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Froude G4 dynamometer ...... again

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BCjohnny

Automotive
Apr 23, 2006
29
Been a while since I’ve posted here, and this might be a bit long, so apologies in advance ……

I’m looking for specific information on the old Froude G4 hydraulic dynamometers, I’ve spent a fair amount of time researching this but it’s a bit of a desert out there

So if you have your comments would be greatly appreciated


What I know ….

The G4 came in several basic versions :

1) The original cast iron rotor/stator/pump impeller ‘G4’ rated up to 600bhp @ 6k rpm

2) The ‘bronze’ rot/stat/pi ‘G4B’ rated up to 1000bhp & 10k rpm with ‘air mist bearings’

3) A ‘90 degree cropped rotor’ version of the ‘bronze’ ‘G490’ rated at up to circa 1400bhp & 14k rpm, with the pump impeller deleted, relying on external feed pump pressure alone

Apart from the 'cropped rotor' the designs have essentially the same hydraulic absorbing elements, the power ratings are mostly related to the increased rpm capability the 'bronze' components allow ...... although I'm aware the cast iron stuff has been spun a lot higher than it's rating, 8k seems not uncommon

Even with the ‘guaranteed water curve’ the ratings are considered conservative, especially when not endurance testing, and control well compared to other dynos


The questions I have relate to modification and control :

Control mostly centres around the input valve, the output being a set bleed that can opened relative to temperature rise within the brake, but subsequently has often been modified to become a function of the two, indeed later Froude ‘F’ series dynos only use output control ….. any detailed information on specific mods to achieve this, especially ‘F’ series control ?

The ‘pump impeller’ delete suggests that at higher rpm it’s not completely necessary …… but what if any negative impact does it have at lower rpm, say 3k ?

I did once see a picture of the ‘90 deg cropped rotor’ and believe it was reduced in diameter at the outer circumference of the vanes only, no further ….. is my memory correct ?

Anecdotal evidence would suggest ‘air mist’ bearings are not strictly necessary (especially with modern high speed types) unless doing endurance testing, if you monitor bearing temps …… comments ?


I do otherwise know a fair bit more about these machines, I have a complete one and a spare ‘pump’, but moving forward to convert mine to ‘sweep control’ and higher rpm, there are clearly gaps in my knowledge that I’d like to fill

My requirements are in the range of 800 bhp / 8k rpm, and a typical 300 rpm / second sweep test will take 10 - 15 seconds, there'll be very little steady state testing ..... I've already got a fair handle on the motorised control valve and software

TIA, John

"It's not always a case of learning more, but often of forgetting less"
 
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