• Welcome to the DeeperBlue.com Forums, the largest online community dedicated to Freediving, Scuba Diving and Spearfishing. To gain full access to the DeeperBlue.com Forums you must register for a free account. As a registered member you will be able to:

    • Join over 44,280+ fellow diving enthusiasts from around the world on this forum
    • Participate in and browse from over 516,210+ posts.
    • Communicate privately with other divers from around the world.
    • Post your own photos or view from 7,441+ user submitted images.
    • All this and much more...

    You can gain access to all this absolutely free when you register for an account, so sign up today!

Infinitengines "Dreamair" pneumatic speargun

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
Like all spearguns it is only as powerful as the user has the strength to load it, plus how much time can be expended on the loading task before you need the gun to be ready to shoot. Any leverage system that spreads or stages the loading effort always takes longer to load the gun. However like any pneumatic gun the pressure used in the "Dreamair” can be adjusted to suit both the user and the shooting task required, although that needs to be done before the gun is taken to the dive site.

As rubber bands both deteriorate and lose some of their strength over time the “Dreamair” should offer a much more consistent shot as bar air leaks the energy storage using compressed air should be a constant. Plus with no bands the gun should have less drag when it is being manoeuvred around because it is a true cable gun with no exposed band battery.

Although carbon fibre when it was first introduced into spearguns was thought of as making for a lighter gun, the full body carbon fibre guns are actually quite heavy, which is what you want from a recoil perspective.
 
Last edited:
Air is also not constant! During cooling, the spring properties of the compressed air are greatly reduced with very small pressure changes according to the temperature coefficient! This is due to entropy!
 
As the gun body totally immersed in water is affected by the surrounding water temperature this is not such a problem. The moderating of temperature in the gun by the large body of water in which it is operated is also why carbon dioxide guns shoot at constant pressures, the gun being reheated by the surrounding water after a shot. The only time water temperature can be a problem is in icy waters as the small channels in hydraulic valve guns such as the Aquatech can freeze up as air expansion inside the gun cools it enough that water inside the gun freezes. Then you have big problems to thaw out the gun.
 
Reactions: Diving Gecko
Nobody uses carbon dioxide with us! Winter hunting in icy water! Effort of loading at home at a temperature of 24 degrees Celsius 30 kg per hand! Loading force in water 4 - 5 degrees Celsius 20 kg per hand! Air temperature coefficient 1 ° C. - 0.003684, which does not lead to a significant loss of pressure in the receiver of the gun and does not explain the loss of loading force in any way! Obviously, you haven't encountered It yet!
 
The point being made was the influence of the water temperature as the gun is operated in it, a much larger thermal mass. Freezing temperatures affect the flexibility of rubber, so band guns are nearly useless unless using a special compound. Temperature affects the expansion and contraction of metal parts, so clearances are changed, however most readers on this board do not dive in freezing conditions and for the most part dive in the sea. Here spearfishing in rivers and lakes is banned.
 
Reactions: Diving Gecko
Interesting... I would never say that would be like that with loading force..
If the pressure in the gun would be 30 bar at 24 Celsius, than it would be 28 bar at 4 Celsius..., if I was right..?
 
Reactions: Zahar and Diving Gecko
I agree, the near-freezing market must be extremely small for pneumatic guns by Western brands and as rubbers suffer more in colder waters, it’s all a bit theoretic;-)


Sent from my iPhone using Tapatalk
 
tromic said:
Interesting... I would never say that would be like that with loading force..
If the pressure in the gun would be 30 bar at 24 Celsius, than it would be 28 bar at 4 Celsius..., if I was right..?
Click to expand...

Quite right Tomislav! Few of the Advanced Guns Constructors figured it out! I have dedicated Time to Study It! When cooled, the spring properties of gas molecules decrease at practically unchanged pressure! Pressure is a quantitative characteristic of gases in a confined space! The spring properties of gas molecules are the bond energy between molecules and elements in atoms! The difference is huge!
 
Reactions: Diving Gecko
The equation for an ideal gas is PV = nRT, hence with the number of moles of gas n and the gun internal volume V constant the equation becomes P/T = nR/V. R is also a constant, Avogadro’s number.

We can then say P1/T1 = P2/T2 with the temperature T in degrees Kelvin which means temperature in Celsius + 273.

Thus 30 bar at 24 Celsius or 297 Kelvin means that the pressure at 4 Celsius or 277 Kelvin is given by

30/297 = P2/277 which transforms to P2 = 30/297 x 277 = 27.98 bar
 
Reactions: Zahar
Something is not logical here... If 30 bar is 30.5 kgf/cm2 and 28 bar is 28.5 kgf/cm2 at 4 Celsius, how could be the loading effort be near to 20 kgf at 4 Celsius? That is very strange...? I would maybe expect that the "spring" property of the air at lower temperature would be like decelerated spring but not like weaker spring..?
 
Reactions: Zahar
The logic inside the air molecules! Warm air is a good spring! Cold air is a bad spring! How are gases liquefied? They are cooled and compressed!
 
The pressure is the measure of a force resulting from the air molecules bouncing off a surface of a certain surface area. The warmer the air then the faster the molecules are moving and the more collisions are occurring with the surface, that is why with increasing temperature the force goes up which we see as increased pressure, which is the force per unit area. The energy from a pneumatic speargun if we neglect losses from friction and throttling is controlled by the start and cocked pressures in the gun. That energy is only less if the start pressure is less as the compression ratio remains the same. When you cock a pneumatic gun there is a slight adiabatic heating as the gas compresses, but as the gun is operating in water which rapidly conducts any heat away this effect can be ignored.

If you doubt this then read any basic physics textbook.
 
Last edited:
Reactions: Zahar
Scuba air pressure - a quantitative measure? Don't confuse Cause and Effect! Force - Consequence of Pressure on the Square!

 
The pressure change in a pneumatic speargun from cocked to discharged is small as the compression ratio is usually around 1.10, so those heating on loading or cooling on shooting effects are negligible.

It is actually pressure that is a consequence of the force applied by the collisions.
 
Last edited:
Zahar said:
The logic inside the air molecules! Warm air is a good spring! Cold air is a bad spring! How are gases liquefied? They are cooled and compressed!
Click to expand...
Air is liquefied at -140.5 Celsious and 37.8 bar. That is far below from +4 Celsius..
 
Reactions: Zahar
When you compress air it heats up, so the compressed air has to be cooled by removing the heat.

liquid air

liquid air, ordinary air that has been liquefied by compression and cooling to extremely low temperatures (see liquefaction). Its commercial preparation involves purification by washing to remove soluble impurities and by passage over calcium oxide
www.infoplease.com

The reason why multistage compressors are used is the air can be cooled before it moves to the next compression stage and you don't get oxidation of the compressor lubricants in each pumping stage. For liquefied air to expand it has to draw in heat, this is why it causes warmer things to cool down by drawing the heat from them. The warm air does not make a better spring as such, it is just the pressure change as the enclosed volume is allowed to expand which also draws in heat. For pneumatic spearguns this heat exchange is small as the pressure change is small.
 
Reactions: Zahar
It's not hard to experiment with a short gun by putting it in the refrigerator! You will be surprised by the difference in loading force! This difference cannot be described as a pressure change!
 
Reactions: tromic
Zahar said:
It's not hard to experiment with a short gun by putting it in the refrigerator! You will be surprised by the difference in loading force! This difference cannot be described as a pressure change!
Click to expand...
You cannot reinvent physics, any effect you are seeing is due to the cooling of the parts of the gun, such as the rubber seals and the metal barrel. It is not due to the changing "spring properties of air".

Everything You Need to Know About Temperature and Rubber Seals

While rubber is often regarded as having strong, durable qualities, there are many outside factors that can have a heavy impact on its performance. Temperature largely affects certain rubber compounds, whether it be extreme heat or cold. Not all rubber is the same. In fact, certain rubber materi
www.applerubber.com

Hydraulic seals battle extreme cold | Sealing & Contamination Control Tips

Low-temperature chemistry and innovative hydraulic seal designs prevent weeps and leaks. By Ryan Webster, Hallite Seals Americas and Mark Haggerty,
www.sealingandcontaminationtips.com
 
Last edited:
Reactions: Zahar
If you think . that your Knowledge of Physics of Compressed Air in spear guns is Thorough, then you are mistaken! I gave you a good Topic for filling the Gap in Knowledge, but you still did not understand Me! I am not a teacher ! I'm not going to teach you! Everything is in Google! Just learn to formulate the Problem correctly and find the Answer! Good luck to you!
 
Zahar, this is so simple that I can not understand how can you see is it different from Pete and me...
The pressure = force/surface, p=F/S, Lets say in kgf/cm2 to be more obvious and simple.. What does mean pressure of 30 kgf/cm2.
It means that the force of 30 kgf is acting on surface 1 cm2. So you would need a force of 30 kgf to start loading the speragun if the surface of the piston would have been 1 cm2. The same is for any other pressure. On 4 Celsius the pressure would be 28 kgf/cm2 if it were 30 kgf/cm2 at 24 Celsius.
The assumption is that there is no friction to the piston.
Happy New year to all
 
Reactions: Zahar
You must log in or register to reply here.
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…