What are the common causes of hydraulic cylinder failure?
Side loading is a very common hydraulic cylinder failure, which is caused from the cylinder being misaligned which creates an unparalleled force on the piston rod. Hydraulic cylinder is a linear motion product that supposed to operate strictly back and forth as well as cylinder is not supposed to play a role of support or frame. Thus a side load of enough magnitude can result in cylinder tube scoring, hydraulic cylinder rod failure, rod guide bands, and most definitely hydraulic seals failure.
Contaminated fluid can cause premature rod seal failure. Abrasive particles in the fluid can damage the seals and the piston rod surface, airborne contamination can be drawn into a cylinder by a faulty rod wiper seal. Contamination occurs in numerous ways, the most common is drawn with hydraulic oil from the hydraulic pump that pushes oil of the oil reservoir. Since hydraulic oil travels in circuit among all hydraulic components, the damage from contamination can occur on any of the following parts: hydraulic cylinder, hydraulic gear pump, hydraulic control valve, check valves, etc. It is always recommended to have hydraulic oil filters in place for the most of hydraulic application.
Rough or scored rod
Rough surface on the hydraulic cylinder rod damages rod seals and reduces their life expectancy, resulting in the necessity for frequent replacement. Rod surface smoothness strictly depends on the quality of rod manufacturer. The proper procedure to manufacture hydraulic steel rod should look like this: rod grinding according to the desired tolerances, polishing to achieve smoothness, then applying chrome plating bath and the final stage would be the finishing polish. Unfortunately a lot of cylinder manufacturers nowadays do not polish rods prior to chrome plating due to the market demand for cheaper alternatives, even though it is vital. Industry standard tolerance for cylinder rod smoothness is f7 which is designed for accurate machines operated at moderate speeds and journal pressures.
With rough cylinder rod, equipment would be able to operate regardless, despite shorter life span of cylinder seals and need for more frequent maintenance. Scored or scratched cylinder rod on the other hand, cause rod seals damage immediately. Damaged rod pressure seal allows oil to pass through the gland and create external cylinder leakage. That’s why cylinder rod has to be installed and operated with care, to prevent mechanical damage. The other way to get around this problem is to use induction hardened (IH) rod instead. IH rod is resistible to scores and scratches, however it comes at a higher cost.
Hydraulic cylinder are often installed on the equipment operating in aggressive environment, such as salt water, salt air and acid conditions. The most common hydraulic cylinder failure under these conditions, is corrosion of steel components. Therefore corrosion can cause fluid contamination, permanent seals damage, and cylinder tightness. Suggested plating for the cylinder rod in the above listed environments would require nickel plating instead of chrome. Nickel plated hydraulic rods can withstand up to 1,000 hours in salt spray tests. The most superior option for the extreme conditions and expensive projects, is stainless steel nickel plated rod. It is definitely the best global solution however it bares proportional cost to it.
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