Re: HP drawn by the power steering pump.

[evangelo@mecf.wustl.edu]

Alan responds that:
>
>
> evangelo@mecf.wustl.edu comments,
>
>>Well that's right if pressure is constant from the begining to the end of
>>the cycle. I think that the case would be that pressure starts at 0 and builds
>>up to 2200, assuming that the relation pressure-distance is linear,
>>the formula would be 1/2 x 2200 x .196 x .2 ie. the result would be
>>half (3.6 ft-lbs).
>
>The hydraulic fluid is just about in-compressable. Your linear
>pressure-distance theory works with compressable fluids ( air,
>steam, burnt hydrocarbons ..)

No, the fact that a fluid is considered incompressible doesn't mean
the pressure on it is constant. Incompressibility has to do
with reduction in volume, not increase or decrease in pressure.
For example you can model water as an incompressible fluid,
but its pressure will increase as you compress it.

>First let be describe the brake circuit.
>
>Two pistons draw fluid from the central chamber, ( which is
>connected to the feed line from the reservior ). the output from
>the pistons feeds the hose connected to the brake accumulator.
>Once the bladder/air chamber inside the accumulator is fully
>pressurized, excess fluid flows through an excess pressure
>relief valve ( inside the accumulator ) back to the main reservoir.
>
>Therefore my feeling is that for THIS CIRCUIT, the pump is
>continuously supplying high pressure fluid, the flow rate
>depending on the RPM at which the pump is running.
>

So you might produce work if the pressure in the central chamber is
lower than the pressure in the accumulator (I don't know what's happening
there). If the pressure is the same than you simply circulate the fluid, not
much power is required for this. If it is not the same then you need to
increase it thus you need power.

>Sorry for droning on and on, I'm just trying to explain my
>reasoning in words.
>
>Alan Cordeiro

I don't know how interesting is the subject to the rest (I guess not much judging
from the responses :) ), so if you wish we can continue with personal mails.

Evangelos