The "Standpipe" in the 737NG hydraulic reservoirs
 

I don't know what a Standpipe is (can't even visualize it). What's it look like roughly?

Can someone please explain how it works in simple terms with respect to the 737NG hydraulic system.

Thanks,

Picture a tank with fluid in it with a hole in the bottom. All the fluid could drain out of that hole.

Now instead of the hole, picture a pipe sticking up from the bottom of the tank half the height of the tank.

Only the top half of the fluid can drain through that pipe because when half the fluid is gone the top of that pipe is standing above the level of the fluid.

This is a stand pipe. It is used to limit or prioritise fluid levels.

Hoppy, reading it the way you describe, all the fluid would still go out the hole in the bottom of the tank if that's where the hole was!. I am sure what you meant to say is that if there was a leak somewhere in a line (or ram or wherever else in the system being served), only half the tank contents could be lost to that system. The remainder would be preserved for an alternate system.
Another place you find stand pipes (but of lesser length) is in some fuel tanks so that any water can collect below the stand-pipe, allowing clean fuel to be drawn off through the standpipe.
And the standpipe is the basis of a fuel reserve system on many motorbikes. When the fuel gets down to the standpipe level, the engine stops unless you open the bypass valve in order to access the remainder in the tank.

I meant instead of the hole. I've edited it. :ok:

Not hydraulic system (well...) but fuel balancing is obtained on the Bell 214 (+ others) by standpipes. See page 128 here: http://www.bellhelicopter.com/en/air...002_r1_web.pdf

Follow up Question from the 737NG FCOM...

"System A Hydraulic Leak
If a leak develops in the engine–driven pump or its related lines, a standpipe in the
reservoir prevents a total system fluid loss. With fluid level at the top of the
standpipe, the reservoir quantity displayed indicates approximately 20% full.
System A hydraulic pressure is maintained by the electric motor–driven pump.

If a leak develops in the electric motor–driven pump or its related lines, or
components common to both the engine and electric motor–driven pumps, the
quantity in the reservoir steadily decreases to zero and all system pressure is lost."


Okay.... so I don't get how if there is a "Standpipe" in the Hyd A System, how can the hydraulic quantity ever get to 0 percent in the case of a leak in the Elec Hyd Motor or its related lines?

In other words, due to the Standpipe, if there is a leak in the Engine Driven Hyd Pump, you'll still have 20 percent hyd fluid left.

But if the leak is with the Elec Hyd Pump, you'll lose all your Hyd A fluid in spite of having the Standpipe?

Me confused!


Other Question regarding Hyd Sys B:

"System B Hydraulic Leak
If a leak develops in either pump, line or component of system B, the quantity
decreases until it indicates approximately zero and system B pressure is lost."


Ummm, so Hyd B Reservoir also has a Standpipe, but if you get a Hyd B leak the hyd quantity will eventually indicate 0.

Again, how can this be given the existence of the Standpipe?

The standpipe supplies the engine driven pump, the 'hole in the bottom' supplies the electric pump... Leak in Elec pump pipework leads to total loss, leak in engine driven pump only empties to standpipe level-> system A

Ahhhhh.....

Cheers!

System A:
- EDP-Supply via standpipe
- EMDP-Supply via the bottom of Reservoir.

System B:
- EDP & EMDP-Supply via standpipe
- PTU-Supply via the bottom of Reservoir

Standpipes are sometimes used when a "reserve" fluid quantity is desired. The BT-13 fuel system is an example. It had two 60-gallon (US) tanks, but a 3-position fuel selector. The right tank had a standpipe at the 18-gallon level IIRC, such that if the unwary student consumed fuel down to that level, and the engine sputtered, there was still 45 minutes fuel available by selecting the "reserve" position (ie the bottom of the tank).

http://www.warbirdalley.com/images/Im000226.jpg