surfaces. Should an initially sealed joint subsequently develop a leak which cannot be stopped by tightening the B-nut to the specified torque, the joint is probably defective and should be repaired. No visible evidence of leakage is allowable for either normal or dispatch operations.
2)  When possible, actuate components through several full cycles prior to performing a leakage check.
3)  Dynamic seals should also be checked for leakage while in a static condition since pistons, slide valves and swivel joints move only during a short time interval. Also many components cannot be closely monitored while operating.
4)  Experience indicates that some static seal leakage has been due to housing cracks. Such leakage increases with increasing pressure. Therefore, each such leakage problem should be considered individually by the operator for the amount of leakage allowable.
501 
May 15/77  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  29-00 Page 601 

(2) Check hydraulic system external leakage.
(a)
Where fluid is present, wipe the surfaces clean.

(b)
Apply hydraulic system pressure and operate the unit if possible.

(c)
Check tube connections, static and dynamic seals for leakage as indicated in Fig.

601.
Seal  Allowable Leakage For Normal Operations (See Note)  Allowable Leakage For Dispatch Operation To Avoid Delay (See Note) 
1. Tube Connections 2. Static Seals 3. Dynamic Seals a. Engine-Driven Pump (1) Inline Pumps (ABEX/VICKERS) (2) Yoke Type or Bent Axis (VICKERS) b. Electric Motor-Driven Pumps (1) Task/ABEX (2) Vickers c. Other dynamic seals under static conditions of full or partial pressure d. Other dynamic seals under dynamic conditions of full or partial pressure  No visible evidence of leakage 1 drop per 10 minutes 30 drops per minute 7 drops per minute 10 drops per minute 20 drops per minute 1 drop per 10 minutes – no repair required 1 drop per 10 minutes to 1 drop per minute – correct at first opportunity 1 drop per cycle  No visible evidence of leakage Determined by operator 60 drops per minute 10 drops per minute Correct at first opportunity 20 drops per minute 30 drops per minute Correct at first opportunity 1 drop per minute up to 30 drops per minute Correct at first opportunity 1 drops per cycle 

NOTE: Leakage rates are based on there being approximately 20 drops per cubic centimeter and/or 75,600 drops per gallon.
Hydraulic System Allowable External Leakage Chart  500 
29-00  Figure 601  May 01/03 
Page 602 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

C.  Hydraulic Systems A and B Internal Leakage Checks
(1)  General
(a)  
This check is to be used as an aid in determining the general internal condition of the hydraulic system; or an aid in trouble shooting the system.

(b)  
The general condition of the system is determined by comparing measured internal leakage rates to the recommended inservice leakage limits provided for the various subsystems. If an inservice leakage limit is exceeded the component or components within the subsystem should be replaced to bring the leakage within limits (Ref Chapter 27 or 32).

(c)  
The leakage rates for the subsystems are determined by measuring changes in flow rates during different operating conditions while hydraulic power is applied. Three methods for measuring the flow rates are available: the ammeter method, flowmeter method and the amp-clamp and multimeter method. 1) The ammeter method uses an ammeter connected in series with one of the

hydraulic system B motor-driven pumps. The leakage rates are determined by measuring the current and current changes of the system B pump. These current changes are then related to a pump characteristics graph relating pump current to pump fluid flow. (See Pump Characteristics Graph, Fig. 604.) Using this method of measuring flow, two men can perform the check in approximately 1/2 hour.
2)  The flowmeter method uses a flowmeter connected to the pressure side of a hydraulic service cart providing the source of hydraulic power. As the system configuration is changed the flow rates can be read directly and recorded. Using this method of measuring flow, two men can perform the check in approximately 2 hours.
3)  The amp-clamp and multimeter method is used by placing the amp-clamp adapter around a selected wire at one of the system B pump relays in the P6-4 panel and connecting to a digital multimeter. The current changes are recorded and are then related to the pump characteristics graph, (Fig. 604). One man can perform this procedure from the control cabin.
(d)  When troubleshooting, it is not necessary to perform a check of both systems. Only the system (A or B) where the trouble is present needs to be checked. By feeling for hot tubing or actuators or listening for fluid leakage, faulty components can be isolated within a subsystem which has excessive internal leakage. Whenever possible, standard tools for detecting heat, vibration or sound should be used. Before checking for internal leakage by these methods, cycle the components to be checked to ensure that personnel will not be injured or equipment damaged when the component moves.
　
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