Telescopic hydraulic cylinders, sometimes called multi-stage cylinders, are a type of linear actuator consisting of a series of tubular rods called sleeves. The sleeves (usually 2 to 6) sequentially decrease in diameter and are nested inside of each other.
Once hydraulic pressure is introduced to the cylinder, the largest sleeve is extended first. Once the largest sleeve has reached its maximum stroke, the next sleeve begins to extend. This process continues until the cylinder reaches its last stage, called the plunger.
There are three common types of telescopic cylinders: Single-acting, Double-acting, and a combination of single and double-acting.