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
process and instrumentation diagram (P&ID) symbol for a dashpot is .
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 coefficients 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.
Applications
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.
Consumer electronics often use dashpots where it is undesirable for a media access door or control panel to suddenly pop open when the door latch is released. The dashpot slows the sudden movement down into a steady and gentle movement until the access door has opened all the way under spring tension.
Dashpots are commonly used in dampers and shock absorbers. The hydraulic cylinder in an automobile shock absorber is a dashpot.
Viscoelasticity
Dashpots are used to form
models of
materials that exhibit viscoelastic or
elastoplastic behavior.
Maxwell and
Kelvin-Voigt models of
viscoelasticity use springs and dashpots in
series and parallel circuits respectively. Models containing dashpots add a viscous, time dependent, element to the behavior of solids allowing complex behaviors like
creep and stress relaxation to be modeled.
External links
References
