I have to agree with cj...I have an email that I will try to share here about hydraulic efficiency.
Hello again Michael,
Do you know when NOT to use hydraulics?
As a fluid power consultant advising clients
in a diverse range of industries, it's an issue
I deal with a lot.
One recent client, the designer of a three-wheeled vehicle,
approached me to design a hydraulic drive. He wanted
to power at least two-wheels, ideally three.
To keep cost to a minimum, the machine designer
asked me to consider gear pumps and motors.
A gear pump or motor in good condition is 85 percent
So a gear pump driving a gear motor has a best-case
efficiency of 0.85 x 0.85 = 0.72. That's 72 percent -
not considering losses through valves and conductors.
But say a gear-type flow divider was included to achieve
multi-wheel drive. The theoretical efficiency would now
be 0.85 x 0.85 x 0.85 = 0.61. That's 61 percent,
not including losses through valves and conductors.
Compare this with a chain drive in good condition,
which is 97 to 98 percent efficient. This explains
why you don't see any hydraulic bicycles around!
In this application where the available input power
was limited by space and weight, the question I had
to ask my client was: Can you afford to lose
40 to 50 percent of available input power to heat?
In his case, the answer was no.
Contrast this example with another client for whom
I'm advising on the design of a 6,000 ton press.
Regardless of efficiency, hydraulic power transmission
is really his only option.
But this is also a relatively efficient use of hydraulics.
One of the reasons for this is the efficiency of a
hydraulic cylinder approaches 100 percent.
And because it's a high-pressure application, piston pumps
are essential. The overall efficiency of an axial
piston pump in good condition is 92 percent. So the
theoretical efficiency of the press hydraulic circuit
is 0.92 x 1.00 = 0.92 or 92 percent - not including losses
through valves and conductors.
A significant, 'built-in' inefficiency in this application
however, is the compressibility of the hydraulic fluid -
the subject of your next hydraulics email in few days time.
Yours for better hydraulics knowledge,
Author of 'Insider Secrets to Hydraulics';
'Preventing Hydraulic Failures' and
'Advanced Hydraulic Control'.http://www.hydraulicsupermarket.com/books.html