Process question: transfer pump during startup

[Voyager]

In the full procedures, I notice that you disable the hydraulic transfer pump before starting the engines, but in the full list, after the right engine is started, you

1. crank the left engine until it's at 3000 psi,
2. turn off the starter crank,
3. then turn the transfer pump on
4. Then turn the pump back off 
5. And go through the normal left engine start-up

What I don't get is, why do you do that? Is this to test the transfer pump? And if so, what are you even looking for it to do? 

Thank you, 

Harry Voyager

[speed-of-heat]

this should give you a really good overview to they why as well as the how 

 

[Sideburns]

Also another good resource to understanding the why https://www.heatblur.se/F-14Manual/general.html#hydraulic-system

TLDR: The F14 has two separate hydraulic circuits, one driven by each engine. The transfer pump allows transfer of pressure and fluid from one to the other if one is failing for some reason. On start up you want to make sure this works in case you have issues. So you deliberately test it by disabling it then re-enabling it into auto mode, with one engine on, and observing for pressure transfer between the two systems. The specific dial you are looking at is the above your left leg and looks like this, you should hopefully see one system healthy at 3000psi and the other equalise around 2400-2600 psi

Edited December 6, 2023 by Sideburns

[Victory205]

The bi-directional pump transfers pressure, not fluid. They use exiting fluid in the system with the failed pump.

Transfer pumps are common on twin engine hydraulic control/systems aircraft. They don’t transfer fluid for obvious reasons, a leak in one system would deplete the other. Basically, it’s redundancy for a failed hydraulic pump, not for a fluid leak.

They do create a single point failure should the bi-directional pump catastrophically itself fail, which happened to me in an airliner, thankfully sitting on the ramp, waiting for a gate.