REFLECTOR: Hydraulic Fluid

Mon May 25 18:15:54 CDT 2009

This raises a question that I've had on my mind as I completed my recent
annual.  Should the gear pump fluid be changed occasionally?  

I think your experience answers that question.  This fluid, like brake
fluid, has additives that absorb (combines with) moisture.  When it gets to
its saturation point, more moisture means free water in your system.  Just
like it is recommended that you bleed fluid off your brake cylinders every
couple of years, we should replace the fluid in the pump reservoir -
especially if you live in a humid climate with lots of temperature changes.

The only source of water that I can think of would be condensation due to
temperature changes, and the fluid level changes drawing in moist air.  The
plane sitting outside would be more subject to these factors.

I wouldn't wish your experience on anyone; but it's great that we get to
learn from it:-)

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Chuck Jensen
Sent: Monday, May 25, 2009 12:17 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Hydraulic Fluid

Update:      After trying/checking most everything, including topping off
the reservoir and checking the dump valve, which I suspected was good
because once I got the pump to prime and pump the mains up, the pump would
shutoff and the valve would hold just fine.  And, when the dump valve was
opened, the mains and nose gear came down and dropped in place as expected.
Yes, the continuously running pump is characteristic of an open dump valve,
but that appears not to have been the issue.

When I removed the reservoir, I was surprise/shocked to find 100-150 cc of
milkish white liquid in the bottom of reservoir with black globules
suspended or settling in the milkish layer below the stratified hydraulic
fluid.  I assume the separated milkish layer was water with hydraulic fluid
emulsified in it from the vigorous pumping.  Everything else seemed to be in
order, but in looking at the check balls with a magnifying glass, the
surface looked like the surface of the moon, with craters and pits covering
15%-20% of the surface.  The roto-gears, which pump the hydraulic fluid all
appear in good order, so it was mostly likely pass-by of the check valves.
Given how corroded they were, it's surprising it worked as long and well as
it did.

The source of the water is a bit of a mystery.  Ken Mishler had the
reservoir off and cleaned when he was doing repair work over at Malcolm's
about two years ago.  He reported finding the same milky garbage in the
bottom of the reservoir.  One must assume is comes from setting outside, but
most of the last two years, it's had a cover on it.  Very surprising that it
could accumulate that volume of water under those circumstances, but there's
no other credible explanation.

I looked at replacing the entire unit or rebuilding the pump.  If the
factory has a repair kit in inventory, I'll probably go that direction as
the balance of the parts all appeared to be in A-1 condition.  In the mean
time, I'll give USelessAir some of my money to make a trip to Buffalo on
Wednesday and hope to have good results to report on Thursday or Friday when
I put things back together.

Ken's recommendation was to use only 5606 fluid, though google searches and
other sources seem to indicate a lot of people having used ATF successfully,
with very few reports of any problems.  Oddly, 5606 is as cheaper, or
cheaper than ATF, so it's not much of a sacrifice to stay with the first
line stuff.  Thanks for all the ideas and comments.  It's always helpful to
have second, third and fourth thoughts.

Chuck Jensen 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Terry Miles
Sent: Monday, May 25, 2009 1:16 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Hydraulic Fluid

Whoops.  I stand corrected on the dump valve inspection.  Terry

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of davedent at comcast.net
Sent: Sunday, May 24, 2009 15:27
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Hydraulic Fluid

Chuck it looks like what we have found on a number off RG planes.  The dump
valve appears to be leaking.   You can first try by tighten up on the
packing nut and if this doesn't work the valve will have to be replaced.  In
most cases the pump will keep running while gear is in the up position and
cavetate to the point that it turns into a vapor and you will loose it
overboard.  

I think you have it plumbed OK but check out the dump valve before you start
taking everything else apart.  In most cases by just tightening the packing
nut that holds the handle on can change it a lot.  Let me know what you
found. 

Dave

----- Original Message ----- 

From: Chuck Jensen <mailto:cjensen at dts9000.com>  

To: Velocity Aircraft <mailto:reflector at tvbf.org>  Owners and Builders list 

Sent: Sunday, May 24, 2009 8:44 AM

Subject: Re: REFLECTOR: Hydraulic Fluid

Al,

Thanks for the comments, but now I have additional information, since I
topped off the hydraulic reservoir with fluid, but the situation remains.  

When I toggle the gear switch to the up position, the pump runs constantly
(appearing, by sound, to be free wheeling, in that it runs with no
resistance).  Joggling the master on/off, eventually the nose hear rose
slowly to it's 3/4 up position, as usual, but the pump continued to run with
no movement of the mains, which would normally follows.

By chance, I pushed down on the nose gear...and the mains moved up a small
amount and the nose wheel moved back up to its 3/4 position when I released
it.  I did this again, and it was quite amusing, pushing down the nose gear
several inches would cause the mains to more up a few inches.  Repeating the
process, it was like I was jacking up the mains by using the nose gear as a
jack handle, all the while, the hydraulic pump was merrily making noise, but
apparently not much pressure.

Until, that is, the mains were about 1' from being nested, when the pump
took over and raised the mains up into their pockets and did that finally
'chinch movement' that says they are snugged away.  I did this a number of
times, with same behavior each time.  After being nested for a couple
minutes, there was that short blip on by the pump to 'snug' the mains tight
again, all as usual, and then the pump shutoff and stayed off.

But moving the switch to 'down', the pump would start running, but nothing.
However, if I opened the dump valve for about a second and then closed it,
the hydraulic would start moving the gear down.  Once in the down position,
the red 'unsafe' light did not extinguish and the pump continued to run,
even though the main and nose appeared locked in place.

The pump acts like it is cavitating and not creating pressure.  However,
once there is some back pressure on the pump, such as when the mains are
close to being nested, then the pump will 'engage' the hydraulic fluid,
creating pressure to snug the mains.  The dump valve must be opening and,
most importantly, closing properly or the pump would keep running when the
mains are snugged away.  Nonetheless, the pump runs as though it is free
wheeling, just like the dump valve was open.

So, there's obviously some things I don't understand about the pump, or
what's going on.  Any guesses?

Chuck Jensen 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Al Gietzen
Sent: Sunday, May 24, 2009 11:32 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Hydraulic Fluid

Chuck;

There are significant differences (primarily in the additives); the most
notable is the change is viscosity with temperature. At very low temps; like
-20F, ATF becomes quite viscous while the 5606 does not.  This is important
for aircraft flying at the flight levels, or in cold climates.  If you do
neither, ATF will work fine.

When I first filled my system, I put in ATF - which is what the pumps we use
are designed for.  Later I thought at some point I may be flying high and
into colder climes; and changed it out for 5606.  I was surprised, and
disappointed, at how much noisier the pump was.

I was concerned about mixing of the two, so developed a method for changing
the fluid that gets most of the old out before putting in the new.  I wrote
up that procedure, and probably still have it somewhere, and could share it
with you it you like.  I don't know that mixing is an issue, but I would
hesitate to do it.

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Chuck Jensen
Sent: Saturday, May 23, 2009 4:39 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Hydraulic Fluid

Okay, I need to add hydraulic fluid and the FBO is shut tight for the
weekend...no 5606 available.  It was speculated that the automatic
transmission fluid (ATF) is just a rebranded/repackaged 5606.  Has people
used ATF in their gear retract system?

Chuck Jensen 

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