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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 process and instrumentation diagram (P&ID) symbol for a dashpot is .
common types of dashpots exist - linear and rotary.
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Encyclopedia
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.
Relays can be made to have a long delay by utilizing a piston filled with fluid that is allowed to escape slowly.
Dashpot arrangement is also used on the Primary suspension of the Indian Railway Coaches in the ICF design. Here the bogie of the coach has four axle boxes. Each Axle box has a lower spring seat and a axle guide arrangement welded to the frame of the bogie. The Lower spring seat which is filled with dashpot oil acts as a cylinder and axle guide acts as piston. The axle guide arrangement has guide bush with a packing ring which acts as a piston ring .This arrangement helps in dampening the vibrations to the carriage during running of the trains.
Viscoelasticity
Dashpots are used to form models of materials that exhibit viscoelastic or elastoplastic behavior, such as muscle tissue. 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
- by Julius O. Smith III of Stanford University's CCRMA
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