[fhhhstix]

I am thinking the clear line from the valves to the T then to the tank is the open return from valves or the loop which is oil that is not used and just passes through the valves as the standby pressure which doesn't have to be filtered. The black line from the valves to the filter and then to the T is the return oil from the cylinders which needs to be filtered before returning to tank. This is a good way to keep the flow going when the machine is at rest and not cause unnecessary heat build up. However if heat is not an issue a secondary filter to filter all of the return oil would not be a bad idea. If heat does become an issue an oil cooler can be added.

Travis