The type of hydraulic cylinder in a system may not seem like the most important component in a piece of equipment or in a machine, but a poor quality or a poor match is going to cause problems with operation and safety.
This is true with all types of cylinders, including hydraulic lift cylinders, and it starts with understanding just what is needed for each component in the cylinder. In most applications and with many types of OEM equipment, having a custom cylinder designed just for the application will be a requirement.
The Components
There are several different components that are standard in all hydraulic lift cylinders, and there are some optional features that may be involved based on the specific use. There are also single and double acting cylinders, and these offer different features based on the use of the equipment.
A single acting hydraulic cylinder has one hydraulic line running from the pump to the bottom of the cylinder. When the pump is engaged pressurized hydraulic fluid flows down the line and into the cylinder bottom.
This pushes the piston up out of the top of the cylinder, moving the load up or pushing the load away. The operator controls the movement of the load based on the pressure supplied through the pump. To retract the piston and lower the load the pump is released, allowing gravity to push the fluid back through the hose to the pump.
The double action cylinder works the same for raising or extending the piston, but to provide more control during retraction, there is a separate hydraulic hose to the top of the cylinder. The pump pushes hydraulic fluid under pressure down this top hose, pushing the piston back down. As there is no pressure on the bottom hose, the fluid in the bottom returns to the pump
Specifications
The choice of the hydraulic lift cylinders for a specific job or use will be determined by the cylinder bore and the rod diameter. The longer the distance the piston extends, the bigger the bore and the rod diameter to avoid bending of the piston under load.
For longer extensions there is the option for a telescoping piston, but this requires additional care and engineering in design to maintain the strength of the piston even with a load under full extension.
There are also different types of cylinders to consider. Ram cylinders are most commonly used for a pulling action. Tie-rod cylinders are used in heavy capacity types of loads, while welded cylinders are most commonly used for medium to heavy loads where strength and durability will be critical factors.
