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Could somebody help me with the following problem?

Reading Emergency Power Unit Schematic (described as typical - T.O. 1F-16CJ-1) I found that in the case of emergency (main and standby generators failure or both hydraulic systems failure), when the high pressure bleed air is not avialable for some reason, the EPU Controller "open" the Valve Assy and high pressure nitrogen through this valve pushes hydrazine fuel out from its board storage to the EPU. So far this is clear for me, but before pushed out hydrazine reach the decomposition chamber of the EPU, there's Control Valve on its way as shown in the mentioned above schematic. That Control Valve is described as responsible for metering hydrazine fuel to the EPU (amount of hydrazine determined by the EPU rpm). Unclear for me is that the Valve Assy is told to do the same. So what regulates the amount of hydrazine fed to the EPU, Valve Assy or Control Valve? Thers is also something called the Speed Monitor (according to schematic monitors the EPU rpm and hydraulic pressure provided to sys A) which controls the Control Valves. Is this Speed Monitor a sub-unit of EPU Controller? And what controls the amount of hydrazine fed to the EPU? Another thing: does the activation of the EPU (except test run on the ground) always mean the the hydrazine is pushed out of its storage to the hose connecting this storage with EPU Control Valves even if there's no need of using it because of sufficient bleed air pressure?

Can you tell where in the web I could find more detailed description of the F-16's emergency power system. Question

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Sounds like you might need to talk to your LM rep!

Well you understanding theory to far in depth, in my opinion. Personally, I do my best to understand theory at the level of replacement for the item I would be working on. Since I wouldn't replace any of the items you mentioned cause the EPU is a (Line Replaceable Unit), then I feel I don't need to understand the inner workings that far in depth. I trouble shoot to the item I would replace, and in this case its the EPU or the EPU Generator, and then replace the faulty item.

I also think 229guy is correct. Talk with your LM rep if you feel the need to get that in depth.

Enthusiast Joined: Jul 02, 2004 Posts: 26 Status: Offline

As for the MLU version the fuel control valve between the hydrazine tank and the decomposition chamber are 2 open/closed valves, primary and secondary. When the EPU runs in monopropelant mode, hydrazine is forced by the pressure in the hydrazine tank through the decomposition chamber. The epu turbine speeds up until the turbine rpm is over 77000rpm, then the hydrazine cuts off and the turbine runs down. When the rpm is under 72000, the valves open and hydrazine goes to the decomposition chamber and the turbine will speed up again. The speed pickups are integrated in the epu package and are as far as I know not line replacable.

As for starting when not in test mode, yes hydrazine is always used. When the epu is supposed to operate and the turbine rpm is under 77000 rpm the epu speed controller (which controls the epu operation) opens the fuel control valve and hydrazine is used. Normaly hydrazine is used for the initial speed up, and then only bleed air is required.

IDCrewDawg wrote:

Well you understanding theory to far in depth, in my opinion. Personally, I do my best to understand theory at the level of replacement for the item I would be working on. Since I wouldn't replace any of the items you mentioned cause the EPU is a (Line Replaceable Unit), then I feel I don't need to understand the inner workings that far in depth. I trouble shoot to the item I would replace, and in this case its the EPU or the EPU Generator, and then replace the faulty item.

I also think 229guy is correct. Talk with your LM rep if you feel the need to get that in depth.

I've read about all that stuff in manual for pilots, so I wondered what could be said about this in manual for maintainers. You're right, of course, on the flightline you do waste time for such academic considerations, just identify and replace the failed part. I was just a little curious. Besides if such detailed info is written for pilots, one could be afraid about the level of know how required for maintainers who keep this thing running.

Sounds like someone fishing. Best left to LM Reps.

If you would like to know more info on the EPU system, go to the nearest recruiter's office and tell him you want to enlist under 2A6X4. Enlist for six years. In about 6 months you should have a brief idea of what goes on in that system. You will even get to play in the "space suit" and clean up hydrazine. You might even get hosed if you're lucky.

Elite 2K Joined: May 13, 2004 Posts: 2945 Location: Utah

See if this attachment helps your efforts, it is from an old training course I took years ago and I mean years ago.........

Newbie Joined: Feb 24, 2006 Posts: 1 Status: Offline

I think I can answer your question on the valve trouble you seem te be having. There's two valves; one that regulates and controls nitrogen pressure to pressurize the hydrazine bottle. This is the Nitrogen Valve Assy.
The other assy is the Control Valve Assy, which indeed consists of two valves, primary and secondary. Secondary is NC type, primary is NO type. The EPU controller controls these valves to regulate EPU RPM. Speed monitor is indeed a part of the EPU controller. (EPU controller also is referred to as Electronic Speed Controller.

Hope this clears something..

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Emergency Power Unit problem