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low suction mystery

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gmosh(at)charter.net
Guest

Posted: Mon Aug 31, 2009 5:34 pm Post subject: low suction mystery

To all Commander aficionados,

  

 Having an issue with low suction specifically when running  the left engine alone.  The right engine system is operating normally  without the left engine running producing about 4.2 Hg of suction.  The  left engine alone will only produce 2.2 to 2.3 Hg max even at  higher RPM settings.

  

 I have a straight 560 fitted with dual wet suction pumps.    The engine driven vac pumps are piped to bulkhead fittings  on each firewall into the nacelle.  The bulkhead fitting is  connected to the regulator (via hose and clamps).  The  regulator is "T"'d  for attaching the low vacuum  switch and check valve, thence to the hardline forward to the  instrument panel.  Ostensibly the dual check valves protect the operating  vacuum source from an open leak on the opposite side

  

 When I rebuilt the instrument panel I relocated the engine gages,  centering them over/above the throttle pedestal to allow for a panel  mounted radio stack AND I added an artificial horizon, DG (airspeed and  altimeter) to the co-pilot side.        

  

 Harry Merrit sent me a used vacuum pump and regulator; both of  which I installed today.  Best I can get off the left side vacuum pump is  2.2 HG of suction.  The regulator adjustments so far have had a  negligible effect on the suction pressure.  I had thought up until today  the problem resided with the (engine driven) pump and/or regulator ahead of the  check valve in the left nacelle but the pump and regulator still won't get me  the required suction off the left side.  

  

 Anyone out there with a theory as to what I should be looking  for?

  

 Gary (c.s "Blaster")    

  

  

   [quote][b]

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yourtcfg(at)aol.com
Guest

Posted: Mon Aug 31, 2009 8:39 pm Post subject: low suction mystery

Sounds like a bad "used" pump??  Need a greaaaaat pair of props for your 560??  jb

 

 

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moe-rosspistons(at)hotmai
Guest

Posted: Tue Sep 01, 2009 7:08 am Post subject: low suction mystery

Gary,

  

 Have you tested the pump alone by  connecting a hose directly to the pump with the remainder of the system not in  the loop?

  

 Moe

 N680RR

 680Fp

  



  From: Gary Moshluk (gmosh(at)charter.net) 

 Sent: Monday, August 31, 2009 6:26 PM

 To: Commander Chat (commander-list(at)matronics.com) 

 Subject: low suction mystery

 



 To all Commander aficionados,

  

 Having an issue with low suction specifically when running  the left engine alone.  The right engine system is operating normally  without the left engine running producing about 4.2 Hg of suction.  The  left engine alone will only produce 2.2 to 2.3 Hg max even at  higher RPM settings.

  

 I have a straight 560 fitted with dual wet suction pumps.    The engine driven vac pumps are piped to bulkhead fittings  on each firewall into the nacelle.  The bulkhead fitting is  connected to the regulator (via hose and clamps).  The  regulator is "T"'d  for attaching the low vacuum  switch and check valve, thence to the hardline forward to the  instrument panel.  Ostensibly the dual check valves protect the operating  vacuum source from an open leak on the opposite side

  

 When I rebuilt the instrument panel I relocated the engine gages,  centering them over/above the throttle pedestal to allow for a panel  mounted radio stack AND I added an artificial horizon, DG (airspeed and  altimeter) to the co-pilot side.        

  

 Harry Merrit sent me a used vacuum pump and regulator; both of  which I installed today.  Best I can get off the left side vacuum pump is  2.2 HG of suction.  The regulator adjustments so far have had a  negligible effect on the suction pressure.  I had thought up until today  the problem resided with the (engine driven) pump and/or regulator ahead of the  check valve in the left nacelle but the pump and regulator still won't get me  the required suction off the left side.  

  

 Anyone out there with a theory as to what I should be looking  for?

  

 Gary (c.s "Blaster")    

  

  

[quote]



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[b]

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scottmain

Joined: 14 Nov 2007
Posts: 29
Location: fort lauderdale, florida

Posted: Mon Sep 07, 2009 4:39 am Post subject: low suction mystery

I had similar experience with my L-26. I  isolated each segment of the  plumbing and tested one by one and eventually found the culprit. the hard line  from the inside upper left of the right engine nacelle that goes through the  bulkhead and connects to another hard line just to the right of the oil cover  had chaffed through and had a fairly large hole allowing ambient air to enter  there. I had to take the inspection covers off that area on the wing upper panel  to repair the hole and then all worked fine. a vacuum cleaner connected to the  hose at the pump made enough of a suction noise at the hole  to find the  problem. Probably been that way for years as the pressure controller was cranked  all the way in in an attempt to compensate for the bleed problem.

 hope that helps

 scott

  

  In a message dated 9/1/2009 11:09:10 A.M. Eastern Daylight Time,  moe-rosspistons(at)hotmail.com writes:

  	  Quote: 	
		     Gary,

    

   Have you tested the pump alone by    connecting a hose directly to the pump with the remainder of the system not in    the loop?

    

   Moe

   N680RR

   680Fp

      



      From: Gary Moshluk (gmosh(at)charter.net) 

   Sent: Monday, August 31, 2009 6:26 PM

   To: Commander Chat (commander-list(at)matronics.com) 

   Subject: low suction mystery

   



   To all Commander aficionados,

    

   Having an issue with low suction specifically when running    the left engine alone.  The right engine system is operating    normally without the left engine running producing about 4.2 Hg of    suction.  The left engine alone will only produce 2.2 to 2.3 Hg    max even at higher RPM settings.

    

   I have a straight 560 fitted with dual wet suction    pumps.   The engine driven vac pumps are piped to bulkhead    fittings on each firewall into the nacelle.  The bulkhead fitting is    connected to the regulator (via hose and clamps).  The    regulator is "T"'d  for attaching the low vacuum    switch and check valve, thence to the hardline forward to the    instrument panel.  Ostensibly the dual check valves protect the operating    vacuum source from an open leak on the opposite side

    

   When I rebuilt the instrument panel I relocated the engine gages,    centering them over/above the throttle pedestal to allow for a panel    mounted radio stack AND I added an artificial horizon, DG (airspeed and    altimeter) to the co-pilot side.        

    

   Harry Merrit sent me a used vacuum pump and regulator; both of    which I installed today.  Best I can get off the left side vacuum pump is    2.2 HG of suction.  The regulator adjustments so far have had a    negligible effect on the suction pressure.  I had thought up until today    the problem resided with the (engine driven) pump and/or regulator ahead of    the check valve in the left nacelle but the pump and regulator still won't get    me the required suction off the left side.  

    

   Anyone out there with a theory as to what I should be looking    for?

    

   Gary (c.s "Blaster")    

    

    

 	  Quote: 	
		  



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href="http://forums.matronics.com">http://forums.matronics.com

href="http://www.matronics.com/contribution">http://www.matronics.com/c





====================================

t href="http://www.matronics.com/Navigator?Commander-List">http://www.matronics.com/Navigator?Commander-List

====================================

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  [quote][b]

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gmosh(at)charter.net
Guest

Posted: Tue Sep 08, 2009 4:11 am Post subject: low suction mystery

It appears the replacement pump I  received was weak as well.  I'm going to try another pump and report the  results.

 [quote]   ---

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