Speed of a falling door:: Physics tells us that the transit time of a free-falling body is sqrt(2x/g), where x is the length of the fall and g is the acceleration due to gravity (32.2 ft/sec^2). If this typical 150 lb door were to fall an equivalent of 3.75 feet, this falling time would be sqrt(2*3.75/32.2) = 0.48 seconds (480 milliseconds). The terminal velocity is gt, or 0.48 seconds * 32.2 ft/sec^2 = 15.5 ft/sec = 10.6 mph.
The Chamberlain Whisper Drive takes control to a higher level than other models with its door and light automation features. The internal control panel has a sensor for motion-activated lighting. In addition, door closing can be instant or set automatically for 1, 5 or 10 minutes. We give this feature a top-notch rating because, should you forget to close your door, your garage will secure itself.
Extension spring systems should always be restrained by a safety cable that runs through the middle of the spring, tying off to a solid point at the rear and front of the horizontal door track. Extension springs represent a hazard to bystanders when a spring, pulley, or cable breaks under tension. Metal parts from extension spring systems can suddenly be launched.
Here are the new replacement springs I ordered from a distributor, which I found using a Google search for "garage door supply" (search that phrase now). You certainly won't find these at Home Depot or Lowe's (although last I checked Lowe's does carry the less daunting extension spring replacements). I also have a list of some suppliers at the end of this page.
A standard residential door raises 7.5 feet, but since the door goes horizontal this is equivalent to raising the whole door for half that distance, or about 3.75 feet. So if the door weighs, say, 150 lbs, then the energy supplied by the springs is 3.75 * 150, or about 563 foot-pounds. This is like throwing a 50-lb sack of cement up a 11-foot flight of stairs. Or catching a 50-lb sack of cement dropped from 11 feet up.
There are such a large number of varied issues with carport entryway repair. Stray pieces will be the dependable wind up being free with time. A bothering sound when you work the entryway opener is a marker that there is an isolated wandering part. Prior to an opening, it ensures that that the power supply is standing alone from the framework, or else you may hurt yourself. Now and again the gaps for stray pieces can expand the extent of to a degree that you can’t fix them. In such a case, you can employ wood fillers or perhaps regular wood pieces to top them off.

Garage Door Repair Co