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fuses, breakers, and hydraulic pumps

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aerobubba(at)earthlink.ne
Guest

Posted: Thu Jan 26, 2012 7:56 am Post subject: fuses, breakers, and hydraulic pumps

Hi Jeff-



 



With regard to:

 	  Quote: 	
		  How about another example ? The popular approach is to use a pullable 

breaker for the hydralic pump for the amphibious landing gear. If I 

use a switch and a fuse, what size fuse ? I appreciate that I can 

always install a bigger fuse if nuisance pops occur, .....


	


 



.....Are there any other reasons why a pullable circuit breaker would be 

 	  Quote: 	
		  preferred for this situation ?


	




There are two seperate potential issues here.  First, is there an alternate source of hydraulic pressure?  If you have a practical hand pump available, then the nuisance trip issue is just that.  If the electric pump is your only practical source of hydraulic power, then things are a little different.  I could envision a scenario where the motor for the hydraulic pump has degraded such that the current draw trips the circuit protection, leaving you with a gear up landing, or potentially worse, a partial gear landing.  Personally, I would prefer resettable circuit protection in that scenario.



 



FYI, YMMV, ETC, ETC 

Glen Matejcek

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 26, 2012 9:17 am Post subject: fuses, breakers, and hydraulic pumps

There are two separate potential issues here.  First, is there an 

alternate source of hydraulic pressure?  If you have a practical hand 

pump available, then the nuisance trip issue is just that.  If the 

electric pump is your only practical source of hydraulic power, then 

things are a little different.  I could envision a scenario where the 

motor for the hydraulic pump has degraded such that the current draw 

trips the circuit protection, leaving you with a gear up landing, or 

potentially worse, a partial gear landing.  Personally, I would 

prefer resettable circuit protection in that scenario.



    Cogent thoughts my friend. In spite of the fact that

    a Beech Sierra was a pig with wings, I appreciated the

    fact that the standby-gear extension system was a simple

    valve on the floor that allowed gear-up pressure to be

    relieved allowing the wheels to fall free.



Personally, I would prefer resettable circuit protection in that scenario.



    I would offer the notion that if power to the motor

    is sufficiently robust (current limiter style

    protection) then a nuisance trip is entirely out

    of the picture. Any time you open a current limiter,

    something is REALLY BAD WRONG and being able to

    "give 'er one more try" is an incalculable long

    shot.



    Bob . . .

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