Air-controlled hydraulic pressure control valves use an external pneumatic pressure signal to proportionally and remotely control a hydraulic pressure. These valves are an alternative to hydro-mechanical or electro-hydraulic pressure control cartridges.
Air-controlled pressure controls provide the same function as hydro-mechanical or electro-mechanical controls, but are adjusted by a control air pressure rather than a mechanical screw or electrical current. They are available from Sun Hydraulics in direct-acting for pilot flows up to 7,5 lpm (2 gpm) or pilot operated for flows up to 760 lpm (200 gpm). Maximum control air pressure for all air-controlled pressure controls is limited to 10 bar (150 psi) to prevent damage to seals.
Sun’s air-controlled, pilot capacity direct-acting relief valve (Series P, T-8A cavity) can be installed into the body of any suitable Sun main stage cartridge containing an integral T-8A cavity. These combinations create air-controlled versions of the main stage function, whether it is for relief, sequence, reducing, or reducing/relieving, with flow ratings up to 760 lpm.
Why use pneumatic control?
Hazardous areas
Many hydraulic equipment applications are in fire-prone, hazardous areas involving combustible or explosive materials, and require that any electrical device used meets ‘Intrinsically Safe’ or ‘Explosion Proof’ standards. Examples of these hazardous areas include:
* Oil drilling platforms.
* Oil and gas handling equipment.
* Chemical industry equipment.
* Dust-laden atmospheres (grain elevators).
* Vehicular lifts.
* Sawmills.
Air-controlled pressure controls in conjunction with pneumatic lines are very useful to proportionally and remotely control hydraulic system pressure in these difficult environments. This pneumatic control of hydraulic valves is often far more cost-effective than using explosion proof electro-hydraulic solenoids and associated intrinsically safe control installations.
Strong electromagnetic fields
Electro-hydraulic controls that must operate in environments with very strong electromagnetic fields can suffer from stray induced currents. Strong electromagnetic fields are often present in manufacturing environments – for instance in close proximity to spot welding operations. Strong magnetic fields can often induce large currents or noise into low level electrical control conductors. This noise can send false signals to sensitive electro-hydraulic devices such as proportional pressure controls.
Using air-controlled proportional hydraulic pressure controls with pneumatic control lines in place of electrical control wires completely eliminates this interference problem.
Electrical isolation
Devices requiring variable hydraulic pressure and complete electrical isolation from another part of a machine, for safety reasons, may find proportional pneumatic control a practical solution. The pneumatic control lines can be rubber or elastomeric tubes and are thus an electrical insulator. With voltage potentials below where ionisation of air occurs, there is no direct electrical connection present.
Cost
Pneumatic proportional controllers and air-controlled hydraulic pressure controls can provide a lower cost solution in facilities where the pneumatic supply is readily available. Air-controlled hydraulic pressure controls can be used without the need to install proportional hydraulic amplifiers, associated electrical wiring, and power supplies necessary for electro-hydraulic systems.
Caution
The only caution is that pneumatically controlled hydraulic pressure control systems typically have a much slower dynamic response time than their electro-hydraulic counterparts.
For more information contact Fritz Kern, Axiom Hydraulics, +27 (0)11 334 3068, [email protected], www.axiom.org.za
| Tel: | +27 11 334 3068 |
| Fax: | +27 11 334 4543 |
| Email: | [email protected] |
| www: | www.axiomsa.co.za |
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