REFLECTOR: Hydraulic Fluid

[Al Gietzen]

Chuck;

 

At first it sounded like your dump valve was not sealing; but as I read on,
I suspect the pump.  As I recall, there are a couple of check valves in
there, and possible one is not seating; or possibly a vane sticking.  I've
never disassembled the pump; so it's just a guess.  You may want to chat
with someone at Velocity on this.  There may be a rebuild kit for the pump.

 

Al

 

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Chuck Jensen
Sent: Sunday, May 24, 2009 7:45 AM
To: Velocity Aircraft Owners and Builders list
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 

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20090524/ab0b143e/attachment-0001.htm>