Hydraulic Machinery

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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.

Pumps

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.

Fittings

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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