Collective term for organic compounds consisting solely of carbon and hydrogen, with the atoms united in chains or rings. The C atoms of a molecule are interlinked by covalent single, double or triple bonds. The demands placed on mechanical seals are extreme: temperatures of -100 °C up to +450 °C; a boiling point and vapour head at working temperature in the case of light hydrocarbons; an often high viscosity at low temperatures in the case of heavy hydrocarbons. Laws, ordinances, administrative regulations and similar pose additional demands. One example is the German "Technical Regulation on Air Pollution Control" (TA-Luft). Low and high product temperatures require suitable face materials such as cast Cr-steel running against antimony-impregnated  hard carbon

or silicon, or tungsten carbide against pure graphite as the material for secondary seals. At operating temperatures close to the boiling point, hydraulic balancing of the mechanical seal can reduce the power consumption rather: friction loss and hence prevent dry running.

Parallel measures such as e.g. steam heating of the seal element keep the viscosity of high-solidifying hydrocarbons within the permissible limits.

Seal selection recommendations are given in the following tables.

Cf. cryogenic mechanical seals for sealing hydrocarbons at temperatures below 50 °C.

Density of the pumped stock at working temperature

Temperature at the mechanical seal