packings and seals - concept and explanation ppt
- 2. NEED FOR SEALS NEED FOR SEALS Seal is a device for closing a gap or making a joint fluid tight ( liquid or gas ) NEED * To minimize leakage * To prevent toxic fluids escaping to atmosphere ( Ammonia) * To reduce power loss .
- 3. TYPES OF SEALS TYPES OF SEALS Static Seals Dynamic Seals
- 4. STATIC STATIC SEALS SEALS Sealing takes place between two parts that don’t move in relation with each other. Application - Pipe flanges ,vessel /Tower nozzles, pump casing joint. - Fan /Blower casing joint , Compressor casing joint. - Turbine casing joint, Heat exchanger joints Types - Gaskets - O-rings - Liquid gaskets
- 5. GASKET GASKET Packing designed to go between two rigid parts in stationary conditions May be in form of sheet , strip , bulk. Properties – Impermeability – Ability to flow into joints – Ageing – Corrosion resistance
- 6. Classification of Gaskets Classification of Gaskets Non-metallic gaskets Metallic gaskets Non-metallic gaskets – Asbestos – Cork and rubber – PTFE
- 7. METALLIC GASKET METALLIC GASKET Corrugated Plain Asbestos filler Metal clad Soft material like asbestos CAF enclosed in metal covering . Provides additional mechanical strength Spiral wound Alternate layers of v- sections , metallic strip and non- metallic filler compressed to a predetermined amount Metal – SS , Monel , Inconel , Titanium. Fillers – Asbestos fibres , PTFE lead, ceramic paper , graphite foils
- 8. O-RINGS O-RINGS Moulded elastomeric circular section ring nipped in cavity in which the ring is located Has initial squeezing pressure , internal pressure applied through one side and o-ring deforms in contact with the opposite side of groove Pressure transmitted is more than the fluid pressure. Limiting factor is o-ring hardness and clearance
- 9. LIQUID GASKET LIQUID GASKET Replacement for O-ring / gasket Compound applied , air drying , adhesion to metal Sealant generally applied on one face , for critical applications on two faces Air trapped is forced out by excessive compound during tightening Compounds Polyester urethane Silicones Types Non-hardening type Semi- hardening type Hardening type
- 10. DYNAMIC SEALS DYNAMIC SEALS Used for sealing fluid between parts that move in relation with each other Application * Centrifugal pump gland, valve gland , bearing housing * Turbine/compressor inter stage and end sealing * Reciprocating compressors cylinder sealing TYPES Mechanical contact seals Gland packings Labyrinth seal Oil seal Oil film seals
- 12. MECHANICAL SEALS MECHANICAL SEALS Components 1. rotary seal face 2. stationary seal face 3. springs 4. retainer 5. sealing /flushing media 6. o-rings
- 14. MECHANICAL SEALS MECHANICAL SEALS CLASSIFICATION By arrangement 1. Single seal - Inside mounted / Outside mounted 2. Multiple design - Double seal/ Tandem seal By design 1. Unbalanced seal 2. Balanced seal 3. single spring 4. Multiple spring 5. Pusher seal 6. Non – pusher seal
- 15. MOC – MECHANICAL SEALS MOC – MECHANICAL SEALS Primary seal 1. Ceramic 2. Carbon - Resin impregnated – corrosive applications - Antimony impregnated – non-corrosive 3. Tungsten carbide - Ni binder - Co binder 4. Silicon carbide Secondary seal Elastomers - Nitrile , Neoprene , Butyl, Hypalon Non –Elastomers - PTFE, Graf oil Spring SS 304, SS 316, Hastalloy, Monel, Alloy-20
- 17. MERITS / DEMERITS MERITS / DEMERITS Merits - Reduced friction - Elimination of shaft/sleeve wear - Zero leakage - Freedom from periodic maintenance Demerits - Space - Careful handling and installation - Initial cost is high
- 18. GLAND GLAND PACKING PACKING Enclosed in a stuffing box Compressive force by tightening the gland plate produces radial pressure Slight leakage is allowed for lubrication Periodic retightening of gland necessary for wear compensation. Lantern ring for cooling /lubrication Stuffing box pressure No of rings (bar) up to 35 4 35-70 6 70-140 8 140 10
- 20. GLAND PACKING GLAND PACKING • packing material vegetable based fibre yarns for oil and water service –cotton hemp flax textile asbestos yarns graphite packings • lubricants graphite mica with Mo di sulphide and PTFE dry lubricant tallow silicone greases
- 21. LABYRINTH SEALS LABYRINTH SEALS Non contact type Number of sealing strips inserted into stationary part Horizontally split Fittings done to shaft sometimes Leakage rate relatively high Leakage depends - number of teeth - diameter of packing - clearance and pressure to be sealed
- 23. OIL SEALS OIL SEALS Shaft oil seals – low pressure Oil film generated between lip and shaft Sealing provided by surface tension of the hydrodynamic oil Increased film thickness – leakage Lesser film thickness – friction and wear Leakage due to - scratches - Abrasives or grit materials MOC - Seal lip – Nitrile, Silicones, polyacrylic - Spring – Closed coil tension – SS 304 / 316
- 24. OIL FILM SEAL OIL FILM SEAL Consist of inner sleeve and outer sleeve Oil at midpoint 5-15 psi greater pressure Babbitt lined steel –sleeve Sour oil – contaminated oil ( with product) Sweet oil – pure oil Costly and complicated , free from wear and tear Important parameters - clearance between bush and shaft - length of the bushing