"An adjustable, hydraulic ram that smoothly slows and stops a moving object." (Definition courtesy JR Clancy's Glossary). Often used on Fire Curtains to slow the curtain to a relatively gentle stop during the last ten or so feet of descent.
Linear dashpots are functionally and structurally similar to double-acting hydraulic rams, with the upper chamber plumbed to the lower chamber through a check valve in parallel with an adjustable restrictor. The check valve allows relatively unrestricted motion in one direction which allows the dashpot to be easily reset, while the adjustable restrictor provides resistance to the flow of fluid to provide a braking load that is directly proportional to velocity. In other words, as used in a fire curtain system the dashpot provides more braking force at the beginning of its stroke when the load is moving faster, and less braking force as the load slows.