Our hydraulics team was recently contacted by a welding contractor at Lauderdale Marine Center to remove a PTO pump off a 150’ Palmer Johnson’s main hydraulics system so they could gain access to the ship to perform their work. What started as a fairly routine job quickly turned into something much more. The splines on the unit had seized, taking what would have been roughly a half day of work to several days.
Typically, we would construct an A-frame rigging to hoist the PTO pump out of the boat but in this case, we were forced to cut the unit apart and remove it in pieces. Because of this, the ship now requires a whole new replacement unit. Once it was uncovered that the first PTO pump could not be removed using standard procedures, the ship’s engineer had us remove the second pump to check the splines. Fortunately, the second unit did not have the same problem.
We highly recommend removing, refurbishing and re-installing these PTO pumps every three years or so for routine maintenance. Just like the top-end of a windlass which should be removed, cleaned and re-installed with new grease ever couple of years; PTO pumps need to be serviced to ensure that they do not experience these types of problems with seizing.
A proactive approach to maintaining these critical components of your hydraulics systems will pay big dividends and potentially save thousands of dollars in the end.
Removal of the pump was extremely difficult due to corrosion between the pump shaft splines and the coupling. The corrosion was due to exposure to saltwater and normal wear and tear. In the marine business, the internal and external splines that make up the coupling usually reside on different pieces of equipment supplied by different vendors. The SAE Involute spline standards are the most commonly used for shaft diameters between ½” and 2”. The tolerances are loose enough to insure multi-vendor interchangeability while still providing torque transmission significantly higher than a keyed coupling. The tight fit avoids any lash and excessive wear in the splines over the life of the pump. There are many benefits in using spline shafts in place of a keyed shaft for this application. The spline connection offers a load distribution which is equal along the teeth sides enabling both to rotate together. Consequently, this load produces a longer fatigue life compared to the keyway drive.