Your loader valve does not have power beyond - it has a tank port which is designed to serve two purposes:
- It provides a low pressure path direct to tank when the valve is in neutral. This is required in an open center system to unload the pump
- It provides a low pressure path direct to tank for exhaust oil coming out of a cylinder when a spool is shifted.
A high pressure carry over port (power beyond) has two different purposes:
- It provides a high pressure path to a down stream device like the 3pt. This path also unloads the pump when ALL of the valves in the sequence are in neutral.
- It provides a separate low pressure path direct to tank for the exhaust oil coming from the cylinders.
When you use the tank port for high pressure carry over a number of undesirable things happen:
- It subjects the inlet relief to back pressure from a down stream cylinder. This prevents the relief from opening and essentially eliminates it from the circuit.
- It puts the upstream cylinders in series with down stream cylinders, This creates a see-saw effect with the loads. It also subjects upstream cylinders to over pressurization via a hydraulic phenomenon called pressure intensification. It can result in rod end cylinder pressures high enough to blow out a gland nut or rupture a cylinder. Inlet pressure relief valves cannot protect from these pressures.
- Seals in the valve may not be able to withstand the reverse pressures and fail.
So that's the engineering story. You currently have a system that is violating those rules but operating without issues. If it were me I would either add the hoe to the circuit as is or replace the loader valve with one that has a power beyond circuit. I would avoid that tipping valve like the plague - it is the least desirable of the possible configurations.
Dan