737 Hyd pumps ops

[Patryk]

I've been wondering whether HYD PUMP switches for EMDP in both systems shall be in ON position during the whole flight (namely from starting the engines to shutting down), or OFF and switched to ON only if EDPs are lost ? I've sought information in 737's maintenance manual and in FOMs, but to no satisyfing effect.

Thanks in adv for posting

[de facto]

Are you rated?

[Patryk]

Unfortunatley I'm not. I'm working on degree related to hydraulics in 737 and needed that info.

[LEVEL600]

EMDP are switched on before engine start usually during cockpit prepartion checklist and switched off after shutdown. EDP sw. are in on all the time, in off position is supplied pump depres. solenoid, which can be overheated/damaged without cooling.

[Patryk]

Thanks so much, but do you know if EMDPs in"ON" work continously or start only when EDP output falls .

[LEVEL600]

EMDP delivers pressure continously togheter with EDP, only output flow is significantly lower, hope that helps...

[Patryk]

Thank You very much. That answer has dispelled all dubiousness !

[de facto]

The engine driven pumps switches are normally left in the ON position as the solenoid energises when the pump is switched OFF.(therefore saving the slolenoid valve when left in the On position).
The only hydr pumps that are switched OFF on the ground(after engine shutdown) are the electrical pumps.
The engine driven A is switched off when tow bar is required and no pins installed.

Some airlines request their crews to always switch OFF the syst A engine and electrical hydr pumps as they have no trust in either the pilots or the ground crew.

[kenguan]

I think you're asking the question probably because some other aircraft types, their EMDP only kicks in (comes on automatically) under certain conditions, normally when load on hydraulics is high such as when flaps or landing gears are operated, or if hydraulic pressure drops to a certain value (maybe due to EDP failure),
At other times the EMDP is automatically off, only EDP is on.
On these aircraft, the switches for the EMDP are most likely labelled OFF, AUTO or ON. The normal position for the switch is AUTO. ON is to force the EMDP to run.

So yes, to answer your question with regards to 737, the EMDP is always on, and so is the EDP when the engine runs.

[yotty]

Hyd Pumps

Does this apply to all 737 variants?

[IFixPlanes]

Speaking about -300 and on:
ENG 1 (EDP) is the main source for system A and the EMDP is the electric backup.
ENG 2 (EDP) is the main source for system B and the EMDP is the electric backup.

If you take a closer look at the hydraulic panel you see that the EMDP for the system A is named ELEC 2 and the B EMDP is named ELEC 1.
This is because the (electric) power for A EMDP comes from the generator mounted on ENG 2 and ENG 1 is the source for B EMDP.
This crosswiring ensure powering of hydraulic system A when you lost ENG 1 or system B when you lost ENG 2 through the electric powered EMDP from the other side without any switching. You have enough to do when you lost one engine ;-)

[LEVEL600]

Pump logic mentioned above is valid at least from 300 to 900, dont know for first 737 generation.

[IFixPlanes]

therefore i wrote:

Speaking about -300 and on:

[LEVEL600]

IFixPlanes:12 mins is not enough for me to recognize your contribuiton, so above means in fact one more row above

[kenguan]

for the 737-200, the hydraulic is different in the sense that (comparing to -300 to -900)
1. System "A" is purely powered by EDP (engines)
2. System "B" is purely powered by EMDP

All pumps are on during normal operation.

Therefore, on the ground with only electrical power available, you can only pressurize system "B" with either 1 or both EMDP. If you on both EMDP, everything runs faster due to the greater flow.
System "A" is pressurized when you motor or run the engines
OR
There is something called an interconnect switch but only used on ground, mainly for maintenance purpose, which enables system "A" to be pressurized by system "B" EMDP.

But this is off track from the original topic...

[B737SFP]

Your post made me laugh fulminn !





Nice one.

[de facto]

Fulmin,


I flew for airlines which had different sops regarding this issue,some always wanted you to keep the Engin HYdr A pump ON,(unless pins were not installled) and some always wanted them OFF.
Please explain where such difference would come from then,since you seem to have such a big mouth for an 18 month F/O....

Please stop BS

When your shade of green turns lighter,get back to us,same goes to you B737 SFP.

[Denti]

In the 15 years on the 737 i had we never switched off System A pumps for push back. However, we always had ground handling that used the lockout pin and depressurized the steering.

In my last airlines we even left the electric pumps on during ground stays up to 60 minutes, which is pretty much all normal turnarounds.

[de facto]

My last 2 airlines SOP were to switch A OFF systematically for pushback.

[fruitloop]

kenguan
Correct regards interconnect switch...With WOW remember to "Park Brakes" or nothing happens..