Extension springs are widely used in engineering due to their ability to exert a pulling force. You will find these springs in various everyday objects such as garage doors and trampolines. Despite their widespread use, the intricacies of extension spring selection and design are often overlooked. Failing to consider key factors, such as the precise tensile strength needed for a safety harness, could lead to a spring that may not extend correctly or withstand the necessary pressure. It is imperative to understand that selecting the right extension spring is not merely about size. The spring's tension must align with the application needs to ensure the system functions correctly and safely.


Extension springs factor into the performance of door hinges. These springs enable the automatic movement of swing doors by mobilizing stored energy. As a door opens, an extension spring expands, storing energy. This energy is discharged when the spring contracts, compelling the door to move towards a closed position. Thus, the spring serves as a mechanism that manipulates energy within the hinge architecture.

In the design of a door hinge mechanism incorporating an extension spring, it is necessary to consider the spring's load capacity and allowable extension. The spring properties should align with the door's mass and the energy required for its movement. For example, doors in commercial facilities, due to their substantial mass and wider range of motion, typically demand extension springs with an elevated load capacity and higher allowable extension.

Indeed, extension springs are frequently employed for their energy moderation functions in door hinge designs, but their usage is not all-encompassing. Doors intended to stay open, such as those in hospitals or elevator cabins, might not require extension springs, or at least not those with an elevated load capacity. As such, critical evaluation of the specific requirements and constraints of the door mechanism is indispensable in selecting a suitable extension spring.

Force Equilibrators

Extension springs contribute significantly to the operation of force equilibrators. These are devices that spread force evenly within a system or object. Their use spans across diverse settings such as industrial weighing scales and drawbridge mechanisms. The working principle of a force equilibrator revolves around the extension of the spring to store energy. This energy is subsequently released to counterbalance the weight or force, thus achieving balance.

Selecting an optimal extension spring is necessary. The tensile strength of the spring, defined as the maximum force it can resist before deformation, should correspond to the weight it is supposed to counterbalance. For example, a spring with insufficient tensile strength in a drawbridge lifting mechanism might cause inadequate force distribution, leading to possible system failure.

On the other hand, using a spring with high tensile strength in a system needing low balancing force, such as certain industrial scales, can result in a rigid system with decreased precision. For ideal performance of force equilibrators, the tensile strength of the spring should match the weight it is intended to counteract.

Garage Doors

Extension springs are often used in garage doors. Positioned on either side of the door, these springs work by offsetting the door's weight, and facilitating its movement. The operation principle is simple: when the garage door is lifted, the springs elongate and store potential energy. Once the door is released, this energy is used to aid in the gradual lowering of the door.

The choice and design of springs for a garage door depend on the specific weight and size of the door. A spring that lacks the appropriate strength for the door's weight might not provide sufficient counterforce, leading to functional issues and possibly, the door falling. On the other hand, a spring that is too strong could make the door difficult to open and potentially cause increased wear and tear on the door's parts.

For example, installing springs designed for a heavy door on a light door could cause problems. The springs, made to support a larger weight, would present an overpowered contraction force. This mismatched force could increase the wear on the door's parts or create safety concerns related to the door opening too forcefully.

Drawbar Springs

Drawbar springs belong to the extension spring mechanisms. They have a distinct feature - a stop mechanism - at both ends. This double-stop permits regulated extension of the spring. For instance, small trampolines use them to release stored energy in a predictable way, promoting safety and repetitive performance.

For cases demanding concise control of extension force, like in hopper loaders, drawbar springs are a common choice. The modification in tension directly affects the loading mechanism. In choosing drawbar springs for these uses, factors such as the necessary level of control, the force applied, and potential dangers from unexpected spring load releases, are to be considered.

Drawbar springs require considerable space due to their built-in stop mechanisms, making them larger than standard extension springs. Hence, in applications where space is limited and high extension control is not a primary need, a traditional extension spring can be a more suitable choice.


To wrap up, extension springs are integral parts within an array of systems, such as hinges, garage doors, or drawbar springs. Proper selection of an extension spring can enhance the function of these systems. As such, knowing the properties of extension springs and how they work in different contexts is crucial. This understanding supports sound engineering design. With adequate knowledge and proficiency, engineers can make accurate decisions regarding spring design and selection.