Gasket, apparatus incorporating same and method

A gasket comprising a closed loop of resilient material, the loop having an inner periphery and an outer periphery, the gasket having a first thickness at a first position which is between 0% and 30% of the gasket width away from the outer periphery, a second thickness at a second position measured at a point at least 50% of the gasket width from the first position, and a third thickness at a third position intermediate the first and second positions and at least 10% of the gasket width from each, the first thickness being greater than the third thickness which is greater than the second thickness, and wherein either

• a said gasket reduces in thickness from the first thickness to the third thickness and then to the second thickness via one or more tapered sections which taper linearly to a reduced thickness in the direction towards the inner periphery, or
• b said gasket reduces in thickness from the first thickness to the third thickness via one or more steps which step to a reduced thickness in the direction towards the inner periphery and then from the third thickness to the second thickness via one or more steps which step to a reduced thickness in the direction towards the inner periphery, or
• c said gasket reduces in thickness from the first thickness to the third thickness and then to the second thickness via a combination of one or more steps and one or more tapered sections as defined above,
• and further wherein
• i) the gasket includes one or more steps and is provided with boltholes, wherein the boltholes do not intersect the steps,
• and/or
• ii) the gasket is provided with a chemically resistant layer of fluoropolymer at the inner periphery.