FIGURE 11.1 below shows a hydraulic lift. The lift needs to raise a maximum load of 4 500 kg at the ram with a diameter of 120 mm. The diameter of the plunger is 32 mm. Answer the questions that follow. 11.1.1 Calculate the fluid pressure in the hydraulic system in MPa. 11.1.2 The force to be applied on the plunger. 11.2 State ONE function of a hydraulic non-return valve. 11.3 Give TWO reasons why a spring-loaded double-action control valve is used in a water line. 11.4 Name the TWO different types of pressure gauges. 11.5 A pulley with a diameter of 375 mm is mounted on a shaft of a concrete mixer. The concrete mixer is driven by a pulley, with a diameter of 85 mm, on a motor which rotates at a speed of 1 320 r/min. The tensile force of the belt in the tight side is 275 N and the slack side is 120 N. HINT: The belt thickness may be ignored. Calculate the following: 11.5.1 The rotational frequency in r/s of the pulley on the concrete mixer. 11.5.2 The power that can be transmitted in watt. FIGURE 11.6 below shows a gear drive system. Driver gear A meshes with driven gear B with 20 teeth on a countershaft. Driver gear C, with 45 teeth meshes with a second countershaft. On the second countershaft is another driven gear, E, with 50 teeth that meshes with the driver gear D, which has 25 teeth. The input shaft is 320 r/min and the rotational frequency of the output shaft is 720 r/min. Answer the questions that follow. Calculate the following: 11.6.1 The number of teeth on the driver gear T_A. 11.6.2 The gear ratio of the system.

Photo AI

FIGURE 11.1 below shows a hydraulic lift - NSC Mechanical Technology Fitting and Machining - Question 11 - 2022 - Paper 1

Question 11

FIGURE 11.1 below shows a hydraulic lift. The lift needs to raise a maximum load of 4 500 kg at the ram with a diameter of 120 mm. The diameter of the plunger is 32 ... show full transcript

Worked Solution & Example Answer:FIGURE 11.1 below shows a hydraulic lift - NSC Mechanical Technology Fitting and Machining - Question 11 - 2022 - Paper 1

Step 1

11.1.1 Calculate the fluid pressure in the hydraulic system in MPa

96%

114 rated

Answer

To calculate the fluid pressure (P) in the hydraulic system, we use the formula: $P = \frac{F}{A}$ Where:

F = force applied by the ram = mass × gravity = 4500 kg × 10 m/s² = 45000 N
A = area of the ram, given by $A = \frac{\pi d^2}{4}$ Substituting the diameter (d = 120 mm = 0.12 m): $A = \frac{\pi (0.12)^2}{4} = 0.01131 m^2$ Thus, $P = \frac{45000 N}{0.01131 m^2} ≈ 3980322.69 N/m^2$ Converting to MPa: $P = \frac{3980322.69}{10^6} = 3.98 MPa$

Step 2

11.1.2 The force to be applied on the plunger

99%

104 rated

Answer

To find the force (F) that needs to be applied on the plunger, we use the same pressure calculated before: $P = \frac{F}{A}$ Where A is the area of the plunger with a diameter of 32 mm (0.032 m): $A_{plunger} = \frac{\pi (0.032)^2}{4} = 0.00080 m^2$ Therefore, $F = P × A = 3.98 × 10^6 N/m^2 × 0.00080 m^2 = 3184 N$

Step 3

11.2 State ONE function of a hydraulic non-return valve

96%

101 rated

Answer

One function of a hydraulic non-return valve is to provide one-directional flow control, preventing back flow of the fluid in the hydraulic system.

Step 4

11.3 Give TWO reasons why a spring-loaded double-action control valve is used in a water line

98%

120 rated

Answer

To protect water supplies from backflow, ensuring that contaminated water does not return to the clean supply.
To prevent water contamination by ensuring that the valve closes if one of the valves is jammed, maintaining the functionality of the system.

Step 5

11.4 Name the TWO different types of pressure gauges

97%

117 rated

Answer

Bourdon tube gauge.
Schrader gauge.

Step 6

11.5.1 The rotational frequency in r/s of the pulley on the concrete mixer

97%

121 rated

Answer

To find the rotational frequency of the pulley, we use: $N_{mixing} = \frac{N_{motor} × D_{motor}}{D_{mixing}}$ Where:

$N_{motor} = 1320 r/min$ (motor rotation)
$D_{motor} = 0.085 m$ (diameter of motor pulley)
$D_{mixing} = 0.375 m$ (diameter of mixing pulley) Converting $D_{motor}$ from mm to m:
$\frac{D_{motor}}{D_{mixing}} = 0.085/0.375 = 0.22667$ Thus, $N_{mixing} = \frac{1320 × 0.085}{0.375} = 299.2 r/s$

Step 7

11.5.2 The power that can be transmitted in watt

96%

114 rated

Answer

The power (P) transmitted can be calculated using: $P = (T_{tight} - T_{slack}) × \frac{D × N}{60}$ Where:

$T_{tight} = 275 N$
$T_{slack} = 120 N$
$D = 0.085 m$
$N = 1320 r/min$ Converting:
$P = (275 - 120) × \frac{\pi × 0.085 × 1320}{60}$ After calculations, this results in approximately 911.9 Watts.

Step 8

11.6.1 The number of teeth on the driver gear T_A

99%

104 rated

Answer

Given the relation between input and output gears: $N_{output} = \frac{T_A × T_C × T_E}{T_B × T_D × T_F}$ Where:

$N_{A} = 320 r/min$ , $N_{F} = 720 r/min$ ,
Substituting known values: $720 = T_A × 45 × 50 / (20 × 25 × 20)$ Solving for $T_A$ gives: $T_A = 10$

Step 9

11.6.2 The gear ratio of the system

96%

101 rated

Answer

The gear ratio can be calculated using: $Gear Ratio = \frac{\text{Product of the number of teeth on driven gears}}{\text{Product of the number of teeth on driving gears}}$ Using provided numbers: $Gear Ratio = \frac{20 × 25 × 20}{10 × 45 × 50} = 0.44$

FIGURE 11.1 below shows a hydraulic lift - NSC Mechanical Technology Fitting and Machining - Question 11 - 2022 - Paper 1

Worked Solution & Example Answer:FIGURE 11.1 below shows a hydraulic lift - NSC Mechanical Technology Fitting and Machining - Question 11 - 2022 - Paper 1

11.1.1 Calculate the fluid pressure in the hydraulic system in MPa

11.1.2 The force to be applied on the plunger

11.2 State ONE function of a hydraulic non-return valve

11.3 Give TWO reasons why a spring-loaded double-action control valve is used in a water line

11.4 Name the TWO different types of pressure gauges

11.5.1 The rotational frequency in r/s of the pulley on the concrete mixer

11.5.2 The power that can be transmitted in watt

11.6.1 The number of teeth on the driver gear T_A

11.6.2 The gear ratio of the system

Join the NSC students using SimpleStudy...