Gaskets & Seals

Nizwa College of Technology

Gaskets& Seals Sealing is the process of preventing

gases, liquids and solids escaping from containers or mechanisms.

Seals can be broadly divided into two categories:

• Static seals - where there is no movement at the contact points.

• Dynamic or Mechanical seal - where there is movement between the contact points.

Selection of seal

The choice of seal to be used on a particular application is determined by the following factors:

• Property of the material being contained

• Amount and speed of any movement

• Operating pressure

• Life expectancy

• Operating temperature

Seal Materials

Non-metallic materials:

• Felt, rubber, asbestos, cork, plastics, P.V.C, paper, cloth etc.,

Metallic materials:

• Copper, lead, tin, plated steel, beryllium, and often a combination of several materials is used to make a particular seal or gasket.

Gaskets Gaskets are static seals used to prevent

fluids or gases passing across mating surfaces, where there is no movement, on a mechanical assembly

Gasket materials- cork, rubber, asbestos, plastic and metallic materials.

Fitting gaskets Important rules to follow when fitting a gasket

Conformation• The sealing pressure should be sufficiently high to

make the gasket conform to the joint surfaces.• Too little pressure can result in voids in the joint where

leakage could occur.• Too much pressure can result in distortion of both

gasket and joint surfaces. Condition of joint surface The mating surfaces of the joint should be:-• Free from burrs and indentations. '• Reasonably flat and mate together.• Clean and free from oil, grease and other materials.

Reasons for leakage in the joint

• Wrong gasket material

• Incorrect fitting gasket

• Poor Joint surfaces

• No conformation

• Distortion of surfaces

• Inaccurate tensioning

Dynamic or Mechanical Seals

Mechanical seals are used where there is movement between the parts being sealed

Types

Radial lip seal

Exclusion seal

Clearance seal

Ring seal

Face seal

Diaphragm seal

Packing

Radial lip seals

Parts of Lip Seal• Frame - stainless steel, Monel metal, titanium, bronze ,hastalloy.

Lip - rubber, nitrile, chloroprene, ethylene, propylene.• Spring -stainless steel, monel, titanium hastallloy.

Features• Take up Little space• Easy to install• Low cost• Accommodate slight misalignment.• One of the most widely used.

Fitting mechanical seals Guide lines to fitting seals

• Make sure that the correct type of seal is used, particularly when replacing a seal

• Ensure that the housing shaft and seal is in good condition and free from dirt and other foreign matter

• Lubricate the surfaces of seal, shaft and housing if necessary

• Use a suitable assembly tool if needed

• Use a cone or sleeve over any sharp corners of the shaft

• Check seal for correct operation before applying power to drive

• After a short period of use inspect seal for leaks or other failures

Seals &Gaskets-Examples