Edward_DiMaria: <font color="red"> Also why is the suction filter design a bad choice? I asked PT - "is 100% of the oil filtered and the answer was yes - I guess I am just confused by all this </font>
This to me is a very confusing topic. I don't think a suction filter is necessarily a bad choice. For one thing it ensures the oil entering the variable volume pump and wheel motor circuit just has been filtered. It does require faithful filter changes though. A lighter bypass valve spring is used and if one fails to change the filter before it clogs the bypass will open and dump the dirt in the filter straight into the pump. I've just added a vacuum guage to my filter to monitor filter restriction. PT's requiring 50 hour filter changes I suspect is very conservative and the vacuum gauge will give me a handle on whether less frequent filter changes are a possibility. Not to be lazy or save money but to limit the number of times the system is opened to possible contamination.
<font color="red">One other thing is that it would seem that we would be constantly talking about pump / wheel motor failure if there was a serious problem with filtration and to my knowledge I only recall hearing about one such failure (a wheel motor on an older machine - was it Davesick?
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I don't know that filtration is a problem. Much of the material I've been reading is aimed at industrial applications where down time as well as the cost of big systems is a major item. There is a trade-off between cleanliness and component life and a point of diminishing returns where the benefit of further cleanliness doesn't warrant the next expensive step. I don't know what PT uses as a design life for these machines, but it's probably reasonable to think most will never see a second engine. So there isn't much point building in a cleanliness level that would give hydraulic components a life expectancy beyond engine life.
I may have mislead the forum here a bit. I'm really not obsessing on this much beyond trying to gain a basic understanding of how it all works. I just put the filtered breather on because it seemed an easy no brainer as long as I had the system open. And the vacuum guage. The cost / benefit seemed obvious. Same with the change in fluids. I wouldn't have considered going through all the hassle of changing fluids in a full system.
Sedgewood,
This to me is a very confusing topic. I don't think a suction filter is necessarily a bad choice. For one thing it ensures the oil entering the variable volume pump and wheel motor circuit just has been filtered. It does require faithful filter changes though. A lighter bypass valve spring is used and if one fails to change the filter before it clogs the bypass will open and dump the dirt in the filter straight into the pump. I've just added a vacuum guage to my filter to monitor filter restriction. PT's requiring 50 hour filter changes I suspect is very conservative and the vacuum gauge will give me a handle on whether less frequent filter changes are a possibility. Not to be lazy or save money but to limit the number of times the system is opened to possible contamination.
<font color="red">One other thing is that it would seem that we would be constantly talking about pump / wheel motor failure if there was a serious problem with filtration and to my knowledge I only recall hearing about one such failure (a wheel motor on an older machine - was it Davesick?
</font>
I don't know that filtration is a problem. Much of the material I've been reading is aimed at industrial applications where down time as well as the cost of big systems is a major item. There is a trade-off between cleanliness and component life and a point of diminishing returns where the benefit of further cleanliness doesn't warrant the next expensive step. I don't know what PT uses as a design life for these machines, but it's probably reasonable to think most will never see a second engine. So there isn't much point building in a cleanliness level that would give hydraulic components a life expectancy beyond engine life.
I may have mislead the forum here a bit. I'm really not obsessing on this much beyond trying to gain a basic understanding of how it all works. I just put the filtered breather on because it seemed an easy no brainer as long as I had the system open. And the vacuum guage. The cost / benefit seemed obvious. Same with the change in fluids. I wouldn't have considered going through all the hassle of changing fluids in a full system.
Sedgewood,
