Will gravity push my wort?

[Richlandbrewer]

I want to graduate to a counter-flow chiller (use an immersion chiller at present) and also incorporate a hop-back. Will gravity push it through these elements from the boiler given a reasonable head or do I have to go to a pump? (Not real good with hydraulic engineering

 

[bajaedition]

once a siphon is started it requires gravity to keep it going
naturally a 4 foot drop will be better than a 1 foot drop
the amt of drop will determine the amt of flow
I know of a commercial brewery that pumps the wort to a tank on the roof so that they can use gravity to pass through the counter flow plate wort chiller