Engineering - Electronic Engineering Review Assignment Hydraulic Motors and Circuits
DeezPump
Unit2StudyGuide2.docxMET230: Hydraulics and Pneumatics
Unit 2 Study Guide 2
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Guidelines
1. Legibly write on each piece of paper, green engineering pad with grid on the back preferred
· Your first and last names
· The course and section number, if applicable
· The assignment number
· The page number
2. Clearly present
· The given data
· The unknowns
· The formulas needed, and
· Sketches, where applicable
3. Write only on one side of the paper
4. Draw a long solid line to separate two different consecutive exercises/problems
5. Use consistent units
6. Round off final answers to proper degree of precision or accuracy
7. Underline your final answer
8. Staple multiple pages (for in seat only)
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Question 1
Which of the following is one of the three important considerations when analyzing or designing a hydraulic circuit?
A. Safety of operation.
B. Performance of desired function.
C. Efficiency of operation.
D. A, B, and C
E. None of the above
Answer D. “A, B, and C”
Question 2
Which of the following is the purpose of a regenerative circuit?
A. To regenerate the viscosity of the working fluid
B. To remove extra moisture from the working fluid
C. To speed up the extending speed of a double-acting cylinder
D. To control the temperature of the working fluid
E. None of the above
Answer C. “To speed up the extending speed of a double-acting cylinder”
Question 3
Which of the following is the purpose of fail-safe circuits?
A. Fail-safe circuits are designed to provide overload protection for system components
B. Fail-safe circuits are designed to regulate the flow rate of the working fluid
C. Fail-safe circuits are designed to control the bulk modulus of the working fluid
D. A, B, and C
E. None of the above
Answer A. “Fail-safe circuits are designed to provide overload protection for system components”
Question 4
Which of the following is one of the reasons for considering pneumatics instead of hydraulics?
A. Liquids exhibit greater inertia than do gases
B. Liquids exhibit greater viscosity than do gases
C. Hydraulic systems require special reservoirs and no-leak design components
D. There are no instances where pneumatics are considered instead of hydraulics
E. A, B, and C
Answer E. “A, B, and C”
Problem 1
A double-acting cylinder is hooked up in the regenerative circuit shown. The relief valve setting is 100 bars. The piston area is 120 cm2 and the rod area is 70 cm2. If the pump flow is 0.0018 m3/s, find the cylinder speed and load-carrying capacity for the
a. Extending stroke
b. Retracting stroke
Solution
Known data
Relief valve pressure p = 100 bars = 10,000,000 Pa
Piston area Ap = 120 cm2 = 0.012 m2
Rod area Ar = 70 cm2 = 0.007 m2
Pump flow rate Qp = 0.0018 m3/s
Unknown (s)
a. Extending stroke
· Cylinder speed VP ext?
· Load-carrying capacity Fload ext?
b. Retracting stroke
· Cylinder speed VP ret?
· Load-carrying capacity Fload ret?
Formula
Detailed calculation
Let’s start by converting units first
The cylinder extension speed VP ext, and extension load carrying capacity Fload ext can now be calculated as follow
Applying the formula related to the retraction, the cylinder speed VP ret, and load carrying capacity Fload ret are then found to be
Problem 2
For the system shown (for the extension strokes of the cylinders), what pump pressure is required if the cylinder loads are 4500 lb each and cylinder 1 has a piston area of 9 in2?
Solution
Known data
Cylinder 1 load F1 = 4500 lb
Cylinder2 load F2 = 4500 lb
Cylinder 1 piston area AP1 = 9 in2
Unknown (s)
Pump pressure p1?
Formula
Detailed calculation
Problem 3
For the meter-in flow control valve system shown, the following data are given:
Desired cylinder speed = 14 in/s
Cylinder piston diameter = 1.8 in (area = 2.545 in2)
Cylinder load = 2600 lb
Specific gravity of oil = 0.90
Pressure relief valve setting = 1100 psi
Determine the required capacity coefficient of the flow control valve.
( Hint: 1 gal = 231 in3 )
Solution
Known data
Cylinder speed vcyl = 14 in/s
Piston diameter = 1.8 in
Cylinder load Fload = 2600 lb
Specific gravity SG = 0.9
Relief valve pressure PPRV = 1100 psi
Unknown (s)
Capacity coefficient CV = ?
Formula
Detailed calculation
The area of the piston is found to be
Replacing all the given values in the formula of the cylinder speed,
However, the units of Cv are , converting
It is worth notice that the Cv could also have been calculated straight from the formula
The conversion into units of done before gives the same answer of 0.992
Problem 4
Air is used at a rate of 40 cfm from a receiver at 90 oF and 140 psi. If the atmospheric pressure is 14.7 psia and the atmospheric temperature is 80 oF, how many cfm of free air must the compressor provide?
( Hint: o Rankine = oF + 460, psia = psig + 14.7 )
Solution
Known data
Let subscript 1 represent atmospheric conditions
V2 = 40 cfm
T2 = 90 oF = 90 + 460 = 550 oR
p2 = 140 psi = 140 + 14.7 = 154.7 psia
p1 = 14.7 psia
T1 = 80 oF = 80 + 460 = 540 oR
Unknown (s)
Volumetric efficiency ηv?
Formula
Detailed calculation
Units conversion was performed within “ known data” step.
Problem 5 Exercise 13-29E on page 505
a. Calculate the required size of a receiver that must supply air to a pneumatic system consuming 27 scfm for 10 min between 130 psi and 110 psi before the compressor resumes operation.
b. What size is required if the compressor is running and delivering air at 8 scfm?
Solution
Known data
Consuming rate Qr = 27 scfm
Supplying time t = 10 min
Maximum pressure pmax = 130 psi
Maximum pressure pmin = 110 psi
a) Output flow Qc = 0 scfm
b) Output flow Qc = 8 scfm
Unknown (s)
a) Receiver size without load Vr?
b) Receiver size with load Vr?
Formula
Detailed calculation
The solution is straight forward. Substituting the known data in the formula gives,
Problem 6
Determine the actual power required to drive a compressor that delivers air at 180 scfm at 110 psig. The overall efficiency of the compressor is 70%.
Solution
Known data
Flow rate Q = 180 scfm
Outlet pressure pout = 110 psig = 110 + 14.7 = 124.7 psia
Inlet atmospheric pressure pin = 14.7 psia
Overall efficiency ηo = 70 % = 0.70
Unknown (s)
Theoretical power HPTheor?
Actual power HPActual?
Formula
Detailed calculation
Pressure is to be expressed in absolute value. Hence, the inlet atmospheric pressure pin = 14.7 psia, and the outlet pressure pout = 110 psig = 110 + 14.7 = 124.7 psia.
Substituting given data into formulas,
Problem 7
Air at 115oF passes through a -in-diameter orifice having a flow capacity constant of 7. If the upstream pressure is 110 psi, what is the maximum flow rate in units of scfm of air?
( Hint: oRankine = oF + 460, psia = psig + 14.7 )
Solution
Known data
Upstream temperature T = 115 oF = 115 + 460 = 575 oR
Orifice diameter = ½ in
Flow capacity constant CV = 7
Upstream pressure p1 = 110 psi = 110 + 14.7 = 124.70 psia
Unknown (s)
Maximum volume flow rate Q = ?
Formula
Detailed calculation
Let’s start by converting temperature and pressure to absolute values.
The downstream pressure p2 is found to be
Substituting all the values in the flow rate formula gives
Problem 8
A single-acting air cylinder with a 2-in-diameter piston and 12-in stroke operates at 105 psig and reciprocates at 25 cycles per min. compute the air compensation in scfm of air.
Solution
Known data
Piston diameter DP = 2 in = 0.1667 ft
Stroke S = 12 in = 1 ft
Pressure p2 = 105 psig = 119.7 psia
Speed N = 25 cycle/min
Atmospheric pressure p1 = 14.7 psia
Unknown (s)
Air compensation Q1?
Needed
Piston Area AP?
Displacement volume VD?
Consumed flow rate Q2?
Formula
Detailed calculation
As usual, let’s state by units conversion for the piston diameter DP, stroke S, and pressure p2
In order to determine the air compensation Q1, we need to first calculate the consumed flow rate Q1 which, requires a prior knowledge of the displacement volume VD. The latter cannot be known unless the piston are AP is evaluated first.
The consumed flow rate Q2 can now be calculate as
Finally, the air compensation Q1 is found to be
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