Hydraulic cylinders fail by physical damage or by deterioration of their seals. Physical damage to a hydraulic cylinder is usually from an external source, such as another machine or a falling object. Damage can take the form of a bent rod or dented barrel, both of which could prevent the cylinder from stroking fully. Physical damage can also occur to the rod threads, breaking the cylinder away from the rod mount as a result. Most failures from physical damage require extensive repair work.
Physical damage can occur from excessive wear, especially as related to cylinder misalignment. If the rod end doesn’t move exactly parallel to the barrel in a perfect vector, damage to the barrel, rod, piston and bearing can occur. Thrust forces perpendicular to rod movement (also called side, or thrust load) will put excessive load against the rod and bearing, and the piston and barrel. Both types of wear result in damage requiring replacement of some or all of the parts discussed.
Cylinders can also fail when their seals give way, either slowly or catastrophically. Hydraulic cylinder seals wear slowly over time, and this cannot be prevented. However, when fluid condition is poor, seal wear is more rapid, such as when contamination or temperature is excessive. Heat can soften a hard seal, which makes them susceptible to damage from particle contamination. Particle contamination can also wear away at the piston, bearing, rod and barrel.
Catastrophic seal damage can occur when seals are extruded, such as the seals between the barrel and head or cap. Excessive rod stretch under pressure can pull the barrel away from the cap, leaving a gap where the seal can extrude, especially if the tie rods are long, as is the case with a long-stroke cylinder. Seals can also be damaged rapidly from uneven wear, such as with a corroded or misaligned rod.
It is best to ensure a cylinder is applied intelligently as to prevent issues related to column strength or misalignment. Also, once a cylinder is commissioned, it is best practice to keep the hydraulic fluid clean, cool and free from water. Contamination is still the primary cause of hydraulic failure, including cylinders. If a cylinder’s application and maintenance are respected, failure would rarely occur.
James Bergman says
I think the big takeaway here is that you should be aware of and maintain your hydraulic system. If keep your eye out for problems with the seals or contamination you should be fine. At least if there is a problem it should be a minor one, and hopefully only because you need to replace your seals.