The general hydraulic jack is suitable for various lifting operations with low lifting heights. It mainly consists of an oil chamber, oil pump, oil reservoir, piston, rocking handle, and oil valve. During operation, by repeatedly rocking the handle, the manual oil pump continuously forces oil into the cylinder. As the oil pressure inside the cylinder increases, it pushes the piston and the load above it upward together. Opening the oil return valve allows the high-pressure oil in the cylinder to flow back into the oil reservoir, causing the load and the piston to descend together.

The specialized hydraulic jack is a dedicated tensioning tool used to apply tension to prestressed steel bars during the production of prestressed concrete components. Specialized hydraulic jacks are mostly double-acting. Common types include the through-hole type and the cone anchorage type.

The through-hole jack is suitable for tensioning steel bar bundles or wire bundles. It mainly consists of a tensioning cylinder, a compression cylinder, a compression piston, and a spring. Its characteristic is that there is a through-hole channel along the axis of the tensioning machine. After the steel bars (or wires) are inserted, they are anchored by the tool anchor at the rear.

During tensioning, the front and rear oil nozzles are opened, and oil is supplied from the rear nozzle to the tensioning working oil chamber, causing the tensioning cylinder to move backward. Since the cable is anchored by the tool anchor at the top of the jack, the jack pulls the steel cable longer through the tool.

When the steel cable is tensioned to the required length, the rear oil nozzle is closed, and oil is supplied from the front nozzle into the compression cylinder, causing the compression piston to extend forward and press against the anchor plug, forcing it into the anchor ring, thereby anchoring the steel cable. The rear oil nozzle is then opened, and oil continues to be supplied from the front nozzle. At this point, the tensioning cylinder moves forward, and the oil inside the cylinder flows back. Finally, the front oil nozzle is opened to allow the oil in the compression cylinder to flow back, and the compression piston returns to its original position due to the reset spring.