Per Phil’s guidance, I used a skydiving altimeter. Specifically, you can use a model called “Altimaster II”, which apparently is a classic and shows up regularly on eBay for about $100. It has an adjust-to-zero knob. If you get hold of one of these, you can print out the attached custom “sub” faceplate on adhesive label paper of the sort you can get at an office supply store for labeling CDs or boxes. Stick the faceplate on upside down, so the zero will be mid-range on the instrument, and install the altimeter upside down in the sub, so the zero on the new faceplate is at the top. The needle pops right off so you can stick on the faceplate. You will then have the same cabin pressure monitor as a Deep Worker.
Cheers,
Alec
The contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it. From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of James Frankland Hi Jim, Yes, altimeter sounds good. i understand what you mean with the test. Was going to do exactly that myself. It was just the gauge I was being a dope about. Its obvious now I've thought about it. Had a quick look at altimeters. Loads of different ones you can get. Cheapies, wrist watch ones, aviation, skydiving etc. What make of altimeter are you using? I do have a proper custom made caison gauge as well which came out of a diving re-compression chamber. That might be ok but it will need to be re-calibrated. Anyway, plenty of other things to do first before I need to fit that. Regards James On 27 March 2012 15:26, <JimToddPsub@aol.com> wrote: James, To clarify: The reading of 5,000 ft. is what I've chosen for pre-dive tests when the pilot is inside and the hatch has been latched. When testing the vessel for leaks in your shop with no one inside you want to take it as far as you can. Even if you could pull a complete vacuum with a pump, the maximum difference you can achieve is 1ATM or about 14.7 psi. which equates to a depth of 33 feet or so in water. In the shop test I'll go as far as the pump and the altimeter can handle (maybe 100,000 feet above sea level). If it passes all that, the next step is dunking it in water to the appropriate depth(s) or testing in a pressure chamber. Jim In a message dated 3/27/2012 8:40:27 A.M. Central Daylight Time, JimToddPsub@aol.com writes: James, I'm planning to install an aircraft altimeter for the same purpose. An altimeter is simply a barometer with a wide range, so you could use that instead. It has the sealed air chamber (aneroid) which expands or contracts in response to changes in external pressure. With the hatch closed and latched you can pump air out with an external vacuum pump, turn the pump off, close the valve, take a reading on the altimeter, wait a few minutes, then take another reading to see if any air leaked back into the sub. This can even be done with the sub unoccupied as long as the altimeter is positioned where you can read it through a viewport. In most cases you can use the adjustment knob to set the altimeter to 0 for the first reading. I plan to run the vacuum pump until the gauge reads 5,000 ft. altitude, shut the valve, and wait 5 minutes. If the altimeter reading drops to 3,000 feet for example, I know a seal is leaking inwardly. One caution: If the sub is sitting in strong sunlight, you could get some increase in internal air pressure just from heat build-up. This test is on my pre-dive checklist on every dive. During a dive the pressure reading should change very little if your scrubber and O2 inlet are in balance. Error! Filename not specified. Comments and criticisms are most welcome. Jim In a message dated 3/27/2012 7:36:00 A.M. Central Daylight Time, jamesf@guernseysubmarine.com writes: Hi All, Mr Numpty here. I kind of know the answer to this already, but i thought someone may be able to clarify my mistake. I was very pleased when i spotted just the sort of gauge i was after mounted on the back of a sewage tanker. A pressure gauge but one that reads a negative pressure as well as a positive. So it starts at 0 and can go to -1 or +1 bar. Idea was that it would go inside the cabin to monitor internal pressure. (I'd like it to be able to measure a negative pressure as well as i intend to drop the internal pressure to test for penetrator seal leaks). I was just thinking about mounting it up and ive suddenly realised that its not going to work is it? It must measure the port pressure relative to the ambient pressure, which if i just mount it on a bulkhead will always be the same no matter what the pressure actually is. I suppose i'd have to make a pressure proof box sealed at surface pressure and pipe the port to the inside of the hull? So its kind of like a caisson gauge. Just thinking aloud really. James
Sent: Tuesday, March 27, 2012 12:21 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Caisson Gauge
Attachment:
Pressure Gauge Faceplate.CAD
Description: Pressure Gauge Faceplate.CAD