Hydraulic pumps on/off sequence

[19AB67 16]

Hi folks, 

 

I still haven't seen the effects of *not* sticking to correct sequence of switching on ...

1. R ELEC Demands

2. C1/C2 ELEC Primaries

3. L ELEC Demands

4. C1/C2 AIR Demands

 

and the other way round 4-3-2-1 to switch them off. 

 

FCOMv1 reads on page NP.21.29: 'Pressurize the right system first to prevent fluid transfer between systems.' 

 

Is this modelled? 

The synoptics does show a connection?! 

 

Thanx in advance. 

[Pilotdude3407 11]

I read this in the DAL manual as well. I am not really sure what would happen with fluid transfer. Maybe overfilling the system. That could cause leaking, possibly over pressure.

[E6BAV8R 88]

Hi folks, 

 

I still haven't seen the effects of *not* sticking to correct sequence of switching on ...

 

Do you have failures on?

[19AB67 16]

 

 

Do you have failures on?

 

Excuse me, I don't understand your question. 

The answer would be yes, but I am talking about the real aircraft behaviour (FCOMv1), that there shall be a (which?) fluid transfer (between L, C, R?), if I don't switch on R ELEC demand pumps on first. 

[MikeHenke 1]

As I recall correct, during my 777 maintenance class they told me that the hydraulic brake accumulator gets pressurized normally by the R system.

 

There is a ball valve which switches from the R system to the CTR system if the wrong system is pressurized first, causing the fluid in the accumulator (which came from the R system) to flow into the CTR system when pressure is applied to the brake system using the accumulator. This can cause an overfill in the CTR system.

 

I might be wrong here, I will look it up in the 777 maintenance training manual to be sure.

[19AB67 16]

There is a ball valve which switches from the R system to the CTR system if the wrong system is pressurized first, causing the fluid in the accumulator (which came from the R system) to flow into the CTR system when pressure is applied to the brake system using the accumulator. This can cause an overfill in the CTR system.

 

I think the other way round then: If you pressurize the R system first, the ball valve will be closed. 

If you don't keep the R system pressurized, the C system will leak into the R system. 

 

Maybe this is wanted: In case see that the R system is low in fluid, you can fill it up cautiously by depressurizing the R system. 

 

But, is it simulated in PMDG777? 

What is the volume per minute? 

 

04:16z   I am on my way from CYYZ-ACA92-SCEL and switch off both R primary and R demand. L-C-R read 0.99, 1.17, 0.99 in volume. Let's see... 

 

04:22z   Still the same... L-C-R read 0.99, 1.17, 0.99 in volume. 

 

04:27z   Still the same... L-C-R read 0.99, 1.17, 0.99 in volume. I switch on again; no transfer... 

Edited September 13, 2013 by 19AB67

[MikeHenke 1]

I think the other way round then: If you pressurize the R system first, the ball valve will be closed.

If you don't keep the R system pressurized, the C system will leak into the R system.

 

Maybe this is wanted: In case see that the R system is low in fluid, you can fill it up cautiously by depressurizing the R system.

 

But, is it simulated in PMDG777?

What is the volume per minute?

 

04:16z I am on my way from CYYZ-ACA92-SCEL and switch off both R primary and R demand. L-C-R read 0.99, 1.17, 0.99 in volume. Let's see...

 

04:22z Still the same... L-C-R read 0.99, 1.17, 0.99 in volume.

 

04:27z Still the same... L-C-R read 0.99, 1.17, 0.99 in volume. I switch on again; no transfer...

The valve is a T-joint where the lower part is connected to the accumulator and the left and right side to the R and CTR system. In the horizontal part of the T there is a steel ball which can move left to right. So if the pressure on the R side is applied first, is closes the CTR system and vice versa.

 

Remember the transfer only takes place when the brake accumulator is your primary source of pressure for the brake system. So transfer should take place when you apply and release the brakes. I worked for KLM Engineering and Maintenance a few years ago and we used this technique on the 747 to level out the hydraulic quantaties.

[MikeHenke 1]

You should take a look in the FCOM v2 which systems power the hydraulic brake system. Then follow these steps to transfer from R to CTR (if the CTR system is applicable)

 

1. Depressurize all systems and apply and release the brakes untill the brake accumulator gauge reads something close to 0.

 

2. Apply R system pressure, this moves the valve, closing the CTR system and filling the accumulator with fluid from the R system.

 

3. Depressurize the R system.

 

4. Pressurize the CTR system, this causes the valve to move and close the R system.

 

5. Depressurize the CTR system. Now the accumulator is the only source for brake pressure.

 

6. Apply and release the brakes untill the accumulator gauge reads something close to 0 again. This causes R system fluid to flow to the brake pistons and back into the CTR system reservoir.

 

6. Repeat.

[E6BAV8R 88]

Excuse me, I don't understand your question. 

The answer would be yes, but I am talking about the real aircraft behaviour (FCOMv1), that there shall be a (which?) fluid transfer (between L, C, R?), if I don't switch on R ELEC demand pumps on first. 

 

My misunderstanding than.  I thought you were asking what would happen if you didn't do the proper sequence as specified in the FCOM.  My point being that you probably won't notice any abnormalities without failures on.

 

I honestly have no idea what the consequence of not doing the proper sequence is, though.

[Flamin_Squirrel 71]

I honestly have no idea what the consequence of not doing the proper sequence is, though.

 

You should do, Mike took the time to explain it to you above.