REFLECTOR: Hydraulic Fluid

Mon May 25 18:34:39 CDT 2009

Well, as I say, my planee was not hangared, but it has been mostly covered, but I still accumulated a significant volume of water.  However, rather than tearing into a perfectly good operating hydraulic system to check it, a simple method would be to take a turkey baster (probably not the one in the kitchen, unless you want to be on the menu for Thanksgiving dinner), connect some tygon tubing on the end and thread it down into the bottom of the reservoir and suck up a little bit of whatever is on the bottom.

If you do this a couple times from different places in the reservoir, and it's nice clean, clear fluid, I'd guess you're in good shape and I'd not mess with it.  Without a doubt, had I used that technique, I would have discovered the contaminated fluid with no problem at all.  In short, I believe the turkey baster would give you reliable results, with less effort, while reducing the likelihood of screwing up other things while klutzing around with the hydraulic system.

Chuck Jensen 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On Behalf Of Al Gietzen
Sent: Monday, May 25, 2009 7:16 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Hydraulic Fluid

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  <mailto:cjensen at dts9000.com> Jensen 

To: Velocity  <mailto:reflector at tvbf.org> Aircraft 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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