Technical Questions

[carmelle0115]

im student,currently having a training on commercial engines,i need someone who can educate me about the functions of the following engine system components: HMU,PRSOV,PRV,HPSOV and IDG, thanks..

[ec155mech]

have a look at this website. I found it very usefull on loads of things when I did my license The Boeing 737 Technical Site (http://www.b737.org.uk/)

[noughtsnones]

Large gas turbine domain


A Hydro-Mechanical Unit (HMU) [alternatively a Fuel Metering Unit (FMU)] is the assembly used to house most (if not all) electrical control to fuel valve interfaces. By this (my) definition, the Hydro-Mechanical Unit must therefore contain: -
a metering valve, with electrical drive and position feedback
a spill valve (return excess HP to the LP fuel system), usually with no electrical interfaces
a high pressure shut-off valve (HPSOV), with electrical drives and position feedback.


The high pressure shut-off valve (HPSOV) is usually designed for both FADEC (e.g. Autostart) and aircraft functions, i.e. related engine run/cut-off switch and fire switch operation. These particular aircraft function examples must be reasonably isolated from the FADEC fuel metering role, so that simple failures can not propagate into an inability to shut-down when the metering system is faulty.


The fuel delivery system has to work over a very wide range of fuel flows and (engine burner required) delivery pressures, whilst some of the valves require high end pressures to satisfy servo force margin designs. It is therefore normal for the Hydro-Mechanical Unit assembly to include a pressure raising function, this can be arranged as one of the following: -
a Pressure Raising Valve (PRV) that acts independently and without electrical interfaces, or
a Pressure Raising Shut-Off Valve (PRSOV), i.e. merged function with the above SOV, or
a Pressure Raising Spill Valve, i.e. merged function with the above spill valve.


In my experience an IDG is an Integrated Drive Generator, this unit provides electrical power exclusively for the aircraft, i.e. it does not directly power the HMU or FADEC. The Boeing 787 combines this generator role with the engine starter motor role, in a starter/generator – this is discussed elsewhere in PPRuNe due to some :sad: battery interactions!

[dixi188]

The "R" in PRV and PRSOV etc. refers to "Regulating" or "Reducing" not "Raising".

[EEngr]

an IDG is an Integrated Drive Generator,Correct. It is a combination of a constant speed drive (CSD) and a generator in one housing. A CSD is a hydromechanical transmission that takes a variable input speed and through some trickery turns the generator input shaft at a constant speed.

The Boeing 787 combines this generator roleThe 787 doesn't have IDGs (or CSDs). The engine gearbox drives the generators at variable speeds, producing variable output frequencies (as opposed to a steady 400 Hz). Power electronics is used to convert this variable frequency power into 400 Hz (or whatever the loads require).

[vi683a]

Rolls Royce Trent 1000 "HMU" uses a PRSOV (Pressure Raising Shutoff Valve) not "Regulating" : It does not regulate pressure. It is a simple valve that is operated by the PRSOV servo valve.

So in essence PRSOV "Raising" is misleading, it neither raises nor regulates.

[buttrick]

Someone on the MH370 forum asked about fluid venting from a pipe inboard of the no.2 engine. Somebody suggested fuel, but that does not seem sensible.
Are there any P-3 techies familiar with the fuel system that can enlighten us. Can you post the answer on the MH370 forum too.
Thanks.

[buttrick]

Someone on the MH370 forum asked about fluid venting from a pipe inbord of the no.2 engine. Somebody suggested fuel, but that does not seem sensible.
Are there any P-3 techies familiar with the fuel system that can enlighten us. Can you post the answer on the MH370 forum too.
Thanks.

[EW73]

In response to the Q regarding the P3 having a 'pipe' laying on top of the wing inboard of the #2 engine, I know of no such pipe.
The only component that 'dirties' the upper wing surface of the wing, as far as I recall, is the fuel jettison pipe. This pipe outlet is only about 2 foot (60 cm) long, and located right back almost at the wing trailing edge, on the left wing, right inboard near the aft wing fillet. It does not run anywhere near the engine nacelle! It's located there because fuel can only be jettisoned from the centre tanks.
It's so close to the fuselage that it can only be seen from the port overwing hatch window, or the port aft observers window.