Hartford loops are also used in spas to keep water from seeping in the air lines. Otherwise, too much water would get in the plumbing and they wouldn’t be able to aerate.
On the Plus Side. Gravity can work for us, too. In a pool system, builders harness the force through gravity-fed plumbing. With no pressure, water is allowed to flow naturally through the plumbing. Gravity-feed lines never run a complete pool system, but they can perform certain tasks:
Equalizing two bodies of water. Sometimes builders want to create the illusion that two bodies of water are one. For instance, a moat in front of the house may appear to run under a walkway when, actually, the two sides are separated. Builders tie them together with an equalizer line to make sure the basins are level with each other. Sharing a circulation system. A similar setup can be used between the main pool and a separate spa or kiddie pool. Now the two can run off the same equipment. In this case, the plumbing is placed directly under the spa’s coping so water can flow back to the pool and, eventually, to a shared filtration system. In perimeter overflow pools. These vessels are also known as total-perimeter vanishing-edge, or rim-flow, pools. Water spills over the bond beam on all sides into a gutter. Usually the gutter leads to a separate holding tank that stores the extra water needed to push over the walls. On its route from the gutter to the surge tank, the water should move through gravity-fed lines. In these applications, gravity-fed lines must be pitched at an angle and sized larger than their pressurized counterparts. The larger size compensates for the fact that the pipe should never be more than one-third full. If gravity lines fill up, it will create suction, and the water will back up, forcing air out of the pipe. The siphon this creates will cause slurping noises.
Reduce entrapment hazards. Research is being done for ways to reduce suction entrapment. One option being explored includes allowing water to leave through the drain via gravity into a separate pot or tank. A pump would then pull water from the tank and back through the circulation system. This method removes suction from direct contact with pool users.
