It serves two closely related jobs: vacuum lines feeding a brake servo on cars and light vehicles, and pneumatic control lines in commercial vehicle braking systems. Both need a hose that will not collapse under negative pressure, resists oil contamination from the engine bay, and survives years of heat and ozone exposure without hardening. It is built to BSAU110 and conforms to SAE J1402.

Because a servo line runs under vacuum, not pressure. Ordinary hose without adequate wall reinforcement will slowly draw shut, and a partially collapsed servo hose gives a hard pedal that comes and goes - a genuinely dangerous and very hard fault to diagnose. This hose is reinforced with high-tensile braided fibre specifically so it holds its bore under vacuum.

Internal diameters of 9.5mm and 13mm, cut to order from 1 metre up to a 50 metre full coil. Those two sizes cover the overwhelming majority of servo and vacuum applications. Measure the outside diameter of the servo spigot and the manifold takeoff and match the hose bore to it - the hose should need a firm push to go on, not slide on loose.

It is oil resistant, which matters because a servo line sits in an engine bay where oil mist, splashes and fuel vapour are unavoidable. That resistance is why it lasts where a general-purpose rubber hose goes soft and swells. It is not intended as a fuel delivery hose though - for carrying fuel use our SAE J30 R6 rubber fuel hose or fluorosilicone-lined silicone.

A synthetic rubber inner tube with braided fibre reinforcement and an ozone-resistant synthetic rubber outer cover. Ozone resistance is the reason the outer does not craze and crack after a few summers under the bonnet - that surface crazing is usually the first visible sign that an old servo hose is on its way out, even before it starts to collapse.

Cut it square, push it fully home over the spigot so it seats past any barb, and secure with a hose clip at each end. Route it away from the exhaust manifold and turbo, and support it so it cannot rub on a bracket or the bonnet slam panel. A vacuum leak from a chafed servo hose gives a lumpy idle as well as a poor pedal, so routing is worth taking care over.