Bleed Air Pressure Rise Due Demand

As previously discussed, the APU will adjust its bleed air output to compensate for bleed demands... up to a point.With two packs in Auto, the Bleed Duct pressure sits at about 20psi. However, when you select them to HI (on the ground, with APU providing pressure), the APU increases the duct pressure to about 26 psi. It seemed to stay at that pressure irrespective of how many packs were in HI.http://members.ozemail.com.au/~b744er/737/...soValveOpen.jpgNote the DUAL BLEED light indication, even though the engines are switched off.The real aircraft has a MAINT selection on the FMC CDU which allows you to look at what signals are going to the APU to influence its behaviour. Here's a photo of one of these pages:http://members.ozemail.com.au/~b744er/737/...itoring2of4.JPGMES = Main Engine StartCheers.Ian.