Environment

Corrosive and abrasive environments affect the service life of the coupling by causing abnormal wear to the component ele­ments. Extremes of heat and cold affect the strength and elas­ticity of the component materials. Oils, chemicals, sunlight and ozone can completely destroy a rubber element. A coupling made entirely of metal such as a diaphragm or flexible spring coupling, for example, is usually the only solution in such cases.

The process industries offer a very poor environment. In the petrochemical industry for instance, in refineries as well as oil and gas tankers, for example, it is necessary to use non-spark­ing couplings.

A non-sparking diaphragm coupling can be manufactured by making the diaphragm of Monel and the remaining components of carbon steel or bronze. Non-sparking types are usually used in conjunction with flameproof electric motors in environments where there is risk of explosion, either continuously or normally during operation. Statutory regulations must be observed, see also EN 14461.

Aflexible spring coupling has the important elements housed in a seal cover and coated with lubricant, in the form of grease. Environmental changes have little effect on the coupling. In­stances of spring breakage are rare, but any parts which could create a spark are fully enclosed, see Figure 12.9.

Another method of overcoming explosion risks, especially on board ship and with engine drivers, is by means of gas-tight bulkheads and bulkhead fittings consisting of two mechanical seals with barrier fluid between them, together with bellows which absorb misalignments. This type of fitting must be equipped with non-sparking shaft couplings.

Figun

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