Seals keep hydraulic cylinders out of hot water

One of the most versatile characteristics of hydraulics is the ability to place a compact actuator in a remote location — with only a hose or two leading to it. That’s exactly the case often found at aluminum foundries. In these applications, a self-guided hydraulic cylinder with non-rotating rod is mounted vertically under a casting tool to provide smooth lowering of the new castings and tooling assembly. Although this may not sound like a particular challenge, the tooling assembly with castings may weigh up to 160 tons, and the cylinder often is submerged in water, which cools the tooling and castings.

To prevent water from getting into the cylinder — and hydraulic oil from getting into the water — a sophisticated sealing system is incorporated into the rod end of the cylinder. The ultra-high-performance sealing system is needed because of the time and expense that would be expended to drain water from the pit in which the cylinder is mounted, remove the cylinder, replace the seal, and put the cylinder back in service in the pit. Furthermore, the seal must be monitored to detect when any leakage occurs.

The sealing system begins with V-packing designed to apply constant contact pressure over a wide range of hydraulic pressures. A key element of the system is an adjustable secondary seal from Hunger Hydraulics USA, Rossford, Ohio — the EVD Seal Ring. The EVD Seal Ring contains an internal chamber that accepts a pressurized gel, which causes it to expand. The expansion increases contact pressure between the seal and the cylinder’s piston rod.

In normal operation, the V-packing and polyurethane seal act as a primary rod seal to keep pressurized hydraulic fluid within the cylinder while allowing linear motion of the piston rod. When the primary seal becomes worn, pressurized fluid can leak past it, and enter the water. However, the fluid instead enters a chamber between the primary and secondary seal. When this occurs, fluid accumulates in the chamber and builds pressure, which is sensed by a pressure transducer.

The pressure transducer signals a pump to inject an inert gel into the EVD seal. The EVD seal then expands and exerts higher contact pressure on the piston rod to contain the fluid that has leaked past the primary seal. If the transducer senses a reduction in pressure in the chamber, this would indicate that the EVD seal has worn. Therefore, more gel would be pumped into the seal to again increase contact pressure on the rod. The EVD Seal Ring substantially extends life of the sealing system, which reduces maintenance and downtime.

For more information, call Hunger Hydraulics USA at (419) 666-4510, or visit www.hunger-group.com.