Hydraulics versus pneumatics

Hydraulics and pneumatics are both examples of fluid power. The difference lies in the fluid used and how those fluids are used. Only fluid power systems are capable of providing constant force or torque despite speed changes.

What does a hydraulic system do?

Instead of air, machines that use hydraulics rely on mostly incompressible liquid material under pressure to lift, hold and move goods. Examples include hydraulic or mineral oil, or water, just to name a few.

Advantages:

• Moves heavier loads with greater force than mechanical, electrical or pneumatic fluid power systems
• Ease and accuracy of controlling the system by levers and push buttons
• Generates large amounts of power
• Uses fewer moving parts than some mechanical and electrical systems, which makes it more durable and less prone to break down

What does a pneumatic system do?

Pneumatic machinery and equipment use pressurized gasses, such as air, for moving and cooling applications. Pneumatic fluid power systems compress air, so movement is not instantaneous, as it is with hydraulics.

Advantages:

• More cost effective than hydraulics – air is free
• Pneumatic safety – system can be used in inflammable environments and does not overheat
• More power in a smaller and lighter unit compared to most other technology systems
• Cleaner technology
• Fluid used absorbs excessive force, which means fewer threats of damage to equipment

What are the components of hydraulic and pneumatic machines?

Hydraulics

 

These systems can be complex depending on its use, but generally, these are the basic components:

• Reservoir – contains the liquid, most commonly, hydraulic oil
• Pump – forces the liquid through the system
• Motor – electric power source to drive the pump
• Valves – controls the liquid’s direction, pressure and flow rate
• Actuator – converts the liquid’s energy into mechanical force or torque
• Piping – carries the liquid from one area to another

 

Pneumatics

 

These systems can range from simple air-driven pistons to equipment with multiple actuators for mining. Generally, the most common components include:

• Compressor – compresses normal air to a higher PSI (pounds per square inch)
• Air reservoir – stores the pressurized air created by the compressor
• Valve –controls the airflow so that the air is released at the right pressure level for the pneumatic equipment being used
• Actuator – converts the energy stored into kinetic energy
• Cylinder – generates motion and force from air pressure
• Feed lines or hose pipe – supplies compressed air to components

Do pneumatic cylinders need oil?

That depends on your system. Older systems typically use a lubricant oil that provides airline lubrication. The oil’s low viscosity allows it to aspirate to form a mist. It’s this mist that provides the lubrication for not only cylinders, but valves, tools and motors. Most of today’s systems have the advantage of more advanced materials, such as nitrile seals on cylinders and valves, making lubricant unnecessary.

When do you use hydraulics or pneumatics?

Simply put, applications of hydraulic devices are best for when higher force and heavy lifting is needed. Use pneumatics for mechanical and lighter engineering needs. Here are some examples of how each is used:

Application	Hydraulics	Pneumatics
Construction equipment – lifts and lowers	x
Dishwashers – increase water pressure	x
Office chairs – lift and lower seat	x
Airplanes – adjust wings and extend landing gear	x
Vehicle brakes and steering – reduces effort needed by drivers	x
Mining tools – compressed air acts as source of energy for power tools		x
Exercise equipment – cylinder creates resistance		x
Dental drills – safe for patients (no chemicals or toxins)		x
Automated production equipment – powers tools on assembly lines		x
HVAC controls – send signals and control the devices to trigger action		x

Why is hydraulic and pneumatic system maintenance important?

The most important reason is safety. Pressurized hydraulic fluid that suddenly escapes presents the threat of explosive velocity. Another hydraulic safety issue concerns the harm that faults can cause with unexpected movement by sharp, heavy equipment, injuring those nearby.

 

Keep in mind that fluid power hydraulic and pneumatic systems are low maintenance, with pneumatics even more so. Pneumatic safety precautions involve ensuring hoses are free from damage. Old or fraying hoses leak air, which causes equipment to malfunction. That, in turn, can cause serious harm to users. To learn more about protecting hoses, don’t miss Hydraulic hose protection to ensure safe designs and Quick Guide: hydraulics and pneumatics protection in specialist vehicles.

Proper maintenance can not only ensure safety, but also reduce downtime and with it, costs. For maintenance tips to protect your systems, check out.

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