The trend of making machines smaller and smaller by using smaller parts is the driving force behind the increasingly widely used rodless cylinders. The three main types of rodless cylinders are piston trunnion plate cylinder, steel wire cylinder and flexible wall cylinder. Most of them are designed for expansion, but some manufacturers use them in low-pressure hydraulic applications.

The design of the piston trunnion works like a traditional cylinder, but it does not move the load through the piston rod, but extends a bolt from one side of the piston and moves along the longitudinal groove of the cylinder. A driving trunnion is fixed at the end of the bolt, which moves directly with the movement of the piston.

In order to seal the groove between the piston and the trunnion, when the bolt passes through, several steel belts pushing each other are separated. The pistons have different widths to meet the bending time required by the load. The stroke of the piston trunnion can exceed 30 feet. Its options include piston switch, brake and bracket to support the load and ensure alignment.

All kinds of piston trunnion cylinders use permanent magnets in the piston to generate magnetic fields, and connect the piston and trunnion through the cylinder barrel. In this way, there is no need for longitudinal grooves on the cylinder barrel, so there is no need for any dynamic sealing ring. The initial resistance of the magnetic field can exceed 200 pounds.

There is a new type of rodless cylinder, which uses brakes for precise movement and position control. This kind of cylinder design, which was introduced not long ago, can realize accurate control proportional to hydraulic pressure by using simple inflation direction control.

In the steel wire cylinder, when the piston moves in the cylinder, the steel wires fixed at both ends of the piston can be pulled. The steel cable bypasses pulleys installed at both ends and is fixed on the frame. When the double-acting piston moves in one direction, the frame moves in the opposite direction due to the pulley.