Pneumatic Control Options for Hydraulic Systems

Air-Controlled Pressure Controls Explained

Air-controlled hydraulic pressure control valves use an external pneumatic pressure signal to proportionally and/or remotely control a hydraulic pressure. Sun offers these valves as an alternative to hydro-mechanical or electro-hydraulic pressure control cartridges. Air-controlled pressure controls provide the same function/performance 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 in direct-acting for flows up to 2 gpm (7,5 L/min.) or pilot operated for flows up to 200 gpm (760 L/min.). Maximum control air pressure for all air-controlled pressure controls is limited to 150 psi (10 bar) 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 be relief, sequence, reducing, or reducing/relieving, with flow ratings up to 200 gpm (760 L/min.).

When to Use

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

Explosion proof equipment such as electro-hydraulic solenoids and associated wiring can be costly. Air-controlled pressure controls are very useful to proportionally and/or remotely control hydraulic system pressure in these difficult environments. In such environments, pneumatic lines can often be used at much lower cost where standard electrical wires and connections would violate safety requirements.

Electro-hydraulic devices 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 with a concentration of large projection and spot welding operations. These processes can create very strong magnetic fields, and can often induce large currents or "noise" into low level electrical control wires. 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.

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 ionization of air occurs, there is no direct "electrical" connection present.

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. The only caution is that pneumatically controlled hydraulic pressure control systems typically have a much slower dynamic response time than their electro-hydraulic counterparts.

To see all Sun air-controlled hydraulic pressure control cartridges, click here.