Lube Mate,
I do not totally agree with some of the answers concerning in line filtration. I believe the filter has to perform based on your application. I have used inline filtration down to 3 microns with great success. This level of filtration is needed for protection when using servo and proportional valves. During our use,we did not experience blockage problems. We did, however, use this inline filtration in addition to a kidney loop system. I am familiar with the system you are using, having worked in a quarry. Most of the problems you are probably experiencing are coming from ingression of contaminants. The contamination will come from your system breather, leaks, or system maintenance. I would reccommend the following for your greatest chance of success. First, you need to correct any leaks in the system. Tighten hoses, fitting, repair seals, etc. Next, install dessicant breathers on your reservoir. Third, look at putting a kidney loop on the system which would incorporate a heat exchanger and a water filter. The water filter will be needed due to the large temperature changes your system probably sees. I would also look at possible inline filtration for critical components. The level of filtration will depend on what type of valves and components are being used. Pall and Parker make some very good pressure filters that can be used in these applications and their reps will be more than happy to help you. Finally, you need to educate your people on what an acceptable level of cleanliness is. Most of the average mechanics working on systems do not understand the level of cleanliness needed in hydraulic systems. I hope this helps. Good luck.