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<div class="moz-cite-prefix">The commercial accumulators are heavy
because they are designed for high service pressures. If you know
for a fact that your vessels will only ever see e.g. 1100 psi, you
can get away with something lighter. The concept is exactly the
same. Pistons require tight tolerances and surface finishes - the
bladder is the easier solution. Since the bladder will never see
any delta-P across it (disregarding it's own elasticity), it
doesn't need to be that substantial - even an inner tube might
work. Just something to allow you to completely purge all air out
of the oil volume, and which is materially compatible with the
oil, and which will maximally expand within the pressure vessel.<br>
<br>
As an alternative to your constant pressure accumulator, you could
go with a sealed accumulator and a small hydraulic pump which is
capable of high pressures but not necessarily high flow rates.
For example, empty the accumulator of oil, and precharge the
bladder to 1000 psi. This ensures that just before going
completely empty, it would still be supplying fluid at 1000 psi.
If you do this, you can use a pressure gauge on the gas side of
the accumulator to monitor the oil level, so you pump oil in until
the gauge reads 3000 psi, and you then know the vessel is 2/3 full
of oil. You can recharge the accumulator over time at a much
lesser flow rate than is actually demanded by the manipulator,
because the accumulator supplies the high flow necessary for
operation.<br>
<br>
Sean<br>
<br>
<br>
On 2016-11-27 08:44, hank pronk via Personal_Submersibles wrote:<br>
</div>
<blockquote cite="mid:B1iTc4aSidmHHB1iUcKnvx" type="cite">
<div style="color:#000; background-color:#fff;
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<div id="yui_3_16_0_1_1480260351346_4982"><span>Sean,</span></div>
<div id="yui_3_16_0_1_1480260351346_4982" dir="ltr"><span>I
agree completely except the operating pressure is </span> not
as high as you suggest. I know for a fact Gamma ran at 1,100
psi from the maintenance records. You do make a point that I
missed. Without a bladder, I could leak oil into the water
when relieving the pressure while surfacing. I was
considering an accumulator either a piston or rubber bladder
type, but they are very heavy. I would like to figure out
how to use this idea with a water pressure tank with bladder
for the light weight. </div>
<div id="yui_3_16_0_1_1480260351346_4982" dir="ltr">Maybe this
is not the way to go, but an interesting brain exercise. </div>
<div id="yui_3_16_0_1_1480260351346_4982" dir="ltr">I do have a
small hyd pump that is pretty light and makes 1,100 ps,i it
is just such a pain in the butt. Mind you with external
batteries and external pump it will not be as bad.</div>
<div class="qtdSeparateBR"><br>
<br>
</div>
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<div dir="ltr"><font size="2" face="Arial"> On Sunday,
November 27, 2016 7:38 AM, Sean T. Stevenson via
Personal_Submersibles
<a class="moz-txt-link-rfc2396E" href="mailto:personal_submersibles@psubs.org"><personal_submersibles@psubs.org></a> wrote:<br>
</font></div>
<br>
<br>
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<div>
<div class="yiv8499684973moz-cite-prefix">Hank, what
sort of total oil volume are you considering? The
immediate problem I see is the loss of pressure in
your HP supply, given the necessary operating
pressure of the hydraulic system. Regulating a
cylinder at e.g. 4000 psi down to 2000 for drive
pressure is still not going to last very long, and
you also have the problem of pressure increase in
the receive tank if it is not vented reducing your
total available delta-P (i.e. you have a drop in
pressure on the drive side combined with an
increase in pressure on the receive side - it may
not take long to become ineffective). If that
isn't an issue for you, then there's no reason it
wouldn't work. You are essentially powering your
system from a precharged accumulator, and draining
into another one at lesser charge pressure. I
would incorporate a check valve between the supply
accumulator and the control valve, so that
pressure pulses are not transmitted upstream and
no sponginess is evident. You might also want to
take a concept from commercial gas charged
accumulator designs and incorporate some sort of
bladder inside each pressure vessel to physically
separate the oil from the charge gas. If you
insist on using air (I still prefer nitrogen),
this would prevent the mixing of high pressure
oxygen with oil, and also allow you to vent the
receive tank to the water without worrying about
oil contamination in either direction. It also
makes the system insensitive to vessel attitude.
Then your pumbing becomes simple - one tank is
charged and one is vented, and when all the fluid
is moved to the receive side, you just switch the
direction.<br clear="none">
<br clear="none">
Such a system gets its energy input from the
compressor that charges the HP air or nitrogen
source, versus having an on-board hydraulic pump
drawing energy from the batteries. The advantage
of the former is that the energy input is
decoupled from the vessel and need not be carried,
but you only achieve constant power for as long as
you can maintain constant precharge pressure,
which will be a function of the pressure setting
and the respective volumes of both the hydraulic
system and the HP gas source. The advantage of
the latter is the ability to run continuously
without having to switch directions, and that
energy storage in batteries is probably more
efficent than energy storage in compressed gas.<br
clear="none">
<br clear="none">
Sean<br clear="none">
<br clear="none">
<br clear="none">
On 2016-11-27 05:47, hank pronk via
Personal_Submersibles wrote:<br clear="none">
</div>
<blockquote type="cite">
<div
style="color:#000;background-color:#fff;font-family:HelveticaNeue,
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sans-serif;font-size:12px;">
<div
id="yiv8499684973yui_3_16_0_1_1480249331941_4890"><span>Alan,</span></div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480249331941_4890"><span
id="yiv8499684973yui_3_16_0_1_1480249331941_5254">Think of it as a
hydraulic system, not an air system. The
arm is identical in every way except it is
powered by air pushing the oil instead of a
pump. It would not be spongy because the
cylinders are full of oil. The air never
leaves the pressurized oil tank. </span>
When the valve is activated, the oil moves as
if it had a pump. Instead of the oil
returning to the pump reservoir, it is sent to
a holding tank that is a HP bottle. The air
in the receiving tank compresses as the oil
flows into it. Nothing is vented, it can not
vent because I need to maintain a balance
between the two tanks for buoyancy. As the
oil leaves the pressure tank, the tank gets
lighter. At the same time the receiving tank
gets heavier, so they are balanced. </div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480249331941_4890">I
am not worried about space, it is weight I am
thinking about and complexity. Of coarse if
you were doing construction with the arm it
would need to be electric. But to grab one
gold bar it can be air driven. Air drive
saves battery power also. Having said all
that, it may have a problem I have not
expected, so speak up and save me some trouble
anyone. </div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480249331941_4890"> I
don't see a problem with a motor submerged in
WD40, my vertical thrusters are full of it.
I could use something else as long as it has a
low enough viscosity for the motor to run. </div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480249331941_4890">Hank</div>
<div class="yiv8499684973qtdSeparateBR"><br
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<div class="yiv8499684973yqt3551329935"
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<div dir="ltr"><font size="2"
face="Arial"> On Saturday, November
26, 2016 8:03 PM, Alan James via
Personal_Submersibles <a
moz-do-not-send="true"
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ymailto="mailto:personal_submersibles@psubs.org" target="_blank"
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wrote:<br clear="none">
</font></div>
<br clear="none">
<br clear="none">
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class="yiv8499684973y_msg_container">
<div id="yiv8499684973">
<div>
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style="color:#000;background-color:#fff;font-family:HelveticaNeue,
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<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480187447224_5856"><span
id="yiv8499684973yui_3_16_0_1_1480187447224_5900">Hi Hank,<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5884"
clear="none">
Wouldn't you have to exhaust
the air as in a pneumatic
system?<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5885"
clear="none">
Also air would have to
displace the volume of oil
in the cylinder<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5886"
clear="none">
as the piston moves in &
out, so there would be
marginal benefits<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5887"
clear="none">
over a pneumatic system. It
would also be spongy like a
pneumatic <br
id="yiv8499684973yui_3_16_0_1_1480187447224_5888"
clear="none">
cylinder because any
bouncing force on the
cylinder would compress the
air<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5889"
clear="none">
that is the source for the
movement.<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5890"
clear="none">
You were talking about
saving space with this idea,
but if compressed<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5891"
clear="none">
air was a good form of power
we would have pneumatic
thrusters <br
id="yiv8499684973yui_3_16_0_1_1480187447224_5892"
clear="none">
instead of batteries &
electric motors..<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5893"
clear="none">
I once did the maths on how
much energy was stored in a
dive tank;<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5894"
clear="none">
can't remember the result,
but there was at least 3 x
more energy in<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5895"
clear="none">
a battery of an equivalent
size.<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5896"
clear="none">
WD40 as hydraulic oil? It is
flammable with a reasonably
low flash point.<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5897"
clear="none">
Also at that viscosity you
would be more prone to leaks
wouldn't you?<br
id="yiv8499684973yui_3_16_0_1_1480187447224_5898"
clear="none">
<a moz-do-not-send="true"
rel="nofollow"
shape="rect"
class="yiv8499684973moz-txt-link-freetext"
target="_blank"
href="https://www.wd40company.com/files/pdf/wd_40tec16952473.pdf">https://www.wd40company.com/files/pdf/wd_40tec16952473.pdf</a><br
id="yiv8499684973yui_3_16_0_1_1480187447224_5899" clear="none">
Cheers Alan</span></div>
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<hr size="1"> <b><span
style="font-weight:bold;">From:</span></b> hank pronk via
Personal_Submersibles
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<b><span
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General Discussion <a
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<br clear="none">
<b><span
style="font-weight:bold;">Sent:</span></b>
Sunday, November 27,
2016 4:59 AM<br
clear="none">
<b><span
style="font-weight:bold;">Subject:</span></b>
Re: [PSUBS-MAILIST]
Hydraulic idea<br
clear="none">
</div>
<div
class="yiv8499684973y_msg_container"
id="yiv8499684973yui_3_16_0_1_1480187447224_5717"><br clear="none">
<div
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id="yiv8499684973yui_3_16_0_1_1480187447224_5716">
<div
id="yiv8499684973yui_3_16_0_1_1480187447224_5715"
style="color:rgb(0,
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<div
id="yiv8499684973yui_3_16_0_1_1480175087437_3060"><span>Sean,</span></div>
<div
id="yiv8499684973yui_3_16_0_1_1480175087437_3060"><span
id="yiv8499684973yui_3_16_0_1_1480175087437_3181">The receiving tank
will take the
full depth
pressure and
be large </span>enough
to take all
the oil
without
building up
excess air
pressure, no
need to vent
off, since it
is only
receiving oil
and displacing
air. I need a
balance with
two tanks to
maintain
neutral
buoyancy.</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480175087437_3060">I
am not worried
about
oxidation of
the oil
because the
oil is not
going through
a pump and the
flow rate is
so small. I
ordered air
cylinders for
the
manipulator
with a 5\8 rod
to reduce the
back pressure.
Gamma's
manipulator
operated at
1,100 psi when
the sub was at
1,000 feed of
depth. The
arm will loose
power, but I
don't expect
that to be an
issue, because
the oil tank
will be
powered from a
separate
bottle of air.
</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480175087437_3060">I
have to work
with what I
have to keep
the cost in
check, so I
can modify an
open centre
valve by
blocking the
final pressure
port drain. I
also have some
HP tanks. If
it does not
work out
easily, I have
a few electric
pumps I can
use. </div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480175087437_3060"><br
clear="none">
</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480175087437_3060">If
I go electric,
I intend to
submerge the
motor pump
unit in the
oil reservoir
with a bladder
top to
compensate.
That means I
will use WD40
as hydraulic
fluid.</div>
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class="yiv8499684973qtdSeparateBR"
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On Saturday,
November 26,
2016 6:25 AM,
Sean T.
Stevenson via
Personal_Submersibles
<a
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wrote:<br
clear="none">
</font></div>
<br
clear="none">
<br
clear="none">
<div
class="yiv8499684973y_msg_container"
id="yiv8499684973yui_3_16_0_1_1480187447224_5803">
<div
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id="yiv8499684973yui_3_16_0_1_1480187447224_5802">
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480187447224_5801">How do you intend to
control the
pressure on
the receive
tank? Just
vent it
through a
check valve to
the water? You
need to design
carefully to
prevent
contamination
in either
direction.</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480187447224_5804">I wouldn't use air as
the drive gas
under high
pressures, in
order to
prevent
oxidation of
the oil.
Charge with
nitrogen if
you intend to
do this.</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480187447224_5805">To generate the same
drive
capability as
a hydraulic
pump, you are
talking about
very high
precharge
pressure -
approaching
the pressure
at which HP
bottled gas is
supplied,
unless you can
source e.g.
6000 psi
nitrogen and
regulate it
down to
2500-5000
depending on
your
manipulator
requirements.
In any case,
if your
cylinders are
single acting,
or even dual
acting with a
single rod,
you have to
contend with
the force from
the ambient
water
pressure, so
your receive
tank pressure
needs to be
this at
minimum, and
with a
pressure
reservoir
source instead
of a pump,
that available
delta-P is
further
reduced the
moment you
demand any
fluid from the
system (i.e.
HP bottle
pressure will
drop), so your
manipulator
becomes weaker
over time.</div>
<div dir="ltr">Just
a few things
to think
about.</div>
<div dir="ltr">Sean</div>
<br
clear="none">
<br
clear="none">
<div
class="yiv8499684973gmail_quote">On
November 25,
2016 5:25:47
AM MST, hank
pronk via
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wrote:
<blockquote
class="yiv8499684973gmail_quote"
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<div
id="yiv8499684973yui_3_16_0_1_1480075807070_2825">Hi
All,</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480075807070_2825">I have an idea to
replace the
hydraulic pump
for my new
manipulator
with a air
over hydraulic
system. It is
quite simple,
the hydraulic
oil reservoir
is a hp tank
that can be
pressurized
from a
designated HP
supply. The
oil return
goes to
another HP
tank to
receive the
oil. This
eliminates the
pump
completely and
that is a
dream. The
manipulator
can go through
54 complete
extensions and
retractions,
that is 54
complete
movements of
all functions.
</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480075807070_2825">After the oil is used
up, the oil
can be
returned to
the pressure
tank by
reversing the
air flow.</div>
<div dir="ltr"
id="yiv8499684973yui_3_16_0_1_1480075807070_2825">Hank</div>
</div>
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<hr><br
clear="none">
</blockquote>
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</div>
</div>
</div>
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</div>
</div>
<div class="yiv8499684973yqt3551329935"
id="yiv8499684973yqtfd18096"> </div>
</div>
<div class="yiv8499684973yqt3551329935"
id="yiv8499684973yqtfd99760"> </div>
</div>
<div class="yiv8499684973yqt3551329935"
id="yiv8499684973yqtfd77821"> </div>
</div>
<div class="yiv8499684973yqt3551329935"
id="yiv8499684973yqtfd98226"> </div>
</blockquote>
<br>
</div>
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