) and
 Positive displacement pumps
1. Dynamic (non-positive displacement) pumps
 Moves fluid by converting kinetic energy from a rotating
impeller into hydrodynamic energy, which increase the
velocity and pressure of the fluid
 Normally suited for low pressure and high discharge.
 They are of little use in the fluid power system.
 In the dynamic group are the centrifugal pumps.

Centrifugal Pump
These pumps are not suitable for high pressure
applications and are generally used for low-pressure
and high-volume flow applications.
The maximum pressure capacity is limited to 20-30
bars and the specific speed ranges from 500 to 1000
rpm.
 Most of the centrifugal pumps are not self-priming
and the pump casing needs to be filled with liquid
before the pump is started.

Conti...
2. Positive displacement pumps
 The positive displacement type is universally used for fluid
power systems.
 a fixed amount of fluid is forced (pushed) through the
system per revolution of pump shaft.
 All such pumps have pressure relief valves for diverting the
flow back to the tank in case of high pressure.
Advantages over dynamic pumps:
• High pressure capability (up to 800 bar)
• Small, compact size
• High volumetric efficiency
• Small changes in efficiency throughout the
design pressure change
• Great flexibility of performance

Gear pumps (fixed displacement)
a. External gear pumps
b. Internal gear pumps
c. Lobe pumps
d. Screw pumps
Vane pumps
a. Unbalanced vane pumps (fixed or variable displacement)
b. Balanced vane pump (fixed displacement)
Piston pumps (fixed or variable displacement)
a. Axial design
b. Radial design
Type of Positive displacement pumps

2.1. Gear pumps (fixed displacement)
A) External Gear Pumps
 Fluid flow is developed by carrying fluid between the
teeth.
Fig.2.2 External gear pump operation

Conti…
 Suction side is where teeth come out of mesh
(volume expansion) and discharge side where teeth go
into mesh (volume decreases).
 Displacement volume of pump is given by
()
Where: and are tip and root diameter of the gears.
 Theoretical flow rate for N (rev/min).
()

Performance curves
Fig2.3 Positive displacement pump Q vs N & P vs Q

 As there is clearance at the tip of the gear teeth oil can leak back
towards the suction line, thus reducing the actual volume flow rate.
 This internal leakage called pump slippage, is identified by
volumetric efficiency (), which is defined as:
 Higher discharge pressure will result in more leakage thus making
the volumetric efficiency lower.
 Too high pressure can also damage the pump parts. Such pressures
can be due to high resistance to flow or a closed valve in the pump
outlet line. This again emphasizes the need for relief valves.
 Spur gears are noisy and helical gears are less noisy. but since they
introduce high thrust, they are limited to low pressures (below 15
bars).
 Herringbone gear pumps eliminate the thrust and run smoothly.
Conti…

Advantages
 used for high speed and pressures
 Quite operation
 Variety of build material operations
Disadvantages
 Bushing wear in liquid areas
 Fixed end clearance
Advantages and Disadvantages External Gear pump

B)Internal Gear
Pumps
Fig.2.4 Operation of an internal gear pump
 Power is applied to any one of the gears. The motion of the gears
forces the fluid around both sides of the crescent seal which acts as
a seal between the suction and discharge ports.
 Industrial gear pumps can run at 1500- 2500rpm with pressures to
200 bars. Flow rates up to about 400l/min

Advantages
 Smooth/pulseless flow
 Slightly more horsepower for size
Disadvantages
 High cost
 Limited size range
 Low to moderate pressure rating
Advantages and Disadvantages Internal Gear Pump

C) Lobe Pump
 It operates in a fashion similar to the external gear pump. But both
lobes are driven externally so that there is no direct contact of the
surfaces.
 It is quieter and has a larger volume flow rate than the other gear
pump types.
Fig.2.5 Lobe pump 16

D) Gear rotor Pump (Gerotor pump)
 It is a form of internal gear pump. Inner gear has one
tooth less than the outer.
 The inner gear is placed eccentrically with respect to the
outer and this gives rise to an alternative increase and
decrease of the
17
Fig.2.6 Gear rotor pump

E) Screw Pump
 This is an axial flow positive displacement unit. The central rotor is
the only one driven and the two idler rotors that are in rolling contact
act as rotating seals.
 Flow rates up to 2000 l/min; and pressure up to 250 bars.
18
Fig.2.7. Screw Pump
 Each thread are driven individual which meshing in parallel
 The fluid does not rotate, but moves linearly as a nut on the thread
 Its very quiet smooth operating pump

2.2. Vane pumps
 Freely moving (radial)vanes are located on the slots of the
cylinder.
 Centrifugal force keeps the vanes out against the housing serving
as a seal. Because of eccentricity (housing forms a cam ring) the
compartments between the slots expand and contract.
 The expansion assists the intake and the contraction assists the
discharge.
 The eccentricity is given by
Where: Dc and Dr are cam
ring and rotor diameters.
Fig.2.8 Vane pump operation

Chapter 2-Pressure pump and regualtion.pptx

Volumetric displacement per revolution
L is width of rotor.
Q can also be expressed as a function of the
eccentricity as
Vane pumps are classified as fixed or variable displacement and
unbalanced or balanced design. The following combinations are
available

• Fixed displacement, unbalanced design
• Fixed displacement, balanced design
• Variable displacement, unbalanced design
The vane pump shown earlier is a fixed displacement,
unbalanced design. There is unbalanced force on the rotor
which results as a side thrust to be taken up by the bearings.
The balanced design uses two inlet (diametrically opposed)
and similarly two outlets (fig 2.9 ). This will eliminate the
side thrust. The cam ring will have an elliptical shape

Fig.2.9 Balanced vane pump principles 25

The volume flow rate can be varied by varying the
eccentricity and such a design is called variable
displacement pump fig2.10
Fig.2.10 Variable displacement vane pump

Advantages
 low viscosity fluids at high pressures
 Dry run for short periods
 Develops a good vacuums
Disadvantages
 Complexity
 Unsuitability for high pressure
 Does not run high viscosity fluids
Advantages and disadvantages vane pump

2.2.3) Piston pumps
 It is the reciprocating motion that gives rise to the pumping process.
A series of reciprocating pistons are involved in this.
 Normally used for pressures in excess of 200 bar.
 Two basic types of piston pumps fixed displacement:
 Axial design, pistons parallel to the cylinder block
 Radial design, pistons around the pump drive shaft at right
angles

A)Axial Design (Swash Plate Design)
 In the axial design (in-line piston pump or swash plate
design), two possible arrangements (fig2.11-14)
 Fixing the swash plate and rotating the cylinder block
(piston revolves (also reciprocating) with the rotor)
 Rotating the swash plate and fixing the cylinder barrel
(piston only reciprocating)
29 Fig.2.11 Schematic of a swash plate design

Axial Design (Bent axis Design)
A bent axis pump fig2.12 and fig2.13 reciprocates the pistons
in the rotating cylinder block through a bevel gear mechanism
(fixed displacement) or a universal joint (variable
displacement) that changes the offset angle (fig2.15)
34
Fig.2.12 A bent axis pump Fig.2.13 Fixed displacement bent axis pump

Fig.2.14 Volumetric displacement changes with offset angle

Advantages
 High Pressure Capability:
 Precision Flow Control:
 Versatility with Fluids:
 Self-Priming Ability:
 Durability:
 Variable Flow Rates:
 Minimal Pulsation (in certain designs):
Disadvantages
 Complexity and Size:
 Higher Initial Cost:
 Maintenance Requirements:
 Potential for Pulsation:
 Limited Flow Rate Range:
Advantages and Disadvantages Piston pump

2.3 Pump performance
 Two types of efficiencies will be considered:
volumetric efficiency and mechanical efficiency.
a) Volumetric Efficiency (ηv)
 This indicates the amount of leakage that takes
place within the pump and given by:
Typical values
 Gear pumps:80% to 90%
 Vane pumps: 82% to 92%
 Piston pumps: 90% to 98%
41
ηv=
actual flow ( rate produced by pump)
T heoretica flow ( rate pump should produce)
=
˙
𝑄𝑎
˙
𝑄𝑡

b) Mechanical Efficiency
 This indicates the amount of energy losses that
occur for reasons other than leakage (friction
and fluid turbulence). Typically runs between
90% and 98%.
Where;
P = pressure rise across pump (Pa)≈pdischarge
= pump theoretical flow rate ()
Ta= actual torque delivered to pump (N. m)

In terms of torques (fig2.18)
The term volume / radian or displacement per cycle is a
characteristic of a specific motor or pump.

Fig.2.15 Terms involving pump mechanical efficiency
44

Mathematically it can be represented
as
𝜼𝑜= 𝜼𝑣 𝜼𝑚
ηo=
act ual powe r de live r ed 𝐛𝐲 pump
a ct ual po we r deli ver ed 𝐭𝐨 pump
x
Overall Efficiency,
Overall efficiency considers all energy losses and hence is defined as
Substituting the values
which agrees with the definition.

Pump Performance Curves
 Pump manufacturers specify pump performance from
actual test data. Typical are shown for variable
displacement piston pump and radial piston pumps.
fig2.16a., fig2.16b. and fig2.17.
Fig.2.16a Performance curves for 6-in3
variable displacement piston pump

Fig.3.16b Performance curves for 6-in3
variable
displacement piston pump

Fig.3.17 Performance curves of radial piston

Fig.2.18 Comparison of various performance factors for
pumps

Summary of Pump Performance Comparison
Gear pumps: least expensive; lowest level of
performance; simple in design and compact in size- makes
them the most common type of pump used in fluid power
systems.
Vane pumps: efficiencies and cost fall between gear and
piston pumps-last for long time; needs clean oil with
good lubricity
Piston pumps: most expensive; provide the highest

Pump Selection
 Select actuator (cylinder or motor) based on the load
 Determine flow-rate requirement
 Select system pressure
 Determine pump speed and select prime mover
 Select the pump type
 Finally, optimization may be required for the system
to operate at minimum cost while satisfying the
design requirements.

Compressor
Types
Of
Compressors-Reading
assignment

What is Compressor ?
• Compressor is a device which is used to increase the pressure of air from
low pressure to high pressure by using some external energy.
• For operation of pneumatic tools i.e. rock drills, vibrators etc.
• For filling the air in tube of vehicles
• In automobile service station to clean vehicles.
• For spray painting in paint industries.
• In vehicle to operate air brakes.
• For cleaning workshop machines.
• For supercharging of an IC engines.
•Positive Displacement: Operate by trapping a specific volume of air and
forcing it into a smaller volume.
•Non-Positive (Centrifugal): Operate by accelerating the air and converting the
energy to pressure.
• Artificially cooled, pressure ratio more than 1.15, fluid medium is Gas

Definitions of Compressor
Compression ratio:- It is defined as the ratio of volume of air before
compression to the volume of air after compression.
Compressor capacity:- It is the quantity of air actually delivered by a compressor
in m3/minute or m3/sec.
Free air Delivered(FAD):- It is the volume of air delivered by compressor under the
compressor intake conditions ( i.e. temperature and pressure ).
Swept Volume:- The volume displaced or swept by piston when it moves
between top dead center and bottom dead center.
Clearance volume:- it is the difference between the total volume and the
swept volume, basically the gap that remains between the piston head and
the cylinder head when at top dead center.

Reciprocating
Rotary – screw compressor
Centrifugal
compressor:
Jet engine
cutaway
showing the
centrifugal
compressor
and other parts
Ejector
Process plant optimization. Gas compression.
Production boosting.
•Quiet operation
•High volume of air,
steady flow.
•Lower energy cost ,
small size
•Suitable for continuous
operation (24/7),
• low efficiency
•Low pressure ratio
Low mass flow rate,
Service life longer,
high pressure ratios,
bigger size, and is
relatively cheap.
Centrifugal compressor is widely used in chemical and
petroleum refinery industry for specifies services.

Reciprocating Compressor
 In reciprocating compressor, a volume
of air is drawn into a cylinder, it is
trapped, and compressed by piston and
then discharged into the discharge line.
The cylinder valves control the flow of
air through the cylinder; these valves
act as check valves.
Suction line
Head
Valve plate
Suction
valve
Connecting
Rod
Crankshaft
Piston
Rings
Discharge valve
Discharge line
Double acting Compressor:
compressor that completes two discharge
strokes per revolutions of crankshaft.
Most heavy- duty compressors are
Single acting compressor: has one
discharge per revolution of crankshaft.

Conti..
Multi-staging :Reduction in power required to drive the compressor.
 Better mechanical balance of the whole unit and uniform torque.
 Increase in volumetric efficiency.
 Reduced leakage loss.
 Less difficulty in lubrication due to low working temperature.
 Lighter cylinders can be used.
 Cheaper materials can be used for construction as the operating temperature is
lower.

Efficiencies
Volumetric efficiency:-
It is the ratio of actual volume of the FAD at standard atmospheric condition in one
delivery stroke (Actual air intake) to the swept volume (theoretical air intake) by the
piston during the stroke.
Isothermal efficiency:-
It is defined as the ratio of isothermal power (Piso) (i.e. required input power at
isothermal process) done to the indicated power (IP) or actual work done.
Mechanical efficiency:-
It is the ratio of indicated power (IP) to the shaft(Brake) Power (Pshaft).
Overall efficiency:-
It is the ratio of isothermal power (Piso) to the shaft(Brake) Power (Pshaft).

Chapter 2-Pressure pump and regualtion.pptx

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