ATA 29-00, Aux Hydraulic Pump (Gear Up Control)

This is an explanation linked from the "Ass Kicking" section.

Have you ever wondered why something is designed in such a weird convoluted way???

The Aux Hydraulic Pump on the G100 is controlled by many separate inputs to insure positive hydraulic pressure for certain aspects of flight. A RCCB is used instead of a contactor for applying power to the pump itself. This is done by making or removing a ground on pin 3 of the RCCB.

This particular problem was related to the "gear up" timing to the pump. When the gear is down and the control switch in auto, the aux pump is commanded on. Upon gear retraction, the aux pump "should" turn off in approximately 10 seconds. Time delay relay 108C uses the gear up signal to remove the ground from the RCCB and shutoff the pump.

Here lies the problem..... the aux pump never shut off after the gear was in the hole. If the crew took the switch from auto to off, the pump did turn off and when it was returned back to auto..... it would remain off.

We looked at EVERYTHING in the pump control system, not a damn thing we did corrected the problem or gave us a clue what to try next.

Off chance, all I could think of was yanking relay 36C (which shared 28VDC coil excitation), with 36C out EVERYTHING WORKED CORRECTLY. When we put it back in, it failed the system again. Pull it.... all was good. We put it back in and....................... everything worked normal and has for a month. A replacement 36C still sits in the office, will it ever get used???

Nobody, including Gulfstream, has a clue.

Now, back to the weirdness. Relays 108C and 36C have external resistors (which we had no frickin clue as to what they were for). It was discovered after some serious digging that these resistors are used to set the timing of the delay. Why not just use the kind with the built in delay timing?????

Oh well.............. A PDF data sheet is included on these types of relays below for your reference if ever come across these damn things. In 25+ years, this was my first exposure.





G100 ATA 29-00
Maintenance Manual 29-00-00
Wiring Diagram 29-00-00