How does a hose burst safety valve hold the load?
A hose burst safety valve is a pilot operated check valve mounted on the cylinder port. In normal use, pilot pressure in the lowering direction opens the valve; if the line suddenly fails, pilot pressure is lost, the valve closes under spring force, and by preventing oil from escaping the cylinder it holds the load in place.
The operating logic is simple: the valve opens only when there is pressure in the opposite line. When the system is intact and you give a lowering command, pressure builds in the opposite line, the valve opens, and the load lowers under control. When a hose bursts, that pressure drops to zero instantly and the valve closes by itself.
The same element addresses two different risks at once:
- Sudden failure: In a hose or fitting burst the load does not free-fall; the oil in the cylinder is trapped behind the valve.
- Slow leakage: The slow descent of the load over hours due to normal internal leakage in the main valve spool is also prevented, because the leakage path stays behind the valve.
The condition for it to be effective is the mounting location. The valve must be connected directly to the cylinder port; if a hose comes in between, protection does not work when the burst occurs in that hose.
On the maintenance side, watch out for: contaminated oil causing valve blockage, an incorrectly set pilot ratio, and removing the valve and fitting a straight fitting in its place. This last item is the most dangerous intervention seen in the field; the protection disappears completely.
Full coverage of this topic: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods