3000 flow control knob

As such, the flow control valve doesn't affect the flow of oil to the lift cylinder, and adjustment changes only the speed of lowering. Adjustment is important with a heavy implement like a scraper to prevent it from crashing down when the 3ph is in lower mode.

Few hitches have down-pressure. Weight and action of an implement is the only thing that holds down a hitch. They will float up over bumps etc, and flow control adjustment changes how fast an implement returns to its position level. As such, the adjustment is important for operations like mowing. Too slow a hitch will leave a long patch before it returns to it's position.

An operation like plowing with a draft control 3ph works similarly. The only difference with draft control is that the hitch gets a powered lift in response to an increase in load rather than a passive upward float. In plowing it's also important to adjust how fast a 3ph returns to it's position.

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Hard for me to say without knowing the tractor. On my own 1710, I'm usually forced to refer to exploded parts diagrams to come up an answer.

I will say that it's doubtful the flow control valve itself is leaking. However, the main possibilities are the packing around the knob itself, a plug for pressure testing or the plug that houses the valve. Most everything else is internal and would leak back to the sump rather than externally. I did refer to the valve as a check valve, but it's better to call it a safety valve, because there is something called a check valve in the 3ph control valve assembly. The part in the flow control valve is called a check ball.

The purpose of the safety valve is to protect the hitch against high load shocks when the 3ph is in neutral or lift mode. It's a ball valve and spring. A high load overcomes the spring and allows oil flow from the cylinder to the sump. These safety valves do fail, and I guess there'd be a chance of a leak in the return passage back to the sump. However, a safety valve failure usually would result in a 3ph that wouldn't lift a heavy load.

Faulty o-rings on the lift cylinder piston would allow oil to pass out of the cylinder under heavy loads and likely would produce an external leak.

Hope this helps. I know it's mostly theory.