There are 2 most common types of springs: Torsion and extension with torsion as most used for double doors. The purpose of having springs system is to eliminate the weight of the door so that the door will be able to be raised up and lowered down by hand or by automatic motor. When a spring is broken the door will feel a lot heavier if you try to lift by hand. The motor also will sense that the weight is too high and it won’t be able to lift it more than 6 inches of the ground- that is to prevent damage to the gear and other parts in the motor.
Properly adjusted springs should give you the ability to lift the door manually and stop it mid-way without falling down heavy or going up too hard. There Is a range of spring sizes and lengths and the reason for it is simply because doors weight can vary depends on materials, insulation, windows etc. We carry all standard size springs that are most commonly used in the Denver area so we can complete the spring replacement in the first visit to save customers time.