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I get several calls each year with problem descriptions something like this:
My PTE won't eject a tool for the first several hours of each day (or after a weekend shutdown); however, it suddenly begins working OK, and then its fine for the rest of the day.
or
I can't seem to change Speeds (or Feeds) for the first several hours of each day (or after a weekend shutdown); however, it suddenly begins working OK, and then its fine for the rest of the day.
or
I can't seem to change Back Gear Ranges for the first several hours of each day (or after a weekend shutdown); however, it suddenly begins working OK, and then its fine for the rest of the day.
Some people will also state that they hear an air leak while the machine is not working right that disappears when the machine begins working again. Some shops are too noisy to hear the air leak.
These are all symptoms of the same problem; 'Piston Seal' O-Rings inside an air cylinder that have rubbed against the I.D. of the cylinder body until they have 'flat spots' rubbed onto the O.D. of the O-Ring. They are frequently also found to be 'stiff and woody'.
Sometimes it's simply time to replace the O-Rings. Sometimes the problem is brought on by O-Rings being used instead of the original equipment 'Cup Seals' in a cylinder, which then don't fit properly into the grooves that were 'sized' for 'Cup Seals'. Then its time to locate 'Cup Seals' that fit the seal grooves and use them instead.
When the air pressure to the machine is shut completely off and the system has had time to 'bleed' to zero PSI, the O-Rings return to their 'natural' position with the flat side 'out'. When the air pressure is restored, they leak.
After enough time has elapsed and a small amount of air line lubricant has 'migrated' into the cylinder or the air pressure fluctuates a small amount, they will suddenly 'roll' slightly in the piston groove. This results in an unworn 'fresh' surface of the O-Ring rolling into contact with the I.D. of the cylinder body and the O-Ring seals properly. As long as air pressure remains on one side or the other of the piston, the O-Ring will stay in contact with the cylinder and seal well. As soon as the air pressure is completely removed and time passes, the O-Ring will return to its 'natural' state and the scene is again 'set' for tomorrow morning's problems.
You NEED to get those seals or O-Rings replaced promptly!
Seal failures of this type can result in the PTE eject cylinder 'creeping' forward until it touches the back end of the PTE mechanism inside the Spindle. This usually results in the need for expensive repairs and a considerable amount of downtime.
Seal failures of this type can result in gearing not being held into mesh with as-designed mechanical forces, resulting in the gearing being pushed out of mesh while rotating. This frequently results in broken gears.