LOGOGasswitchblock TR300

WARNING: rebreather diving is different. Any use of the equipment or parts thereof, is at your own risk, it is assumed liability for any resulting damages!


In order to be able to switch between the two gases, a gas switch back “switch block” was designed.

About the switch, the gases are switched respectively to the bypass and the needle valve. The flow of the needle valve is based here on the largest required flow and is directly related to the mixtures and the planned dive.

This is possible because the normal calculation of the flow emanating from a single gas supply.  Therefore, had the proportion of oxygen in the circulation large enough (> 0:21 PPO 2) to be from the circuit surface can be breathed in too.

This changes, however, when between two (or more) gases can be switched. The “richer” mixture is used for the surface until switching (MOD).  The flow calculation for the “lean” mixture now needs to be (not the surface) calculated from the point of switching gases.

Switch on the gas block then the larger of the two flows is set.

A dive would look like this:

  • turned on at the surface “rich” mixture
  • dive with the “rich” mixture to the MOD
  • switch to “lean” mixture, possibly rinse cycle
  • dive with the “lean” mixture to the planned depth
  • Bottom Time dive
  • Ascent to the MOD (“rich” mixture)
  • switch from the “lean” mixture “rich” mixture, rinse cycle must
  • show up with “rich” mixture to the surface (Deko!)

“Rich” mixture = main mix or Dekomix (eg Nitrox 50)

“Lean” mixture = Bottommix (eg Trimix 21/35)

In Bailoutfall can the respective mixtures at all times open to respire without a complicated bailout / Dekotabelle to use extra.  It just needs enough Bailout breathing gas available

Table Dekomix, Flow, Bottommix

Dekomix Flow-Dekomixmin Tumschalt Bottommixmin für Flow TTmax
100% 2 l/min 6 msw 70% 10 msw
80% 3 l/min 10 msw 50% 21 msw
50% 8 l/min 22 msw 25% 53 msw

T = Shift Umschalttiefe

TT = max.  Depth of Bottommix

Bottommix “would lean as Bottommix elected, then min, the flow corresponding to the T switches (Umschalttiefe Bottomix) is set to be the if. It is then for the Dekomix too high which means a little more gas, but a better “rinsing effect” results in the decoration.

Dekomix Flow-Dekomixmin Tumschalt Bottommix TTmax
50% 8 l/min (Dekomix)

11 l/min (Bottommix)

22 msw 21% 63 msw

A separate flow can be enforced by the 1 Stufen auf unterschiedlichen Mitteldrücken stehen. Levels at different average pressures are. Furthermore, the use of helium in the depth range brings additional flow again in Bottommix.

According to the above table I would have with 4 liters of breath gas bottles for decoration / Bottom (with no bailout!) Approx 54min available.  This results in a maximum 60m/22min TG (21/35) with 40 min and 54 min Bottommix Dekomix

For the bailout should have at least a 10 and a 10 Bottommix Dekomix are available!

The gas switch block

Watching is integrated in the stainless steel needle valve block outlet to the bypass, connection from Dekomix (main mix) and Bottommix.  The gases supplied to the ball valves can be switched on and off.The gas is supplied with UNF 7 / 16 (connections of 2nd stage regulator) and disposals are UNF 3 / 8.


Alternatively, switch to a fixed block is still the possibility of switching from gas couplings.  Here, a hose (coupling) connected to the metering unit connected (eg the dolphin) and the various gases via connector (similar to the inflator) is important here is a good piping, so that the correct tube is found at the right time too.

The TR300 has no metering, but a bypass and a separate entrance for the flow (needle valve).  In consequence, a plug-in coupling option, would at least need a gas block (where bypass and needle valve are combined).


These remarks are necessary to prevent the usual word in diving circles battles.

  1. No one should rebuild it or try it even
  2. Such diving equipment can be anything but dive
  3. Who but it appears, will surely die immediately