by Tom Nash, Applied Industrial Technologies
Published January/February 2006, Fluid Power Journal
Here’s a challenge for plant managers: Have your purchasing department total how much you’ve spent on hydraulic fluid in the last six months to a year. No matter what the total, odds are good it’s more than you should have spent. Barring the installation of a new hydraulic system, you should have little need for new hydraulic fluid.
Take a look at your entire facility and you’ll find that the cost of new hydraulic fluid is just the first of many extra unnecessary expenses. Here are a few ways to stop your systems – and profits – from leaking.
One of the more obvious signs of avoidable expenses is the presence of drip trays and oil-absorbing media under and around machinery. While sometimes necessary, theses should be viewed as a bandage, not a cure. The best-designed systems utilize connections with a rubber seal or o-ring. With the higher pressures and vibrations in hydraulic system, metal-to-metal seals will tend to leak as imperfections develop over time. New products on the market address leakage in JIC Seals made from molded products to eliminate these issues. If you must use a metal-to-metal seal, such as an NPT thread, use a thread sealant suitable for high pressures and leave the Teflon tape in the toolbox. Teflon tape was widely accepted in the past when internal clearances were larger. Now that components have become more efficient, small pieces of Teflon can migrate into the system if not installed properly and cause system failures.
When it comes to mechanical failure, most hydraulic systems fail due to particulate contamination or poor fluid condition. Temperature is a key component of keeping fluid in good condition. If you can hold your hand on the side of the reservoir during normal system operation, the temperature is probably within range. If you can only keep your hand on the reservoir for a few seconds due to the heat, your system is too hot and the chemical properties of the additives in the fluid are likely breaking down. If the system is hotter than it should be, ask yourself if the system always ran hot? If it has been getting warmer over the months and years, internal leakage in one or more components is turning inefficiency into heat. Those leakages need to be addressed. If, however, the system always ran hot, you may want to consider adding a heat exchanger. Offline cooling circuits can be added economically with minimal disruption to your operation. You may want to add a filter to that circuit as well for even more efficiency.
Excess heat notwithstanding running a too-cold hydraulic system can be costly too. Just as you let your car warm up before driving, so should you run a warm hydraulic system. If the power unit is in an unheated area of the plant, lower temperatures in colder months can increase the fluid’s viscosity, causing strain on the pumps’ suction sides during startup. Using an easily maintained heater can keep fluids at a minimum temperature that won’t affect system operation.
It is understandable that in today’s market, everyone is looking for that extra edge. A few extra cycles per minute can mean many dollars saved to the bottom line each day. But, while the attention of the many plant managers is focused on the capability of the components in the hydraulic system, often they look for a few more horsepower, a little extra pressure of flow to make things happen a little quicker. Quite often, they have overlooked the affects these extra capabilities have on the hydraulic fluid. Is the reservoir still sized large enough to allow air and particulates to separate from the fluid? Can the filters handle the added flow or do they go into bypass during high flow surges?
Take care of your fluids and they will reap dividends far exceeding the cost of the oil.