April Contamination Control Lubrication Lubrication Management & Technology

Lubrication Checkup: Hydraulic Leaks

EP Editorial Staff | April 22, 2014


By Dr. Lube, aka Ken Bannister


After running a newly purchased hydraulic system for several weeks, we’ve noticed that two of the cylinder seals are leaking. How can this happen in brand-new equipment?


You may have suffered “contamination effect.” Most hydraulic and lube-delivery systems incorporate tightly toleranced valves and pistons. Since these components are NOT dirt-tolerant, they can be easily damaged by solid particles. In your case, large solid particles (15 microns and above) have probably made their way through the system, scoring hydraulic valves and cylinder surfaces and causing an opening that allows lubricants to bypass the seal.

In new systems, solid-particle ingression can be built-in or ingested. The “built-in” type refers to burrs, swarf, filings, dust, fibers and other types of particles left by the manufacturer in uncleaned reservoirs and lines. Once lubricant is added and new equipment starts up for the first time, debris cycles through the system and damage occurs—before any work is done.

If, however, your unit was cleaned prior to startup, its leaks are probably associated with self-introduced “ingested” debris—i.e., raw material and airborne contaminants that can enter a reservoir if a breather or fill-cap is inadvertently left off, or through dirty lubricants and/or dirty transfer equipment.


To correct your leaking system, use detection dye and black light to determine and mark the location of leaks. Then, evacuate the lubricant from the system and mechanically clean all lines and hoses with a projectile cleaning system (i.e., a pneumatic gun that shoots a cleaning wad through the open line or hose to clean sidewalls of all debris). The reservoir must then be thoroughly cleansed inside and out.

Replace all pressure/return/bypass filters and clean or replace the suction filter. Assess spool valves and piston rods for score damage and the need to repair or replace them, and insert new seals. Make sure all hydraulic-lubricant-transfer equipment is cleaned prior to filling the reservoir with pre-filtered oil. Once the fill-cap and breather are checked in place, you’re ready to restart your system.

If your system failure was caused by built-in debris, you may have a warranty claim: Be sure to discuss the issue with the manufacturer before performing any of the above work. Save damaged parts for training purposes!

Regarding future purchases, ask to be present for any system cleaning and testing prior to startup. Good Luck! MT&AP

Dr. Lube, aka Contributing Editor Ken Bannister, is, among other things, a Lubrication Management Specialist and author of Lubrication for Industry and the Lubrication Section of the 28th Edition Machinery’s Handbook (both from Industrial Press). Email your lubrication checkup and training questions to: kbannister@engtechindustries.com; or telephone: (519) 469-9173.




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