Lab Report #1: Basic Hydraulic Technology
This is a sample lab report for lab
#1. It contains all the comments I
made during the grading process.
-- Jim Kamman
Organization and presentation of report
/20
Grammar and spelling
/20
Technical presentation, content, analysis
/60
____________
Total
/100
very well written report with
strong technical content.
Monday, August 20, 2012
ME/ECE 4710 Motion and Control
Instructor: Dr. James Kamman
Mechanical and Aeronautical Engineering
Western Michigan University
Kalamazoo, MI 49008
19/20
19/20
60/60
-------98/100
Abstract
A hydraulic test bench is used to study the relationship between pressure and flow rate of fluid
through various hydraulic circuits. Three simple circuits are used in total. The first measures the flow
rate of the pump at various system pressures. The second measures the flow rate and pressure
difference through a restriction in order to calculate the constant of proportionality, and the third uses
LabView software with pressure sensors to export pressure data to text files. These experiments are
used to understand the relationship between the volume flow rate and the pressure of the fluid. Other
concepts that were learned include building fluid circuits on the test bench, safe start-up and shut-down
procedures, and using the LabView interface for recording measurements. The experiments found that
the test bench is flow-limited to 2.75 GPM, and the flow over the relief valve must be considered to
understand the dynamic behavior of the system.
iii
Contents
Abstract ........................................................................................................................................................ iii
Introduction .................................................................................................................................................. 1
Procedure...................................................................................................................................................... 2
Part 1: ........................................................................................................................................................ 2
Part 2: ........................................................................................................................................................ 3
Part 3: ........................................................................................................................................................ 4
Results: .......................................................................................................................................................... 5
Analysis and Conclusions .............................................................................................................................. 7
iv
Introduction
Hydraulic systems are used to transmit power through fluid to plants such as actuators. The
hydraulic systems used for these experiments are made up of a tank, a pumping device, and a circuit
including a flow meter, pressure gages, and a variable restriction valve. The pumping device is a fixed
displacement pump that has a theoretical maximum flow rate of 3 GPM. The tank has a filtered return
line that returns the fluid at atmospheric pressure, and the gages are used to measure the pressure and
flow rate of the fluid at various points in the circuit. The experiments are divided into three parts. The
first part records the flow rate of the pump at various system pressures resulting in the maximum flow
rate of the pump. The second part uses pressure readings at the inlet and outlet of a restriction to find
the coefficient of proportionality (k) of the restriction, and the third part uses electronic sensors in
conjunction with LabView to export spreadsheets of data to text files. The experiments are designed to
help the participant understand the behavior of basic hydraulic components while deriving the
maximum pump flow rate, coefficients of proportionality, and the power lost over a restriction.
Complete instructions for the laboratory procedure are found on the class website under Lab #1: Basic
Hydraulic Technology.
1
Procedure
Part 1:
The first exercise is used to measure the flow rate of the pump. A simple circuit is constructed using
a hydraulic test bench. The pump is connected to a parallel configuration of a flow meter and a pressure
relief valve with a dead-headed pressure gage as shown in figure 1. The circuit is assembled using hoses
fixed with quick connects attached to permanently fixed valves and gages on the test bench. The
pressure relief valve is initially set to 250 psi and decreased in random steps until the pressure relief
valve is fully open. System pressure and flow rate are recorded for each change in the set pressure of
the relief valve.
Figure 1: Experimental Setup 1
2
Part 2:
In part two, the hydraulic system is connected to a variable flow control valve. The variable flow
control valve restricts the flow of the system as it is closed; resulting in a higher pressure. The pump is
connected to a pressure gage as well as to the inlet of the variable flow control valve. The outlet of the
valve is then connected to a flow meter and another pressure gage. This all is finally connected back to
the tank through a filter (see Figure 2). The pressure relief valve is initially set to 250 psi. After
assembling the system, the system pressure is recorded as the flow control valve is slowly closed from
100-0% in 10% increments. After varying the flow valve, the next step in the experiment is to set the
flow valve and vary the relief valve to see at what pressure the flow begins to decrease in the circuit.
Begin with the variable flow valve set to 60% open, and record system pressure as the relief valve set
pressure is decreased in steps of 10-20 psi.
Figure 2: Experimental Setup 2
3
Part 3:
For part three, a hydraulic circuit is fixed with sensors that are connected to LabView software
as shown in figure 3. Two pressure sensors are attached to the inlet and outlet ports of a variable
restriction valve. The valve is in series with a flow meter. Set the pressure relief valve to 250 psi and the
variable flow valve to 50% open. Record the inlet and outlet pressures and the system flow rate as the
relief valve is opened similar to the procedure for part 2.
Figure 3: Experimental Setup 3
4
Results:
The pressure and flow rate values are recorded by visually inspecting coarse lines on the flow
meter and radial tick marks on the pressure gage. The course scale of the flow meter may result in
some human error, and the pressure gage does not have tick mark indications below 30 psi resulting in
estimated readings for that range. The values are satisfactory for finding relationships between the
variables but are not satisfactory for detailed system modeling. Part three initiates the use of electronic
pressure sensors that are both more accurate and precise than previous readings of the pressure gages,
however the electronic pressure sensors sample at 1000Hz. The recorded measurements display all of
the fluid pulsations resulting from the pump and the geometry of the system. The sensors are also
susceptible to noise from other electronic devices. Consequently, test data appears as a noisy oscillating
function when graphed. By averaging the data over a certain range and combining it, a more filtered
pressure can be used for analysis and modeling. The pressures and flow rates recorded from LabView
are much more accurate than the data collected visually in earlier exercises. By taking away the human
error of visually reading the gages and relying on the accuracy range of the electronic sensors, the values
become much more precise. The test data in part three is, therefore, more reliable and can be used for
modeling purposes.
In part one of the experiment, pressure and flow rate were recorded in table 1. The fluid
pressure in the circuit is limited to the set pressure of the relief valve.
Table 1: Pressure Vs. Flow as relief valve is opened
Pressure (psi)
73
58
Flow Rate (GPM)
2.75
2.5
40
2
Relief Valve Open
2
Part two of the experiment results in four sets of data. The first set is from the configuration
with the relief valve set to 250psi and the flow valve closed incrementally. The data was recorded in
table 2. The second, third, and fourth data sets have the relief valve set to 250 psi and the flow valve
5
set to 60% open, 50% open, and 40% open respectively. The data results from gradually opening the
relief valve in 20 psi increments and is recorded in tables 3-5.
Table 2: Pressure relief valve set to 250psi, flow valve closed incrementally
Valve % Open
100
90
80
70
60
50
Pin (psi)
40
30
20
Pout (psi)
170
80
170
78
190
75
220
53
220
37
225
30
230
27
230
20
233
0
Flow (GPM)
2.65
2.65
2.65
2.20
1.55
1.30
1.10
.80
.50
Table 3: Flow valve at 60% open, relief valve opened incrementally
Pin
220
200
180
160
135
120
Pout
35
30
30
30
30
29
Flow
1.45
1.45
1.45
1.33
1.25
1.21
100
29
1.12
80
25
1.00
60
23
.85
50
21
.75
Table 4: Flow valve at 50% open, relief valve opened incrementally
Pin
240
220
198
183
155
138
Pout
30
30
29
29
28
27
Flow
1.28
1.26
1.25
1.24
1.15
1.05
120
25
1.00
100
23
.9
80
21
.77
60
20
.7
Table 5: Flow valve at 40% open, relief valve opened incrementally
Pin
240
220
200
180
156
140
120
Pout
25
23
20
20
19
19
19
Flow
1
1
1
1
.95
.8
.75
100
18
.70
80
18
.55
60
17
.50
Table 6 shows the data collected from part three. For part three, the flow valve is set to 50%
open. The relief valve is set to 250 psi and closed in 20 psi increments, and LabView is run after each
adjustment. LabView records the voltage output of the sensors and writes that information with
respect to time in a text file. The table shows the difference between the values visually recorded from
the gage and the values electronically recorded in LabView. The values from LabView are averaged over
a steady state pressure period for each change in the setting of the relief valve.
6
Table 6: Flow Valve 50% relief opened, LabView analysis
Pin gage 240
220
200
180
155
Pin
230
211
190.6
171.3
149.8
LabVIEW
Pout
26.3
24.3
22.9
21.3
19.8
Flow
1.5
1.3
1.28
1.26
1.2
138
129.9
120
113.2
100
92.2
80
71.2
60
55.3
18.2
1.15
17.1
1.05
15.5
.90
13.9
.80
12.4
.70
Analysis and Conclusions
The fluid pressure in the circuit is limited to the set pressure of the relief valve. As the relief
valve pressure increases, less fluid will flow over the relief valve and more fluid will flow through the
circuit. From the data collected in part one, fluid power at the flow meter can be calculated using the
following equation. The results are shown in table 7. It is clear that as the relief valve of the system is
opened, the fluid power of the system decreases due to the alternate path the fluid is allowed to take.
HP
P
Q
Power in HP
Pressure in psi
Volumetric Flow Rate in GPM
1714
Conversion factor for HP
Table 7: Calculated fluid power (part 1)
Pressure (psi)
Flow Rate (GPM)
Fluid Power (HP)
73
2.75
0.117
58
2.5
0.085
40
2.0
0.047
In part two, the flow rate decreases and the change in pressure across the variable flow valve
increases as the flow valve is closed. The power loss through the restriction at each setting can be
calculated using the equation at the end of this paragraph. The results are shown in table 8. As the flow
is restricted, power increases with increasing pressure differences until the inlet pressure approaches
the set pressure of the relief valve. At this point, flow is reduced across the flow valve as fluid begins to
7
flow over the pressure relief valve. This shows that the relief valve doesn’t open fully when the crack
pressure is reached. It opens gradually based on the spring constant inside the valve.
HP
Q
Pin
Pout
Power Loss
Flow Rate
Inlet Pressure of the flow valve
Outlet pressure of the flow valve
Table 8: Horse power with decreasing valve position
Flow Valve
100
90
80
70
Position (% open)
HP
.1391
.1422
.1778 .21435
60
50
40
30
20
.1655
.1479
.1303
.098
.06797
In steps (e) and (f) of part 2 (see lab instructions) experiments were done with constant flow
valve position and varying relief pressure. An important value that can be calculated from the data
collected is the constant relating the root of the pressure difference to the flow rate as shown in the
equation below. The values are stored in tables 9-11.
Q
k
Pin
Pout
Flow Rate
Constant of Proportionality
Inlet Pressure of the flow valve
Outlet pressure of the flow valve
Table 9: Flow valve 60 % open
Q
1.45
1.45
1.45
ΔP
185
170
150
k
.1066
.1112
.1184
1.33
130
.1166
1.25
105
.1219
1.21
91
.1268
1.12
71
.1329
1
55
.1348
.85
37
.1397
.75
29
.1393
Table 10: Flow valve 50 % open
Q
1.28
1.26
1.25
ΔP
210
190
169
k
.0883
.0914
.0962
1.24
154
.0999
1.15
127
.1020
1.05
111
.0997
1.00
95
.1025
.90
77
.1026
.77
59
.1002
.70
40
.1107
Table 11: Flow valve 40 % open
Q
1
1
1
ΔP
215
197
180
k
.0682
.0712
.0745
1
160
.0791
.95
137
.0812
.8
121
.0727
.75
101
.0746
.7
82
.0773
.55
62
.0699
.5
43
.07625
8
From the data in tables 9-11, it is clear that k increases slightly with decreasing set pressure of
the relief valve. This trend is due to the fact that the difference in pressure across the flow valve is
quickly decreasing; while the flow rate is decreasing at a much slower rate which results in a slight
increase in the k value. Based on the trends in the data, k for these valve positions can also be found
using a best fit line. The data is plotted in excel and a least squares best fit curve is used to find the k
value for each flow valve position. The k value is shown on the graph as the slope of the line. Table 12
compares the average computed k values with the best fit k values.
Q (GPM)
Best fit curve approximation of k
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
y = 0.1029x
y = 0.1192x
y = 0.0968x
y = 0.0741x
0
2
4
6
8
10
Sqrt(Pin-Pout)
12
14
16
Part 3 k
Valve 60% open k
Valve 50% open k
Valve 40% open k
Linear (Part 3 k)
Linear (Valve 60% open k)
Linear (Valve 50% open k)
Linear (Valve 40% open k)
Figure 4: Best fit approximation of k
Table 12: % error of average and best fit k values
LabView
60% open
50% open
40% open
Average k
0.1038
0.1248
0.0992
0.0744
best fit k
0.1029
0.1192
0.0968
0.0741
% error (%)
0.88
4.52
2.44
0.53
9
In part three, the system is connected to LabView data acquisition. The sampling rate for the
pressure sensors is 1000 Hz. This allows the sensors to read all of the fluid pulsations resulting from the
pump and the geometry of the system. The sensors are also susceptible to noise from other electronic
devices. The resulting test data appears as a noisy oscillating function when graphed. By averaging the
data over a certain range and combining it, a more filtered pressure can be found. The pressures and
flow rates recorded from LabView are much more accurate than the data collected visually in earlier
exercises. By taking away the human error of visually reading the gages and relying on the accuracy
range of the electronic sensors, the values become much more precise. The test data is, therefore,
much more reliable and can be used for modeling purposes. The flow rates were also recorded visually
throughout this process and used to calculate the flow over the relief valve using the following equation.
The values are stored in table 13.
Volumetric flow rate over the relief valve
Maximum volumetric flow rate = 2.75 GPM
Volumetric flow rate through the circuit
Table 13: Flow rate of the relief valve
(GPM) 1.5
1.3
1.28
(GPM)
1.25 1.45 1.47
1.26
1.49
1.2
1.55
1.15
1.6
1.05
1.7
0.9
1.85
0.8
1.95
0.7
2.05
10