Technologies change, products change, and even practices change over time. Isn't it ironic, with all we know about contamination and the effect it has on hydraulic systems, there hasn't been any significant changes in one of the key areas of ingression: human error?
The storage and handling of oils, transfer methods, cross-contamination from different oil types, and improper labeling of oils, all fall into this category. Additionally, systems must deal with inadequate air breathers, poor quality filter carts, lack of condition monitoring, and little effort to clean oils after catastrophic failures.
The old way of oil handling requires opening of oils and inserting foreign matter (hoses or hose wands) in order to gain access to oils. This is a primitive practice that allows no control over airborne contamination. In some applications, this is a very unsafe practice. It also does little to control ingression. In fact, it could easily be makingthe condition of the oil worse. Quick-acting couplings should be used for all oil handling. They provide simple, safe, and clean connections to the oil and require minimal time or tools. When properly used, they also prevent aeration of the oil, which is caused by pumping or pouring oils above the fluid level. Adding quick-acting couplings to most hydraulic systems is very simple, as shown in the table below.
Once a hydraulic reservoir is equipped with quick-acting couplings — one for adding oil and one for removing it — off-line filtration becomes a simple and effective resource. Adding, removing, or filtering the oil in the reservoir is all done through the quick-acting couplings. The result is no tools, less airborne contamination, and no more mess.
Air filtration is just as important as the oil filter to a hydraulic system. Most hydraulic breathers are 25-40 µm filters — not adequate filtration for most hydraulic systems. These breathers generally don't address any humidity or moisture that may be in the air. It will be very difficult to control contamination if the breather is allowing airborne particulate and moisture freely into the system.
Desiccant-style breathers are a good choice. They are made with pre-filters, desiccant, and secondary filters, which provide 2 µm filtration. Particulate, as well as moisture, is filtered with this style of breather.
The silica gel changes color when the breather needs to be replaced, which by itself is better than the old style of breathers, which are rarely changed.
There are several manufacturers of desiccant breathers and many sizes available. Features include small to very large flow rates, severe duty (including high humidity or vibration), miniature sizes, inline styles, and even fume and odor removal.
Filter carts should not sit in a corner collecting dust or used only to transfer oils. They can be very effective at off-line filtration (also known as kidney loop). With the addition of quick disconnects, rotating a filter cart from machine to machine becomes a very simple task and a valuable resource.
Off-line filtration is usually more effective than the filters on the hydraulic system, because the oil flow is lower, allowing the filters to retain more contamination.
The filter elements on a filter cart may be much finer, capturing more contamination and, in some cases, water. Depending on the application, off-line filtration can often be performed whether the hydraulic system is operating or when it is shut down. In the event of catastrophic failure (a pump, cylinder, or motor destroys itself and contaminates the system), what happens next will determine the life of the new replacement and the integrity of the entire system. Time usually is a factor when deciding to remove a failed component and install a replacement without first cleaning the oil. What time is actually saved, when the second, third, or fourth pumps fail?
Proper purging and flushing techniques vary dramatically from system to system. However there are some universal procedures:
- Immediately connect the portable filter cart and start the process of filtering the oil — even while decisions are being made on how to proceed next.
- Don't forget about the oil in the lines, valves, cylinders, and motors. It is best to clean the oil in the reservoir first and then run one function at a time, in short intervals, to cycle clean oil out into the system.
- Using a filter cart to purge the lines and components can sometimes-help speed the clean-up process, but safety might prevent it. Do not put hydraulic pressure or flow into a system that is being worked on, unless absolutely certain that it will be safe for personnel and equipment.
- What caused the failure? Rather than allowing it to happen again, inspect the failed component and investigate ways to prevent it in the future.
- Some hydraulic systems have purging connections, flushing connections, oil sampling ports, oil access ports (below the oil level), or desiccant-style filters. Some manufacturers provide an operator's manual with schematics and written procedures on purging and flushing. If you don't have a manual, ask for one.
Steven D. Anderson is manager of Y2K Fluid Power, Inc., Stacy, Minn.