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You're riding a new track, following a mate who just dodged a jump; but you didn't. You get launched and brace hard for the landing, expecting to land with a bang and be launched back. Instead the fork stays quiet, sucking up the hit with no hard shock and a composed rebound.
How is such sorcery possible? With hydraulics! Hydraulic Bottom Out or HBO for short. It's not just a movie channel.
Hydraulic Bottom Out is a feature shared by a few top-end forks. It consists of oil immersed cup and cones which meet near full travel to suck the life from the impact and prevent hard bottoming. The bump energy is absorbed by squeezing oil out of controlled size holes under high pressure. The rebound energy is also constrained as the cup and cone take extra resistance to pull apart at speed.
The beauty of HBO is how it reacts to compression speed. Double the speed of engagement and it takes 4 times as much energy to compress. Which matches exactly how your energy scales with impact speed.
HBO only works in the last part of the travel; 20 mm for the Mattoc parts shown above. So you can run compression damping to suit the bumps rather than the jumps and still not punish the fork.
You will find HBO in Manitou Dorado, Manitou Mattoc/Magnum Pro, Manitou Circus Pro, some Manitou Minute/Machete and some Fox 40. It also existed in some older Marzocchi's and is available in aftermarket damper cartridges from Avalanche.
Some HBO systems (like Manitou Mattoc) are adjustable. There is a relief valve which is adjustable to limit the rate of pressure/force buildup and the maximum, ensuring lighter and more gentle riders can still easily get full travel while harder riders have the backup they need.