Diving automatons differ in certain solutions that can affect their operation and service, and depending on your needs – these solutions can be advantages and disadvantages of a particular model.
Automakers can be divided or described as:
- Automated first stage piston and diaphragm machines
- Automatic machines with co-rotating or counter-rotating valves
- Unloaded and unloaded automatics
- Automatics with assistance – Venturi venturi tube/Venturi nozzle
- Automatics with adjustable and non-adjustable booster and mushroom pressure.
Exhaust valve
Before we focus on the various detailed solutions, let’s discuss the problem of the exhalation valve in the 2nd stage of any breathing machine. The exhaust valve is slightly covered by the so-called exhaust wheel, but in the photos near the article it was partially exposed. This valve allows air to be exhaled outward into the water in a typical breathing apparatus, or open-circuit apparatus. At the same time, during inhalation, the valve adheres to its seat and prevents water from being sucked into the II stage and thus into the diver’s mouth. However, sometimes (as shown in the photos) the valve gets undercut (for example, when jumping into the water) and the automaton gives some water with the inhaled air during inhalation. This is especially dangerous with octopus – so always take 3 breaths from the octopus with your face submerged in the water after entering/jumping into the water.
Automated first stage piston and diaphragm machines
Although the first piston and diaphragm stages are fundamentally different in construction, from a practical point of view, the principle of operation of them is a curiosity rather than a selection criterion for purchase. There are pros and cons to each design, but both types top the list of the best slot machines. Piston first stages have fewer moving parts than diaphragm stages, making them faster and easier to service. The first membrane stages, on the other hand, have their internal parts separated from water contact, which reduces corrosion and fouling accumulation. To achieve this in the piston variant, a so-called “dry first chamber” solution is used. Piston solutions can be easily designed with rotating elements. Popular models offer five low-pressure ports while most membrane solutions have only four.
Automatic machines with co-rotating or counter-rotating valves
Automakers have two basic types of valves. Concurrent and counter-concurrent. Concurrent is more popular. Concurrent means that the valve opens like a door in a movie theater in accordance with the flow of air. In this solution, the valve opens according to the direction of gas flow. Concurrent valves have several advantages. The first is that it is mechanically simpler, resulting in their high reliability. Secondly, the air flow presses on the valve which makes precise adjustment easier. Third, when a valve is damaged, the damaged valve almost always remains in the open position. This means that when air flows continuously through the valve (bubbling automaton), you can still breathe from the automaton and emerge safely. This feature is called fail-safe.
Relieved and unrelieved
Since we have about 200 atm in the cylinder at the beginning of the dive and about 50 atm at the end, the valve in stage I is affected by a variable pressure balanced by the spring. However, with less pressure in the cylinder, more and more negative inhalation pressure is needed to open the valve, that is, such an automaton at the end of the dive gives air with increasing resistance. To avoid this problem, the designers of the automats created relieved I stages. The photo shows relief by the flow piston method (a piston with a small calibrated hole that transfers variable pressure to the other side of the piston). Technical solutions vary, but in general relieved automatics have similarly low breathing resistance regardless of cylinder pressure.
Venturi venturi tube | Venturi nozzle
Another way to reduce breathing resistance in automatons is to use a nozzle (or venturi) that lowers breathing resistance according to Venturi’s law, which states that a flowing fluid (liquid or gas) causes a drop in pressure. Using a booster with a Venturi nozzle, the gas flow reduces the pressure and reduces the force required to keep the air supply valve open. To activate Venturi assist, the air outlet of the second stage is directed toward the mouthpiece. This placement makes it easier to boost to the point that automatons with boosters tend to excite when they are not placed in the mouth. To prevent this, most automatics of this design have a dive/surface setting. In the surface setting, there is a reduction in flow, which reduces the impact of the Venturi effect making it more difficult for gas to flow when not diving.
Adjustable and non-adjustable booster and plug pressure
All first and second steps have internal adjustment, which technicians set during installation and service. Higher-end automatics often have the adjustment on the 2nd stage brought outward allowing the user to adjust the automaton’s operation during the dive. The adjustment involves changing the pressure of the valve plug by changing the breathing resistance. On some models, the adjustment can be set at extremes from bubbling to almost complete shutdown of the flow. Adjustable second steps offer two benefits. First, you can temporarily reduce the flow almost to zero to avoid bubbling, for example, by swimming against a strong current that presses on the membrane. Since the best automatics are very sensitive, it may be appropriate to set the octopus at a low opening sensitivity, with possible adjustment when it is used. Technical divers who switch between multiple automatics during a dive may also want to vary the sensitivity of the valve opening depending on whether the automatics are currently in use or not. Another benefit of regulation is that automatic machines, with wear and tear between successive servicing, reduce their performance; in a regulated model these changes can be levelled out. It is important to remember that setting the automatic to feed air harder does not result in savings in air consumption. This can even be dangerous causing insufficient air supply. The more effort we put into taking a breath, the greater the oxygen demand our body has, resulting in increased air consumption. To consume as little air as possible, it is appropriate to set the automaton to breathe as easily as possible, minimally below the bubble limit.
Choosing the right machine
If the described features and design differences seem too complicated to choose the right model, let’s consider the resulting consequences for the diver and make a decision on such a basis.
*Safety
Safety is very important, yet when you buy a modern automatic from a well-known manufacturer, you get a product with a reasonable and proven design. It is not necessary to check which automats work and which do not 🙂
*Investing in the best models.
On the one hand, just as a novice driver can drive a good model car, a novice diver can use a good model automatic. Every diver will benefit from the improved performance and durability of better models. If price is important in making a choice, it is a good idea to just buy a simpler model but a good/known company. At Deepspot, divers have the opportunity to test both simple automatics without adjustments and more advanced models including those prepared for twine or sidemount diving.
*Respiratory resistance
Resistance breathing ease and serviceability. Choose an automatic that is easy to breathe from and that you know can be serviced in your area. In modern automatics, differences in breathing resistance are due to service problems rather than the choice of a particular model or brand. There are a lot of good brands out there, but some of them may be impossible to service where you live and require sometimes expensive shipping.
*Seek advice from a dive center.
You are likely to have a number of top models with low breathing resistance and easy serviceability not far away. If you are not sure, advise a professional at your nearest dive center, such as Deepspot. If you are planning to dive in cold waters as is the case in central or northern Europe, a first stage dry chamber may be a key feature in your choice.
Maintenance and service of the machine
The automatic requires more care than other pieces of diving equipment, but about that in the next text.
