Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/756816
www.machinerylubrication.com | November - December 2016 | 21 high-capture-efficiency filter (ISO 16889) that matches the target cleanliness level of the system. Unless the oil is severely degraded, it is not necessary or even desirable to change it. After the reser voir is cleaned, run the oil through the filters while refilling. The entire system should then be flushed to clean the oil in the lines to the valves and actuators. System flushing is done by connecting the inlet and outlet lines of the cylinders and motors. If possible, electrically or manually actuate the directional valves to allow the fluid to recirculate through the piping. If this is not possible, bypass the directional valves by connecting the pressure and tank lines to the outlet lines of the actuators. Utilize the machine's existing pump to recirculate oil through the lines. Connect a high-velocity flushing unit so it recirculates oil in the reservoir through the filters during the flushing process. Allow the system to run for as long as possible. Verify the Reservoir Heater Setting Many times the heater is disconnected during the summertime or may have been omitted from the reservoir when it was initially built. Check the heater thermostat on the reservoir to confirm that it will turn on at a minimum of 70 degrees F. If the pump is mounted on top of the reservoir and the oil temperature drops below approximately 60 degrees F, then some cavitation of the pump may occur. Adjust Oil Level Switches Most reservoirs utilize two switch settings — warning and shutdown. The problem is that the difference between these two levels may be several hundred gallons of oil. By eliminating the warning switch and setting the shutdown at a higher level, oil loss will be minimal if a hose ruptures. Check the Breather Cap The breather cap is usually the most neglected component on the reservoir. Verify that the breather cap filter has a capture efficiency that matches the target fluid cleanliness. This is the first line of defense for contaminants entering the tank. Depending on the location, the breather cap may need to be changed a couple of times a year. Many breathers have a mechanical indicator that will provide a visual indication when the element is dirty. Other options include pressurizing the reservoir with an internal bladder or using a moisture-removal type of breather. Remember that money spent upgrading your breather cap is never wasted. Set High-temperature Switch Mineral oil will begin breaking down at 140 degrees F, but many systems will not shut down the unit until the oil temperature reaches 160 degrees F. Hydraulic systems are designed to operate below 140 degrees F. For every 15 degrees F that the oil increases above 140 degrees F, the life of the oil will be cut in half. If the oil temperature rises above that level, then a problem exists in the system. This could be caused by a cooler malfunction or excessive bypassing at the pump. Set the high-temperature switch at 140 degrees F to shut off the pump, preventing oil breakdown. Heat Exchanger Flushing and Cleaning In a shell-and-tube type of heat exchanger, oil flows over the tubes. Water flow is ported through the tubes in the opposite direction. The heat in the oil is transferred from the oil to the water. To achieve the most efficient heat transfer, the water flow should be 25 percent of the oil flow. The water flow can be controlled by manual valves, a water-modu - lating valve or an electrical solenoid valve. Circulating hot wash oil or light distillate through the tube or shell side can effectively remove sludge or similar soft deposits. Soft salt deposits may be washed out by circu - lating hot, fresh water. A mild alkaline solution such as Oakite or a 1.5-percent solu- tion of sodium hydroxide or nitric acid can be used. The tubes should be flushed in the opposite direction that the oil normally flows. If an air cooler is employed, verify that the cooler fan is turned on at approximately 120 degrees F and turned off at about 105 degrees F. Keep the fins clean so daylight can be seen through them. If necessary, combs should be utilized to straighten the fins on the unit. When cleaning the fins with an air hose, care should be taken so as not to damage them. Pump Testing On variable-volume pumps, check the flow out of the case drain line by porting the line into a container and timing it. This A flushing unit can be used to remove solid con- taminants and water from the oil. Oil purity is shown for a system before it was flushed (left) and then after one, four and 16 hours. This par- ticular system had high water content prior to flushing. By performing these tests, your systems will operate safer and at maximum efficiency while reducing unexpected downtime.