Spring index lower limit: DASMA standard 102-2004 provides a lower limit of 6 for the spring index, which is symbol C in our formulas above (section 9.3). Other interesting items in this standard include an upper limit for how much the door sags when raised (no more than 1/120 of its width, section 9.2.1), that each of the two bottom brackets should sustain twice the door assembly's weight (section 9.2.2) for a total safety factor of about 4, and that the lift cables should provide a safety factor of 5.
Now 13 pounds of force must be respected when backed by many hundreds of foot-pounds of stored energy, waiting to be released. Holding this torque is equivalent to stalling a 3 horsepower DC motor. But holding and turning these handles does not require extraordinary human strength. Note that this maximum tangential force depends only on the weight of the door, and the radius of the drums, and is divided by the number of springs (some designs have only one longer spring, as mine did originally, instead of two shorter ones). Higher or lower lift distances imply more or less turns to wind the spring (and thus a different spring geometry), but not more force on each turn.
Drive type Garage door openers work in a variety of ways. A chain-drive model raises and lowers doors with a metal chain — these tend to be inexpensive and able to handle heavier doors, but they’re loud. A belt-drive opener uses a belt and operates more smoothly and quietly. Screw-drive openers, which lift doors with a threaded steel rod, are also quiet and don’t require much maintenance. Finally, a direct-drive opener operates as a single unit — the whole contraption moves to lift the door. These tend to be the quietest, smoothest mechanisms available.
Plus, we carry all the best and high quality products from the top garage door brands. Whatever is your requirement or need for your garage door, we are sure to have them in our comprehensive inventory. We have garage doors in different styles, materials, colors, designs and what-have-you. If you still cannot find what you are looking for, we can always source them out for you.
Security Lights: Most newer garage door openers have at least two bright light bulbs, as well as lights activated by motion. On the other hand, some older or cheaper openers are limited to a single light bulb. This doesn't help much with a garage darkened by shadows, leaving you unsure if the rustling in the corner is your cat … or a skunk that snuck into the garage.
You might genuinely need some extra parts when you thought you simply needed a broken spring replaced, and a good serviceman will perform a simple inspection to identify such parts. Nor is it unreasonable for a business to charge separately for a service call versus repair work actually performed. But the best protection for you as a buyer, being somewhat at the mercy of whomever you decide to bring on site, is to understand what is being done, and ask intelligently for a clear explanation or demonstration of why extra parts are required.