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Is there an over-priming hydraulic lock monster?

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samira.h(at)shaw.ca
Guest

Posted: Tue Jun 26, 2012 10:43 am Post subject: Is there an over-priming hydraulic lock monster?

Numerous times I have read about the

possibility to get a hydraulic lock by

over-priming.



Today I have pulled the primer line on

my CJ and measured the exact amount of

gasoline per priming stroke at 20 degrees

Celsius ambient temperature.



I have repeated the test 60 times and

each time it was almost exactly 7.15 ml

per stroke.



In the past I was told one needs at

least 120 ml of any kind of fluid per

cylinder to evoke the infamous hydraulic

monster.



So here comes my question, either

I did something wrong or is it nearly

impossible to cause a solid hydraulic

lock by over-priming?



Your opinion on this matter is highly

appreciated.



cheers



Elmar

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brian(at)lloyd.com
Guest

Posted: Tue Jun 26, 2012 12:21 pm Post subject: Is there an over-priming hydraulic lock monster?

On Tue, Jun 26, 2012 at 2:40 PM, Elmar & Manuela Hegenauer <samira.h(at)shaw.ca (samira.h(at)shaw.ca)> wrote:

 	  Quote: 	
		   I have repeated the test 60 times and

 each time it was almost exactly 7.15 ml

 per stroke.

 

 In the past I was told one needs at

 least 120 ml of any kind of fluid per

 cylinder to evoke the infamous hydraulic

 monster.

 

 So here comes my question, either

 I did something wrong or is it nearly

 impossible to cause a solid hydraulic

 lock by over-priming?

 

 Your opinion on this matter is highly

 appreciated.

	




There you go, trying to apply science and engineering to understanding the airplane. That will just NOT do!





-- 

Brian Lloyd, WB6RQN/J79BPL

 3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

+1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)



  [quote][b]

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Rob Rowe

Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK

Posted: Tue Jun 26, 2012 4:16 pm Post subject: Re: Is there an over-priming hydraulic lock monster?

That also tallies with the 8cc stated capacity of the YAK primers, so unlikely you'll ever solid lock a cylinder through over priming.



However 6 or 7 primes worth could still get you the best part of 40cc into the lowest cylinder, which would increase the compression by about a third.



Apparently it's that iterative shock that leads to the Russian plug cores blowing (as well as mishandling them). Don't know if the same holds true for Chinese plugs. So while better than bending a rod it's still a scary ride on 8 cylinders with one open to the atmosphere ... the power is usually only slightly down but the vibration is extreme.



Happened twice on my -52 in the first couple of years of ownership, then fitted a manifold drain 12 years ago without further re-occurrence. Now while that was probably more oil than fuel related it makes sense, having addressed the oil risk, not to replace it with another fuel one.



Given engines start / run on vapour anyway, not liquid fuel, I always leave the manifold open after priming until the bulk of the excess drains out ... usually starts first time and avoids the iterative risk IMHO.



Rob R.

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cjpilot710(at)AOL.COM
Guest

Posted: Tue Jun 26, 2012 6:57 pm Post subject: Is there an over-priming hydraulic lock monster?

In the some 2,000 hours of operating a M-14 (over the last 17 years) I've  never needed more than 6 pumps (I usually just pump 4 times) of the primer to  get a M-14 started.  No where does one need to pump 20 times, or did I read  that wrong.  A hydraulic lock by over priming?  Very un likely.

  

 Jim "Pappy" Goolsby

  

  In a message dated 6/26/2012 8:19:19 P.M. Eastern Daylight Time,  yak-list(at)robrowe.plus.com writes:

  	  Quote: 	
		  -->    Yak-List message posted by: "Rob Rowe"    <yak-list(at)robrowe.plus.com>



That also tallies with the 8cc stated    capacity of the YAK primers, so unlikely you'll ever solid lock a cylinder    through over priming.



However 6 or 7 primes worth could still get you    the best part of 40cc into the lowest cylinder, which would increase the    compression by about a third.



Apparently it's that iterative shock that    leads to the Russian plug cores blowing (as well as mishandling them). Don't    know if the same holds true for Chinese plugs. So while better than bending a    rod it's still a scary ride on 8 cylinders with one open to the atmosphere ...    the power is usually only slightly down but the vibration is    extreme.



Happened twice on my -52 in the first couple of years of    ownership, then fitted a manifold drain 12 years ago without further    re-occurrence. Now while that was probably more oil than fuel related it makes    sense, having addressed the oil risk, not to replace it with another fuel    one.



Given engines start / run on vapour anyway, not liquid fuel, I    always leave the manifold open after priming until the bulk of the excess    drains out ... usually starts first time and avoids the iterative risk    IMHO.



Rob R.





Read this topic online    here:



http://forums.matronics.com/viewtopic.php?p=376686#376686

	


 [quote][b]

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Rob Rowe

Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK

Posted: Wed Jun 27, 2012 3:12 am Post subject: Re: Is there an over-priming hydraulic lock monster?

 	  Quote: 	
		  No where does one need to pump 20 times, or did I read that wrong. 	




The M14P manual proposes using 8-12 primes in summer(!) & 15-20 in winter(!!), which is asking for trouble IMHO.



Personally for a cold start I use 5 primes in summer & 6 in winter, drain excess, and then wait for it to vapourise for 1-2 minutes in summer & 4-5 in winter, before starting (as per the book) ... this pause makes it much more likely to fire up first time.



If it does fail to start I'll give it a couple more primes / pause ... still no joy then open the manifold to drain surplus before trying again.



FWIW on cold starts I leave the throttle closed and the primer on 'cylinders' (pushed in) ... this gives a gentle start at low 30s rpm. Promptly centralise the primer to avoid fouling plugs and after 5-10 secs slowly bring the rpm to 40%. Helps reduces engine wear until lubricated and particularly in winter places less stress on prop seals / oil cooler matrix (cold thick oil). Picked this tip up from a Russian instructor a few years back ... seems to work well. YMMV.



Rob R

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samira.h(at)shaw.ca
Guest

Posted: Tue Jul 03, 2012 11:16 pm Post subject: Is there an over-priming hydraulic lock monster?

Thank you everyone who replied

to my posting.



Please keep in mind that the CJ has a

different fuel system compared to the Yak.



I usually prime 2 to 3 times and in the

winter 4 to 5 times. But on a hot summer

day sometimes it is hard to tell if one is

pumping air or fuel, over-priming could

happen even to the most experienced pilot.



After priming I open my manifold drain

valve and watch some fuel dripping out.

Then I close it, get in the plane and while

pushing the starter button I prime one

more shot while the prop is turning - the

engine springs to life.



Thanks again.



cheers



Elmar

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