Apeks 2nd stages are split into 3 categories. MTX-R is the simplest, with no diver adjustable controls. Next is the 20/40 series with a Venturi Lever. Finally the 50/100/200 & RC Regs with both the Venturi lever and an inhalation resistance control knob.
This is an explanation of what these simple controls do and how you should use them.
Venturi Lever / Switch
This is the simple lever with a + or – setting. The venturi is a deflector which changes the direction of airflow to limit freeflow when not in use and allow for an easy breathe during the dive.
On the + setting, gas is allowed to flow freely towards the mouthpiece. When the diver starts to inhale the diaphragm is drawn it with vacuum to operate the lever and release the gas. As the gas flows to the diver it increases the vacuum on the diaphragm and pulls it further in allowing for maximum gas flow. Think of it like a “servo assist” feature that should always be in use when breathing from the regulator. You could also think of it as “Dive Mode”
On the – setting, a deflector moves around the opening of the tube inside the 2nd stage which directs the gas to flow away from the mouthpiece. The redirected gas pushes the diaphragm back towards the resting position. The regulator will still breathe and work, but the effort required to breathe will be greatly increased. This is great for on a 2nd stage on the surface or an octopus during the dive to minimize freeflows. You can also think of this setting as “pre-dive” or “pre-breathe” in the case of an octopus or unused twinset reg.
You can test how the Venturi works, by setting it to + and tapping the purge button. The reg will likely freeflow. Then move the Lever to the – position. The freeflow should stop. Don’t do this in the water!
Note that the reg may not freelow out of the water. This could be because of the mouthpiece acting as a deflector. Some regs also have a lesser purge button movement
Inhalation Resistance Control Knob
Fitted to higher-end regulators, it allows the diver to adjust the ease of breathing before and during the dive. This is achieved by directly adjusting the spring pressure inside the 2nd stage body and valve. The higher the spring pressure, the higher the resistance to the vacuum created by the diver during inhalation. The vacuum required to open the valve and allow gas to flow from the diver’s cylinder is called “Cracking Effort”
Turning the knob clockwise increases the “Cracking Effort” while turning the knob anti-clockwise reduces the cracking effort.
If the cracking effort is too low, the regulator will be prone to freeflow and over-breathing. This is where the regulator continues to deliver gas after the diver has stopped inhaling.
The ideal cracking effort is as low as possible without and freeflow or over-breathing. This setting may change dependent on the dive conditions and breathing rate of the diver. An easy dive might allow for a lower cracking effort, while a tidal dive might require a higher cracking effort to minimize freeflow. A diver working hard and breathing heavy might prefer a slightly higher cracking effort to minimize over-breathing and have a greater feeling of resistance to breathing.
Cracking effort is measured using a vacuum gauge using the unit mmH20. This is the amount of vacuum required to lift fresh water inside an open ended tube called a “Manometer” a certain distance in millimeters (mm).
The amount of cracking effort allowed is determined by the ISO standards the manufacturers must adhere to when designing and building regulators. The technician then uses the settings as listed in the workshop manuals. Typically this is set out as a maximum allowed.
A typical primary regulator would have a CE of 35 mmH20 and an Octopus or Pony would have a CE of 45. These are the settings I use after a service on a non-adjustable 2nd stage.
For a 2nd stage with an adjustment knob, I use a full-open CE of 25, which means that the diver will have the knob in approximately 1 turn to get the usual CE of 35. This is a measurement that I make during setup and from 12/23 I will note the gained CE per knob turn on the service report.
This offers the benefit of not having the knob unscrewed all the way in normal use. It wont come unscrewed but often seizes in place hard against the pin that stops the knob from coming all the way out.
New regulators have a wide-range off settings in my experience and I’ve often seen regs with the minimum set to the maximum allowable. This makes no sense to me as it means that the diver can only increase the CE over the maximum allowed. CE will in many cases increase as corrosion ect builds up on the regulator between services.
For a regulator without a control knob the technician will be able to make the same adjustments on the bench. So if you feel that you would prefer a different CE setting please ask. It’s not a big job, but does require the tools to do it properly. There may also be a need to adjust the lever height along with the CE.
Where should my Venturi Lever be?
When in use it should be “+” for a primary regulator and “–“ for an Octo or Pony
What setting should I have my control knob?
Check your service report, 1 turn in is a good starting point
My Reg doesn’t have Adjustable Controls, is it inferior?
No. Provided it’s serviced regularly and setup properly.
My personal MTX-R’s don’t have these features and I consider them to be the best regulator on the market today.
This guide is also availible as a PDF download