Re: HP drawn by the power steering pump.

[cordeiro@adi.com (Alan Cordeiro)]

 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 ..)

And to reply to a comment from  Arun Rao
<rao%frisbee@frisbee.pixar.com

>So your calculations would be correct if the actuating pistons were	>de-pressurizing the system (accumulator?) at the same rate as the
>pump was pressurizing it, or if there was a leak in the system.  I
>suspect that it would take a lot of steering wheel turning/brake
>operation to keep the pump operating at full capacity continuously.

There are two independant pumps in one mechanical package. One 
provides fluid to the steering, and the other to the brakes.

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.

Let me throw in another reason why I know that there must be a 
continuous flow. If your damper pipe ( built into the hose that
goes from the pump to the accumulator,) ever gets clogged, you will
have a  almost unstoppable leak at the banjo connector at the pump.

Next, onto the steering circuit. The pistons pump through one way 
valves into a cavity behind the pump. ( Well the rear of the pump
is a large high pressure reservoir.) The high pressure cavity has
a relief valve that opens at 2200 psi, and allows fluid back
to the central chamber ( the main low pressure fluid container
that both pump circuits draw from. ). Since the oil is
non-compressable, each stroke of the pump must force oil into
the high pressure chamber, from where it returns ( at 2200 psi )
to the low pressure chamber.

The continuous flow of high pressure fluid through a high
pressure restrictor valve must ( in my opinion ) consume power, 
and generate heat.

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

Alan Cordeiro