Hydraulic ram: great force on a small point

The term “hydraulic ram” is colloquial for hydraulic cylinder. The more precise definition describes the hydraulic ram as a device consisting exclusively of an extending hydraulic cylinder. It is required for applying a large force to a defined point.

Application of Hydraulic Rams

A classic application for a hydraulic ram is the bottle jack. It is a small and extremely compact yet powerful device that can lift even heavy vehicles. In addition, there are also universal hydraulic rams that can be used for any application. This device is also frequently used in general industry. They serve to lift heavy loads just enough until a wooden beam can be inserted underneath. Once a gap is present, a forklift or overhead crane can lift the load using straps or chains.

Design and Function of the Hydraulic Ram

A hydraulic ram is the smallest and most rudimentary version of a hydraulic system. It consists of:

• Housing with base
• Tank
• Closable check valve
• Master cylinder
• Lever mount
• Lever
• Slave cylinder, which is the actual hydraulic ram

Like all hydraulic systems, the hydraulic ram is completely filled with hydraulic oil. It is very important that no air is present in the system, as it significantly reduces or completely stops the device’s functionality. Air, unlike liquids, is compressible. A trapped air bubble would be compressed by the pressure and the desired pressure would be lost.

A long lever arm is inserted into the lever mount of the master cylinder. Through pumping movements, the small master cylinder presses small amounts of hydraulic fluid into the tank. The pressure is transmitted through the valve to the slave cylinder. With each stroke, the slave cylinder lifts slightly out of the housing. With sufficient strokes, the slave cylinder, or hydraulic ram, is fully extended. It has now developed its full force and height. It maintains this state until the check valve is opened again. Then the hydraulic fluid flows back and the system relaxes. This process is faster when the slave cylinder is lightly loaded. The check valves on hydraulic rams are typically equipped with a screw cap. This allows the return speed to be precisely controlled and prevents sudden dropping of the load.

Manual hydraulic rams can lift loads up to 10 tons, depending on type and design.

Hydraulic Ram in the Telescopic Cylinder Variant

A variant of the hydraulic ram with somewhat greater lifting height capacity is the telescopic cylinder. The central ram is surrounded by several sleeves. During pumping, the central main ram extends first. Once it reaches its upper end position, it pulls out the next inner sleeve via an internal stop. When this is extended, it pulls out the next one and so on. This allows interesting lifting heights to be achieved with very compact devices.

Handling a Bottle Jack

When using a bottle jack, it is very important to position the device exactly at the designated points on the vehicle. If the hydraulic ram is positioned at an arbitrary location, it will push a hole or large dent into the vehicle’s underbody. In the worst case, incorrect use of the hydraulic ram will bend the vehicle’s frame to such an extent that it results in a total economic loss.