Hydraulics - Seafish

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67 Oil A is said to have a low viscosity index and could have a typical value of 20. Oil B is said to have a high viscosity index and could have a typical value of 100. For most hydraulic systems, a viscosity index of at least 90 is recommended. The terms viscosity and viscosity index have different meanings and each value must be considered when checking if an oil is suitable for a hydraulic system. The necessary information for checking a hydraulic oil is usually found in the operator's manual provided by the manufacturers of the hydraulic system. Pour point The pour point of an oil is the lowest temperature at which the oil will flow satisfactorily. The pour point of any oil used in a system should be at least 10°C below the lowest temperature which the hydraulic system is expected to operate in. Other Properties As well as having a suitable viscosity range, viscosity index and pour point, a hydraulic oil must: • Prevent rusting. • Resist the formation of sludge, gums and varnish. • Resist foaming if air is mixed into it. • Allow any water contamination to separate from it easily. • Not attack or dissolve the material of seals and gaskets. <strong>Seafish</strong> Open Learning
68 Additives in Hydraulic Oils Many parts of a hydraulic system are made of steel and rust can form on steel surfaces if oxygen and water are present in the oil. It is not possible to keep all air out of the system and air contains both oxygen and water vapour. Corrosion is a reaction between different metals when water and acid is present. An unprotected metal surface will be 'eaten awayf by corrosion and the surface becomes pitted. Acid can be formed in the oil when oxygen is mixed in it and particularly when the oil is allowed to become overheated. This will also cause sludge, gums and varnish to form in the oil. •f Particles of rust and particles resulting from the corrosion can cause wear on surfaces which rub together and also damage the seals on pumps and actuators. Additives in the oil are used to put a protective film on the metal surfaces so that they resist rusting and corrosive attack. Additives also help to prevent the formation of gums, sludge and varnish in the oil which can cause valves to stick and also block small, restriction orifices which may be in the system. Additives are blended into the oil by the oil manufacturer and cannot be added to the oil by the operator of a hydraulic system. © Not all the hydraulic oils which are available contain these additives in sufficient quantities and only oils recommended by the manufacturers of the system should be used. <strong>Seafish</strong> Open Learning
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SEA FISH INDUSTRY AUTHORITY Hydraul
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Hydraulics in Fishing Vessels An Op
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SEGMENT FIVE - HYDRAULIC OILS AND F
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A Guide for Open Learners This will
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VII S.A.Q/S are shown by a box with
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IX • Time spent just reading a mo
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XIII Objectives After completing th
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Working cylinder V 7 3 •< ► Loa
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Write down a list of the main compo
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In this type the rotor shaft is off
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8 Pressure Control Valves Positive
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10 Relief valves are either pre-set
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12 (A) From Pump (P) i a(B) Raise H
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14 Out Out Globe valve Figure 17. S
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16 (?) SAQ25 Explain how a relief v
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18 The cylinders shown in Figures 2
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20 Figure. 31. Figure 32. Port A Po
Page 37: 22 Which types of pumps can be used
Page 41 and 42: 24 Hydraulic Pressure The pressure
Page 43 and 44: 26 In order to help you to compare
Page 45 and 46: 28 ® SAQ18 Using Figure 35 on page
Page 47: 30 ® SAQ29 When a hydraulic motor
Page 51 and 52: 32 Rotor Inlet External Gear Pump F
Page 53 and 54: 34 The vanes are pushed out by cent
Page 55 and 56: 36 Piston Pumps All piston pumps de
Page 57 and 58: 38 Drive shaft flange Piston Yoke c
Page 59 and 60: 40 Eccentric Oil outlet Figure 49.
Page 63 and 64: 43 Segment Four — Hydraulic Syste
Page 65 and 66: 45 K4SS^^ LINES AND LINE FUNCTIONS
Page 67 and 68: 47 PUMP ONE-WAY VARIABLE OUTPUT PUM
Page 69 and 70: 49 • Pilot pressure means that oi
Page 71 and 72: 51 ® A reversible motor with a bra
Page 73 and 74: 53 (?) SAQ15 Using the information
Page 75 and 76: 55 First, identify each of the item
Page 77 and 78: 57 ® SAQ28 Using the diagram of Fi
Page 79: 59 SUMMARY You have now completed S
Page 83 and 84: 62 PROPERTIES OF HYDRAULIC OILS The
Page 85 and 86: 64 (2) SAQ20 How is the viscosity o
Page 87: 66 (?) SAQ26 Using Table 3 determin
Page 91 and 92: 70 CONTAMINATION Dirt and other for
Page 93 and 94: 72 • Metal wear particles • Pac
Page 95 and 96: 74 Full flow filters are all fitted
Page 99 and 100: 77 Segment Six — Maintenance and
Page 101 and 102: 79 Cleanliness has top priority.
Page 103 and 104: 81 Do not 'grip' a hot pipe. Try a
Page 105 and 106: 83 Faulty Seals Faulty Seals on pum
Page 107 and 108: 85 Excessive Noise Table 4 Seafish
Page 109 and 110: 87 Incorrect Flow Table 6 Seafish O
Page 111 and 112: 89 Faulty Operation Table 8 Seafish
Page 113 and 114: 93 So you can see that there are ma
Page 117 and 118: 95 Responses to the Self Assessment
Page 119 and 120: 97 SAQ 6 Did you show the change in
Page 121 and 122: 99 SAQ9 The various properties whic
Page 123 and 124: 101 SAQ15 SAQ16 A linear actuator p
Page 125 and 126: 103 SAQ20 (a) Viscosity increases a
Page 127 and 128: 105 SAQ26 SAE 20W/30 oil will have
Page 129 and 130: Other modules in this series which
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Hydraulics - Seafish

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