Earlier this month, the Washington State Department of Transportation held the grand opening of the Governor Albert D. Rosellini Bridge replacement, also known as the Evergreen Point Floating Bridge and more commonly the SR (State Route) 520 Bridge.
The unveiling of any new bridge in a busy urban corridor is an impressive enough event to begin with, but the SR 520 has the further distinction of being the world’s longest floating bridge. And it wouldn’t be possible without a simple float switch to keep things in check.
What is a Floating Bridge? How Does it Work?
Sometimes referred to as a “pontoon bridge,” a floating bridge uses a series of flat, floating pontoon boats as a base to lay a bridge across. Usually floating bridges are temporary, useful in wartime or for emergency situations like floods. In some cases, as with the SR 520 Bridge, they can also be used as a permanent solution in situations where normal suspension bridges are impractical.
But where temporary floating bridges might rely on wooden floats for ease and speed of set-up, a permanent floating bridge like the SR 520 needs something a little more robust. Each of the bridges 21 longitudinal pontoons is 28 feet tall, 75 feet wide, and a whopping 360 feet across. Each 11,000 ton float is secured by dozens of anchors that themselves weigh dozens of tons. In addition to all this, the bridge boasts two cross pontoons and 54 additional pontoons for supplemental stability.
All this makes the new SR 520 Bridge far more safe and stable than its predecessor, notably in terms of earthquake and wind resistance.
Enter the Float Switch
Each of the SR 520’s pontoon includes a sophisticated topside control room, as well as a large and empty lower gallery two floors below. While the high-tech control room will probably garner the most attention, something a little more modest in size an appearance is working just as hard on the float’s bottom half.
A simple vertical float switch, not at all unlike SMF Fluid Controls’ FS12 miniature plastic float switch, is suspended 3 inches from the bottom of the lower gallery. In the event of a breach, an alarm will activate to let workers know which pontoon is taking on water, and to start pumping from a line controlled in the main control room. It goes without saying that any prolonged leak in even one of the SR 520’s pontoons would be disastrous. In the absence of such a simple alarm system, the possibilities for catastrophic failure would multiply to an unacceptable extent.
Float Switches from SMD Fluid Controls
But you don’t need to be building a record-breaking bridge to need a float switch. Float switches are used for applications in aerospace, HVAC, food and beverage processing, industrial manufacturing, wastewater treatment, medical equipment, and more.