Sunday, May 18, 2008

Hydraulic Machinery

Hydraulic machinery are machines and tools that use fluid power to do the work. Almost all types of heavy equipment is a common example. With this type of equipment, hydraulic fluid is pumped to a high pressure then transmitted through the machine to various actuators.

The hydraulic pumps are powered by engines or electric motors. The pressurized fluid is controlled by the operator with control valves and then distributed through hoses and tubes.

The increasing popularity of hydraulic machinery is due to the large amount of power that is transferred through small tubes and flexible hoses. The high power density and wide array of actuators can make use of this power.

Hydraulic power

The theory that lies behind hydraulic equipment is fluid pressure.

1. A force that acts on a small area can create a bigger force by acting on a larger area by hydrostatic pressure.

2. A large amount of energy can be carried by a small flow of highly pressurized fluid.


A hydraulic pump will supply the fluid to the components in the system. Pressure in the system will develop in reaction to the load. Pumps have a power density of around ten times greater than an electric motor. The pumps are powered by an electric motor or engine, which is connected through gears, belts, or a flexible elastomeric coupling to reduce the heavy vibration.

The common types of hydraulic pumps for hydraulic machinery applications include:

1. Gear pump - the gear pump is cheap, durable, and simple. It is less efficient, simply because it is constant displacement and suitable for pressures that are below 3,000 psi.

2. Vane pump - vane pumps are cheap, simple, and reliable. They are good pumps for higher flow low pressure output.

Hoses and tubes

A hydraulic hose is graded by pressure, temperature, and compatibility of fluid. A rubber interior is surrounded by multiple layers of woven wire and rubber. The exterior of the hose is designed for resistance against abrasion.

The bending radius of the hydraulic hose is designed very carefully into the machine, since a hose failure can be deadly, and violating the minimum bend radius of the hose can also cause failure.

A hydraulic pipe is thick enough to have threads cut into it for connections. It's rarely used for high pressure systems though, which prefer to have tubes or hoses. The pipe itself lends to weldings and can also be used to fabricate the manifold.

Hydraulic pipes on the other hand are preferred over hoses whenever possible, as they are simply more durable. Tubes are also preferred over pipes, as they weigh a lot less. Hydraulic tubes will normally have flared ends and captive nuts to make connections. They can also be steel welded with floating nuts and face seal fittings on the ends.

Both tubes and pipes for hydraulic applications traditionally haven't been plated or painted, since the temperature and oil they operate under drive away moisture and reduce the risk of rust.


The fittings with hydraulic machinery serve several purposes:

1. To bride different standards, such as the O-ring boss to JIC or pipe threads to the face seal.

2. Allows proper orientation of components, as a 45 or 90 degree, straight, or even swivel fitting will be chosen as it is needed. They are designed to be positioned in the correct orientation and then tightened as needed.

3. To incorporate bulkhead hardware.

4. A quick disconnect fitting may be added to a machine without having to modify hoses or valves.

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