Machinery Lubrication

Machinery Lubrication Jan Feb 2016

Machinery Lubrication magazine published by Noria Corporation

Issue link:

Contents of this Issue


Page 18 of 89

entering the manifold. Hoses can help absorb a pressure spike. You should never pipe rigid into a cylinder except in the case of a suspended or vertical load. If a velocity fuse is mounted at the cylinder port, then a hose can be used. The velocity fuse will close if the hose ruptures, preventing a free- falling load condition. The length of the hose generally should not exceed 3 to 4 feet. The only exception is if the cylinder or motor is mounted on a movable carriage. During operation, the length of the hose can change by nearly 10 percent. Hoses that are too long end up rubbing against another hose, beam, catwalk or machine part. Even if the initial system installation used the proper length, the hose may "magically" increase in length over several years. This usually occurs because maintenance personnel cut the hose a little longer each time they replace it. A hose that is too long will prematurely fail and cause a significant loss of oil from the reservoir. If hose rubbing cannot be avoided, a sleeve or protective cover should be installed. Many companies make sleeves that can be purchased by the reel. To avoid a considerable loss of oil from the reservoir, ensure the level switch is set just below the lowest level that the oil reaches when the cylinders are extended. Another cause of leaks is improper clamping. Many times the wrong type of clamp is used. Beam and conduit clamps are not designed to prevent lines from moving when oil flow rapidly starts and stops in the line. Clamps made specifi- cally for hydraulic pipes and tubing should be used and spaced approximately ever y 5 feet. A clamp should also be installed within 6 inches of where the pipe or tube terminates. Common materials used in clamps include santoprene, polypropylene or other types of ultra-high-molecular-weight polyethylene. Clamps should be tightened periodically, as the bolts that connect each half can vibrate loose over a period of time. To prevent the clamp base from loosening, it should be welded (not bolted) to the beam. Hydraulic pumps and motors often leak at the shaft seals. Shaft seals in single-direc- tion pumps are usually rated at 10 psi. Shaft seals in hydraulic motors that have external drain lines are generally rated from 25 to 50 psi. The drain lines of pumps and motors should be run directly back to the tank and not in with the system return line. Filters and coolers are frequently located in return lines and will create some back pres- sure as the oil returns to the reservoir. In addition, high-flow surges in the return line can cause pressures to exceed the rating of the shaft seals. HIGH TEMPERATURES Most hydraulic systems are designed to operate at 120 degrees F, with a maximum temperature of 140 degrees F. High oil temperatures can create a variety of problems within a system, with one of those being leakage. At high tempera- tures, O-rings tend to flatten out, become pitted and leak. The most common cause of heat in a hydraulic system is improper pressure settings. When a hydraulic problem Improper clamping is one of the main causes of oil leaks. COVER STORY Hoses that are too long often rub against another hose or machine part resulting in leakage. 14 January - February 2016 |

Articles in this issue

Links on this page

Archives of this issue

view archives of Machinery Lubrication - Machinery Lubrication Jan Feb 2016