What temperature limits apply to rubber hoses compared with plastic hoses?

You determine the right hose based on the full application: the size, the medium, the temperature, the pressure, the length of the hose and the couplings to be fitted. There is no fixed formula; just like choosing a car, it depends on what you are going to use it for.

When specifying the size, pay close attention to the difference between inside and outside diameter. Pipes are specified by their outside diameter: a 50 x 5 mm pipe has an outside diameter of 50 mm and a wall thickness of 5 mm, and therefore an inside diameter of 40 mm. Hoses are always specified by their inside diameter, often in inches:

• 1/2" = 12.7 mm
• 1" = 25.4 mm
• 1 1/4" = 32 mm
• 1 1/2" = 38 mm
• 2" = 51 mm

The required working pressure follows from the maximum pressure in your installation, combined with the temperature and the medium. When making an enquiry, provide the full application details so that SCHIEMA can recommend the right combination of hose and couplings. You can request a quote directly.

The working pressure is the maximum pressure at which a hose may be used in practice; the burst pressure is the pressure at which the hose fails. The ratio between the two is the safety factor, which depends on the standard the hose is manufactured to.

Some examples from the range:

• NARCORFLEX® OILROUNDER: 5 bar working pressure, 20 bar burst pressure (factor 4)
• FLOWINFLEX® OILOHM: 10 bar working pressure, 30 bar burst pressure (factor 3)
• FLOWINFLEX® OILREXTOR and FLOWINFLAT® PROBUNKER: 20 bar working pressure, 60 bar burst pressure (factor 3)
• FLOWINTUBE® VAPORTOR-18-D (steam, EN ISO 6134): 18 bar working pressure, 180 bar burst pressure (factor 10)

For hoses manufactured to an EN or ISO standard, the ratio is fixed by the standard; some EN standards for chemical hoses, for example, prescribe 16 bar working pressure with 64 bar burst pressure. For non-standardised hoses, the ratio is agreed with the manufacturer.

Important: the stated working pressure applies at 20 °C with water as the medium. At a higher temperature or with a different medium, the permissible pressure may differ. In that case, have the suitability of the hose checked in advance, for example for a product at 50 °C pumped at 10 bar. SCHIEMA can also test and certify hose assemblies.

That depends on the type of reinforcement. You need a helix as soon as the hose must be suitable for suction or may be exposed to vacuum: without a helix, the hose collapses. For discharge only, a helix is not necessary. Textile or steel plies determine the pressure resistance of the hose; without plies, a hose would expand under pressure.

This is how a rubber hose is built up: unvulcanised rubber is first wrapped around a mandrel to form the inner lining. This is followed by the plies, then the helix, and then another layer of unvulcanised rubber for the outer cover. The complete mandrel, often with a hose length of 40 metres, then goes into a vulcanising autoclave, where heat bonds all layers into a single unit.