It varies a lot how much power an ESC can deliver to the RX. I would look up the spec on your ESC to see if it can power the RX plus three servos (for your valves). If you have the model number or product name, I can help you look it up.
If the ESC does not deliver enough power, then you can buy a separate SBEC/UBEC:
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Hobbywing 5V/6V 3A Switch-mode UBEC
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Turnigy 5A (8-26v) SBEC
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Hobbyking YEP 20A HV (2~12S) SBEC
Also you should not use both ESCs (or any two sources) to power the RX at the same time, as this could damage the ESC depending on how its BEC circuitry is build. Just use one ESC and remove the power line from the other, like this guy does:
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https://www.youtube.com/watch?v=clNvfjhMQ5w
If you end up using an external BEC, then remove the power lines from both ESCs.
Best regards,
Stein :-)