Hydraulic question.

[Chainsaw]

I purchased a ym2000D with a home built loader on it. My question is in regards to the hydraulic system and pressure relief. I have a service manual en route but from what I can tell the hydraulic pump is a gear pump, meaning no by-pass. The factory pressure side line has been split, with the pressure going straight to the valve body for the loader. On this valve body is what appears to be a relief valve. Should I assume this is correct? Would the engine stall if it in fact did NOT have a relief valve? Could I test my theory by seeing if there is flow past valve body while running?

Thanks in advance.
Charlie.

[Aaron]

Loader valves will typically have a built in relief to protect the loader circuit (think of it like a fuse or circuit breaker) but it will not protect anything before or after the loader valve. If the loader cylinders stall out (maximum travel or lifting something too heavy) the relief valve bypasses and lets the oil through the relief valve and back to the tractor's reservoir.

If something prevents the fluid flow from making a complete circuit from the pump to the tank then you have a deadhead. The engine might stall if the pump was deadheaded but, more times than not, the pump shaft key shears or the pump shaft twists off or the pump body cracks open.