Dashpot

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A dashpot is a mechanical device, a damper which resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly used in conjunction with a spring (which acts to resist displacement). The diagram symbol for a dashpot is: .

[edit] Types

Two common types of dashpots exist - linear and rotary. Linear dashpots are generally specified by stroke (amount of linear displacement) and damping coefficient (force per velocity). Rotary dashpots will have damping coeffients in torque per angular velocity.

A less common type of dashpot is an eddy current damper, which uses a large magnet inside of a tube constructed out of a non-magnetic but conducting material (such as aluminum or copper). Like a common viscous damper, the eddy current damper produces a resistive force proportional to velocity.

[edit] Applications

dashpot in a Stromberg carburetor

A dashpot is a common component in a door closer to prevent it from slamming shut. A spring applies force to close the door and the dashpot, implemented by requiring fluid to flow through a narrow channel between reservoirs (often with a size adjustable by a screw), slows down the motion of the door.

Dashpots are commonly used in dampers and shock absorbers. The hydraulic cylinder in an automobile shock absorber is a dashpot.