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Carling S700 2-3 switch failure.

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bbradburry(at)verizon.net
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Posted: Tue Jan 19, 2016 5:39 pm Post subject: Carling S700 2-3 switch failure.

This manual switch is in a high (8 amps?) fast switching injector circuit.  I use it to disable the primary or secondary injectors prior to flight to determine if the engine will run on only one set of injectors.  It failed in flight and the engine went very lean running on only one set of injectors.  

The switch initially had no continuity but made a high resistance contact after flipping it back and forth a few times.  

   

Should I replace this switch with a more robust one and if so, where would I find a suitable switch?  

   

Bill

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Tue Jan 19, 2016 7:59 pm Post subject: Re: Carling S700 2-3 switch failure.

Yes, the switch should be replaced.  Choose a switch rated at 10 or more amps.  There are some switches that have the terminals riveted to the plastic housing.  Do NOT use that kind.  They depend of the rivets to conduct the current.  Bad idea because rivets in plastic loosen over time.  Switches need to be exercised periodically to wear away corrosion.  Switches in airplanes do not get much exercise and will fail from corrosion before mechanically wearing out.  The S700 2-3 is B & C's part number for a generic DPDT ON-ON switch.

 If the load is inductive, a diode connected between the load side of the switch and ground will protect the switch against arcing.  The diode arrow should point towards positive.

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 20, 2016 8:04 am Post subject: Carling S700 2-3 switch failure.

At 07:38 PM 1/19/2016, you wrote:

  	  Quote: 	
		   This manual switch is in a high (8 amps?) fast switching injector circuit.  I use it to disable the primary or secondary injectors prior to flight to determine if the engine will run on only one set of injectors.  It failed in flight and the engine went very lean running on only one set of injectors.

 The switch initially had no continuity but made a high resistance contact after flipping it back and forth a few times. 	


   First, I would REALLY like to have that switch

   for failure analysis. How much time did you

   have on the switch?



   How is this switch wired? does the switch carry

   injector currents in BOTH positions?    

  	  Quote: 	
		   

 Should I replace this switch with a more robust one and if so, where would I find a suitable switch? 	


   There are many more robust switches suited to

   the task not the least of which is this device



  http://tinyurl.com/jhkg6ep



   . . . but it's not clear to me that the S700-2-3

    was not suited to the task either. It would be useful

   for us to study the circumstance of the failure and

   the in-flight situatin you encounted when it did.

    



 

   Bob . . .

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