Hydraulic Cylinder Pressure Intensification

A typical single rod hydraulic cylinder, such as the one illustrated above, extends and retracts by applying hydraulic pressure to either the cap end (extend side) or rod end (retract side). As we can see, the two sides are unequal in area, as the rod side is reduced by the area that the rod displaces. The larger the rod diameter, the smaller the retract area. If the rod takes up two thirds of the area of the bore, the cylinder will have a 3:1 ratio. In other words, the extend side will have three times the area as the retract side. If the cylinder is supplied with the same pressure to each side, it will produce three times the force extending as it will retracting.

Now for the intense part. If the cylinder is connected to the circuit with quick disconnects, and the operator forgets to connect the coupling on the retract side, the oil will be trapped in the cylinder and will be intensified once pressure is applied to the extend side. In the example above where the ratio is 3:1, if 3000 PSI is applied to the extend side, it will result in the pressure rising to 9,000 PSI on the retract side, causing the cylinder to fail.

Also, if the retract port on the cylinder is blocked for any other reason and oil can not be evacuated, intensification will occur when the cylinder is extended.

Incorporating a pressure relief valve into the circuit is one method of protecting the cylinder from intensification failure. In most cases, a pressure relief valve can be integrated within the cylinder itself, reducing the overall footprint of the circuit and eliminating the cost of excess plumbing. This type of custom solution is best initiated during the design stage, as it may slightly change the dimension of the cylinder. Another example of how custom cylinders can offer both optimum performance and cost-effective solutions that are tailored to each application.