Hydraulic Bench and Accessories
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Transcript of Hydraulic Bench and Accessories
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MAGSIPOC, Jay Anthony | Hydraulic Bench and accessories
Hydraulic Bench and
Accessories(Unit Operations
Laboratory)
LANSANG, Jelanie C.MAGSIPOC, Jay Anthony S.
SABULAO, Vina B.
CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
1. INTRODUCTION
HYDRAULIC BENCH
2. DESCRIPTION
2.1 General
Hydraulics Bench, its various accessories and the associated experimental
equipment have been developed to provide a comprehensive range of experiments
in fluid mechanics. Although the experiments are generally small in scale, they are
manufactured to a high quality standard and are designed to produce experimental
results which compare favourably with theoretical and empirical data.
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
2.2 General Arrangement
The bench consists of a steel frame which supports a fibre glass worktop with
integral weir channel and volumetric measuring tank, a sump tank, variable speed
centrifugal water pump with appropriate pipework and valves. The worktop is
manufactured from fibreglass reinforced plastic, with additional balsa wood
reinforcement, moulded to provide a recessed area for mounting experimental
apparatus, an integral weir and a volumetric measuring tank equipped with sight
glass and scale. The measuring tank is stepped with a 10 litre lower portion and 35
litre upper portion to ensure accurate measurements of both low and high flow
rates. The measuring tank discharges into a fibreglass sump tank of approximately
120 litre capacity, via a quick acting ball valve located in the PVC pipework. An
overflow pipe is provided in the volumetric measuring tank to prevent the sump
tank from running dry. A V-notch weir, mounted at the discharge end of the weir
channel is provided in clear acrylic plastic complete with a scale calibrated in litres
per minute so that a continuous reading of flow rate can be made. A centrifugal
pump delivers water to the outlet at the bench working surface, for connection to
either individual experiments or to a flow stilling basket. Provision is made for fitting
an additional pump. The flow is regulated by a chromium plated valve. The variable
speed control box also provides a much more convenient method of regulating flow
to experiments, particularly where the required flow rate is very low. A pressure
gauge is provided coupled to a rotary selector switch mounted on the panel;
pressure measurements can be made at the first and second pump delivery points,
the experiment input point and at another external position when required. A
vacuum gauge mounted in the pipework immediately prior to the pump is provided
to read the pump suction pressure. The component parts are mounted on a robust
stove enamelled steel frame, which is provided with castors for ease of mobility.
2.3 Water Circulation
The circulation pump is mounted on a lower platform and this allows full
accessibility to the unit. Water flows to the pump from the storage reservoir via a
transparent suction pipe fitted with a stop valve at the reservoir outlet. Thus any
cavitation taking place can be immediately seen in the transparent section. The
water is delivered from the pump through a second transparent pipe passing
through the panel above the pump. The pipe is connected to the bench regulating
valve, the control knob of which is mounted on the left hand side of the instrument
panel viewed facing the panel.
2.4 Electrical System
A flexible electrical cable is provided for connection of main electricity. The cable is
fitted with a connector which plugs into the speed control box located on the shelf
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
under the working top. The speed control box incorporates a switched socket for the
supply of electrical power to the water circulating pump and the second pump or an
accessory. The connection to the mains supply should be carried out in accordance
with the installation.
2.5 Pump and Motor Units
The pump is a high speed centrifugal type manufactured by 'Stuart Turner’. The
spilt flanged brass body is attached to the motor casing and the impeller is on an
extension of the motor shaft giving the arrangement known as "close-coupled. At
maximum speed of approximately 5400 rev/min the pump flow rate is 42 litres per
minute against a head of approximately 5 metres and the maximum head at zero
flow is approximately 20 metres.
2.6 Pressure Gauge and Selection Valve
A Bourdon type pressure gauge mounted on the panel of the Hydraulic Bench Unit
is connected via a special 4-way selector valve to various tapping points in the
apparatus.
a. First pump outlet
b. Supply to the apparatus
c. Auxiliary tapping - Do not turn the valve selector to 'Auxiliary' when this
position is connected
d. Second pump outlet - Where only one pump is fitted, connection (d) is
plugged
2.7 Hydraulic Bench Accessories
The basic bench unit can be augmented by a number of accessory units, some of
which are essential for certain of the experiments which are described later. The
available accessory units are listed below and, with the exception of the Auxiliary
Pump P6101, are illustrated in figure 1.
2.7.1 Auxiliary Pump & Speed Control Unit
A second variable speed centrifugal pump with associated pipework is available to
increase the water flow capacity, enabling the Bench Unit to service a series of
larger scale experiments The valving arrangements also enable the two pumps to
be run in either series or parallel configuration. Figure 2 shows a hydraulics bench
fitted with the auxiliary pump. The speed control units allow continuously variable
speed control of both the main and auxiliary pumps so that pump characteristic
curves may be obtained at different speeds.
2.7.2 Pump Speed Display
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
This unit provides a constant display of the speed of either the main or auxiliary
centrifugal pump. The method of connecting this display unit is shown in figure 3.
The circuit diagram for this unit is shown on P6102/10 reproduced as figure.
2.7.3 Constant Head Inlet Tank
The inlet tank provides a constant head of water for experiments requiring it, a two
position overflow is arranged so that either a 250 or 500mm head can be provided
to suit the experimental requirements. The tank is fitted with two screwed
connection points, one in the base and one in the side, for the attachment of
experiments. The tank is shown in figure 5.
2.7.4 Variable Head Outlet Tank
The outlet tank is used in conjunction with the inlet tank P6103 to mount various
experiments and to provide a regulated total head across the experiment. The
discharge pipe on the variable head outlet tank can be set at any value between
50mm and 300mm above the experiment centre line height. The tank is shown in
figure 5.
2.7.5 Feed Block
The feed block is provided for use instead of the constant head inlet tank for those
experiments which require more than 500mm inlet head. The feed block which is
shown in figure 5 can supply the full head available from the pump(s).
2.7.6 Manometer
The manometer is required for use with those experiments where the measurement
of pressure drop or head loss is necessary. The unit, which is shown in figure 6,
consists of four open vertical manometer tubes, thus enabling measurements to be
made at four points simultaneously, and a water on mercury 'U'-tube for the
measurement of higher values of differential pressure. The tubes are all mounted on
a back board which locates onto fixing brackets mounted on the Bench Top.
Connections to the experiments are made in clear flexible tube which should run
from the manometer to the experiment without forming an inverted 'U' in order to
prevent air traps. The manometer legs above mercury level are to be filled with
water, any air bubbles being present are to be bled via the valve positioned at the
top of the mercury manometer. This valve is a 3 position one, enabling equalisation
between the legs, bleeding of air, and normal operation to take place. Allowance
should be made for the relative specific gravity of 12.6 [i.e. (Hg - H2) = (13.6-1)]
when measuring heads using the water on mercury manometer.
2.7.7 Hook Gauge and Scale
The hook gauge enables vertical measurements to be made with a scale, at a series
of points along the horizontal length of the weir tank. It is intended for use with
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
P6223 and P6224 orifice experiments for plotting the trajectory of horizontal jets,
and with P6225 and P6226 for determination of the water height above a weir.
Precise positioning of the gauge is ensured by the use of accurate positioning rails
onto which the gauge can be fitted. The positioning rails and the hook gauge are
dual purpose having an orifice trajectory scale for use with the crosswire gauge,
(datum point at the centre of the orifice), and a water level scale for use with the
hook gauge, (datum point at the lowest point of the weir knife edge). Figure 7
illustrates the installation.
2.7.8 Rotameter
A variable area flow meter can be supplied to be mounted from the front left hand
leg of the frame between the pump delivery and the flow regulating valve, as shown
in figure 1. The meter provides a direct reading of the flow rate obtained from the
pump or pumps, rates from 0.4 - 4.0 m3/h can be measured.
2.7.9 Wattmeter
The Wattmeter is used to measure the electrical power input to the pump motor.
Figure 3A . 1-14A shows the installation of the Wattmeter and the circuit diagram is
shown in figure 8.
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
3. HYDRAULIC BENCH EXPERIMENTAL CAPABILITY.
3.1 Introduction
A series of additional experimental apparatus are available which, when used in
conjunction with Cussons hydraulics bench and its various accessories allows a very
wide range of experiments to be conducted as illustrated below.
3.1.1 List of Symbols
A cross sectional area (major area) m2
a cross sectional area (minor area) m2
ac cross sectional area at vena contractor m2
B,
b
Breadth m
CP specific heat at constant pressure J/kgK
CC coefficient of contraction dimensionles
s
Cd coefficient of discharge dimensionles
s
Cm meter coefficient dimensionles
s
Cv coefficient of velocity dimensionles
s
D characteristic dimension m
D,d internal diameter of pipe or tube m
E velocity approach factor dimensionles
s
F Force N
F configuration constant (bends, elbows etc.) dimensionles
s
f
& f’
friction factors dimensionles
s
g acceleration due to gravity 9.807 m/s2
H,
h
Head m
hf friction head m of fluid
ht total or pitot head m of fluid
Hm manometric head m of fluid
I Current Amp
i hydraulic gradient dimensionles
s
K, k Constant dimensionles
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
s
L, l Length m
M Mass kg
M mass flow rate kg/s
m area ratio dimensionles
s
N speed of rotation rev/s
Ns specific speed of rotation rev/s
n Constant dimensionles
s
P, p Pressure N/m2
pt total or pitot pressure N/m2
Q Volume m3
Q volume flow rate m3/s
Re Reynold’s number dimensionles
s
R, r Radius m
S reaction on vane N
T Temperature C or K
t Time s
V Velocity m/s
W work done J
W Power W
Wh hydraulic power W
Wi input power W
x Distance m
y distance from centre m
Z height above datum m
z correction factor dimensionles
s
Density kg/m3
absolute viscosity Ns/m2
Efficiency dimensionles
s
h hydraulic efficiency dimensionles
s
o overall efficiency dimensionles
s
shear stress N/m2
Torque Nm
kinematic viscosity m2/s
Angle
Difference
infinitesimal difference
angular velocity rad/s
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
function in dimensional analysis
3.1.2 Abbreviations
B position of centre of buoyancy
ac alternating current
dc direct current
L length (dimensional analysis)
M mass (dimensional analysis)
T time (dimensional analysis)
3.1.3 Suffices
a,b,c
,
indices used in dimensional analysis
d Discharge
f Float
m Meter
n number of parts, pumps or elements
s Specific
3.2 Performance of a Centrifugal Pump
This experiment utilises the pump supplied as part of the P6100 Hydraulics Bench.
The experimental capability can be extended by using the P6102 Pump Speed
Display Unit to indicate the pump speed and the P6109 Wattmeter to measure the
electrical power input to the pump. The experiment allows the performance of the
pump to be presented as characteristic curves of head plotted against flow rate.
Refer to Part 2 for details of the theory, experiment and typical results.
3.3 Performance of Two Pumps Connected in Series or Parallel.
By installing the Auxiliary Pump Unit P6101 onto the Hydraulics Bench it is possible,
with the pipework and valving supplied, to operate the two pumps in series or in
parallel. Part 2 of the manual also covers these experimental procedures. Figure 2
illustrates the installation of the Auxiliary Pump onto the Hydraulics Bench. The use
of two pumps also allows the Hydraulics Bench to act as a service unit for larger
items of experimental equipment, such as the wall mounted Friction in Pipes
Apparatus P5160 and Flow Channel P6245.
3.4 Laminar and Turbulent Flow In A Pipe
To carry out experiments on laminar and turbulent flow in a pipe Cussons P6220
Laminar Flow Experiment is required. This is mounted between the Constant Head
Inlet Tank (P6103) and the Variable Head Outlet Tank (P6104) and requires the
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
Manometer Board (P6106) to be mounted to the back of the bench for measuring
differential head across the laminar flow tube. The arrangement of a similar
experimental set up (P6221) can be seen in figure 1, which clearly shows the Inlet
Tank, the experiment, the Outlet Tank and the Manometer Board. To allow
experiments to be performed at higher flow rates than can be obtained with a
500mm inlet head it is necessary to use the P6105 Feed Block instead of the P6103
Inlet Head Tank. This experiment is discussed in detail in Part 3 of the manual
3.5 Losses In Pipes and Fittings
Cussons P6221 provides two straight pipe lengths of different bore (7mm and
10mm), one 10mm bore pipe containing 90 bends, one 10mm bore pipe containing
4 90elbows, one length of pipe with a ball valve and one length of pipe with an
angle seat valve. Any one of these pipes may be installed between the inlet and
outlet head tanks (P6103 and P6104). The Manometer Board (P6106) is required for
measuring head loss and to allow the relationship between head and flow to be
investigated. To allow experiments to be performed at higher flow rates than can be
obtained with a 500mm inlet head it is necessary to use the P6105 Feed Block
instead of the P6103 Inlet Head Tank. Experimental details are given in Part 3.
3.6 Entry and Exit Losses to a Pipe
The P6222 apparatus consists of two test pipes with an inlet bore of 10mm and an
exit bore of 20mm, one with sudden transition the other with a 30 transition, these
two pipes can be used to study either expansion or contraction losses. Adaptor
pieces are also supplied to allow sudden and tapered entry and exit geometries to
be obtained. The pipes and adaptors are again used between the inlet and outlet
head tanks (P6103 and P6104). The Manometer Board (P6106) is required which
allows the head-flow relationship to be investigated. Part 3 of the manual provides
all the experimental details.
3.7 Orifices
Cussons Elementary Orifice Set (P6223) comprises a set of three sharp edged
orifices of 3, 5 and 8mm diameter. The Advanced Orifice Set (P6224) comprises
square, triangular, Borda and bell mouthed orifices. The orifices are used in either
the side or the base of the Inlet Head Tank (P6103) to study the discharge
characteristics of orifices. When used in the side of the Inlet Head Tank the
trajectory of the issuing jet of water can be studied with the aid of the accessory
Hook Gauge (P6107). These experiments are presented in Part 4.
3.8 Weirs
Cussons provide two sets of weirs: P6225 Elementary Weirs comprising a
rectangular weir and two 'V' notch weirs (90 and 60 ); P6226 Advanced Weirs
consisting of a trapezoidal (or Cippoletti) weir, a linear weir and a full width (or
suppressed) weir. Any one weir can be attached to the end of the weir channel to
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
replace the standard 60acrylic V notch weir supplied with the bench. The Hook
Gauge (P6107) is an essential accessory for use with the weirs which enables
accurate measurement of the head over the weir. Part 5 gives detailed information
on experiments with weirs.
3.9 Flow Measurement by Tapered Area Meter
The tapered area flow meter or Rotameter P6108 is an accessory to the Hydraulics
Bench which, if purchased, may be permanently mounted between the pump
delivery and the bench regulating valve. Once fitted not only can it be used to
provide instantaneous reading of the flow rate but can also be used as an
experiment in it’s own right. See Part 6 for a detailed treatment of this topic.
3.10 Flow Measurement by Venturi
Cussons P6227 Venturi Meter is a classical 21 inlet conical venturi designed
generally in accordance with British Standard BS 1042. The venturi is used between
the inlet and outlet head tanks (P6103 and P6104) and can also be used with the
feed block (P6105) to allow higher flow rates to be achieved. The manometer board
(P6106) is essential for measuring differential pressure. The experimental work is
presented in Part 6.
3.11 Flow Measurement by Orifice Plate
The Orifice Plate Experimental Apparatus consists of two square edged orifice plates
(8 and 12mm) which can be trapped between the flanges of a 22mm bore pipe
installed between the inlet and exit head tanks (P6103 and P6104). The feed block
(P6105) can also be used and the manometer board (P6106) is essential. The pipe is
equipped with both corner tappings and D and D/2 tappings to allow both types to
be compared. The design is otherwise in accordance with BS 1042. Part 6 contains
full experimental details.
3.12 Flow Measurement by Turbine Meter
The pulse producing turbine meter is installed in a 25mm bore pipe which is
mounted between either the feed block (P6105) or the inlet head tank (P6103) and
the outlet head tank (P6104). The manometer board is not required as an analogue
display unit is provided. Part 6 of the manual discusses this method of flow
measurement.
3.13 Flow Measurement by Pitot-Static Tube
The pitot-static tube is installed in a 20mm bore tube which can be mounted
between the inlet and outlet head tanks. Alternatively the feed block can be used.
The manometer board is an essential requirement to measure the differential pitot-
static pressure. Part 6 provides experimental details.
3.14 Demonstration of Bernoulli’s Theorem
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
The flow of water through a convergent-divergent clear acrylic passage of
rectangular cross section is studied to demonstrate Bernoulli's Theorem. Fourteen
manometer tappings and tubes are provided for the measurement of the static
pressure distribution along the passage. The apparatus includes a dye injection
system which may be used to demonstrate the onset of turbulent flow. Part 7 of the
manual provides full details.
3.15 Hydraulic Ram
The hydraulic ram is an example of an early design of hydraulic machine in which a
large quantity of water falling through a small head is used to raise a small quantity
of water through a large head. Refer to Part 8 of the manual.
3.16 Impact of Jets
This apparatus is used to investigate the reaction of a jet of water on three
interchangeable vanes. Two sizes of jet nozzle are supplied and three target vanes,
namely:- one flat plate, one cone and one hemispherical bucket. Part 9 contains
experimental details.
3.17 Calibration of a Pressure Gauge
The apparatus consists of a simple but accurate dead weight calibration system
which can be used to calibrate the pressure gauge fitted to the hydraulics bench.
Refer to Part 10 of the manual.
3.18 Metacentric Height of Floating Vessels
The floatation characteristics of floating vessels may be studied using Cussons Flat
Bottomed Vessel P6235. The flat bottomed vessel is fitted with a detachable bridge
piece and mast, which can also be used with Cussons Alternative Hull Sections
P6236. A simple inclinometer is provided together with hull and bridge loading
system. Experimental details are covered in Part 11 of the manual.
3.19 Centre of Pressure Apparatus
Cussons Centre of Pressure Apparatus allows the force and centre of pressure
acting on partially submerged and fully submerged rectangular planes to be
determined. Part 12 of the manual presents the theory and experimental details
concerned with this topic.
3.20 Free and Forced Vortices
The Free and Forced Vortices Apparatus comprises a transparent cylindrical vessel
in which both free and forced vortices can be established. The profile of the water
surface can be measured as can the angular velocity of the vortex. Part 13 of the
manual contains the details.
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
3.21 Pelton Wheel
This hydraulic machine is fitted with a friction dynamometer to measure rotor
torque. An optical tachometer (P4740) is available to measure the Pelton Wheel
speed thus allowing the determination of power and efficiency. Part 14 of the
manual specifies the experimental capability of this unit.
3.22 Large Scale Friction in Pipes
This wall mounted unit allows a full range of experiments to be conducted on the
loss of head due to friction in pipes of various diameters in an annulus, in a smooth
and artificially roughened pipe, in various valves and fittings, and also features flow
measurement by variable area flow meter, venturi meter, orifice plate meter and a
pitot static tube. The hydraulics bench which is used to serve this experiment
should be fitted with a second pump P6101. A separate manual is provided with this
item of equipment.
3.23 Flow Channel
Cussons flow channel has a 55mm wide by 175mm deep cross section and is
2500mm long. Used with a hydraulics bench fitted with two pumps the flow channel
provides experiments in the uniform flow in open inclined channels, in the flow
under a sluice gate and over sharp and broad crested weirs. The study of the flow
over triangular hump weirs and long base weirs is provided for as is the study of
hydraulic jumps. See Part 15 of the manual.
12
CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
4. OPERATING INSTRUCTIONS
4.1 Starting Procedure.
a. Ensure that the pump inlet valve is fully open.
b. Check the water level in the 'reservoir tank' and top up if required to within
20mm of the top.
c. Either position the stilling basket in the left hand end of the weir channel or
mount the required experimental apparatus on the working surface of the
bench using the appropriate locating pegs. Connect the bench flexible water
supply hose to either the apparatus or the stilling basket.
d. Ensure that the bench regulating valve is in the closed position.
e. Adjust the knob on the speed control unit to approximately mid-range.
Connect the electrical supply to the bench and switch on.
f. Adjust bench regulating valve and pump speed control to give the required
water flow.
4.2 Flow Control.
4.2.1 Constant Speed Operation.
Although there are two valves on the main pumping circuit, the control of flow
should be made only with the valve on the instrument panel i.e. the bench
regulating valve. The other valve (pump inlet valve) should be kept wide open at all
times when the pump is running. The only exception to this is during the cavitation
demonstration.
4.2.2 Variable Speed Operation.
The pump speed can be varied from 30-7200 revs per min by using the pump speed
control unit. The ac supply to the pump is varied using the control knob mounted on
the unit. Speed is increased by turning clockwise.
4.3 Flow Measurement.
Flow measurements may be obtained in 3 ways:
4.3.1 Volumetric Tank.
a. Close the measuring tank outlet valve.
b. Start the timing watch when the water level in the measuring tank is at
zero or some other convenient level.
c. Time the collection of a suitable quantity of water. For low flow rates,
only the lower section of the measuring tank need be used. For high
13
CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
flow rates use the 15 litre mark as the starting point to ensure that
hold up of water, as it flows across the tank, does not cause an error.
d. After the measurement has been completed, open the measuring tank
outlet valve completely. Note that an overflow valve for the measuring
tank has been provided so that if the outlet valve is inadvertently left
shut, excess water will flow directly into the reservoir ensuring that the
pump will not run dry.
e. The mean volumetric flow rate can be calculated by dividing the
volume collected by the time taken:
The mass flow rate can then be obtained by multiplying by the density
At normal ambient temperature may be taken as 1·00 kg/l
4.3.2 Weir Measurement.
A scale calibrated in litres per minute is to be found on the weir notch. For readings
above 10 litres per minute this scale may be used to give an instantaneous reading
of flow rate.
4.3.3 Rotameter
This too will give an instantaneous direct reading of flow rate for values above
0.4m3 per hour.
4.4 Pressure Measurements.
Pressure at the pump delivery, supply hose delivery and at an auxiliary position can
be monitored on the panel mounted pressure gauge by selecting the appropriate
position on the selector switch. The pump suction pressure is measured directly by
the in line pressure gauge mounted on the pump inlet pipework. Note that when
pump delivery pressures are measured an allowance should be made for the fact
that the gauge is positioned 0·7m higher than the tapping point i.e. 0.07 bar should
be added to the gauge reading.
Note that it is advisable to rotate the pressure selector switch anti-clockwise in
order to minimise the possibility of a previously locked in jet of water being emitted
from the auxiliary tapping point if this is not in use.
4.5 Stopping Procedure.
a. Close the bench regulating valve.
b. Ensure that the measuring tank outlet valve is open.
c. Switch off the power supply on the hydraulic bench.
d. Close the pump inlet valve.
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
e. Turn the pump speed control to the minimum speed position.
4.6 Storage.
If it is required to store the equipment the water should be drained from the unit.
Most of the water can be drained from the unit using the pump with the flexible
supply hose directed into a drain. For complete drainage a drain plug is provided
underneath the reservoir tank. When storing the unit, leave all valves slightly open
to prevent them seizing in the closed position. Cover the unit with a sheet of
polythene or similar material in order to prevent it becoming dirty.
15
CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
Experiment No.1
THE HYDRAULIC BENCH
Introduction
In most of the experiments in this laboratory you will use a hydraulic bench to
determine the flowrate of water through various sets of apparatus. The purpose of
the present experiment is to gain some familiarity with the used of the hydraulic
bench.
The hydraulic bench
The operating principles of a hydraulic bench are surprising simple. It consists of
the following
• A tank that contains a reservoir of water.
• A pump to remove water from the tank and direct it to a piece of fluid apparatus.
• An on-off switch to start-stop the pump.
• A valve to control the rate at which water is pumped from the tank.
• An inlet in the top of the apparatus to collect water after it has been used.
• A water-container immediately below the inlet in the top of the hydraulic bench.
The water container also has a valve in its base that can be opened or closed by a
handle set into the hydraulic bench.
• A lever arm connected to water-container. The lever arm has a base upon which a
set of weights can be placed. The lever arms have a 3:1 mechanical advantage, i.e.
a 1.5 kg mass
of water is required to lift a 4.5 kg mass placed on the balance. Note, the weights
that come with the weighing tanks give the masses of the water in the containers.
• There are some sensors connected to an LED to detect the motion of the lever
arm past a reference point
Front view of one of the hydraulic benches. The sets of weights are placed
on the base connected to the lever arm in the centre of the photograph.
The on-off switch is located to the top right of the bench with the control valve
located immediately to its left. The weighing container is the white plastic
container in the centre of the tank.
Side-view of the hydraulic bench. The lever arm is the metal bar sitting at
16
CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
an angle. The lever to open/close the base of the weighing tank is in middle of the
tank towards the top of the weighing container.
The operation of the hydraulic bench is relatively simple.
• The pump is started with the valve in the base of the weighing tank open.
• Once you have got organized, close the valve in the base of the weighing tank.
• The lever arm will rise and hit the sensor on the top rim of the bench. You should
start the stop-watch the instant the arm hits the rim.
• You should then place an appropriate mass on the hanger at the end of the lever
arm. The lever arm will then go down.
• The lever arm will start to rise again when the additional mass of water in the
weighing tank approaches the mass placed on the hanger.
• Stop the stop-watch when the lever arm triggers the sensor again.
• The flow-rate is just the mass divided by the elapsed time.
Experiment
Set the flow rate using the outlet valve located at the front of the hydraulic bench.
The valve should be about 55% open.
Measure the actual flow rate using the weigh tank in the hydraulic bench and a
stopwatch. Repeat this measurement ten times. There should be two independent
measurements of the time taken to fill the weighing tank. You should record your
readings in a table. A suggested Table design is shown below
• Determine the mean flow rate of water through the optical bench.
• Determine the standard deviation of the flow rate?
• To what precision do you think it is possible to determine the flow rate?
17
CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
• Was there any discernible change in your readings from run number 1 to number
10. Now open the valve fully and determine the maximum possible flow rate of the
hydraulic bench.
Equipment details
Hydraulic benches.
Stop-Watches (at least 2 per experimental group)
18
CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
Experiment No. 2
DEMONSTRATION OF VARIOUS PARTS OF HYDRAULIC
BENCH .
HYDRAULIC BENCH
Hydraulic bench is a very useful apparatus in hydraulics and fluid mechanics it is
involved in majority of experiments to be conducted e.g. to find the value of co
efficient of velocity ‘Cv’, coefficient of discharge ‘Cd’ and contraction ‘C’ to study
the characteristics of flow over notches, to find met centric height, in finding head
losses through pipes, verification of Bernoulli’s theorem etc
CENTIFUGAL PUMP
Centrifugal pump is used for drawing water form sump tank and supply it for
performing experiments.
SUMP TANK
The fluid used in hydraulic bench is stored in sump tank located at the bottom of
hydraulic bench. The water from the sump tank is supplied through pump. Sump
tank has the capacity of 160 liters.
VERTICAL PIPE
Water from the sump tank is supplied to the upper portion of bench through vertical
transparent pipe using a pimp.
CONTROL VALVE
It is used to regulate the flow in the pipe i.e. to increase or decrease the inflow of
water in hydraulic bench.
CONNECTOR
The connector allows flow for rapid substitution of accessories special purpose
terminations may be connected to the pump supply by screwing connector. No
hand tools are required for dong so.
CHANNEL
It is used in number of experiments .it provides passage in water for different
experiments.
DRAIN VALVE
Drain valve is used for discharging of water form sump tank.
SIDE CHANNELS
Side channels are provided to support the accessory on test.
VOLUMETRIC TANK
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
Water discharging form the accessory (channels) on test is collected in a volumetric
measuring tank .this tank is stepped to accommodate low or high flow rates.
STILLING BAFFLE
Volumetric measuring tank incorporates a stilling baffle inclined to reduce
turbulence.
SCALE AND TAPPING
A sight tube and scale is connected to tapping in the base of the volumetric tank
and glass an instantaneous indication of water flow.
DUMP VALVE.
Dump valve is in the base of the volumetric tank opening the dump valve allows the
entrained water to return to the sump tank to recycling.
ACTUATOR
Dump valve is operated by a remote actuator lifting actuator opens the damp valve.
When lifted and twisted through 90* .the actuator will retain the dump valve in the
open position.
OVERFLOW
An over flow adjacent to the sump returns the water to the sump tank in the event
of incorrect use of.
MEASURING CYLINDER
A measuring cylinder is provided to measuring a very small flow rater the cylinder is
stored in the compartment house e.g. the sump.
STARTER
Electrical supply to the pump motor is via a starter.
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
Experiment No. 3
CALIBRATION OF PESSURE GAUGE USING DEAD WEIGHT
PRESSURE GAUGE CALIBRATION
APPARATUS
Dead weight calibrator, weights, hydraulic bench and calibrator.
CALIBRATION
To check error with comparison to some standard device is called calibration.
ABSOLUTE PRESSURE
The pressure that is taken with reference to absolute zero is called absolute
pressure and at absolute zero there is a perfect vacuum means no air.
P=rh
GAUGE PRESSURE
The pressure that is taken with reference to atmospheric pressure is called gauge
pressure. Gauge pressure may be positive or negative .
Gauge pressure when taken above the atmospheric pressure then it is positive and
when taken below atmospheric pressure then its is negative. Gauge pressure is
always measured with atmospheric pressure that is why when gauge pressure is at
atmospheric pressure it results zero.
Pabs=Patm + Pgauge
PROCEDURE
I placed the pressure gauge and calibrator assembly on bench top then I
connected the inlet tube to the gauge manifold
A length of tube was connected to the calibrator drain and laid into the
channel to prevent spillage of water on the bench top.
The calibrator was leveled by the adjustable feet level observing the sprit
level
I removed the piston and accurately determine its mass and the mass of
calibrator weights.
I closed the control valve of bench and open both corks then operate the
pump starter, to open the valve and admitted water to cylinder
After the removal of air bubbles from the table connecting the gauge and
calibrator I closed both corks simultaneously along with the flow control valve
on bench and switched off the pump.
I noted the gauge reading corresponding to the piston mass of 0.5 kg while
the piston is spinning (to minimize the friction effect).then I added .05kg of
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
mass each time and noted the corresponding gauge readings using above
procedure.
Then a graph was plotted between percentage gauge error and cylinder.
OBSERVATIONS AND CALCULATIONS
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
Experiment No. 4
EXPERIMENTAL STUDY OF LAMINAR, TURBULENT AND
TRANSITIONAL FLOWS (VISUAL ANALYSIS)
APPARATUS
Osborne Reynold apparatus, hydraulic bench and glass marbles.
LAMINAR FLOW
The flow in which fluid moves in liquid particles moves in form of thin sheets in
which the particles are not intersecting the path lines of each other such type of
flow is known as laminar flow.
TURBULENT FLOW
The flow in which liquid particles move in zig zag path and intersecting the path
lines of each other is called as turbulent flow.
TRANSITION FLOW
The flow that takes place during the inter conversion of laminar and turbulent flow
is called transition flow or Transition zone between laminar flow and turbulent flow
is called transition flow.
REYNOLD’s NUMBER
It is the ratio of inertial force to viscous force
RN = Inertial force / viscous force
RN =VL/F
For Laminar flow Reynold number = 0—2000
For Transition flow Reynold number = 2000—4000
For Turbulent flow Reynold number = 4000— on ward.
PIPE FLOW
When liquid is touching a solid surface from all side then such type of flow is called
as pipe flow. i.e. full flow in a pipe
CHANNEL FLOW
When the flowing liquid is not touching a solid boundary form any one side such
kind of is called as channel flow, i.e. flow in a channel ,partial flow in a pipe.
VISUAL ANALYSIS
As it is a visual test is no need to take any reading the visual analysis of these flows
is given below.
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CHE 173.1 HYDRAULIC BENCH AND ACCESSORIES
A device Osborne Reynolds is used in this test and is observed for different types of
flow. The equipment operates in a vertical mode. A header tank containing stilling
media A dye usually KMNO4 provides a constant head of water through a bellmouth
entry to the flow visualization pipe. Flow through this pipe is regulated using a
control valve at the discharge end.
The operation of valve increases and decreases the flow through the visualization
pipe.
First it was observed that when the velocity of flow was small the dye appears like a
very narrow needle flow in between the water showing laminar flow and when the
velocity of water was increased gradually using control valve the dye appears to
move little randomly showing transition flow and when velocity is more increased
dye starts moving in zig zag path which show the turbulent flow.
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