Many types of equipment have hydraulic cylinders. A hydraulic cylinder is a piston that slides within a cylindrical body. A rod attached to the piston passes through a seal at the end of the cylindrical body and moves in and out to do useful work. The rods on most hydraulic cylinders are highly polished plated steel. They must be uniformly smooth to provide a good seal with the cylinder body.
A common problem with hydraulic cylinders is rust and pitting of the cylinder rods (Figure 1). If equipment that incorporates hydraulic cylinders is stored outside with the cylinder rods extended, the rods are exposed to weathering. Eventually, the rods will begin to show specks of rust that develop into pits. Once rusting and pitting occur, the rod will destroy the cylinder seal the next time it is activated. Once pitted, it is virtually impossible to restore a cylinder rod to an acceptably smooth condition through repolishing.
This problem of cylinder-rod pitting is most common with hydraulic cylinders on equipment that is both stored outside and seldom used or used only seasonally. If the hydraulic cylinders are operated every few days, the rods will always have a thin coating of oil that will provide protection, and rust will not start. Good examples are backhoes and bulldozers that are always stored out in the weather but are used almost daily.
The solution to this problem is to prevent rust and pitting. There are three ways to accomplish this, and it is possible to use more than one of these approaches simultaneously. The best way to avoid corrosion and pitting of the cylinder rods is to store the implement with the cylinder rods retracted. If the rods are retracted, the sensitive plated surface of the rod will be inside the cylinder, immersed in hydraulic fluid and thus fully protected. Unfortunately, it is not always possible to store equipment with the cylinders retracted. In some cases, the cylinders must be extended to unhitch an implement or must be extended to park the equipment. Another way to reduce the chance of corrosion is to park equipment with hydraulic cylinders inside a building where the cylinders are protected. This will significantly reduce corrosion and pitting, although humidity and condensation can still occur in some storage sheds. A final method of protecting cylinders is somewhat less effective but can be used in all situations. The exposed cylinder rods can be coated with heavy grease whenever the equipment will not be used for a few weeks or longer (Figure 2). The grease should be as heavy and sticky (tacky) as possible. Wheel bearing grease is better for this purpose than general chassis grease because it tends to be tackier. A heavy coat of grease will provide several months of protection, but for a machine used only one season a year, it may be necessary to renew the grease every three to four months.
Hydraulic cylinders can be ruined by pit rust if left extended and not protected. They are expensive to replace. You can protect your cylinders by (a) storing them in a retracted position, (b) storing them inside or (c) coating any exposed portion of the rods with heavy grease.