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Attn: Hydraulic experts - oil pressure relief fix?



 
 
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  #1  
Old November 1st 04, 07:42 AM
MikeremlaP
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Default Attn: Hydraulic experts - oil pressure relief fix?

Okay, here's the deal. Lycoming O-320 in a Glasair. On full power, whether
oil is hot or cold, oil pressure will be higher than the regulator is set for.
(Shoots to top of yellow arc - 90 psi. I think all Lyc's do that.) Upon power
reduction, say turning downwind, you can "see" the ball jump off the seat when
the oil pressure gage goes "sproing" and the pressure suddenly drops to the
regulated 60 psi in a classic 2nd order damped sinusoidal response. It will
stay at regulated pressure until the ball seats itself again, say on final
approach with the engine at idle where the pump isn't making as much pressure.
Then the process starts over again, on the next touch 'n' go. I'd like to have
regulated oil pressure all the time.

I'm theorizing that there's some kind of venturi effect, where the ball is
actually sucked down harder on the seat when lots of oil is flowing past it on
the engine side. Seems counter-intuitive, I know, but what else could be
holding the ball down?

Anyone got a simple fix I can try? Larger ball bearing? Smaller ball bearing?
Cutting groves in the seat to help ball break free? Different angle on the
face of the seat?

Thanks,

Mike Palmer
Excellence in Ergonomics

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  #2  
Old November 3rd 04, 04:18 AM
Ron
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Posts: n/a
Default

On my O320 the pressure is on the side away from the ball, trying to open
the bypass valve. The ball stays seated until pressure builds to the level
of the bypass setting, then the bypass is forced open, allowing the excess
pressure (oil) to be relieved back to the sump.


"MikeremlaP" wrote in message
...
Okay, here's the deal. Lycoming O-320 in a Glasair. On full power,

whether
oil is hot or cold, oil pressure will be higher than the regulator is set

for.
(Shoots to top of yellow arc - 90 psi. I think all Lyc's do that.) Upon

power
reduction, say turning downwind, you can "see" the ball jump off the seat

when
the oil pressure gage goes "sproing" and the pressure suddenly drops to

the
regulated 60 psi in a classic 2nd order damped sinusoidal response. It

will
stay at regulated pressure until the ball seats itself again, say on final
approach with the engine at idle where the pump isn't making as much

pressure.
Then the process starts over again, on the next touch 'n' go. I'd like to

have
regulated oil pressure all the time.

I'm theorizing that there's some kind of venturi effect, where the ball is
actually sucked down harder on the seat when lots of oil is flowing past

it on
the engine side. Seems counter-intuitive, I know, but what else could be
holding the ball down?

Anyone got a simple fix I can try? Larger ball bearing? Smaller ball

bearing?
Cutting groves in the seat to help ball break free? Different angle on

the
face of the seat?

Thanks,

Mike Palmer
Excellence in Ergonomics



  #3  
Old November 3rd 04, 11:36 AM
GeorgeB
external usenet poster
 
Posts: n/a
Default

Mike, open and reseat pressures differ. A typical relief cartridge,
the Sun RDDA (www.sunhydraulics.com) says that reseat is 90% of set
pressure. They don't say, but I suspect this is a Bernoulli force
thing. Also, there is "override", the increase in pressure with
increase in flow. I've not seen a response such as you describe on a
direct-operated relief (spring/ball). I have seen gauges and
transducers show one when there was air in the sense lines. Air other
places could cause that, as well. Specifically, air in the oil stream
would cause changes in flow through the relief valve in the
setting-reseat region.

On Tue, 2 Nov 2004 20:18:10 -0800, "Ron" no one @home.com wrote:

On my O320 the pressure is on the side away from the ball, trying to open
the bypass valve. The ball stays seated until pressure builds to the level
of the bypass setting, then the bypass is forced open, allowing the excess
pressure (oil) to be relieved back to the sump.


"MikeremlaP" wrote in message
...
Okay, here's the deal. Lycoming O-320 in a Glasair. On full power,

whether
oil is hot or cold, oil pressure will be higher than the regulator is set

for.
(Shoots to top of yellow arc - 90 psi. I think all Lyc's do that.) Upon

power
reduction, say turning downwind, you can "see" the ball jump off the seat

when
the oil pressure gage goes "sproing" and the pressure suddenly drops to

the
regulated 60 psi in a classic 2nd order damped sinusoidal response. It

will
stay at regulated pressure until the ball seats itself again, say on final
approach with the engine at idle where the pump isn't making as much

pressure.
Then the process starts over again, on the next touch 'n' go. I'd like to

have
regulated oil pressure all the time.

I'm theorizing that there's some kind of venturi effect, where the ball is
actually sucked down harder on the seat when lots of oil is flowing past

it on
the engine side. Seems counter-intuitive, I know, but what else could be
holding the ball down?

Anyone got a simple fix I can try? Larger ball bearing? Smaller ball

bearing?
Cutting groves in the seat to help ball break free? Different angle on

the
face of the seat?


  #4  
Old November 3rd 04, 04:39 PM
MikeremlaP
external usenet poster
 
Posts: n/a
Default

Hi Ron:

On my O320 the pressure is on the side away from the ball, trying to open
the bypass valve. The ball stays seated until pressure builds to the level
of the bypass setting, then the bypass is forced open, allowing the excess
pressure (oil) to be relieved back to the sump.


Mine is the same. Still, I'll bet you see more than regulated pressure on take
off. Therefore, the ball must not be popping off the seat for some reason
until something changes. For us it's either a power reduction or when the
venatherm opens, which probably causes a momentary drop in oil pressure as oil
is redirected to the cooler.

Like I said before, it seems counterintuitive, but I can make a hand waving
argument about how lots of oil (as during takeoff) flowing perpendicular to the
ball could actually cause the ball to pull down tighter. Kinda like when the
Voyager took off for its round the world flight... remember how the wings bent
down before they finally bowed up?

Mike Palmer
Excellence in Ergonomics


  #5  
Old November 3rd 04, 11:25 PM
Whunicut
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Default

Okay, here's the deal.
snipped
Sounds like the oil pressure relief valve spring cound be hanging on the lip of
the spring retainer cap.
Take the cap off and chamfer the hole the spring goes into. Check for burrs on
the inside of the cap and also check the spring to see if it is bent or
deformed in any way.
(Shoots to top of yellow arc - 90 psi. I think all Lyc's do that.)

I dont think so. The oil pressure is generally higher when cold, 5 to 10psi or
so, and comes down to normal gradually when warm but does not jump suddenly.

Good luck,
Warren



  #6  
Old November 6th 04, 03:31 AM
MikeremlaP
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Default

Howdy Warren:

Sounds like the oil pressure relief valve spring cound be hanging on the lip
of
the spring retainer cap.
Take the cap off and chamfer the hole the spring goes into. Check for burrs
on
the inside of the cap and also check the spring to see if it is bent or
deformed in any way.


Okay, even tho I hadn't seen any burrs, I surfaced and chamfered the cap
anyway. I also tried to chamfer a bit the oil drain back holes in the cap, to
allow them to bleed when the ball just begins to move off the seat. Lastly, I
noticed the -3 washers that Lyc specifies seem a little too small. But -4's
are too large. So I ground down a -4 and put that in to minimize any spring
wobble on the washers.

I also forgot to put back one of the washers. The end result is that oil
pressure is better behaved, although I don't know which variable is
responsible. The oil pressure doesn't rise as high on takeoff as it used to
and still holds 60 psi when oil is hot. I keep meaning to watch to see if it
goes "sproing-g-g-g" but have been in the right seat and since it's not right
in front of my face, haven't noticed.

Thanks for the help so far... will squawk if the problem persists.

Mike Palmer
Excellence in Ergonomics

  #7  
Old November 6th 04, 01:02 PM
Blueskies
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Posts: n/a
Default


"MikeremlaP" wrote in message ...
Howdy Warren:

Sounds like the oil pressure relief valve spring cound be hanging on the lip
of
the spring retainer cap.
Take the cap off and chamfer the hole the spring goes into. Check for burrs
on
the inside of the cap and also check the spring to see if it is bent or
deformed in any way.


Okay, even tho I hadn't seen any burrs, I surfaced and chamfered the cap
anyway. I also tried to chamfer a bit the oil drain back holes in the cap, to
allow them to bleed when the ball just begins to move off the seat. Lastly, I
noticed the -3 washers that Lyc specifies seem a little too small. But -4's
are too large. So I ground down a -4 and put that in to minimize any spring
wobble on the washers.

I also forgot to put back one of the washers. The end result is that oil
pressure is better behaved, although I don't know which variable is
responsible. The oil pressure doesn't rise as high on takeoff as it used to
and still holds 60 psi when oil is hot. I keep meaning to watch to see if it
goes "sproing-g-g-g" but have been in the right seat and since it's not right
in front of my face, haven't noticed.

Thanks for the help so far... will squawk if the problem persists.

Mike Palmer
Excellence in Ergonomics



How thick are the washers? Do you know what the spring rate is, or do you know what the force is when the spring is
compressed to installed length? What is the size of the orifice/seat?

You are probably best off with a sharp edged seat where the ball sits, to minimize any hysteresis. You do not need a
leak free seal.

Most likely, loosing one of the washers was the reason for the lower regulated pressure....

Check out:
http://tinyurl.com/47d2w
http://tinyurl.com/5lqpd



  #8  
Old November 6th 04, 08:34 PM
Whunicut
external usenet poster
 
Posts: n/a
Default

Glad I could help, Mike.

Warren


Howdy Warren:

Sounds like the oil pressure relief valve spring cound be hanging on the lip
of
the spring retainer cap.
Take the cap off and chamfer the hole the spring goes into. Check for burrs
on
the inside of the cap and also check the spring to see if it is bent or
deformed in any way.


Okay, even tho I hadn't seen any burrs, I surfaced and chamfered the cap
anyway. I also tried to chamfer a bit the oil drain back holes in the cap,
to
allow them to bleed when the ball just begins to move off the seat. Lastly,
I
noticed the -3 washers that Lyc specifies seem a little too small. But -4's
are too large. So I ground down a -4 and put that in to minimize any spring
wobble on the washers.

I also forgot to put back one of the washers. The end result is that oil
pressure is better behaved, although I don't know which variable is
responsible. The oil pressure doesn't rise as high on takeoff as it used to
and still holds 60 psi when oil is hot. I keep meaning to watch to see if it
goes "sproing-g-g-g" but have been in the right seat and since it's not right
in front of my face, haven't noticed.

Thanks for the help so far... will squawk if the problem persists.

Mike Palmer
Excellence in Ergonomics









 




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