5.2 Pump packing material
Pump packing material
The most common pump packing material is plaited or braided fibre, but packing compounds and fabricated rings are also used. See figure 5.2a for a survey of packing materials. A plaited packing consists of a bearer, basic material and impregnation.
- Vegetable fibres (hemp, linen, cotton) used for temperatures up to 100°C. Poor chemical resistance.
- White chrysotile asbestos and blue asbestos have a large operating range and can be used for temperatures up to 500°C. The use of blue asbestos is now forbidden by legislation in most countries and where possible white asbestos should be replaced by other materials*.
- Synthetic fibres have excellent sliding properties and are resistant to all liquids. Maximum temperature 250°C.
- Graphite fibre has a very low friction coefficient and good thermal conductivity properties as well as good chemical resistance, apart from oxidizing acids such as, nitric acid.
- Glass fibre replaces blue asbestos. Glass fibre is not resistant to hydrofluoric acid and strong alkalis.
- In order to reduce friction the packing is impregnated with a suitable animal, mineral, vegetable or synthetic based lubricant. The lubricant impregnation withstands temperatures of up to 125°C and a pH value between 5
and 10. PTFE-impregnation withstands temperatures of up to 250°C and pH 0-14.
The basic material can be as follows:
Figure 5.2a Operating limits for various pump packing material
* Chrysotile (source Wikipedia)
Chrysotile has been included with other forms of asbestos in being considered to be a human carcinogen by the International Agency for Research on Cancer (IARC) and by the U.S. Department of Health and Human Services. These state that “Asbestos exposure is associated with parenchymal asbestosis, asbestos-related pleural abnormalities, peritoneal mesothelioma, and lung cancer, and it may be associated with cancer at some extra-thoracic sites”. In other scientific publications, epidemiologists have published peer reviewed scientific papers establishing that chrysotile is the main cause of pleural mesothelioma.
Chrysotile has been recommended for inclusion in the Rotterdam Convention on Prior Informed Consent, an international treaty that restricts the global trade in hazardous materials. If listed, exports of chrysotile would only be permitted to countries that explicitly consent to imports. Canada, a major producer of the mineral, has been harshly criticized by the Canadian Medical Association for its opposition to including chrysotile in the Convention.
According to EU Regulation 1907/2006 (REACH) the marketing and use of chrysotile, and of products containing chrysotile, are prohibited.