Hydraulic power control valve

The world's most popular advanced trainer of WWII
new reply
gnocgnoc
Airman First Class
Posts: 68
Joined: 02 Feb 2014, 10:16

Hydraulic power control valve

Post by gnocgnoc »

Hi All,

After looking at the Hydaulic System diagram from the pilot handbook, can someone tell me what’s the purpose of the power control valve?
BTW I unsuccessfully tried to post the diagram image... Is there a way to post images on this forum ?
Marc

User avatar
Paughco
Senior Master Sergeant
Posts: 2095
Joined: 30 Nov 2014, 12:27

Re: Hydraulic power control valve

Post by Paughco »

I believe variants of the T-6 prior to the T-6G had a separate "power push" lever that supplied hydraulic power to the landing gear after the pilot had selected up or down on the landing gear.

Use of the power push lever is described in my favorite YouTube video on takeoffs, approaches, and landings in the T-6: https://www.youtube.com/watch?v=3UZmEha ... 0A&index=2. I still watch this thing just before taking my T-6 out if I haven't flown her for a few days.

According to this article, "With the T-6G, movement of the gear or flap handle actuates the respective system." http://flynata.org/content.aspx?page_id ... _id=241058.

Here's another good one: http://www.warbirdalley.com/articles/t6-sf.htm. Please read it all the way to the end.

Here's what a set of power push levers (front and rear) look like: https://www.ebay.com/itm/NEW-T-6-SNJ-Ai ... 1753639659.

Seeya
ATB
Image

gnocgnoc
Airman First Class
Posts: 68
Joined: 02 Feb 2014, 10:16

Re: Hydraulic power control valve

Post by gnocgnoc »

OK thank you very much. Very interresting and as I understand, previous versions were fitted with a “power push lever” which (probably) actuated the power control valve. Now the question remains. What’s the power control valve function ?

Here is a link to the diagram I’m talking about :
https://www.dropbox.com/s/u20b55ot1b9ok ... s.jpg?dl=0
Marc

User avatar
Paughco
Senior Master Sergeant
Posts: 2095
Joined: 30 Nov 2014, 12:27

Re: Hydraulic power control valve

Post by Paughco »

OK, I found this web site on the Internet: http://www.avialogs.com/en/aircraft/usa ... l#download. They want money for a full download, but you can look at the pages in a small viewer for free. Go to page 66. Zoom in to the picture of the left side of the front cockpit interior. The controls for the gear and flaps look different from what we have in a T-6G. The "power push" is item 1 in the illustration. Scroll down to page 67 and you'll see that item 1 is labeled as the "Hydraulic Power Control."

Looks like that is the same as the Power Control Valve in the hydraulic system diagram in your Dropbox link. Note how the hydraulic fluid has to pass through the power control valve before it can get to either the wing flap or the landing selector valves. This is like the electricity has to pass through the master switch before it can get to the lights, radios, etc.

I remember reading somewhere that you operate the gear or flaps on an early T-6 by first moving the gear or flap lever from the neutral position to the desired (up or down) position, then you press the power push lever which allows flow of hydraulic fluid through the gear or flap selector valve, then finally to the gear or flap actuator. I believe that the power control valve shuts off automatically after remaining open for long enough for the gear or flaps to be extended or retracted.

The gear or flaps on a T-6G is set up so that when you move the flap or gear handle from the neutral to the desired position (up or down), there's a lever or rod that operates the power push (power control valve) automatically. This is probably why the power control valve and the wing landing gear selector valve and the wing flap selector valve and all highlighted in red and the note below states that they are all incorporated in one unit.

That landing video on YouTube shows the operation of the old style setup, in which you move the flap or gear lever, then hit the power push lever, which operated the power control valve.

It would be really nice if we could go out on the flight line and look at the two different setups, but that's not happening.

Here's another question: What is that red light in the leading edge of the left wing for?

Seeya
ATB
Image

User avatar
AKar
A2A Master Mechanic
Posts: 5208
Joined: 26 May 2013, 05:03

Re: Hydraulic power control valve

Post by AKar »

gnocgnoc wrote:After looking at the Hydaulic System diagram from the pilot handbook, can someone tell me what’s the purpose of the power control valve?
It seems you figured it out before I noticed your question. :)

The purpose of the power control valve is to divert the hydraulic flow to the appropriate demand. The valve is mechanically actuated by appropriate selectors. Importantly, note that a hydraulic pump such as installed in T-6 has no means of control, it produces fluid flow proportional to its rotational speed, in turn depending directly on engine's speed. When there is no hydraulic demand, the power control valve allows the fluid to return into the reservoir, kind of freewheeling the system.

There is also a relief valve that limits the pressure when the actuators are against their stops for instance. Hydraulic system can be designed in such a way that a relief valve is the primary mean to control the pressure, and therefore is constantly open when the flow exceeds the demand. This is identical to the engine oil system, where constant pressure is needed and is therefore held up by a relief valve (yes, this is something to think about: your engine's life depends on a single, small spring!). Because our hydraulic system on a T-6 is not needed for most of the time, we want to depressurize it to avoid leaks and to reduce the load on the pump. It takes quite a bit of power to hold open a pressure relief valve: in fact, power demand of a hydraulic system driven by a fixed-displacement pump and regulated by a relief valve is the highest when the system idles!

Hope this explains it a bit! :)

-Esa

gnocgnoc
Airman First Class
Posts: 68
Joined: 02 Feb 2014, 10:16

Re: Hydraulic power control valve

Post by gnocgnoc »

Thanks to you both, that exactly replies to my question!

BTW I've found this about the red light in the leading edge:
https://aviation.stackexchange.com/ques ... 3451#43451
Marc

new reply

Return to “T-6 "Texan"”

Who is online

Users browsing this forum: Google [Bot] and 6 guests