RE: [PSUBS-MAILIST] Altimeters as leak indicators

I am using a full scale 4 inch gauge 0-15 psi.

Take off the needle and put it pointing to 7.5 psi using another decal with 0 in the centre. Negative pressure will be clockwise positive pressure anticlockwise.

Pipe the gauge to a small reference cylinder. You can use an old fire extinguisher body or CO2 cartridge. This is not absolutely necessary but a bleed valve for zeroing is an option.

Hugh

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of JimToddPsub@aol.com
Sent: Wednesday, 28 March 2012 9:58 a.m.
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Altimeters as leak indicators

Thanks, Jon,

I found the chart below that helps. An increase in cabin air pressure of just half a pound (14.7 to 15.2 psi) would register 1,000 feet on the altimeter. I wouldn't have guessed that. If that happened in 10 seconds I would definitely notice with my ears; if it happened over 2 minutes I probably wouldn't. An increase of 1.9 psi would register 3500 feet on the altimeter.

In order to avoid false alarms, I surmise the main thing to consider is how much variation in pressure might occur in normal operation of the scrubber and O2 metering system. I think some auto-metering O2 systems respond to the drop in air pressure caused by the removal of CO2 by the scrubber and replace it with the indicated amount of O2. I have no idea what drop in pressure it would take to trigger the O2 release, but it must be rather small. A while back someone set the O2 feed manually based on calculated consumption and found it worked well without requiring adjustment. Was that you, Alec?

Jim

Altitude Above Sea Level		Absolute Barometer		Absolute Atmospheric Pressure
feet	meters	inches Hg	mm Hg	psia	kg/cm²	kPa
-5000	-1524	35.7	914	17.5	1.23	121
-4500	-1372	35.1	898	17.2	1.21	119
-4000	-1219	34.5	882	16.9	1.19	117
-3500	-1067	33.9	867	16.6	1.17	115
-3000	-914	33.3	852	16.4	1.15	113
-2500	-762	32.7	837	16.1	1.13	111
-2000	-610	32.1	822	15.8	1.11	109
-1500	-457	31.6	807	15.5	1.09	107
-1000	-305	31.0	793	15.2	1.07	105
-500	-152	30.5	779	15.0	1.05	103
0¹⁾	0	29.9	765	14.7	1.03	101
500	152	29.4	751	14.4	1.01	99.5
1000	305	28.9	738	14.2	0.997	97.7
1500	457	28.3	724	13.9	0.979	96.0
2000	610	27.8	711	13.7	0.961	94.2
2500	762	27.3	698	13.4	0.943	92.5
3000	914	26.8	686	13.2	0.926	90.8
3500	1067	26.3	673	12.9	0.909	89.1
4000	1219	25.8	661	12.7	0.893	87.5
4500	1372	25.4	649	12.5	0.876	85.9
5000	1524	24.9	637	12.2	0.860	84.3
6000	1829	24.0	613	11.8	0.828	81.2

In a message dated 3/27/2012 3:08:21 P.M. Central Daylight Time, jonw@psubs.org writes:

Probably somewhere around 2-3psi I would think. Not sure about the rest of you but I have to start clearing my ears at around 6-8 feet of water pressure. If you need to clear your ears in a 1ATM during operations, that indicates a problem of some kind which should send you to the surface. The two main issues I can think of that you want to avoid is an internal pressure/dive duration that ends up requiring decompression; a high enough pressure level that introduces O2 toxicity. Both of those situations would be difficult to get to without the pilot knowing something was wrong since even without any gas monitoring you'd be clearing your ears plenty of times. Unless you are drawing a vacuum as part of the pre-dive systems check (like DW-2000 does) there should be no clearing of ears unless there's a problem maintaining 1ATM within the cabin.

Jon

On 3/27/2012 1:35 PM, JimToddPsub@aol.com wrote:

I think I'll add an onboard checklist for possible causes if the alarm goes off. This brings up the question: What level of cabin pressure increase should activate the alarm?

I'd like to hear some answers on that one.

__________ Information from ESET NOD32 Antivirus, version of virus signature database 7004 (20120327) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com