The negative pressure induced at and for some distance below the apex of the hairpin syphon you describe will cause fluid vaporization of the rising side column unless you pump it up to the top from below. But, yeah, about 130 PSI at the pump will get it to the top. Let's say you coul pump it to the top and over thus filling the downward 600 feet that has a valve on the bottom, valved off the bottom of the downflow side to let the water fill that side, and had a bleeder on top to let the air out and then closed the bleeder once both columns and the hairpin turn were filled with water. You'd have about 130 PSI at the bottom of the pump side and about 260 PSI on the downflow side. Then, turn the pump off and open the valve on the downflow side. What happens? You don't get no continuing syphon because from the hairpin down on both sides the water vapors off into a gas because the outflow down both sides due to gravity creates vacuum up at the top. Eventually, flow will stop when enough water vapors off on both sides to create a level of about I'd guess 35 or 40 feet or so of water on either side depending on temperature. How did I do?