Views: 10 Author: Brian Wu Publish Time: 2020-12-05 Origin: Jiangmen Great Fluid Seals Co., Ltd
TYPES OF HYDRAULIC CYLINDER
SINGLE ACTING HYDRAULIC CYLINDERS
Single acting cylinders work where either a push or a pull force is required, so the hydraulic fluid only acts on one side of the piston rod. Another force (such as gravity, the weight of the load or a spring), operates the cylinder in the other direction.
DOUBLE ACTING HYDRAULIC CYLINDERS
A double acting cylinder forces the piston rod into both the advance and retract directions by hydraulic operation.
Telescopic cylinders use a cylinder within a cylinder to increase the distance that can be lifted in one stroke. The stroke is the amount of lift that a cylinder is capable of in one movement. Typically used in machines such as tipping trucks, they can also be used within any fabrication that requires an increase in the stroke (the amount of movement that the cylinder generates), without increasing the space that is required for the envelope. Telescopic cylinders can be double or single acting. One potential issue is that a standard telescopic cylinder can have sudden changes in speed, due to changes in volume size for the different cylinder stages. However, specialist engineering can produce dual acting telescopic cylinders that can move at a constant speed.
Jack cylinders are mobile cylinders that come in a range of sizes. Usually one hand pump can be used with multiple cylinder sizes, meaning that companies can select the best cylinder size for each job. Jack cylinders don’t have a mount – they are generally simply used on the floor. Typical lifting weights are 5 tonnes, 10 tonnes, 20 and 50 tonnes. The standard sizing and mobile nature of jack cylinders makes them ideal tools to hire if not needed regularly. In many cases, instead of owning a hydraulic cylinder companies will rent jack cylinders when required for a specific job.
HOW DOES A HYDRAULIC CYLINDER WORK?
Pascal’s law shows that:
Force = Pressure x Area
Within a hydraulic system, the pressure is given by a HPU (Hydraulic Pumping Unit). The area is the size of the hydraulic piston. These two components determine the force that can be exerted by the cylinder.
Therefore, the weight that can be pushed or lifted by a hydraulic cylinder is equal to the pressure provided by the pump multiplied by the size of cylinder rod.
Most pumps have a standard range; usually from 3000 psi to 10,000 psi (210 to 690 Bar). The average tends to be at the lower end of the range; around 210 Bar. A pump can lift an infinite amount of weight, depending on how big the cylinder is. Increasing the PSI may require adjusting the seals, valves and cylinder design to cope with increased pressure.
The pump also dictates the speed at which the cylinder can operate, as it provides hydraulic fluid at the necessary flow rate.
HOW TO SIZE A CYLINDER
Hydraulic cylinder designers need to think about the scale and size of a hydraulic cylinder. A cylinder that has an excessive reach poses the risk of buckling – meaning that the rod and barrel have to be engineered to be larger. However, this increase in area would have a bigger force, potentially over engineering the fabrication and making it heavier.