Common Sense Maintenance: Who Cares?
Traveling on business is about as much fun as trying to fish using a cane pole with a safety pin as the hook. Such as getting up early in the morning to drive to the airport, to fly somewhere to meet a client with a drill problem, after having someone else that had installed a ton of new parts - that didn't correct his problem - work on his drill.
This may be the story of my life! Not that there's any thing wrong with this type of work, especially when you're compensated well for doing the work. I'll now try to explain just how this problem came about, and what was done to correct the problem.
Subject drill in question is a 1976 vintage track-mounted blast-hole rig, used mostly in small coal or stone quarries throughout the country. This drill is hydraulically operated, both propel and rotation, with a 400 cfm @ 100 psig compressor to clean out the holes.
The problem that started some months back was while moving the rig in reverse, the drill pipe started operating in reverse. As explained to this writer, the drill pipe unscrewed and was caught by mast guard a couple of times. As I studied the hydraulic schematic from the instruction book - which was a MUST - I found that the subject rig has two large-volume hydraulic pumps that are cable operated to control the volume output.
On the output, or pressure end, of the pumps there are two mounted aluminum directional blocks, each containing two spring poppets with small orifice valves that are pressure operated. The steel poppets have an o-ring seal encased in an aluminum bore. The major operation of these aluminum directional valves is to direct hydraulic oil flow to the propel motors when the tracks are moving, and to the head motor when rotation is called for. Hydraulic oil drain flow is controlled by a direct-acting electric solenoid, through numerous one-way check valves, then back to the hydraulic tank. My problem is internal leakage in one of the aluminum block valves.
I was a little apprehensive when disassembling these aluminum block valves - as the parts book did not give any internal dimensional specs - so I could tell how much internal wear was in the aluminum bore. Therefore, common sense and visual inspection would be all I would do, other than replace the o-ring on the steel poppet. Both internal springs looked in good shape. There was some wear to the bore, but no scoring. I cleaned everything and reassembled, replaced a couple of drain hoses, then started drill machine.
Everything worked fine until the hydraulic oil warmed up, then ever time I would switch the drain block solenoid from propel to drill, then back to propel, the drill pipe would rotate backwards.
I found out if I waited approximately one minute before moving the propel cable on the pump, oil drainage through the drain hose would allow oil flow to move out of the hose, and drill rotation/propel would operate normally.
Needless to say, I spent hours changing/repairing aluminum blocks, checking one-way valves, hoses, solenoid electric control valves, and then rechecking all components. By switching direction of the aluminum on the one pump, we reversed the directional rotation of the drill pipe, so if the drain problem appears, the drill pipe will turn forward as the track turns in a forward mode.
All other drill components are operating normally, so we know where our oil leakage is, and what is causing the drill problem. I phoned the drill manufacturer and found this subject system is no longer used, so lead time to purchase a new directional block valve is quite long - "months." So we phoned some friends looking for good used parts, which we found at half the price of the new one - guaranteed operational!
During my stay on the job site, we noticed we would lose air pressure from the compressor every now and then, then the air was gone. The compressor rotors did not rotate while turning the engine over - so we had a broken rotor shaft or the drive coupling was loose on the shaft. The customer had just spent money on compressor repair. We pulled compressor back away from the engine to find that the compressor drive coupling was loose on the shaft. Coupling taper-lock bushing was apparently never correctly tightened on the compressor drive shaft, thus allowing shaft key to become loose to the point that the key broke out the side of the compressor drive shaft.
We removed the compressor and had compressor drive shaft repaired - then installed new drive shaft bearing and reassembled compressor. When installing drive coupling on the repaired shaft, we torqued the allen screws to the proper torque in the new taper-lock bushing. We replaced the compressor on drill and checked out operation.
This hydraulic problem was a result of wear over a period of years of operation. As explained to us by the manufacturer, any time steel and aluminum is used, after years of operation, the aluminum has a tendency to washout or "wear." Rotation and propel are functions that are used continually, so after 20 some years of operation we have some leakage - our problem. Understanding the problem, we can overcome the problem. This is not poor maintenance, but a malfunction after years of productive operation. This rig I would recommend to anyone! Customer now understands his problem while waiting on the used repair valve, and the unit is in service!
Despite this reality, it's the people who shun normal maintenance programs who cry "foul" the loudest when they finally get stuck, as well as people who "shotgun" your repairs with a stream of unnecessary repair parts. It's a cinch the best place for drill service work will not be the lowest bidder.
When a crisis arises, be sure you have a good service provider. Most companies would walk on broken glass for a regular client because they know how important they are to a company's survival. This customer knows the importance of scheduled preventive maintenance. It is one of the easiest and least expensive ways to avoid an unscheduled breakdown. This customer has also allowed us an opportunity to get to know them -- but some people would say, "WHO CARES?"