[PSUBS-MAILIST] Hydraulic idea

Sun Nov 27 16:46:39 EST 2016

I am not talking about a pneumatic system, there is no air in the cylinders to make it spongy.  I am using pneumatic cylinders filled with oil.  It really is a hydraulic system with air cylinders is all.  There is oil in the cylinder and the lines to the valve, how can it be spongy unless the accumulator is acting spongy, but that would be SO minimal with 1\8 lines.   I do like the individual liniar actuators driving individual cylinders.Alan, I was not planning to build HP cylinders, I have a dozen or so aluminum CO2 bottles I can use. Hank

    On Sunday, November 27, 2016 2:09 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 The problem with pneumatic actuators is that you can't meter the flow rate properly because air is compressible, and the moment you experience any change in ambient pressure, the force balance changes because of the exposed rods. Pneumatics will also be spongier than anything you could do with oil. You could get away with pneumatic actuators for applications which have the cylinders on or off (fully extended or fully retracted), but for an application requiring intermediate positioning, fluid power is the way to go.On that note, one other possibility if you don't require a tremendous amount of force would be to do away with a central oil reservoir, and have a small piston reservoir supplying each action, where the piston is connected mechanically to an electric linear actuator. Then instead of valving you just stroke the electric actuators, and the hydraulics respond accordingly.Sean

On November 27, 2016 12:50:54 PM MST, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
Hank,
in addition to my other negative comments; you aren't saving any air
by doing it the way you are. You are making the system a little less 
spongy if you do as Sean says & have a check valve in the system.
But it would be way simpler to just have a pneumatic system. 
With even 100psi you can get quite a strong holding power with a relatively
small cylinder.
   Also I get nervous hearing about home made pressure vessels like
hard tanks etc. Dive tanks need regular testing & inspection as there have
been numerous fatalities from them. But you could go for years without 
checking a homemade tank, or on sell a potential bomb.
Cheers Alan

      From: Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Monday, November 28, 2016 8:16 AM
 Subject: Re: [PSUBS-MAILIST] Hydraulic idea

Hank,
I may not be understanding it, but the concept seems fundamentally floored.
Take one double acting hydraulic cylinder. You open a valve & let the air 
pressure in your accumulating tank force the oil into the hydraulic cylinder,
moving the piston along & forcing the hydraulic oil on the other side of the piston
in to your low pressure tank. So you loose oil into this tank! How is it recovered again?
Or do you have a large suppply of oil that goes from the high pressure to the low
pressure tanks & when it has all gone from one side to the other you are done.
With the cylinder moving the other way it would also be lost to the low pressure tank.
   With the WD40 I was under the impression you were going to use it inside the hull.
Maybe I got it wrong. If you are using a motor for a short time maybe WD40, but we
did conclude that it can be detrimental to any plastic parts & o-rings over time also
there were the other aspects covered recently in Brian's post.
CheersAlan

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Monday, November 28, 2016 1:47 AM
 Subject: Re: [PSUBS-MAILIST] Hydraulic idea

Alan,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.    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.  I am not worried about space, it is weight I ! amthinking 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.   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.  Hank 

    On Saturday, November 26, 2016 8:03 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Hank,
Wouldn't you have to exhaust the air as in a pneumatic system?
Also air ! wouldhave to displace the volume of oil in the cylinder
as the piston moves in & out, so there would be marginal benefits
over a pneumatic system. It would also be spongy like a pneumatic 
cylinder because any bouncing force on the cylinder would compress the air
that is the source for the movement.
You were talking about saving space with this idea, but if compressed
air was a good form of power we would have pneumatic thrusters 
instead of batteries & electric motors..
I once did the maths on how much energy was stored in a dive tank;
can't remember the result, but there was at least 3 x more energy in
a battery of an equivalent size.
WD40 as hydraulic oil? It is flammable with a reasonably low flash point.
Also at that viscosity you would be more prone to leaks wouldn't you?
https://www.wd40company.com/files/pdf/wd_40tec16952473.pdf
Cheers Alan

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Sunday, November 27, 2016 4:59 AM
 Subject: Re: [PSUBS-MAILIST] Hydraulic idea

Sean,The receiving tank will take the full depth pressure and be large enough  to take all the oil without building up excess air pressur! e, noneed to vent off, since it is only receiving oil and displacing air.  I need a balance with two tanks to maintain neutral buoyancy.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.  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.  
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. 

    On Saturday, November 26, 2016 6:25 AM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 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.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.To gen

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