Pressure Per Square Inch

Atmospheric pressure is 14.7PSI. Just add water. Sea water weighs roughly 63-64 # per cu ft.

For every 33 ft. pressure increases by one atmosphere, which is 14.7 PSI. Now do the math.

Think you'll find it's closer to 34ft for 1atm.

Please check my math and undertsanding of this:

• at 100 feet we have 48 psi
• at 3000 feet we have 1336 psi

Correct?

At 100 feet I get:

Using #1 gives 58PSI

Using #2 gives 58.45 PSI

Using # 3 gives59.2 PSI

I've added the weight of the column of air pushing downward on the water's surface, as well.

But then, my abacus batteries are low.

Yea.....I understand.....my Slide Rule batteries did me the same thing .

I just got a solar powered slide rule. No more battery fuss. It clips onto my beanie, in place of the propeller!

.....hard to convince the younger generations that a whole world was built with just an abacus and then a slide rule........long before computers were even imagined much less invented.............

I believe that someday an implantable chip will allow mathematical illiterates, such as myself, to perform complex calculations, "in your head".

Cheers!

Thank you.

I just a need a close estimate, nothing exact.

The 14.7 figure will give me something to get close enough calculations. I do not need exact anything.

Thank you and the others for helping once again.

Hi Smitty,

I have written this chart below which gives Pressures at up to 1000 Feet. I have worked in psi because that is what you asked for. At Sea Level the Pressure is 14.7 psi. Each 33 feet (~10 Metres) is equal to another Atmosphere. So at 33 feet, add the Sea Level Pressure to the Pressure at 33 feet (~10 M), which gives a value of 29.4 psi. There after you add 14.7 psi every 33 Feet (~10 M) Depth----PSI....................Depth----

PSI

033 <==> 29.4...............528 <=> 249.9

066 <==> 44.1...............561 <=> 264.6

099 <==> 58.8................594 <=> 278.3

132 <==> 73.5................627 <=> 294

165 <==> 88.2................660 <=> 308.7

198 <==> 102.9..............693 <=> 323.4

231 <==> 117.6..............726 <=> 338.1
264 <==> 132.3..............759 <=> 352.8

297 <==> 147.................792 <=> 367.5

330 <==> 161.7..............825 <=> 382.2

363 <==> 176.4..............858 <=> 396.9

396 <==> 191.1..............891 <=> 411.6

429 <==> 205.8..............924 <=> 426.3

462 <==> 220.5..............957 <=> 441

495 <==> 235.2..............990 <=> 455.7

......................................1023 <=>470.4

I hope you find this helpful.

Take care.

PS.

I have tried sending this after Formatting several times. The previous post # 41 was Formatted wrongly, and the list of figures were too close and difficult to discern. I apologise and the post 41 will be removed soon.

Thumb rule 1/2 psi per foot. If you are on a submarine and you read 1000 psi on the seawater gauge you may want to stick your head between your legs and kiss your ass goodbye.

..........don't forget to loosen all tight clothing first.......very imprtant.........especially if you are of the "beachball" shape.............not me though..........I am only 7 months!!!!

I didn't realize I wasn't logged in the last attempt at humor was mine.

If you add atmospheric pressure to the depth pressure, you get absolute pressure (commonly written as psia). If you just use the pressure of the water, you get gauge pressure (commonly written as psig). Most of our customers specify psig which is the difference between pressure at the surface and pressure at depth.

Hi welderman,

"psia", I asume the 'p' is for 'Pascals', which is a pressure measure?

---------------------------------------------------------------------------------------------

The SI unit for pressure is the pascal (Pa), equal to one newton per square meter (N/m² or kg/m·s²). This special name for the unit was added in 1971; before that, pressure in SI was expressed simply as N/m².

---------------------------------------------------------------------------------------------

Take care.

Hi, BB,

In this context, "psi" is "pounds per square inch".

Rgds, John

Hi John,

Thanks for the clarification. I lost concentration when writing the post you replied to. As the pressure would be written as: Pa mm², I think.

Anyway, it aint inportant and I am having a doze.

Take care.

No! No!..............Pa.............or 1N/m²

or

MPa (Megapascal)...........1N/mm² or 1MN/m²

6.895kPa = 1 psi................1kPa........1N/cm² or 1kN/m²

Pressure and stress have the same units

I hope that helps to confuse the issue.

Hi MOBI,

how you doing?

Many thanks for the advice my friend. It was a month or so since I used this Pascal and MPa so I do not have it tucked away ready for use. But when I am working with pressures and forces I get it correct................ Well most of the time!

Yes MPa because there is a million square mm in a square metre.

Thanks and I really do appreciate your reply post.

Take care.

Not a problem bb............I know one thing it beats the crap out of the imperial system of weights and measures.............and I was brought up on that.

..........but the Pascal????? What a stupid base measurement!!!!

I don't do well in metric. Sorry. In the USA PSI is "Pounds per Square Inch'.

Also, for water pressure i use 2.31 pounds per foot of depth. -- JHF

Hello CB,

I very much appreciate the advice my friend.

I am trying to 'juggle' European, UK old measures (avoirdupois) and US measures and I sometimes forget. I know the unit of pressure or force is a Pascal (Pa) for short and at first reading thought in the "psia" in the post I answered, I thought the 'p' was Pascal, which is equal to 1 Newton Meter (Nm). I do realise it must sound real odd when you are already used to using a measure and then hear me mention a Pascal.

But, no matter what we all have our own 'rule of thumb's' to figure stuff out, do we not? Just as long as it makes sense in the place you use it eh?

A pascal sounds like something to suck right? LOL!

Take care.

Yea, it keeps us old farts confused. At least, most newer gages have US (PSI) and metric (KPa) on them so if the specs are in metric I don't have to convert, I just look (through my bi-focals) at the metric scale. The only problem is after 45 years I know when pressures in PSI sound OK or out of whack, metric is any body's guess! -- JHF

A pascal sounds like something to suck right? LOL

Pascal is also a confectionery company (I do not know the origin)...........so you can suck it.

Hi MOBI,

Should that not be pas-stille, or more common pastil, which was a Medicated or flavoured Lozenge, or Troché............ sorry back to the french again!

Pascal, of course was just someone Name.

Blaise Pascal's earliest work was in the natural and applied sciences where he made important contributions to the construction of mechanical calculators.

Sorry, but once I hear a word I always have to research it!

Pascal is also a confectionery company (I do not know the origin)...........so you can suck it.

Take care.

Yes bb, Pascals Triangle and Pascal also liked his hydraulics, I think he invented the hydraulic press and of course we have Pascal's Law.

Medicated or flavoured Lozenge, or Troché

The Pascal confectionery company only makes those "lollies" that are "bad" for you, like chocolate eclairs, toffees, jubes, etc., they aren't too bad............you know the old story........open the bag and have one or two............next thing, you have scoffed the whole bag.

Can't eat just one? -- JHF

Hi MOBI,

Thanks for the reply post my friend...............

Yes it does seem 'impossible' to just eat a couple!

Take care.

PRESSURE P=dgh where

d=density in lbs/in cube

g=gravitational constant

h=height in inches

Irshad

Doesn't realy matter what the pressure is on a flat surface ans it will be the same on the bottom of the surface as well it only matters when you are trying to keep the water out.

No real point going lower that 100 foot everything just gets cold and dark and a touch scary to boot

after reading this whole topic

I am so confused now

can some one give me the answer to this

I need to know this

I am at 500 ft of sea water

I am at 1000 ft of sea water

what is the definition of pressure

and what is that pressure

what is the definition of pressure

Probably best defined as: pressure= force/unit area

i.e. Force in Netons Area square millimetres = N/mm² or MPa (Megapascals)

Hi MOBI,

I am using PSI and Newton and pascals, and their diminutive brothers Nm and MPa mm^2.

I may not have written is correctly here but when I am working with it I know what I am doing!

Yes exactly so.

i.e. Force in Netons Area square millimetres = N/mm² or MPa (Megapascals)

.........diminutive brothers Nm and MPa mm²

Now lets get this right bb:

Force = Newtons (N) The force required to give a mass of 1kg an acceleration of 1m/sec²

Moment of a Force = Force (N) x Distance metres(m) =Nm

Pressure/Stress = Force(N)/unit area(m², cm² or mm²) (F = P x A or F = m x g)

Therefore: Pascal(Pa) = 1N/m²

1 kiloPascal(kPa) = 1N/cm² or 1 000N(1kN)/m²

1 MegaPascal(MPa) = 1N/mm² or 1 000 000N(1MN)/m²

I just thought this may be handy bb

Cheers

Hi MOBI,

Dunno if I can take der pressure init?

It is useful and You are now saved to my 'come in handy floder folder', makes more sense! I do not have a 'filed 'floder' on my computer! LOL!

I am really keeping it for future use. We are not in what I consider to be a serious Newton Metre thread 'thang' here but when we and I am, I will take a peek to see my nomenclature is correct.

Many thanks my friend

Hi bb,

Nice to know I'm in somebody's good folder........it's a change.

Whoever heard of 6.2283 gallons/ft³ (Imperial of course)

That is ridiclious (haha)

1 000 litres(l)/m³.............much more better!!

Cheers

Hi MOBI,

Yes it sounds and looks really odd. It is another language really and like any other language, the people there, on the ground, understand it. Unfortunately, like the difference between 'Chinese' and 'English' there is no common ground at all.

I am pleased we use the Metric System now. Just a case of adding a zero?

Take care my friend.

I don't recall the website I got this from, but the conversion I have been using is: Feet of sea water @ 50°F, 35 PPT X 0.445235975 = PSI. So per each 100 feet of sea water, there is 44.5235975 PSI.