cameroon gce A level 2024 mechanical design 3
cameroon gce A level 2024 mechanical design 3
THEME: MOTOR PUMP UNIT
I- SET-UP
The assembly drawing in appendix 1 represents a displacement pump intended to supply water for, the watering of
gardens or other farmlands and for the supply of households. This motor pump unit can also be used by drainage
vehicles for fighting against insects, fire control . ..etc.
II- DESCRIPTION AND FUNCTIONING
Due to its linear reciprocating movement, piston 50 sucks up water via valve 55 and sends through the valve 56. The
rotational movement of the crankshaft 38 is transmitted to the multiple discs clutch through the set of pulley 33 and
belt 34.
Phase 1: Inlet: Piston 50 going toward the top dead center causes a pressure drop of water which maintains the ball
of valve 56 on its scat and raises the ball of valve 55. It then occurs water suction.
Phase 2: Back flow: Piston 50 going toward the bottom dead center causes an increase of water pressure in the
chamber. This pressure pushes down the ball of valve 56 and seals valve 55. Thus the water contained in the
chamber is driven back in the distribution lines.
Ill- WORK TO BE DONE
SECTION A: TECHNOLOGICAL STUDY (20 marks)
QUESTION 1: FUNCTIONAL ANALYSIS
1. The set of parts: 1- 9 – 2 5- 1 2- 1 0- 4 2- 7- 3 4 – 3 3- 38- £7- 50, are involved in the power transmission
from the electrical motor shaft 1 to the piston 50. Complete the chain diagram showing the flow of power from
(0.75 marks)
(1.5 marks)
(lmark)
(0.75 marks)
(4 marks)
the electrical motor shaft X to the piston 50.
2. Precise the function of the parts: 20; 56; and the set (37- 40).
3. Indicate in order, four operations to be carried out for the replacement of the belt 34.
4. Indicate the order of dismounting of the set comprising the connecting rod 47 and the piston 50.
QUESTION 2: TYPE OF LINKAGES (4 marks)
1. Complete the following equivalence classes: A- B- C- D.
2. Specify the type of link between the following classes mentioned about, then complete the minimal kinematic
diagram.
3. Give three characteristics and the mode of the link between the following parts: 38 and 33; 50 and 41;
41
.
and 38
4. Name the parts establishing the link between 38 and 33.
5. The standard designation of the material of bushing 37 is CuZn33. Give the interpretation
of this designation.
(1 mark)
(1.25 marks)
(1 mark)
(0.25 marks)
(0.5 marks)
QUESTION 3: FUNCTIONAL DIMENSIONING AND FITS (4 marks)
1. Justify the presence or the necessity of the clearance b between 38 and 37 and a between M and 38. (0.5 marks)
2. Draw the chain of dimensions for the following clearances: (0.5 marks)
a Between 38 and 31
b Between 38 and 37
3. The chain of dimensions related to the clearance c is given in figure 3 below.
0000/7145/3
(1 mark
