Luckily us engineers don't really like a "does it, doesn't it" kinda scenario, so we have invented a way of defining pressures and how they relate to the world around us...... :-) So we refer to ABSOLUTE pressures that are pressures relative to the universal and constant pressure of a total vaccuum, actually somewhere where there is no pressure at all ie relative to an absolute zero pressure and seperately to GUAGE pressures that refer to a pressure relative a local ambient pressure, which isn't fixed and may change. These different references are normally indicated by the letters "abs" or "guage" appended to the units of pressure as in PSI(abs) or PSI(guage), sometimes shortened to PSIA and PSIG. (on this side of the pond we are of course in bar, so our pressures are bar(abs) and bar(g) ;-) So, at the surface before your dive under, on a nominal atmospheric pressure day, where the barometric (air) pressure is 14.7 psi (1 bar) if your IP is set to 150 PSI(g) then it is actually also 164.7 PSI(abs) because 150 + 14.7 = 164.7 . Dive down to 10 meters, and here where the water pressure around you has risen to 14.7 psi(g) due to the weight of water now above you and pressing down on you from all sides, your IP is still 150 PSI(g) ie 150 psi above that local ambient, however it has actually risen to 179.4 PSI(abs). By using the correct notation, we can ensure we are all talking about the correct pressure reference, and hence accurately define the pressure we are refering too! A typical pressure indicating gauge, reads in GAUGE pressure. (which is why GAUGE pressures are called what they are) because it reads the difference in pressure between the fluid supplied to its inlet port and the pressure in which the gauge is immersed. When you are holding the gauge at the surface in ambient air, that pressure in which the gauge itself is immersed is of course normal atmospheric pressure. You'll normally see a small hole or vent on the back of the gauge that allows that ambient pressure into the gauge. ABSOLUTE pressure indicating gauges do exist of course, and during their manufacture a carefully controlled pocket of gas, of a known pressure is introduced into the gauge and then sealed, whcih allows those gauges to read independently of the ambient pressure in which they are used.. everyday is school day eh! BTW, an idea for a video, although a bit more advanced, would be for you to explain how "balanced" pressure regulators manage to reduce the effective seat area to very nearly zero, and hence an substantially unaffected by the instantaneous pressure difference across that seat! (and hence why they maintain the same gauge pressure irrespective of the pressure at any given moment in your cylinder (which of course varries as you consume the air it holds) The balance of forces and areas is actually incredibly elegant and really quite subtle, and balanced regulators allow a much greater oeprating window of constant pressure difference across a wider total mass flow capability (at the cost of more, er cost and more complexity)
Wow. Thanks for the detailed lesson. I hope others read it too. I did a video on how balanced regulators work for the general population. Any more detail and I would need a teaching degree (which I have). Much appreciate your sharing this information with everyone Max. Alec
Such a simple mechanism for what, at first, seems like a tricky problem. 150 Spring + whatever local water pressure is = no hassle auto adjust! Yours if the first explanation that really made total sense. Thank you!
Hi Alec, another great video, thank you! I've just submitted a hungarian translation to this video and is waiting for your approval. Thank you Alec and Kevin!
Do I need to learn about intermediate pressure at different depths? All I know is that if Alex is talking about it then I'm going to listen. I'm sure to learn something cool. :-)
I wish my grand kids listened that closely. Nothing else other that the IP is always 150 (or manufactures value) + ambient pressure. This is why breathing is consistent at any depth. Thanks Ron. Alec
So, if I understand this correctly. The tank is about 3000psi, and this valve needs the tank's pressure to be greater than atmospheric pressure in order to push back against the diaphragm. What would happen, theoretically, if you were to dive further than 3000psi of atmospheric pressure? Would the tank no longer be able to press against the diaphragm? Super interesting video, Alec! Honestly blew my mind how simple and interesting this mechanism is! :D
Key point is atmospheric pressure, not tank pressure. So at 33ft / 10m, ATA is 2 atmospheres ambient pressure. The 1st stage takes tank pressure to ambient PLUS IP (say 150psi). For depth atmospheric pressure to equal 3000psi, your depth would be around 92 atmospheres or a depth of 3,000 ft (using my head this early). Not possible with scuba, only a submarine. There is more on IP and depths so search for more to keep your mind blown! Thanks Spanky.
Alec, off topic, but could you provide advice on emergency strobe beacon options for use in situations where you might find yourself separated from the dive boat on a night dive. I have a sausage but am interested in an emergency light. Do i need one if I already carry a torch?
Look for past video's on dive lights and SMB/DSMB. Don't remember the number but I think that was covered. Some SMB's have a tube to hold long light sticks/strobes for very long visibility. Alec
The firs stage is environmentally sealed (no water touches the working parts), just the diaphragm. Other than a good soak and rinse with clean water, nothing else to do between service intervals. Thanks for watching Nick. Alec
Is the upper pad more like a cylinder which is able to move up and down while still maintaining a seal between the upper area (where the top spring is located) and the intermediate chamber? I assume so, since otherwise water would get in at depth.
Never mind! I think I understand now, that it's all a flexible diaphragm and that the pad is just built-in for rigidity so the rod and spring can push and pull on it without tearing the softer, more flexible material around it.
Hi Alec, I was wondering to what pressure is the spring below the high pressure seat set? I imagine that spring is just to keep the seat in place, is that correct? Or does the spring adds to the pressure, next to the air in the high pressure chamber? Thanks for the informative video. Dion
I'm assuming you're referring to the big spring in a piston regulator. I tend to slide past that spring & its function since it is not the easiest to understand. One of its primary functions is, as you say, to hold the piston in place off of the HP seat. That way the valve is in the open position whenever there is no high pressure air supply. If you followed my video, you know that the piston is closed by air pressure acting on the top of the piston. The piston is pushed down by that pressure and when the pressure is correct, the valve closes. The spring opposes that movement so it actually acts to keep the valve open and allow the IP to increase. Of course, it must eventually surrender to the increasing pressure and at the right time, the spring is compressed and the valve closes. This function is to stop the valve from slamming shut as soon as pressure starts to push it down. With the spring acting to keep it open, the IP must increase slowly and smoothly to overcome both the high pressure acting on the small end of the piston and the spring pressure. The spring smooths out the action. BTW, when I say slowly, I'm talking milliseconds. All of this happens almost instantly. So you see that the spring is an important part of the regulator function. Those silly springs are precision made - the metal, the spring pressure, the rebound rate and more. All of this is calculated to ensure the right IP for each regulator. Take care. Alec
I don't know about commercial divers but hooka is not recommended for that depth as there is no 1st stage to automatically adjust the IP to ambient. Alec
Hi Alec, I've got a question. Here at Lake Constance in Switzerland, people dive with two separate first stages, one for their main second stage, one for their safe second. Now somebody suggested to me that I could just take the safe second off the first stage and attach it to the other first stage like one normally does, e.g. when I go on vacation into the warm climate for instance. Can that be done? Can first stages and second stages be tuned so well that they are interchangeable?
I guess people diving in Constance are worried that cold water may cause their 2nd stage to freeze if there's a lot of air going through it (adiabatic cooling) when 2 people are sharing one cylinder, especially as when this happens at least one of you is likely to be stressed and breathing hard! Only having one second stage per first stage will help prevent this. However, if you have a modern sealed, cold-water-rated first stage it should be capable of supplying 2 divers at only a few degrees (
@@oconnor4132 I swap 2nd stages frequently, and they work fine. While the IPs of the two 1st stages may not be exactly the same, they are close enough. If yours aren't close enough, you need to find another service tech.
Hey all, thanks for the nice replies! I guess I'll try to get the 1st stages tuned in well enough that the 2nd stages become interchangeable (I know a guy who can probably help me there) and if that doesn't work, I'll just get a second safe second for my first first stage (wow, what a whacky sentence is that?) - anyway, belt and suspenders style.
SeikiBrian it’s not that it doesn’t work, it’s just that the breathing effort won’t be optimal (or it might free flow a little). A service tech will adjust the second stage so that it is on the edge of free flowing and therefore gives you a minimal breathing effort. This will not be the case if you swap it to another first stage. The IP of the first stage needs to be within a specific range, not a precise number, and if it is within the range it does not need to be modified further, the final and precise adjustments is made on the second stage.
Your tech tips are great! This is what should be taught in the equipment specialist course. Thank you for sharing your knowledge and experience!
Wow, thanks!
A
Luckily us engineers don't really like a "does it, doesn't it" kinda scenario, so we have invented a way of defining pressures and how they relate to the world around us...... :-)
So we refer to ABSOLUTE pressures that are pressures relative to the universal and constant pressure of a total vaccuum, actually somewhere where there is no pressure at all ie relative to an absolute zero pressure and seperately to GUAGE pressures that refer to a pressure relative a local ambient pressure, which isn't fixed and may change.
These different references are normally indicated by the letters "abs" or "guage" appended to the units of pressure as in PSI(abs) or PSI(guage), sometimes shortened to PSIA and PSIG. (on this side of the pond we are of course in bar, so our pressures are bar(abs) and bar(g) ;-)
So, at the surface before your dive under, on a nominal atmospheric pressure day, where the barometric (air) pressure is 14.7 psi (1 bar) if your IP is set to 150 PSI(g) then it is actually also 164.7 PSI(abs) because 150 + 14.7 = 164.7 .
Dive down to 10 meters, and here where the water pressure around you has risen to 14.7 psi(g) due to the weight of water now above you and pressing down on you from all sides, your IP is still 150 PSI(g) ie 150 psi above that local ambient, however it has actually risen to 179.4 PSI(abs). By using the correct notation, we can ensure we are all talking about the correct pressure reference, and hence accurately define the pressure we are refering too!
A typical pressure indicating gauge, reads in GAUGE pressure. (which is why GAUGE pressures are called what they are) because it reads the difference in pressure between the fluid supplied to its inlet port and the pressure in which the gauge is immersed. When you are holding the gauge at the surface in ambient air, that pressure in which the gauge itself is immersed is of course normal atmospheric pressure. You'll normally see a small hole or vent on the back of the gauge that allows that ambient pressure into the gauge. ABSOLUTE pressure indicating gauges do exist of course, and during their manufacture a carefully controlled pocket of gas, of a known pressure is introduced into the gauge and then sealed, whcih allows those gauges to read independently of the ambient pressure in which they are used..
everyday is school day eh!
BTW, an idea for a video, although a bit more advanced, would be for you to explain how "balanced" pressure regulators manage to reduce the effective seat area to very nearly zero, and hence an substantially unaffected by the instantaneous pressure difference across that seat! (and hence why they maintain the same gauge pressure irrespective of the pressure at any given moment in your cylinder (which of course varries as you consume the air it holds) The balance of forces and areas is actually incredibly elegant and really quite subtle, and balanced regulators allow a much greater oeprating window of constant pressure difference across a wider total mass flow capability (at the cost of more, er cost and more complexity)
Wow. Thanks for the detailed lesson. I hope others read it too. I did a video on how balanced regulators work for the general population. Any more detail and I would need a teaching degree (which I have). Much appreciate your sharing this information with everyone Max.
Alec
That’s extremely interesting on how the 1st and 2nd stages work. I love these videos pls keep them coming. Than you for all your hard work
Thanks Will. More coming to increase your brain size.
Alec
Such a simple mechanism for what, at first, seems like a tricky problem. 150 Spring + whatever local water pressure is = no hassle auto adjust!
Yours if the first explanation that really made total sense. Thank you!
It is simple but divers tend to overthink it. Thanks for watching.
I love videos like this! Thank you from sweden..
Glad you like them!
Thank you for sharing your knowledge Alec another great video. Thanks Kevin
Welcome Leon.
Alec
Thanks for the explanation Alex! Great job as always
I try to make difficult subjects interesting for everyone. Some ask for more details, others less. Thanks for watching Thomas.
Alec
Very interesting and informative... I love these Tech Tips!
Thanks for watching Seven.
Alec
Great video as always, but the imperial system makes it harder to understand for non-americans.
That's true. I grew up with Imperial and understand metric in Canada but still use the 'old' system.
Alec.
Hi Alec, another great video, thank you! I've just submitted a hungarian translation to this video and is waiting for your approval. Thank you Alec and Kevin!
Just published it. This is my first Hungarian translation so thanks for the effort and hope others benefit from it.
Alec
Do I need to learn about intermediate pressure at different depths? All I know is that if Alex is talking about it then I'm going to listen. I'm sure to learn something cool. :-)
I wish my grand kids listened that closely. Nothing else other that the IP is always 150 (or manufactures value) + ambient pressure. This is why breathing is consistent at any depth.
Thanks Ron.
Alec
So, if I understand this correctly. The tank is about 3000psi, and this valve needs the tank's pressure to be greater than atmospheric pressure in order to push back against the diaphragm.
What would happen, theoretically, if you were to dive further than 3000psi of atmospheric pressure? Would the tank no longer be able to press against the diaphragm?
Super interesting video, Alec! Honestly blew my mind how simple and interesting this mechanism is! :D
Key point is atmospheric pressure, not tank pressure. So at 33ft / 10m, ATA is 2 atmospheres ambient pressure. The 1st stage takes tank pressure to ambient PLUS IP (say 150psi).
For depth atmospheric pressure to equal 3000psi, your depth would be around 92 atmospheres or a depth of 3,000 ft (using my head this early). Not possible with scuba, only a submarine.
There is more on IP and depths so search for more to keep your mind blown! Thanks Spanky.
Nice video, Alec.
Thanks Roman.
Alec
:) Nooane spefies the "above ambient"
Thanks.
Alec
Alec, off topic, but could you provide advice on emergency strobe beacon options for use in situations where you might find yourself separated from the dive boat on a night dive. I have a sausage but am interested in an emergency light. Do i need one if I already carry a torch?
Look for past video's on dive lights and SMB/DSMB. Don't remember the number but I think that was covered. Some SMB's have a tube to hold long light sticks/strobes for very long visibility.
Alec
Could you do a diagram showing how and why they ice up? Thanks again!
Yep.
Keep watching.
Alec
What happens to the water in the primary regulator after a dive? Is this something that needs attention?
The firs stage is environmentally sealed (no water touches the working parts), just the diaphragm. Other than a good soak and rinse with clean water, nothing else to do between service intervals.
Thanks for watching Nick.
Alec
Is the upper pad more like a cylinder which is able to move up and down while still maintaining a seal between the upper area (where the top spring is located) and the intermediate chamber? I assume so, since otherwise water would get in at depth.
Never mind! I think I understand now, that it's all a flexible diaphragm and that the pad is just built-in for rigidity so the rod and spring can push and pull on it without tearing the softer, more flexible material around it.
Knew you would get it if watching a second time. Look how smart you are watching these! Thanks for watching Tim.
Hi Alec, I was wondering to what pressure is the spring below the high pressure seat set? I imagine that spring is just to keep the seat in place, is that correct? Or does the spring adds to the pressure, next to the air in the high pressure chamber? Thanks for the informative video. Dion
I'm assuming you're referring to the big spring in a piston regulator.
I tend to slide past that spring & its function since it is not the easiest to understand.
One of its primary functions is, as you say, to hold the piston in place off of the HP seat.
That way the valve is in the open position whenever there is no high pressure air supply.
If you followed my video, you know that the piston is closed by air pressure acting on the top of the piston. The piston is pushed down by that pressure and when the pressure is correct, the valve closes. The spring opposes that movement so it actually acts to keep the valve open and allow the IP to increase. Of course, it must eventually surrender to the increasing pressure and at the right time, the spring is compressed and the valve closes. This function is to stop the valve from slamming shut as soon as pressure starts to push it down. With the spring acting to keep it open, the IP must increase slowly and smoothly to overcome both the high pressure acting on the small end of the piston and the spring pressure. The spring smooths out the action.
BTW, when I say slowly, I'm talking milliseconds. All of this happens almost instantly.
So you see that the spring is an important part of the regulator function. Those silly springs are precision made - the metal, the spring pressure, the rebound rate and more. All of this is calculated to ensure the right IP for each regulator.
Take care.
Alec
@@AlecPeirceScuba_SeaHunter thank you Alec for your detailed answer!
its all about the balance of opposing pressure.
Absolutely!
A.
so when people are diving on hooka and hit 66 ft their ip drops to around 120. and commercial divers have their gas adj to their depth.
I don't know about commercial divers but hooka is not recommended for that depth as there is no 1st stage to automatically adjust the IP to ambient.
Alec
Hi Alec, I've got a question. Here at Lake Constance in Switzerland, people dive with two separate first stages, one for their main second stage, one for their safe second. Now somebody suggested to me that I could just take the safe second off the first stage and attach it to the other first stage like one normally does, e.g. when I go on vacation into the warm climate for instance.
Can that be done? Can first stages and second stages be tuned so well that they are interchangeable?
I guess people diving in Constance are worried that cold water may cause their 2nd stage to freeze if there's a lot of air going through it (adiabatic cooling) when 2 people are sharing one cylinder, especially as when this happens at least one of you is likely to be stressed and breathing hard! Only having one second stage per first stage will help prevent this. However, if you have a modern sealed, cold-water-rated first stage it should be capable of supplying 2 divers at only a few degrees (
Your second stage will need to be readjusted if you put it on another first stage. The IP of your two first stages will never be exactly the same.
@@oconnor4132 I swap 2nd stages frequently, and they work fine. While the IPs of the two 1st stages may not be exactly the same, they are close enough. If yours aren't close enough, you need to find another service tech.
Hey all, thanks for the nice replies! I guess I'll try to get the 1st stages tuned in well enough that the 2nd stages become interchangeable (I know a guy who can probably help me there) and if that doesn't work, I'll just get a second safe second for my first first stage (wow, what a whacky sentence is that?) - anyway, belt and suspenders style.
SeikiBrian it’s not that it doesn’t work, it’s just that the breathing effort won’t be optimal (or it might free flow a little). A service tech will adjust the second stage so that it is on the edge of free flowing and therefore gives you a minimal breathing effort. This will not be the case if you swap it to another first stage. The IP of the first stage needs to be within a specific range, not a precise number, and if it is within the range it does not need to be modified further, the final and precise adjustments is made on the second stage.
Want to know (much) more: “ Scuba Regulator Savvy” by Pete Wolfinger, scubatools.com.
Thanks for sharing the link.
Alec