[PSUBS-MAILIST] Closed view

[hank pronk via Personal_Submersibles]

 Alec, your system does not provide for increased pressure on the opposite side of the piston.  Or am I missing some thing?  If you are pressurizing the the bottom side to ambient then at depth you're relying on the shaft seal to hold 450 psi approximately if it is a double acting cylinder.Hank 
    On Thursday, December 20, 2018, 10:57:39 AM MST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  
 
 I'm driving them with air from a first stage, so it's always about 150psi over ambient. The air supply is not shut off when the valves have been actuated, so the seal should always see those 150 regardless of depth.
On Thu, Dec 20, 2018 at 12:54 PM hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Alec,I was just about to ask you about the bleed system.  I like your idea of operating the valve in both directions but I still think the bleed holes are important.  Without the bleed port, the water pressure can overwhelm the seal.  The pressure on the back side of the piston becomes compensated.   I am just not sure where the best place for the bleed hole is.  Should it be at the cylinder or down stream at the hull penetration?Anyone?Hank
    On Thursday, December 20, 2018, 8:07:11 AM MST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  
 
 Hank, I should mention that although Shackleton's valves were originally to use bleed-driven closing, I ended up canceling that feature and instead plumbed them for manual actuation in both directions. I made the change because, although they have a spring to make them NC, I liked the idea of clamping with air for a more positive seal, and I didn't like the idea that a very small orifice becoming fouled could lead to a valve staying open. But the initial dives convinced me that bi-directional control is a good idea for a completely different reason. If you use the bleed approach to close the valves, they close slowly. When diving a K boat, and probably most subs, you'll often find either the bow or the stern is settling a little faster and getting you out of trim. The remedy is to temporarily shut one MBT valve while the other remains open. In Shackleton's recent tests it was the exact same process, just faster. I found myself closing a valve for a couple of seconds and then reopening it once back on level trim. It was very easy to do because the valves had immediate response times, but latency would have made it much harder to pilot.  
I love the simplicity of your design  - wish I hadn't spent all that time building valves from scratch!
: )
Alec
On Thu, Dec 20, 2018 at 7:24 AM hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Alec, thanks for the inspiration.  Watching your sub sink is just friggin amazing.  The air cylinders are double acting and will be spring loaded to stay closed.  The air pressure will open them with a permanent air leak via a tiny drilled hole like you have.Hank
    On Thursday, December 20, 2018, 5:09:56 AM MST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  
 
 Now that is clever, I never thought of moving the whole valve instead of just a lid, and it sure simplifies things! Are those actuators NC though, or can they be made so? Just so you don’t need HP in order to stay on the surface. 

Thanks,
Alec


> On Dec 19, 2018, at 8:02 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
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