Turning rotor backwards - damage to hydraulic system

[gipsymagpie]

Originally Posted by CTR

If you check the full 429 schematic (you cut off the right half), you will see the check valve I referenced that can cause cavitation located at the base of the reservoir can.

No 1 hyd

Nothing marked as a check valve. What element are you referring to?
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[CTR]

Check Valve

Originally Posted by gipsymagpie

No 1 hyd

Nothing marked as a check valve. What element are you referring to?
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The check valve does not have a call out, but you can see it in the schematic (circle in V).

[gipsymagpie]

Originally Posted by CTR

The check valve does not have a call out, but you can see it in the schematic (circle in V).

Thank you. Just what I needed

[Paul Cantrell]

Originally Posted by rotorfun

When installing main rotor tie down, AFM for Bell 505 indicates rotating rotors in the opposite direction. Not sure why...

"Rotate main rotor blades in opposite direction of rotation until main rotor blades are aligned with tail boom."

The 505 rotor system is derived from the Long Ranger rotor system. In that system, it's recommended to turn the rotor backward after shutdown to prevent coking in the labyrinth seal... Turning forward won't rotate the engine because of the freewheeling unit.

In most cases, the cause for N2 rub or seizure is carbon buildup on the rotating labyrinth seal of the power turbine rotor. When this problem is experienced, owners and operators should refer to the above referenced DDA Commercial Service Letters reprinted as part of this Hughes Service Information Letter.

As stated in CSL-1037, walking the main rotor backwards while the engine is cooling after shutdown will definitely help to eliminate this cause for seizure and will not harm the engine.

The parent thread about not turning 429/135 backward is very interesting, and not something I would have thought of...

[CTR]

Gear Pump versus Variable Displacement Piston Pump

The 206A/B, like the 505 use a gear pump. The 206L, 407, 429, and 412 use variable displacement piston pumps.

Internal leakage in gear pumps prevents them from generating any significant pressure at low RPM. This is not the case with variable displacement piston pumps.

Therefore no issue turning a 505 rotor backwards slowly.

[Agile]

Originally Posted by CTR

The 206A/B, like the 505 use a gear pump. The 206L, 407, 429, and 412 use variable displacement piston pumps.

Internal leakage in gear pumps prevents them from generating any significant pressure at low RPM. This is not the case with variable displacement piston pumps.

Therefore no issue turning a 505 rotor backwards slowly.

Yes gear pump at low speed are good for nothing, AS350 same (single and dual hydraulics)

important note: displacement piston pump produce pressure in the same direction regardless of direction of rotation