Very common with many lifting machines - man lifts, telehandlers, hydraulic cranes, etc. Generally they either use a counterbalance valve or a pilot operated check valve. One valve is used to control one direction (extend or retract), but they are often used in pairs so both directions are protected. In either case you need pressure on both sides of the piston to allow oil out. PO check just needs X pressure to open (opening pressure can be custom ordered), but the CB valves work on a ratio like 60:40.
Originally Posted by buckfever
Now that makes sense. Might not be a bad thing to have something like that on a boom lift cylinder. There have been a few times were I was setting a beam or manhole and thought this would get ugly if a line blows.
Originally Posted by icestationzebra