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RAT HYDRAULIC PUMP LEAKAGE

The Ram Air Turbine (RAT) Hydraulic Pump shows signs of seepage, stain or a wet area.

• Ram Air Turbine (RAT) (A196)

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Leakage of hydraulic components is difficult to describe in a quantitative manner. Since static or dynamic seals are not functionally perfect, external leakage is expected and allowable to certain limits. Dynamic seal interfaces, which are designed to leak, are the primary source of external leakage.

Allowable leakage, which can exist on even new or overhauled units, will usually show as a seepage, stain or wet area. However, it is possible for seepage or an allowable leakage to collect over time in cavities within a stowed RAT. A collection of fluid therefore may falsely indicate excessive leakage when the RAT is first deployed.

Measurement of Leakage:

Measurement of fluid leakage should not occur immediately after RAT deployment. Collected fluid must first be allowed to drain (or normalize) in order to obtain the true leakage rate. Where fluid dropping from a component may be directly observed, do not wipe surfaces but monitor the component until a drop falls free. Continue monitoring the component until another drop falls and compare results with leakage criteria.

For tests requiring long period of time, and where fluid can drop, wipe the surface clean and dry but do not use a solvent. Secure or place a clean blotter or white cloth immediately below the suspected leak. Examine the blotter or cloth after the system has been idle the required period of time.

1. Perform a visual inspection of the RAT to determine where the hydraulic system is leaking.

   1. If no leaks are found, do close out.
   2. If leaks are found, continue with next step.

2. Collected fluid in cavities must first be allowed to drain (or normalize) in order to obtain the true leakage rate. Compare the leakage rate with the table below:

   Component	Seal function	Seal type	Permissible leakage rate
   RAT Hydraulic Pump	Shaft seal	D	40 drops per hour
   	Shaft seal	S	1 drop/30 minutes
   	Shaft seal Housing (Mating Surfaces)	S	External leakage not sufficient to form a drop is permitted at all locations

   1. If leakage rate is within permissible limit, do close out.
   2. If leakage rate is outside permissible limit, continue with next step.
      NOTE: External leakage not sufficient to form a drop is permitted at all locations, except for the pump shaft seal drain. If wetting is noticed around the pump shaft seal drain, the wetting shall be cleaned and the unit monitored to make sure the shaft seal leakage does not exceed 1 drop in 30 minutes of static.

3. Replace RAT.
4. Do close out.