Design and Development of a Hydraulic Circuit Bench for Education Purposes A. F. Kheiralla Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan
[email protected]
O. A. Rahama 1, A.A. Saadelnoor 2, Dina M. Abd-lkareem 3, Ghada M. Nasr4 Abstract - As a response to feedback from academic and industry, University of Khartoum has successfully designed and developed an educational hydraulic circuit bench. Design formulas for computing the flow, torque requirement, input/output power, volumetric and power efficiencies of the pump and motor are presented. The developed bench consisted of gear pump driven by 7 HP/3 phase electric motor, 1 unit of double acting cylinder having 200mm stroke and 34mm cylinder bore encapsulated in spring load, 1 set of gear motor, 2 unit of directional control valve (manual and solenoid), 1 set of manual operated valve, 4 ways-3 position, 1 set of double solenoid valve 4 ways-3 position, hydraulic pressure gauge, filter and reservoir. Two sets of relief valves are used to limit the pressure in a hydraulic circuit to a safe level. Two sets of check valve and 2 sets of restrictor are also used to regulate and control the fluid rate to motor and hoses. The bench has facilities to measure oil hydraulic flow, pressure and temperature. The main bench testing circuit options include circuit to operate hydraulic pump, hydraulic motor and hydraulic cylinder and can be upgraded. In addition, cut-away sections for various hydraulic components are also developed for demonstration. The developed bench is self-contained mobile unit that can be used wherever electrical power is available. The unit total cost is less than 8,000 US Dollars. Index Terms – University of Khartoum, Engineering education, Hydraulic system, Teaching Aid INTRODUCTION Hydraulic systems are widely used in many industrial applications and off-road vehicles. Over half of all industrial products have fluid power systems or components as a part of their basic designs. These systems removed the need for the vehicle operator to have great physical strength. Through use of hydraulic motors, the hydraulic system can transmit power more conveniently than with mechanical drives. Extensive research workers on hydraulic system were reported by many researchers and industry groups. MAHA Fluid Power Research and Teaching Laboratory at Purdue University allowed steady state and dynamic
measurements on pumps, motors, hydrostatic transmissions and linear and rotary actuators [1]. Two central hydraulic power supply nets using three pressure compensated pumps, which were independently controllable and installed with a total power of 260 kW. Georing et al. [2] presented extensive review about of hydraulic systems in their text book off road vehicle engineering. Their text book showed that the reader will learn the basic principles of hydraulic components and systems. The National Fluid Power Association (NFPA) standard symbols were introduced as a way of describing the logic of hydraulic circuits. Finally, their text book introduced mechatronic as applied to hydraulic systems. Krutz et al. [3] reported on design of a hydraulic actuator test stand for non-linear analysis of hydraulic actuator systems. Servo-hydraulic systems were inherently non-linear creating various nuances when analyzing the stability of the system. Friction, port flow, saturation, impact loading, line dynamics, and boundary conditions were a few of the many non-linearities found in servo-hydraulic systems which were to be analyzed using advanced non-linear stability analysis techniques. Johan van der Kamp [4] reported on electro-hydraulic steering in off road vehicles. The SKF Electro-Hydraulic Steering system was developed using the SKF approach for mechatronic design. This electro hydraulic steering solution will provide substantially increased functionality, added value and features when compared to today's fully hydraulic steering. Various software were developed for design, control and simulation of hydraulic, pneumatic, and motion control [5]. HyPneu processed the information in the graphical circuit and allowed the user to assign specific element to the system, to run both steady state and dynamic simulations of the component and/or system, and display the results in a meaningful manner. Several powerful add-on packages were also available, such as, Frequency Analyzer, Thermal Simulator, CAE Co-simulator, Client/Server Module, etc. Knowledge and understanding of hydraulic systems and their components make engineers better qualified to performance their job in industrial. The significant feedback received from employers in industry stated that the department’s graduates need better training in hydraulics. As a response to that feedback, the Agricultural Engineering
1
O. A. Rahama, Faculty of Engineering , University of Khartoum, P.O. Box 321, Khartoum, Sudan A.A. Saadelnoor, Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan 3 Dina M. Abd-lkareem, Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan 4 Ghada M. Nasr, Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan 2
September 3 – 7, 2007
Coimbra, Portugal International Conference on Engineering Education – ICEE 2007
Department, Faculty of Engineering and Architecture, University of Khartoum has initiated its Hydraulic laboratory to include benches with industrial motor, pumps, cylinders and valves. Before starting the proposed hydraulic and pneumatic course, the department did not offer an undergraduate course dedicated to hydraulics in its curriculum. The skills offered by such a course are required in the industry. However, there are no similar courses that were offered through other departments at University of Khartoum, while the existing other related courses do not cover many important hydraulic skills required in agricultural and biological engineering that suits its own need. Therefore, University of Khartoum needed to create a new laboratory in hydraulic system that is most relevant to the agriculture and food industries. The overall objective of this study is to design and develop a hydraulic circuit bench based on fundamental components to be use for educational purposes.
Pump performance included pump delivery, drive power, torque at pump shaft, input power, and hydraulic power and torque efficiency. The selected pump had displacement of 9
11 10
6
8
7
I. Hydraulic Circuit Description The hydraulic circuit was designed to actuate all components of hydraulic bench (Figure 1). The system consisted of gear pump driven by 7 HP/3 phase electric motor, 1 unit of double acting cylinder 200 mm stroke with 34 mm cylinder bore, 1 set of gear hydraulic motor, 2 unit of directional control valve (manual and solenoid), 1 set of manual operated valve, 4 ways-3 position, 1 set of double solenoid valve 4 ways-3 position, hydraulic pressure gauge, filter and reservoir. Two sets of Relive valves were used to limit the pressure in a hydraulic circuit to a safe level. Two sets of check valve and 2 sets of restrictor were also used to regulate the fluid rate to motor and so give speed control, hydraulic hoses of 0.5 inch diameter. In addition, a hydraulic tester was also included. II. Computation of Circuit Design Computations for the hydraulic circuit design were made by formulas, standard tables and nomograms from National Fluid Power Associations (NFPA) [6,7]. The hydraulic circuit design for the bench computation started from the main hydraulic pump. Gear pump model GHP2-D-20 working at speed of 1400 rpm and pressure 150 bar was selected because its cheapest cost, availability and simplicity. III. Hydraulic Pump Performance
6
5 12 4
2
3
MATERIALS AND METHODS The following criteria were considered in establishing the basic design of the hydraulic bench: 1. Simple in design, construction and operation, 2. Completely integrated system capable to be used for educational purposes. 3. The design includes maintainability for components, 4. The design can be up graded, 5. Low cost with in the reach of the department in Sudan.
10
1
1. Reservoir (tank)
7. Manual operated valve 4/3-N.C directional control valve 8. Double solenoid valve 4/3-N.C. -220 V 9. Hydraulic Cylinder 10. Flow control valve with check valve 11. Hydraulic motor 12. Shot off valve
2. Electric motor 3. Hydraulic pump 4.Releif valve 5. pressure gauge 6.Check valve
FIGURE 1 HYDRAULIC CIRCUIT DIAGRAM
14.1 L/min at driven of 1400 rpm and maximum pressure of 150 bar. The pump had volumetric efficiency and overall efficiency of 85% to 97%, and 80% to 90%, respectively. Pump delivery in the proposed bench can be calculated by the following formula:
QP
v * Dp * N p 1000
(1)
where Qp is pump delivery in L/min, DP is displacement of pump in cm3/rev, Np is pump speed in rpm, and v is volumeric efficiency of pump, 0.85 – 0.97. Knowing the pump displacement of 14.1 L/min, pump speed of 1400 rpm and average volumetric efficiency of 91%, the computed pump delivery was 17.96 L/min. The drive power of pump was calculated of by the following formula:
PEL
Pp D p N p 6 10 5 overll
(2)
where PEL is motor electrical power in kW, Pp is operating pressure in bar, DP is pump displacement in L/min, and overall is pump overall efficiency, 0.8 – 0.9. Having the pump displacement of 14.1 L/min, maximum working pressure of 150 bar, pump speed of 1400 rpm, the overall efficiency 85%, the computed drive power was 5.8 kW (7.7 hp). The torque at pump shaft is given by the following formula:
September 3 – 7, 2007
Coimbra, Portugal International Conference on Engineering Education – ICEE 2007
TP
D p Pp 2 overall
(3)
where Tp is torque at pump shaft in N.m, Dp is pump displacement in cm3/rev, Pp is operating pressure in bar, and overall is pump overall efficiency, 0.8 – 0.9. Considering pump displacement of 14.1 L/min, maximum working pressure of 150 bar, pump overall efficiency, the computed torque at pump shaft was 39.6014 N.m Pump hydraulic power can be calculated by the following formula:
PHY
QP P 600
(4)
where Qp is flow rate of pump in L/min, and P is pump pressure in bar. Considering pump flow rate of 17.96 L/min and pump pressure of 150 bar, the computed hydraulic was 4.49 kW (6 hp). The pump input power can be calculated by the following formula:
PIN
PHP
Overal
(5)
Knowing the pump hydraulic power of 4.49 kW, and average overall efficiency of 85%, the computed input power was 5.282 kW (7.09 hp). The torque efficiency of the pump can be calculated by the following formula:
T
overal v
(6)
Consider the pump average overall efficiency of 85% and pump average volumetric efficiency of 91%, the computed torque efficiency of the pump was 93.4%. III. Cylinder Selection Hydraulic cylinder selection included effective area, bore diameter, piston rod diameter of the cylinder. The exerted force on proposed hydraulic cylinder was based on a spring having a capacity of 3 Ton. For double acting cylinders, if the desired force is required from the cylinder in retraction. The effective area equals the piston area minus the piston rod area. The cylinder effective area can be calculated by the following formula:
A
F P 10 M
(7)
where A is effective area in cm2, F is cylinder force in N, P is pressure difference across cylinder ports in bar, and M is mechanical efficiency, 0.85 – 0.95. Having exerted force of 29,430 N (3 Tons), oil pressure difference of 150 bar, mechanical efficiency of 90%, the computed effective area was 21.8 cm2. The piston diameter of the proposed cylinder can be calculated by the following:
DP
A 0.00785
(8)
where DP is piston diameter of the cylinder in mm, and A is effective area is cm. Having cylinder effective area of 21.8 cm2, the computed piston diameter of the cylinder was 52.69 mm.
The piston rod in a hydraulic cylinder will act as a strut when it is subjected to a compressive load or it exerts a thrust. Therefore the rod must be of sufficient diameter to prevent buckling. Euler’s strut theory is used to calculate a suitable piston rod diameter to with stand buckling. The piston rod buckling with one end fixed can be expressed by the following Euler’s formula:
K
2 EJ 2
L
with L
CS 2
(9)
where K is buckling load in kg, E is modulus of elasticity in kg/cm2, J is second moment of area of the piston rod is cm, L is free (equivalent) buckling length in cm, and CS is cylinder stroke in cm. Having piston buckling load of 3000 kg, modulus of elasticity of chromium rod of 2.9106 kg/cm2, cylinder stroke of 200 mm, the computed second moment of inertia was 0.021 cm4. The cylinder rod diameter can be calculated by the following formula:
d 4
64J
(10)
Having second moment of inertia of the rod of 0.021 cm4, the computed cylinder rod diameter was 8 mm. Based on the computed cylinder piston diameter of 52.8 mm and cylinder rod diameter of 8 mm and the Standard tabulated cylinder bore and rod size (BS: 5785 1980), the recommended piston diameter and rod diameter of the cylinder was selected to be 50 mm and 28 mm, respectively, for safer buckling load [6]. V. Hydraulic Motor Selection The motor flow rate required by motor will be depending on pump displacement and pump shaft speed and volumetric efficiency. Pump displacement in terms of motor flow rate can be expressed by the following formula:
Dp
Qm 1000 N p v
(11)
where Dp is pump displacement in cm3/rev, Qm is flow rate required by motor in L/min, and v motor volumetric efficiency, 0.85- 0.97. Having pump displacement of 14.1 L/min, pump shaft speed of 1400 rpm, average motor volumetric efficiency of 91%, the computed motor flow rate was 17.96 L/min. Motor displacement can be calculated by the following formula:
Dm
Qm 1000 v Nm
(12)
where Qm is motor flow rate in L/min, D m is motor displacement in cm3/ rev, Nm is motor shaft speed in rpm, and v volumetric efficiency of motor, 0.85- 0.97. Having motor flow rate of 17.96 L/min, motor shaft speed of 1220 rpm, motor volumetric efficiency of 91%, the computed motor displacement was 13.39 cm3/rev. VI. Hoses and Pipes Selection The velocity of hydraulic fluid through hoses and pipes is dependent on flow rate and cross sectional area. The September 3 – 7, 2007
Coimbra, Portugal International Conference on Engineering Education – ICEE 2007
selected velocities of suction/return line and return line were 0.6 m/sec and 1.5, respectively, based on the recommended fluid velocities through pipes and hoses in hydraulic systems [6]. From flow/velocity nomogram for hydraulic pipes and hoses, for flow rate of 17.6 L/min and 17.6 L/min and velocities of 0.6 m/sec and 1.5 m/sec, the selected diameters of suction and return line of were 25 mm and 15.2 mm, respectively.
The hydraulic bench after fabrication was successfully demonstrated without hydraulic tester. All hydraulic circuits were function well with minor problems. Oil leakages were encountered during demonstration test. Seals and resins were used to solve the problems. After demonstration and function test trials, the hydraulic bench was extensively tested with the incorporated hydraulic tester. The main bench testing circuit options included circuit to operate hydraulic pump only, hydraulic cylinder, and hydraulic motor.
VIII. Design of Reservoir I. Hydraulic Pump Testing The main objective of the reservoir is to supply fluid to pump and provide storage for fluid returning from the hydraulic circuit. Fluid storage, separation of air, dissipation of the heat and settling of contaminants were criteria considered in the design of hydraulic reservoir. Recommended reservoir fluid volume is to be 3 to 5 times the pump flow rate L/min with a 10% air cushion. Therefore, the reservoir volume can be expressed by the following formula: (13) V 3 Q p 1.1 where V is reservoir volume in L/min (gallon/min) and Q p is flow rate of pump L/min (gallon/min). Considering pump flow rate of 17.5 L/min, the estimated reservoir volume was 57.85 L/min or 12.7 gallon/min. DEVELOPMENT OF HYDRAULIC BENCH The development and fabrication of the hydraulic bench was carried out at Sudanese German Hydraulic System Factory Workshops. The developed bench consisted of gear pump driven by 7 HP/3 phase electric motor, 1 unit of double acting cylinder having 200mm stroke and 34mm cylinder bore encapsulated in spring load, 1 set of gear motor, 2 unit of directional control valve (manual and solenoid), 1 set of manual operated valve, 4 ways-3 position, 1 set of double solenoid valve 4 ways-3 position, hydraulic pressure gauge, filter, band reservoir. Two sets of relief valves are used to limit the pressure in a hydraulic circuit to a safe level. Two sets of check valve and 2 sets of restrictor are also used to regulate and control the fluid rate to motor and hoses. The bench has facilities to measure oil hydraulic flow, pressure and temperature. The main bench testing circuit options include circuit to operate hydraulic pump, hydraulic motor and hydraulic cylinder and can be upgraded. The whole hydraulic bench laboratory was depicted in Figure 2. CUT-AWAY SECTIONS OF HYDRAULIC COMPONENTS Cut-away sections for various hydraulic components were also developed for demonstration. Figure 3 depicted the cutaway of hydraulic vane pump, hydraulic piston motor, double acting cylinder, and directional control valves. The main functions of these cut-away sections are to show the internal parts of these components. These developed cutaway sections give in depth understanding and allows coherent viewing of circuit configuration, and components assembly. HYDRAULIC BENCH DEMONSTRATIONS
The pump generated force for the whole hydraulic system. Pump testing was carried by connecting the hydraulic tester to pump circuit. Before testing, oil pressure was released from system by disconnecting the pressure line between the pump and the control valve. The pump testing configuration started by attaching the pressure line from the pump output to the hydraulic tester inlet port and connecting hydraulic tester outlet port to the reservoir. Testing was carried by slowly close the tester load valve to load the system so that not exceed the system's maximum rated pressure. The test reading was carried by loading pump at every 10 bar increments up 150 bar and recorded the corresponding oil flow. Figure 4 shows pump flow rate versus pressure exerted in the pump. From the pump test results, the pump flow rate decreased as pressure exerted by the pump was increased. The pump pressure maximum flow was 150 bars at zero flow rates. Maximum flow rate was 19.5 L/min at pressure at pressure zero. Based on the obtained results, maximum pressure of 150 bar and maximum flow rate of 19.5 for the tested pump were agree with the design computation and specification of the maximum pump pressure of 150 bar and maximum flow of 17.5. Consequently, the pump was successfully tested. II. Hydraulic Motor Testing The hydraulic motor was driven by the pump. Motor testing was carried by connecting the hydraulic tester to motor circuit. Before testing, oil pressure was released from system by disconnecting the pressure line between the motor and the control valve. The motor testing configuration started by attaching the pressure line from hydraulic motor output to hydraulic tester inlet port and connecting hydraulic tester outlet port to the reservoir. Testing was carried by slowly close the tester load valve to load the system. The test reading was carried by loading motor at every 2 L/min flow rate increment from 9.5 to 17.5 L/min and recorded the corresponding motor speed. Motor pressure was constant 150 bar as supplied from pump. Figure 5 shows hydraulic motor speed versus flow rate. From the motor test results, the motor flow rate increase linearly as the motor speed was increased. The maximum motor pressure was constant as the pressure exerted by the pump. Maximum flow rate was 17.5 L/min at motor speed 400 rpm. Based on the obtained results, maximum pressure of 150 bar and maximum flow rate of 17.5 for the tested motor were agree with the design computation, however, the obtain result not reach the maximum motor capacity of flow rate of 60 L/min and September 3 – 7, 2007
Coimbra, Portugal International Conference on Engineering Education – ICEE 2007
operating
speed
of
1220
rpm
and
pressure
150.
Consequently, the hydraulic motor was oversize. Based in
FIGURE 2 DEVELOPMENT OF HYDRAULIC BENCH
(A) HYDRAULIC VANE PUMP
(B) HYDRAULIC PISTON MOTOR
(C) DOUBLE ACTING CYLINDER
(D) DIRECTIONAL CONTROL VALVES
FIGURE 3 CUT-AWAY SECTIONS FOR VARIOUS HYDRAULIC COMPONENTS
minimum cost and availability of motor and pump by a local hydraulic company, there is no harm to use these components for educational purpose. In general, the hydraulic motor was successfully tested III. Hydraulic Cylinder Testing The hydraulic cylinder was actuated by the pump. Cylinder
testing was carried by connecting the hydraulic tester to cylinder circuit. Before testing, oil pressure was released from system by disconnecting the pressure line between the cylinder and the control valve. The cylinder testing configuration started by attaching the pressure line from hydraulic cylinder output to hydraulic tester inlet port and connecting hydraulic tester outlet port to the reservoir. Testing was carried by slowly close the relief control valve September 3 – 7, 2007
Coimbra, Portugal International Conference on Engineering Education – ICEE 2007
load the system. The test reading was carried by loading cylinder at every 10 bar pressure increment from 0 to100 25
Flow, L/min
20 15 10 5 0 0
20
40
60
80
100
120
140
160
Pressure, Bar
FIGURE 4 HYDRAULIC SPEED VERSUS FLOW RATE 450 400
Speed, rpm
350 300 y = 28x - 78 R2 = 0.9561
250 200 150 100
obtained results, the hydraulic cylinder was successfully tested. CONCLUSIONS The following conclusion could be drawn from the obtained results: 1. Hydraulic laboratory circuit bench had been successfully designed and developed for agricultural Engineering Department, Hydraulic and Pneumatic laboratory. The system included various basic hydraulic component incorporated with hydraulic tester. The system facility had ability to demonstrate hydraulic pump, motor, and testing. Cut-away sections for various hydraulic components were also developed. The bench has facility for testing hydraulic pump, hydraulic motor and hydraulic cylinder The total cost of the developed bench is less than 8,000 US Dollars 2. The developed bench was participated on the Scientific Forum for Engineering and Computer Students, Khartoum, Friendship-Hall, 20-22 Dec. 2005 and on 23rd International Fair of Khartoum, 1-10 Feb. 2006. Recommendations and Future works
50 0 0
5
10 Flow rate, L/min
15
20
FIGURE 5 STROKE VERSUS PRESSURES 18 16
Stroke, cm
14 12 10
y = 0.1578x
8
R2 = 0.9945
6 4
The following agenda should be taken for future work: 1. A complete facility for the new hydraulic and pneumatic course should be provided for Agricultural Engineering Department due to response feedback from the industry and rapid development. 2. Design, control and simulation of hydraulic and pneumatic and motion control software should be incorporated in the new laboratory to process and run information in the multimedia circuit and allow to display the results in meaning full manner.
2
ACKNOWLEDGEMENTS
0 0
20
40
60 80 Pre ssure , Bar
100
120
The research project is sponsored by University of Khartoum under laboratories budget allocations. The authors are very grateful to Sudanese German Hydraulic System Factory for technical support.
FIGURE 6 STROKE VERSUS PRESSURES 160
2
y = 0.0132x + 0.0571x - 0.3414
140
2
R = 0.9985
120
REFERENCES
Load, kN
100 80 60
[1] Krutz, Gary, J. Lumkes, and Monica Ivantysynova. MAHA Fluid power
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Research Centre Purdue University. Paper presented in Agricultural Engineering Equipment Technology Conference 2005. ASAE, Paper No. AETCO5002. http://www.asae.org Accessed on July 2005. Georing, Carrol E., Marvin L. Stone, David W. Smith, and Paul K. Turnquist. Off-road vehicle engineering principles. American Society of Agricultural Engineering, St. Joseph. Mich. ASAE, 2003. Krutz, Jill E., David F. Thompson, Gary W. Krutz, and Randall J. Allemang, Design of a hydraulic actuator test stand for non-Linear analysis of hydraulic actuator systems. Paper presented in Automation Technology for Off-Road Equipment, Proceedings of the July 26-27, 2002 Conference, Chicago, Illinois, USA, ASAE, Paper No. 701P0502, pp. 169-183. Johan van der Kamp, Electro-hydraulic steering in off road vehicles. Paper presented in Automation Technology for Off-Road Equipment, Proceedings of the July 26-27, 2002 Conference, Chicago, Illinois, USA, ASAE Paper No. 701P0502, pp. 374-387. Fluid Power and Hydraulics Consultants, Testing, and Software. BarDyne, Inc. http://www.bardyne.com/fluidpower-software/ Accessed on July 2005.
20 0 -20 0
20
40
60
80
100
120
[2]
Pressure, Bar
FIGURE 7 LOAD VERSUS PRESSURE
bars and recorded the corresponding extended distance from cylinder. Cylinder stroke versus cylinder pressure and cylinder load versus pressure are presented in Figures 6 and 7, respectively. From the cylinder test results, the cylinder stroke increased linearly as the cylinder pressure was increased while the cylinder load tested was 135 kN at pressure 100 bars and flow rate 17.5. The flow rate was kept constant at maximum flow rate of 17.5 L/min. Based on the
[3]
[4]
[5]
September 3 – 7, 2007
Coimbra, Portugal International Conference on Engineering Education – ICEE 2007
[6] Michael J. Pinches and John G. Ashby, Power Hydraulics. 1st Ed. Prentice Hall, New York, 1989. [7] http://www.hydraulicsupermarket.com/ Accessed on July 2005.
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Coimbra, Portugal International Conference on Engineering Education – ICEE 2007
