"We are investigating an issue encountered by the maintenance team. When they shifted to a newer and better oil, the seals started to leak. It was determined that the oil in the cylinder was contaminated with metallic debris. Is the new oil the culprit or has it identified an issue in the piston cylinder?"

Based on the information provided, it appears the problem involves seals and piston cylinders of a hydraulic system or a large reciprocating compressor. The answer to the question is that both issues could be contributing to the leaking seals along with a list of other factors. In any case, root cause analysis should be performed to help determine the source of the problem.

To help mitigate the issue of seal leakage and select the best solution, you must first consider the type of seals being used. There are four basic seal types: static seals (gaskets and O-rings), dynamic rotating contact seals (lip seals and mechanical end-face seals), dynamic rotating non-contact seals (labyrinth seals), and dynamic reciprocating contact seals (piston rings and rod packings), which are the type of seals discussed here.

The purpose of a seal is to keep contaminants out while keeping lubricants in. Dynamic reciprocating seals attempt to seal against a sliding metal surface. With every stroke, oil will leave the system, and contaminants will be pulled back in, so determining the cause of a seal failure can often be difficult and even harder to eliminate.

There are many factors that can affect sealing including the lubricant, temperature, pressure, shaft speed and misalignment. Most conventional oil seals are designed for low-pressure applications. Seals must also be continuously lubricated with a lubricant that has the correct viscosity and that is compatible with the seal material. Both the temperature of the oil and the environment should be assessed, as the temperature range cannot exceed the range of the seal elastomer. In addition, if the shaft and bore are misaligned, it will cause wear to be centered on one side of the seal. However, when selecting a seal, shaft speed is one of the most important factors and governs all the other factors.  

The main reasons for seal failure and leakage are the result of incomplete procedures, lack of condition monitoring equipment, poor maintenance practices and cost-cutting by machine designers. Establishing a regularly scheduled oil analysis program, performing consistent maintenance on your system and ensuring correct sealing design with the proper lubricant will go a long way in your efforts to prevent leaking seals and machine failures.