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FREQUENTLY ASKED QUESTIONS
Dashpots exert forces because of pressure differences around the dashpot piston. The end of the piston where the rod attaches is always subjected to atmospheric pressure. The pressure on the other side of the piston can either be higher than atmospheric or a partial vacuum. In one direction of movement (push damping), an external force (gravity, springs, solenoids, etc) causes a mass (a slide, a lever arm, etc.) to start to move. With an air dashpot attached, the piston in the dashpot is forced to move towards the closed end of the cylinder, reducing the volume of air in the dashpot. Because the air can only escape through a tiny orifice, the pressure in the dashpot builds. The pressure will be higher if the external force is higher. In fact, the pressure will rise to the point where the dashpot force (pressure x piston area) equals the external force. In the other direction (pull damping), an external force (gravity, springs, solenoids, etc) causes a mass (a slide, a lever arm, etc.) to start to move. With an air dashpot attached, the piston in the dashpot is forced to move away from the closed end of the cylinder, increasing the volume of air in the dashpot. Because the air can only enter the volume through a tiny orifice, the pressure in the dashpot drops below atmospheric pressure. The pressure will be even lower if the piston moves faster and/or the orifice is smaller. Lower pressure means higher pressure differential and that means higher dashpot force (Force = pressure difference x piston area) .In fact, the pressure will drop to the point where the dashpot force (pressure x piston area) equals the external force. If a constant external force is applied to a mass, the dashpot force will equal the external force, causing a zero net force on the mass. This means that the acceleration on the mass is zero (a=F/m=0/m=0). The useful part of this a dashpot will cause the mass to move at a (nearly) constant velocity. And if the dashpot is adjustable, the velocity can be dialed in to the desired value.
Dashpots exert forces because of pressure differences around the dashpot piston. The end of the piston where the rod attaches is always subjected to atmospheric pressure. The pressure on the other side of the piston can either be higher than atmospheric or a partial vacuum. In one direction of movement (push damping), an external force (gravity, springs, solenoids, etc) causes a mass (a slide, a lever arm, etc.) to start to move. With an air dashpot attached, the piston in the dashpot is forced to move towards the closed end of the cylinder, reducing the volume of air in the dashpot. Because the air can only escape through a tiny orifice, the pressure in the dashpot builds. The pressure will be higher if the external force is higher. In fact, the pressure will rise to the point where the dashpot force (pressure x piston area) equals the external force. In the other direction (pull damping), an external force (gravity, springs, solenoids, etc) causes a mass (a slide, a lever arm, etc.) to start to move. With an air dashpot attached, the piston in the dashpot is forced to move away from the closed end of the cylinder, increasing the volume of air in the dashpot. Because the air can only enter the volume through a tiny orifice, the pressure in the dashpot drops below atmospheric pressure. The pressure will be even lower if the piston moves faster and/or the orifice is smaller. Lower pressure means higher pressure differential and that means higher dashpot force (Force = pressure difference x piston area) .In fact, the pressure will drop to the point where the dashpot force (pressure x piston area) equals the external force. If a constant external force is applied to a mass, the dashpot force will equal the external force, causing a zero net force on the mass. This means that the acceleration on the mass is zero (a=F/m=0/m=0). The useful part of this a dashpot will cause the mass to move at a (nearly) constant velocity. And if the dashpot is adjustable, the velocity can be dialed in to the desired value.
