In its basic form, a flow control valve can be just and orifice.
In the top symbol, we see a flow control valve with a variable area adjuster shown by the cross arrow through it. Note also how the restriction is shown as two curves. In the lower symbol, the restrictor is shown as two sharp corners. Sharpe edges indicate a higher quality flow control valve with a higher degree of viscosity independence e.g. more stable flow with temperature changes.
The middle symbol also shows a pressure compensated valve because of the arrowhead on the line through the valve. The short T-end to the angled line through the orifice indicates a fixed setting rather than an adjustable setting. The third line shows that the excess flow is diverted into a third line.
Learn more about flow control valves