Hydraulic oil: Keep it clean for peak performance

Call me old fashioned, but in plastics processing machinery, I like hydraulics. It’s not that there’s anything wrong with all-electric machines; on the contrary, the electric revolution has lowered operating costs and increased productivity across the industry. Hydraulics, however, aren’t going away soon, if ever, and this month’s column is about the “blood” of your system: hydraulic oil.

Most P/M programs specify oil change intervals and filter service, but in a system critical to resin throughput it’s surprising how many processors simply “fill and forget”.

Does your extruder or press operate on a three shift schedule? Do the hydraulics run continuously at 75 percent or higher than the system’s maximum flow and pressure? Is the working environment very hot and dirty? Any of these conditions suggest a P/M plan for “severe service”, including the oil. Filtration is key, with the size of the particles captured determining the effectiveness of a filter. How small is a trapped particle? The human eye can just detect a 40-micron speck, while a white blood cell is about 25 microns wide. Your hydraulic system filters should trap particles of 10 micron size, or smaller. If you can see or feel particulates in an oil sample, “stop the presses”!

How does the gunk get in there in the first place? Essentially, from any opening in the system, but mainly from the fill port. Filling from clean equipment is a no-brainer, but have you considered the cleanliness of the new oil? It’s not a clean as you might think, and since the crap you need to filter is too small for the human eye to distinguish, the product can look like Canadian Club, yet be poison to your seals, pumps and cylinders. A good solution is to install a 3-micron filter in the fill transfer pump, and avoid decanting oil from drums into pails or jugs for system filling.

Breathers are another entry point for contaminants. The ancient Van Dorn and Engel presses I learned on used breather screens which wouldn’t keep out flies, and if your system’s breather isn’t filtered properly, trouble is on the way. A ten-micron filter here is appropriate, but check it regularly, because a clogged breather can cause erratic operation and possibly air entrainment (“foaming”) of the system oil, which carries it’s own set of headaches.

Oil analysis is a great way to set oil and filter change intervals, but resist the temptation to sample with a dip tube in the fill spout. Install a sampling valve in the reservoir and drain off samples with the fill port closed. Believe it or not, a common “technique” for loading up hydraulic oil is to run the system with a low oil level. Hydraulic oils contain additives that trap microscopic dirt particles, but there is only so much of those detergent additives in each litre of oil. Dirt, however, seems to be in unlimited supply, and keeping the system full not only gives the lube a fighting chance, but reduces overall oil temperatures. There are literally hundreds of other ways to keep your system healthy, and every one will save a processor time and money. Clean oil, changed regularly, is cheap insurance.