Torch, can you explain deadheading to me? What could I have done differently?
Deadheading means that the flow does not return to the reservoir and there is no relief valve. The flow is completely cut off. The positive displacement hydraulic pump will increase pressure until something fails.
I'm not sure if you should have done anything differently, I'm trying to verify what you did first.
So looking at the banjo bolt that failed, I believe it was home made and drilled out. It was drilled and tapped at the bolt head as this is where my blade used to get it’s supply. Between the bolt not having much wall thickness and being tapped, it’s easy to see why it failed.
Yes, from the pictures, I have to agree that the banjo bolt may have been home made. And it is possible that it could fail at less than the designed working pressure of the system (as limited by the relief valve).
However, with an open centre system, the pressure should nominally be zero until and unless a spool valve is activated in the system. If I understand correctly, both the 3ph control and the FEL controls were all still in neutral when the bolt blew, correct? And the directional control valve (which is really just a by-pass valve) was closed -- ie: fully clockwise.
What should happen when the engine is started is:
Pump sends fluid to hydraulic block.
Directional valve is closed, forcing fluid to the FEL spool valves.
FEL spool valves are in neutral, so fluid is directed out PB port back to block.
Block sends fluid to 3ph spool valve.
3ph valve is in neutral, so it directs fluid back to the reservoir.
When the FEL control is operated, fluid no longer flows to the 3ph valve. The hitch cannot be raised while the FEL is being operated. Fluid flow is directed to one end of the appropriate FEL cylinder(s). Fluid from the *other* end of that/those cylinder(s) is forced back to the spool valve and returned to the reservoir via the "tank" line at the block.
When the 3ph valve is moved to the "raise" position, flow to the reservoir is cut off and directed to the 3ph lift cylinder. If the implement is too heavy, the pressure relief valve opens and dumps fluid into the reservoir instead. If the valve is in the lowering position, the fluid in the cylinder is dumped back into the reservoir.
SO: for that bolt to blow, something had to be preventing the fluid from returning to the reservoir. Either the 3ph was in the lift position and the implement was too heavy for the home-made bolt, or something is plugging up the 3ph spool valve circuit.
Again though with the directional valve clockwise on the block, should there even be pressure back at the 3 point?
As described above, the directional control valve does not affect pressure at the 3ph valve, it only diverts flow to the FEL. If it is closed, and if the FEL ports are plugged, then it would deadhead the piping between the pump and the block, but not the 3ph.