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If your four-post or scissor lift is left in the down position for an extended period of time, there is a chance that rust may form in the Hydraulic Cylinder. How does this rust form and how can it be prevented? Let’s take a look. First, let’s review the parts that we will be discussing. The Hydraulic Cylinder is made up of the Cylinder Housing, a Piston Rod, a Piston, and a Breather Plug.
The Piston Rod goes in and out of the Cylinder Housing, and is what you see fully extended (when lift is down) or collapsed (when lift is fully raised). The Piston is attached to the end of the Piston Rod inside of the Cylinder Housing. The Piston is what has all the important seals on it and will never come out of the Cylinder Housing. The Breather Plug lets air in and out of the cylinder during lowering and raising of the lift. Four-post lift Hydraulic Cylinders are installed in a horizontal position under the runway that is nearest to the electric/hydraulic power unit. Scissor lift Hydraulic Cylinders are normally located between the lifting surfaces.
Next, we need to understand how the hydraulic cylinder in a four post lift or scissor lift operates. Pressurized oil from the power unit is pumped into the “front” part of the Cylinder Housing and forces the Piston Rod to move toward the “rear” of the Cylinder Housing. This pulls the Cable Block lifting system, which is attached to the end of the Piston Rod, toward the rear of the Cylinder Housing as well. The cable system raises the front and rear cross beams to which the ramps are attached, and the vehicle is raised. When the vehicle is being lowered, the Piston Rod moves in the opposite direction. As it moves out of the Cylinder Housing, it creates a pocket of air between the top of the Piston and the rear of the cylinder. When the runways reach the ground, the Piston Rod is fully extended from the Cylinder Housing and there is large pocket of air between the back of the cylinder and the top of the Piston. The air moves into this pocket through the Breather Plug located at the back of the cylinder when the Piston Rod moves forward. When the Piston Rod is forced back into the cylinder (with pressurized oil), the trapped air is forced out of the back of the cylinder again through the Breather Plug. The air that is drawn into the back of the cylinder through the Breather Plug, as the Piston Rod is extended, probably contains some moisture/humid air. Water may settle to the bottom of the cylinder and surface rust can occur after an extended period of time. Also, if the shop floor is cleaned periodically, the spraying water can enter the back of the cylinder through the Breather Plug.
Cylinder while lift is on the ground
Cylinder while lift is in the air
The easiest way to prevent accumulation of surface rust inside the cylinder is to operate your lift from the lowest to highest position at least once every two weeks. For those customers that store their vehicles in the raised position, there is little chance for cylinder surface rust to occur because the majority of the cylinder is full of hydraulic oil. Remember, the piston is fully retracted when the lift is in the air so there is only a small empty cylinder space between the top of the piston and the back of the cylinder. Another solution to preventing surface rust from occurring inside the cylinder is to remove the Breather Plug and install a “Return Line”. The Return Line (normally a small plastic hose) connects the back of the cylinder to the oil reservoir of the power unit and essentially seals the system from outside air and water.
This Return Line provides an escape route for air pressure and any other fluid that may be trapped between the top of the Piston and the back of the cylinder. If the Piston seals are torn and some oil is leaking around the seals, this oil is forced back into the power unit’s oil reservoir through the Return Line as the Piston moves to the back of the cylinder. Because the Return Line provides a seal at the back of the cylinder (no Breather Plug), humid air or sprayed water cannot be introduced into the cylinder. Most automotive scissor lifts and four post lifts do not have cylinder Return Lines. This is because automotive lift manufacturers “assume” that automotive lifts will be used each week so the Piston movement will not allow for accumulation of water. But atmospheric conditions could be working against you too. If your garage has high humidity levels then there could be moisture accumulation inside the oil reservoir of the power unit, even if the Return Line is connected. The moisture could be transferred to the cylinder, and it does not take very much moisture to produce surface rust inside the cylinder. Again, if the lift is operated frequently, the oil in the cylinder will prevent the rust from accumulating.
Above are pictures of surface rust on the cables and the cylinder. So the owner of this lift either has a garage that has high humidity and/or the operators wash the lift or the floor with the lift runways on the ground. Cable rust accumulation is a signal that your cylinder is at risk. A small amount of water will somehow find its way into the cylinder and the water will produce the rust if the lift runways stay on the floor for a long period of time. The easiest way to prevent the rust from occurring is to operate the lift several times per week so that the oil will coat the inside of the cylinder. Two post lifts (with vertical cylinders) do not normally have an issue with water collection inside the length of the cylinder.