Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/934530
16 | January - February 2018 | www . machinerylubrication.com HYDRAULICS If the oil level is low, determine where the leak is in the system. Leaks can be difficult to find. A press- roll hydraulic system at a paper mill in South Carolina had a continual problem with low oil levels, but the leak could not be found. e hydraulic unit was in the base- ment, and the piping ran up through the deck to the roll upstairs. To help find the leak, dye was added to the reservoir. An ultraviolet flashlight and goggles were then used to locate the leak, which was 30 feet in the air just below the second level. Sound Checks What does the pump sound like when it is operating normally? Vane pumps generally are quieter than piston and gear pumps. If the pump has a high-pitched whining sound, it most likely is cavitating. If it has a knocking sound, like marbles rattling around, then aeration is probably occurring. Cavitation Cavitation is the formation and collapse of air cavi- ties in the liquid. When the pump cannot get the total volume of oil it needs, cavitation occurs. Hydraulic oil contains approximately 9 percent dissolved air. When the pump does not receive adequate oil volume at its suction port, high vacuum pressure occurs. is dissolved air is pulled out of the oil on the suction side and then collapses or implodes on the pressure side. e implosions produce a very steady, high-pitched sound. As the air bubbles collapse, damage is caused inside the pump. Aeration Aeration is sometimes known as pseudo cavitation because air is entering the pump suction cavity. However, the causes of aeration are entirely different than that of cavitation. While cavitation pulls air out of the oil, aeration is the result of outside air entering the pump's suction line. A number of things can cause aeration, including an air leak in the suction line. is could be in the form of a loose connection, a cracked line or an improper fitting seal. One method of finding the leak is to squirt oil around the suction line fittings. e fluid will be momen- tarily drawn into the suction line, and the knocking sound inside the pump will stop for a short period of time once the air flow path is found. Last year I received a troubleshooting call from a paper mill in Wisconsin where one of the pressure- compensating pumps had been changed because it would not build and maintain pressure. When the new pump also did not build pressure, the manual valve in the outlet line was closed to isolate the pump from the system. Pressure still would not build up. Since there were no other valves in the outlet line, the issue had to be in the A pump with a cracked mounting bracket led to shaft misalignment and a worn seal. An arrow on the gear pump's housing indicates the direction of rotation. The compensator setting limits the maximum pressure at the outlet port of a variable displacement pump. Compensator Case Drain Crack in mounting bracket found here