Re: [PSUBS-MAILIST] hatch squeeze

Dan, Thanks for the info ! yeh I tend to jump head first into things, but even if I have to do some things over again I think it will be worth it.----- But I don't think I will go too far off from my design. I have constructed a mock up pressure hull out of barrels so I can get an idea of where everything goes. This thing is so different than any other sub I wouldn't be suprised if I had to build it twice. There are some unknowns that can only be understood by actually building it (refering to the ferro-cement part) But the pressure hull will follow all the same rules as every other sub so that part will not be different. I was if fact looking at the pictures you posted - Wow that is a mega lathe use were using ! I was squinting to see the details on the hatch. My table set up is for the mill, I have a rotary table at the collage which I have modified to hold the hatch cover secure while milling. I have actually painted my self into a few corners though !

Is the "o" ring on the hatch or the hatch seat?

Brian

----- Original Message -----

From: Dan H.

To: personal_submersibles@psubs.org

Sent: Tuesday, April 27, 2004 5:14 AM

Subject: Re: [PSUBS-MAILIST] hatch squeeze

Brian,

As I recall you got a Parker O-Ring Manual, correct? In it, or any other manuals on O-ring applications, you will find either tables or recommendations for O-ring squeeze. It's the difference between the O-ring thickness and the thickness of the remaining groove when the two mated surfaces are put together. Follow the guide for a "Static Application." They usually give the example of a flange seal where two pipes are joined together with bolted pipe flanges. Your hatch is the same thing.

There is one alteration to the standard groove that is helpful in a hatch seal. When machining the inner diameter of the groove for the O-ring, it helps to put a bit of an angle on it sloping into the groove to better retain the O-ring when the hatch is opened. Put about a 10 degree angle on the inner diameter wall and size the ring so it is a bit smaller then the diameter of the groove so it snaps in similar to an elastic band around a rolled up bunch of papers. Not so much stretch as to reduce the cross section of the O-ring but enough to hold it in the groove.

How are you going to machine this on a table? Either chuck it in a lathe, or a rotary table on a miller or a machining center.

Brian, I don't want to sound critical, but are you sure your ready for welding parts together? It's real easy to work yourself into an expensive corner if your assembling before you have the design details worked out.

Good luck, Dan H.

----- Original Message -----

From: Brian Cox

To: Personal_Submersibles@psubs.org

Sent: Tuesday, April 27, 2004 1:50 AM

Subject: [PSUBS-MAILIST] hatch squeeze

Hi All, Been working on my hatch, had the ring welded on to the hemisphere by my neighbor ( who did the most professional weld job I've ever seen ! ) . Anyway, spent the afternoon fitting up a support table so I can machine the hatch cover true and flat. As it is it's only 30 thousandths off. Then I will need to machine the hatch seat. Since I have never actually seen a hatch, other than in pictures, I feel at a bit of a loss as to certain aspects of the hatch. Like I need some type of "o" ring right? Or will the hatch seal if self if both mated pieces are perfectly true? I'm having a little trouble with physics of the hatch seal. With an "o" ring , like in a thru hull fitting, the sealing action of the "o" ring works because water pressure is pushing the rubber "o" ring tight against the surrounding wall, But with the hatch you have the large area of the hatch pushing the whole hatch against the hatch seat - the "o" ring or gasket is not acting the way it would be in a thru hull fitting. Would the specs for the squeeze on "o" ring be different than on a thru hull fitting? Any comments would be greatly appreciated.

Brian Cox