Mechanical shaft seals for pumps - Grundfos

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Water or water mixed with glycerine is the most common liquid in closed pressurized back-to-back arrangements because it is non-poisonous and compatible with many types of pumped media. The barrier fluid chosen must always be compatible with the pumped medium. To maintain the overpressure in the barrier fluid in relation to the pumped medium pressure, various pressure sources can be used as described in the following sections. Fixed pressure A pressure vessel with fixed pressure in the barrier fluid with 10 % or 2 bar higher than the pressure in the pumped medium. See fig. 2.3. The advantages are as follows: • compensates leakage • cools the seals by means of natural convection or forced circulation 6 • indicates the pressure in the barrier fluid 10 15 • possibly gives alarm when the barrier fluid level is low/high 5 0 20 25 4 8 7 • allows refill of barrier fluid with pressure maintained in the vessel • constant air pressure secures the barrier 1 fluid pressure 2 • indicates temperature and liquid level. Fig. 2.3: Pressure vessel with fixed pressure connected to a Grundfos CR pump with a back-to-back seal arrangement 3 5 1. Manual pump for refill 2. Level indicator 3. Thermometer 4. Manometer 5. Pressure vessel 6. Constant air pressure connection 7. Safety valve 8. High-/low-level switch 33
34 Mechanical shaft seal types and sealing systems Fixed pressure obtained by means of a dosing pump Another way of obtaining a fixed pressure in the seal chamber is by means of a dosing pump. The pump automatically keeps the level set for the overpressure. This solution is mainly used in dead-end applications where cooling from the seal chamber is sufficient. See fig.2.4. 1 2 Fig. 2.4: Dosing pump maintaining a fixed pressure for back-to-back seal in a Grundfos CR pump 3 1. Seal chamber with barrier fluid 2. Pump 3. Membrane vessel 4. Dosing pump 5. Pressure switch 6. Manometer for barrier fluid 7. Reservoir with barrier fluid 6 4 5 7
Page 1 and 2: Mechanical shaft seals for pumps
Page 3 and 4: Contents Preface 5 Chapter 1. Intro
Page 6 and 7: Chapter 1 1. Types of shaft seals 2
Page 8 and 9: Fig. 1.2: Braided stuffing box pack
Page 10 and 11: O-ring, stationary O-ring, rotating
Page 12 and 13: The rotating part The rotating part
Page 14 and 15: Closing force The parts of the seal
Page 16 and 17: In the examples above, where the ar
Page 18 and 19: Non-parallel seal faces System In p
Page 20 and 21: Atmosphere A B C D Vapour pressure
Page 22 and 23: 1993 Rubber bellows seal introduced
Page 25 and 26: 26 Mechanical shaft seal types and
Page 31: 32 Mechanical shaft seal types and
Page 43 and 44: Chapter 3 Materials 1. Seal face ma
Page 45 and 46: The metals used for metal-impregnat
Page 47 and 48: Silicon carbide (SiC) 100 µm Fig.
Page 49 and 50: 2. Seal face material pairings Carb
Page 51 and 52: WC against WC A shaft seal with WC
Page 53 and 54: 3. Testing of shaft seals Various t
Page 55 and 56: [ °C ] 250 200 150 Organic film bi
Page 57 and 58: Chemical adhesion of surfaces All s
Page 59 and 60: 5. Materials of other shaft seal pa
Page 61 and 62: 64 Tribology The science of frictio
Page 63 and 64: 66 Tribology Duty parameter The mec
Page 65 and 66: Surface film 68 3.5 Tribology 3.0 2
Page 67 and 68: 70 Tribology The lapped surface has
Page 69 and 70: 72 2.0 1.5 Tribology 1.0 0.5 Dry ru
Page 71 and 72: 74 Tribology Summary This section d
Page 73 and 74: 76 Failure of mechanical shaft seal
Page 83 and 84:
86 Failure of mechanical shaft seal
Page 85 and 86:
88 7. Shaft seal failure analysis T
Page 87 and 88:
s of shaft seal failure Incorrect i
Page 89 and 90:
Chapter 6 Standards and approvals 1
Page 91 and 92:
Example of designation for a mechan
Page 93 and 94:
2. Approvals Specific approvals of
Page 95 and 96:
The guideline on in-place cleanabil
Page 97:
Summary Different applications requ
Page 100 and 101:
contact points 65 contact surface 8
Page 102 and 103:
M magnetic-drive system 40 malfunct
Page 104 and 105:
spring force 13, 15 springs and bel
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Mechanical shaft seals for pumps - Grundfos

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