Controlling Hydraulics with Electronics

Hey,

I was just wondering how large machines such as hydraulic compactors are controlled by electrical interfaces?

What about pneumatics?

Cheers

Peter_wadley said:

Hey,

I was just wondering how large machines such as hydraulic compactors are controlled by electrical interfaces?

What about pneumatics?

Cheers

Click to expand...

Special electrically activated valve actuators and/or solenoid valves are used to control hydraulic equipment, depending if it's a linear travel or on/off type control. These tend to be quite expensive due to the very high pressures (>1000psi) used in hydraulic equipment.

Pneumatics equipment uses simular interface hardware, but is not nearly as expensive because of the lower pressures (<100psi) of most pneumatic equipment. A common pneumatic control component is called an I to P converter. It accepts a DC 4-20ma analog input control signal and outputs a 3-15 psi output pressure, using a 25-100 psi air supply.

Lefty


Lefty

The dinky compactor we have at work has a pressure sensor to determine the load on the ram (when it's getting full) and a mechanical limit switch to determine when it's at it's full extension. The hydraulics themselves are controlled by a couple solenoid on/off valves. Analog control of hydraulics requires a lot more feedback than simple pressure/mechanical comparators and control loops and gets very expensive and very complicated very fast.

In the areas where I work (oil production) commonly used hydraulic pressures are 207 bar and 517 bar (3000 and 7500psi).
These hydraulic supplies are controlled (on/off) by a fairly simple solenoid operated valve.
Some of the advantages of hydraulics over say an electric motor, are that for a given power rating, an hydraulic motor is much smaller than the equivalent electric motor, an hydraulic motor does not burn out if it is stalled by the load, and hydraulic equipment is not affected by water in the same way as electrics.

Pneumatics is not used at such high pressure because of the amount of stored energy in compressed gas, makes it quite dangerous.
Also consider a linear actuator, pressurise it with hydraulics and the distance it moves is proportional to the volume of fluid which is put into it, irrespective of the load.
However if compressed air is put into the actuator which is applying a force to some load. If the load force is removed, the actuator can shoot out at full speed as soon as the air is applied to the actuator.

JimB

Problem with hydraulic is that they won't work without electric power to the hydraulic pump.

In an old design I worked on, a cooling water pump discharge valve, the valve operates via hydraulic but the hydraulic oil also compress a volume of high pressure N2 in a sealed pressure vessel. When all power is OFF or lost, the valve is shut using the hydraulic oil pressure provided by the N2.

In newer design, the pressure vessel is replaced by raising a dead weight on the operating ram.

eblc1388 said:

Problem with hydraulic is that they won't work without electric power to the hydraulic pump.

Click to expand...

Yes true, but if you have...

eblc1388 said:

the hydraulic oil also compress a volume of high pressure N2 in a sealed pressure vessel.

Click to expand...

...a thing usually referred to as an accumulator, the unit will work for a reasonable amount of time without power to the electric motor, diesel engine or w.h.y., it all depends on the size of the accumulator.

JimB