Compression washers
A washer that can be compressed or crushed is often used where a liquidtight seal needs to be achieved, such as the fitting of an engine oil drain sump plug. Avoid over tightening the sump plug (refer to a workshop manual for the correct torque setting) as it could flatten the washer and fail to achieve a seal. If a solid copper washer is used, it must be soft copper because one that has not been annealed will be too hard and may well end up leaking.
Aluminium compression washers are usually softer than the copper equivalent and are used for engine oil sump drain plugs, or pneumatic and low-pressure hydraulic systems. Just like a copper washer, it’s important to follow any recommended torque-tightening settings to ensure the compression washer is sufficiently tightened to form a seal.
Crushable steel washers are fitted to most spark plugs, which help to create a leak-free seal and also explain why the recommended torque setting for most spark plugs (especially if threaded into aluminium) is usually no more than 30Nm. Once a new spark plug has been fitted, its washer will have been crushed, so if the spark plug is extracted, the washer should ideally be renewed if you intend to refit the spark plug. However, we have never heard of anybody encountering problems when refitting old spark plugs.
And finally, a Dowty bonded seal consists of a rubber seal bonded (vulcanised) to metal, such as a washer with a rubber insert around the inside or a sump drain plug with rubber bonded to the underside of its head. They provide a great seal in high pressure environments.
Our thanks for help and advice with this feature go to the friendly, helpful and knowledgeable staff at Sterling Bolt and Nut Co Ltd in Peterborough. They have a huge range of fastenings of all types. Call 01733 563022 or visit them at 25 Royce Road, Peterborough PE1 5YB.