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The Siphon Effect and Ponding Water

The Roof Sentinel Solar Roof Pump uses a pump to initiate the siphon effect. The Roof Sentinel’s patent pending “smart-chip” technology ensures that the siphon effect will continue.

The Siphon Effect

The simplest definition of the Siphon Effect is, atmospheric pressure pushes the liquid up and gravity pulls the liquid down. The siphon effect when pertaining to removing ponding water from a flat roof is quite simple. Water always flows from an area under higher pressure to an area of lower pressure. It also always flows from a high point to a low point, if allowed to do so, converting potential energy (height) into kinetic energy (flow). The water on the roof (under higher pressure) flows up into the pipe or hose (lower pressure area). Gravity will then allow the water to flow out the end of the pipe or hose.

Once the water flow has begun, the water will continue to flow draining the ponding water area off the flat roof, as long as it is undisturbed. The pressure difference between top and bottom of the down pipe keeps the water flowing. So the farther down your hose goes below the roof pump line ("drop") the faster the water will flow.

One of the biggest issues that can inhibit the siphon effect from draining ponding water from a flat roof is the introduction of air. If air is introduced anywhere in the chain the siphon effect will be inhibited or even stop. It is important that all connections are securely tightened to maintain the siphon.

The other main enemy to a siphon is the tubing itself. All tubes have inherent resistance per foot and adding things like kinks, bends, and collapses only add more resistance. Resistance reduces the effective pressure difference that pushes the water along the tube. Many times longer runs or small kinks can be countered with a taller drop to regain some of this pressure loss. A kink in a hose could inhibit or stop the siphon effect. PVC piping is highly recommended when using your Sentinel Solar Roof Pump. Each connection will be airtight and there is no chance of “kinking” or collapsing. Most garden hoses are designed to operate with higher than atmospheric pressure from water mains, and many may collapse under the weight of the atmosphere when used for the siphon operating at lower than atmospheric pressure.

Higher Altitudes and the Siphon Effect

One limit to the use of siphon to remove ponding water from a flat roof area is imposed by the height to which atmospheric pressure can lift liquid. At sea level with a magical lossless tube, atmospheric pressure can raise water to a height of about 30 feet (9 m). At higher altitudes the pressure is less, as is the height to which the water can be raised.

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