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DHC8 mod 8-2781

Old 11-23-2011, 06:19 AM
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Default DHC8 mod 8-2781

With this mod, DHC incorporated a ISO VLV in order to isolate the rudder from the rest of the hydraulic consumers.

The hydraulic Isolation Valve closes when there is a low quantity in the hydraulic reservoir, and the HYD ISO VLV caution light illuminates.

If the leak continues - the hydraulic reservoir will be emptied and the Engine driven pump will have no fluid to pump and the ENG HYD PUMP caution light will illuminate.

This is what I know.

My question is - does the HYD ISO VLV open again when the reservoir is completely empty?
The sim that I am in right now does that.
The checklist for complete hydraulic failure reads - ENG HYD PUMP and HYD ISO VLV illuminated - which leads me to believe that the HYD ISO VLV should be on.

Any ideas? References?
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Old 11-23-2011, 07:02 AM
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Pardon me cause I'm typing from my phone, but with the illumination of the HYD ISO VLV light it means the valve has worked properly and you still have about a half quart of fluid in the system. The only thing that will still function on the respective system is the rudder actuator. If you had a complete HYD failure and the ISO valve fails I would not expect to see the HYD ISO VLV caution light and quantity would obviously read 0.
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Old 11-23-2011, 07:36 AM
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With a complete loss of fluid

Would both ENG HYD PUMP and HYD ISO VLV be on or just ENG HYD PUMP, assuming everything is working as advertised?
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Old 11-23-2011, 09:10 AM
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Never mind you are working the Q 400 right??

Last edited by skid; 11-23-2011 at 09:23 AM.
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Old 11-23-2011, 09:21 AM
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If you have a complete loss of fluid that means the ISO valves did not work and you will not see the HYD ISO VLV caution.. So to answer your question with complete loss.. You will only have ENG HYD PUMP.

If you see a HYD ISO VLV you do not have a complete loss only a partial loss.
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Old 11-23-2011, 09:26 AM
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I will say I'm speaking to the 100&300 series the 200 may be different.
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Old 11-23-2011, 10:12 AM
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Originally Posted by skid
Never mind you are working the Q 400 right??
Currently I am doing some classic training though.
The Q400 I know how it responds.
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Old 11-23-2011, 10:17 AM
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Originally Posted by piper338
If you have a complete loss of fluid that means the ISO valves did not work and you will not see the HYD ISO VLV caution.. So to answer your question with complete loss.. You will only have ENG HYD PUMP.

If you see a HYD ISO VLV you do not have a complete loss only a partial loss.
what if the leak is in a rudder actuator?
Then the iso valve would close in response to the low fluid quantity, the leak would continue until all fluid is drained. Then the ENG HYD PUMP light would come on due to low output pressure from the EDP.

Would the ISO VLV stay closed in this instance?
Would the ISO VLV caution light stay on?

The sim responds with an initial ISO VLV light
then when the reservoir is empty the HYD PUMP light comes on and the ISO VLV extinguishes.

Is that correct.

I am mostly familiar with a Q400 and I know what that aircraft does, I am just wondering what the 100-300 will do/is intended to do?

It is a 100 simulator that I am working with.
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Old 11-23-2011, 10:50 AM
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That's just a bad day when that happens.... Honestly I don't know.

I think it would open and the light go out in that instance just because it is a float switch. Can't "float" with no fluid...

Just a guess, I'd go test it out but I might get into some trouble.
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Old 11-23-2011, 12:50 PM
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Originally Posted by omniair
what if the leak is in a rudder actuator?
Then the iso valve would close in response to the low fluid quantity, the leak would continue until all fluid is drained. Then the ENG HYD PUMP light would come on due to low output pressure from the EDP.

Would the ISO VLV stay closed in this instance?
Would the ISO VLV caution light stay on?
ISO VLV activation and illumination of the caution light is essentially due to a "float switch" in the respective hydraulic reservoir. Valve operates in order to keep the respective rudder actuator working by using the limited fluid quantity remaining in the reservoir, pumps, filters and lines upstream of the isolation valve.

If there is a leak in the rudder actuator, then when the float switch in the reservoir activates: 1) the ISO VLV stays closed. 2) the ISO VLV caution light remains illuminated. 3) the ENG HYD PUMP caution light illuminates due to low output pressure from the EDP. 4) other associated rudder caution lights will also illuminate and remain on such as RUD PRESS and RUD FULL PRESS.

Originally Posted by omniair
The sim responds with an initial ISO VLV light
then when the reservoir is empty the HYD PUMP light comes on and the ISO VLV extinguishes.

Is that correct.
Nope, not correct at all. Better find a sim tech to look at it.

Last edited by trent890; 11-23-2011 at 01:18 PM.
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