50 Years Ago — Boeing 727 Hydraulics: More and Better

July 9, 2014
The 727 makes greater use of hydraulic power over its predecessors, the 707 and the 720.
The 727 makes greater use of hydraulic power over its predecessors, the 707 and the 720. That’s the story from author James E. Klansnik, Hydraulic Group System Engineer at The Boeing Co., Seattle, in our July 1964 issue. Reliability and maintainability studies determined the areas on which system and component-design development should be focused — all flight controls and the aft passenger-entry stairs, integral parts of the airplane. To provide this, the 727 has dual hydraulic systems, as well as a smaller, isolated standby system offering alternate power for the leading-edge slat and flap system. This standby system is also a third power source for the rudder because it doesn’t have a manual backup system. All three systems use Skydrol 500A hydraulic fluid and operate at 3,000 psi.

Improvements to the 727 include:

  • Plumbing — Tube fittings, hose materials, and static and dynamic seals were updated. Unions, tube bends, and angled fittings replaced universal-type fittings (locknuts, O-rings, and banjo fittings) to reduce leaks. The 727 has approximately 20% fewer tube assemblies than normally used.
  • New seals developed — Static and dynamic seals made from elastomers have long been a problem because they don’t have the resiliency, abrasion resistance, and volumetric stability required. Recently developed ethylene propylene rubber has the necessary qualities and seals made from this are being phase in.
  • Teflon hose — All hose assemblies are Teflon-lined, exposed wire-braid type with swaged-on couplings. Swaged-on couplings were chosen because they offer the tightest joint and are foolproof for assembly and installation.
  • Pump choice — Two engine-driven pumps are available. A new specification was developed for a 6-gpm motor pump. It comes in two versions — one is a redesign of an existing pump adapted to work with Skydrol 500A. The other is an outgrowth of two design objectives in the motor-pump requirements: one, that the motor pump has no external dynamic seals, and two, the gearbox needs to be eliminated.
  • Filter design — Filtration in and out of pumps was improved with metallic-element filters. They feature 10-μm nominal, 25-μm absolute ratings. Filters in the pump-case drain and pressure lines are nonbypass types.

Read the complete article by clicking here.

Continue Reading

Handbook Simplifies Advanced Aspects of Mobile Hydraulic Controls

May 10, 2017
Author Brendan Casey lays out his hydraulics know-how that he acquired over 27 years in a simple handbook made for people that want to improve their skills in troubleshooting ...

Kidney loops: They aren't just for hydraulics any more

Sept. 1, 2004
When was the last time you changed the oil in your refrigerator's compressor? That was a question posed to me by Ken Stofen of Racine, Wis. The answer, of course, is never, and...

Sponsored Recommendations


May 15, 2024
Production equipment is expensive and needs to be protected against input abnormalities such as voltage, current, frequency, and phase to stay online and in operation for the ...

All-In-One DC-UPS Power Solutions

March 13, 2024
Introducing the All-In-One DC-UPS, a versatile solution combining multiple functionalities in a single device. Serving as a power supply, battery charger, battery care module,...

Motor Disconnect Switches

March 13, 2024
With experienced Product Engineers and Customer Service personnel, Altech provides solutions to your most pressing application challenges. All with one thought in mind - to ensure...

DC Power Solutions: Streamlined Power Supplies for Every Need

March 13, 2024
CBI All In One UPS Power Solutions combine the requirements for several applications in just one device which can be used as power supply unit, battery charger, battery care module...