[PSUBS-MAILIST] altimeter ?

Sun Sep 6 18:37:25 EDT 2015

You're welcome, Brian,

I'm not sure your ears would tell you if you had a an increase  in pressure 
to 17.5 psi if it happened gradually.  That's just equal to  descending in 
a plane from 5,000 ft. MSL to sea level.  It would  depend on the rate of 
the pressure change and the ability of a given individuals  ears to rapidly 
equalize.

There are others who can tell you more than I can about the  range of 
cracking pressure adjustment on OP valves.  I expect you would  want one that you 
could adjust to less than one pound differential.  One  pound isn't much, 
but when you multiply it by the number of square inches on a  dome or hatch 
it can get significant.  Another major consideration is how  rapidly the 
valve can vent compared to your rate of ascent.  There was a  thread discussing 
this in June 2015 (actually two threads  simultaneously).  I'll forward one 
of those emails and you can then open  others from around that date.

Jim

In a message dated 9/6/2015 12:04:34 P.M. Central Daylight Time,  
personal_submersibles at psubs.org writes:

Jim,    Thanks !    Yes, I figured that  those units would not register so 
much on the negative sea level side.   But it looks like they do go a few 
psi ( 17.5)  which would be 6.2 feet  of water depth.  Enough that your ears 
would tell you you have a pressure  increase.  

Do they make  over pressure valves that are sensitive to just a few pounds? 
  And  I assume I should have one, since I don't want my windows blowing 
out from a  uncontrolled over pressure accident, although they would probably 
just bleed  air in that situation.  Do all the Kittridge subs have OP  
valves?

Brian

--- personal_submersibles at psubs.org  wrote:

From: via Personal_Submersibles  <personal_submersibles at psubs.org>
To:  personal_submersibles at psubs.org
Subject: Re: [PSUBS-MAILIST] altimeter  ?
Date: Sun, 6 Sep 2015 10:16:06 -0400

Brian,

Assuming your starting point is sea level pressure or 0 feet  of altitude, 
if the altimeter reading moves to -1000 feet you would have an  
over-pressure of a half pound (scroll down to the chart below).   Since altimeters are 
designed primarily to register pressures less than 14.7  psi, I'm not sure 
what effective range most of them have at pressures greater  than that.  As 
referenced in Lasse's first link, the ANSI standard for  accuracy goes down to 
-700 feet.  The higher the pressure, the lower  the altitude (cabin 
pressure altitude, not depth in the water).

In a sub I would generally prefer an  analog altimeter.  Set the pointer 
straight up at 0 to start, and  any decrease or increase in cabin pressure 
quickly registers by the pointer  moving left or right.

Jim T.

.

The table  below indicates air pressure at elevations below and above sea  
level. 

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   
7000  
2134  
23.1  
590  
11.3  
0.797  
78.2   
8000  
2438  
22.2  
568  
10.9  
0.768  
75.3   
9000  
2743  
21.4  
547  
10.5  
0.739  
72.4   
10000  
3048  
20.6  
526  
10.1  
0.711  
69.7   
15000  
4572  
16.9  
432  
8.29  
0.583  
57.2   
20000  
6096  
13.8  
352  
6.75  
0.475  
46.6   
25000  
7620  
11.1  
284  
5.45  
0.384  
37.6   
30000  
9144  
8.89  
227  
4.36  
0.307  
30.1   
35000  
10668  
7.04  
180  
3.46  
0.243  
23.8   
40000  
12192  
5.52  
141  
2.71  
0.191  
18.7   
45000  
13716  
4.28  
109  
2.10  
0.148  
14.5   
50000  
15240  
3.27  
83.6  
1.61  
0.113  
11.1

In a message dated 9/6/2015 3:02:15 A.M. Central Daylight Time,  
personal_submersibles at psubs.org writes:

Brian,  

They usually show reference pressure in Inches Mercury or  Millibars.
The one I have goes from 1040 to 930 Mbar, calibrated to 20.000  feet.

I can recommend this MGL instrument, it also shows if you are  descending 
or rising. The price is good for such an instrument. It is  digital, 
background lighted and light.
http://www.aircraftspruce.com/catalog/inpages/11-05684.php

Other altimeters are found here:
http://www.aircraftspruce.com/menus/in/altimeters.html

Lasse

2015-09-06 5:24 GMT+02:00 Brian Cox via Personal_Submersibles 
<_personal_submersibles at psubs.org_ (mailto:personal_submersibles at psubs.org) >:

Hi  All,
I was thinking about getting an altimeter,  The question I have is:  What 
is the top end range of pressure those things will  read?   I assume that 
they start at 14.7 psi.    But I  guess they are calibrated in feet of air.  So 
If you had an over  pressure situation what is the highest reading you 
would  see?

thanks,
Brian

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-- 

Lasse Schmidt Westrén

Upplevelsepresent.se
070-28 32  660

Upplevelser, events och  kryssningar.

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