Sentinel Expedition Rebreather Optocon



Closed Circuit eCCR //
1 August

READ THIS FIRST!

Read this first!

Rebreather tests

People ask me many times which rebreather is the best one in the market. I usually reply that it depends on the application of the rebreather and the diving experience by the user. Does he/she travel a lot? Does he/she wants to make only recreational dives? Is he/she a cave diver? Or deep diver?

Rebreathers differ a lot. Very important are the “roots” of the manufacturer/inventor. Is he (yes: we have only male manufacturers…) a metalworker, a programmer, a marine, an engineer, …? It can have a big impact on the design of the rebreather.

There is also a difference in build quality, safety features and additional features. And of course: the price.

I have quite a lot of experience (in the field) with rebreathers. Some rebreathers are better than others (depending on the type of dive I make with them). So I tried, based on my personal experience, to rate the rebreathers. Five stars is the highest rate. One star is the lowest. The overall rating is the average of the ratings of the subcategories, which are:

1.  Ease of use (set-up, maintenance)
2.   Buoyancy/trim
3.  Work of breathing (WOB)/automatic Diluent Valve (ADV)/lungs 
4.  Travel (modularity) 
5.  Safety 
6.  Price 
7.  Service/after sales/availability of parts 
8.  Build quality 
9.  Cave diving 
10.   Deep and X-treme diving (deeper than 100 mtr)

All subcategories have the same weight for the total “verdict”.

Regarding safety: this is a difficult category. Does adding safety-items to a rebreather (such as CO2 monitors, auto-breathe-detection, etc.) really increase the safety? Those items can brake and might make rebreather-divers technology-dependent… It’s like cars: safety equipment (like ABS, airbags, brake assist, etc.) makes cars also accessible for bad drivers… Is a rebreather without electronics safer than a rebreather fully loaded with electronics? Check out the tests… I didn’t perform tests on the rebreathers in a lab. E.g. when I talk about the WOB, it is my personal experience and NOT the result of a lab test. I understand that some manufacturers will not be happy with my conclusions and that they want react on the rating. They can do so by sending an e-mail or replying on the forum on my website. Again: the verdict is based on my personal experience and I have personal preferences as well. Those preferences will have an effect on the way I view rebreathers. Another individual might have a completely different view on the rating. Furthermore I want to make absolutely clear that any rebreather manufacturer does not influence me in any way. I’m only interested in their product: rebreathers!

CCR Computer tests 

I have quite a lot of experience (in the field) with rebreathers and CCR computers. Some rebreathers and computers are better than others (depending on the type of dive I make with them). So I tried, based on my personal experience, to rate the CCR computers. Five stars is the highest rate. One star is the lowest. The overall rating is the average of the ratings of the subcategories, which are:

  1. Ease of use (set-up, maintenance)
  2. Functionality
  3. Operating depth
  4. Reliability and build quality
  5. Price
  6. Service/after sales/availability of parts

All subcategories have the same weight for the total “verdict”. 

I didn’t perform tests on the computers in a lab. E.g. when I talk about the batteries, it is my personal experience and NOT the result of a lab test. I understand that some manufacturers will not be happy with my conclusions and that they want react on the rating. They can do so by sending an e-mail or replying on the forum on my website. Again: the verdict is based on my personal experience and I have personal preferences as well. Those preferences will have an effect on the way I view computers. Another individual might have a completely different view on the rating. Furthermore I want to make absolutely clear that any computer manufacturer does not influence me in any way. I’m only interested in their product: ccr computers!

Pim van der Horst

Director Pim’s Tekdiving PTD


 

Name:

Sentinel Expedition Rebreather Optocon

Manufacturer:

VR Technology

Website:

http://shop.technologyindepth.com/

Since:

2009

Type:

eCCR

CE:

Yes, since 2009

Lungs:

Back mounted (one transparent lung only!)

Weight:

30 - 35 kg (ready to dive)

Scrubber duration:

3 hours, axial canister . 40m, air, 4 degrees C. 1.6l/min CO2.  160 mins, 100m, heliox, 4 degrees C, 1.6l/min

Weight Scrubber:

2.2 kg

ADV (Automatic Diluent Valve):

Yes. With isolator

HUD (Head Up Display):

Yes, two HUD’s

BOV (Bail Out Valve):

Yes (with CE rating)

(Deco-) computer:

Yes

Tanks:

2 ltr. 3l possible in diluent side or larger with Travel Kit

My deepest dive with the unit:

120 mtr (Egypt)

Price:

8500-11.500 EUR (ex shipping, incl. taxes) Depending on exchange rate GBP/EUR

 

General:

3 stars (was 2 stars)

 

I discussed the first version of my review with the manufacturer. As a result I made some changes in the text. Where it affected the rating, this is indicated. VR assured me that many of the problems with the unit are solved and that there are positive reports from the field. As I said earlier: the low general rating was mainly caused by the practical use of the unit The conceptual design of the Sentinel is far above average. So I decided to give the Sentinel the benefit of the doubt and upgrade the rating to 3 stars. When VR keeps improving and creates a stable unit, the rating might go up to 4 stars.

The concept of this highly (too?) advanced rebreather is ok. But… all the (too?) advanced electronics and possibilities make this a very difficult CCR. The build quality is less than it’s mother: the Ouroboros. The unit’s design is balanced such that when in water no or very little additional lead is required. (most other units have to add an amount of lead)  The downside of this is the travel weight goes up. However it is possible to either split the canister out and use it as ‘carry on’ or but the optional ‘Travel Kit’.

 

In the last year there have been several technical updates to the unit.  The prime goal was to remove all cable and connector systems from safety critical parts and to increase system redundancy. VR has had some teething problems with this but reports from the field now suggest that the issues have been dealt with and older units have or are being upgraded. The WOB is very low: but that needed very large hoses and a very big BOV/DSV.  Also the BOV/DSV has to be this big using current technology to give the WOB and meet EN250.

1. Ease of use (set-up, maintenance)

2 stars (was 1 star)

The unit automatically calibrates in air. One needs also to (manually) calibrate the CO2 sensor  The scrubber is launched by a trigger mechanism into a special seal in the canister. The spring base is used as historically we have seen many safety issue on other units where people get involved with aligning the CO2 scrubber and CO2 seal up or even not fitting the seal. This is why on Sentinel this is an automated process using a self adjusting triple lip seal. “Unscrewing” the canister needs some force.  Electrical wire is as much as possible replaced by fiber optics. When in a dark room, the Sentinel looks like a Christmas tree: flashing lights all over the place: the two HUD’s, the tow pressure sensors, the O2 sensors, the temp sticks (to measure the temperature of the scrubber  More people have died as a result of forgetting to turn their units on. Hence the safety system of remaining ion sleep mode, looking for breathing.

it is always on. Certain parts of the Sentinel are completely sealed, with the battery. When the battery is empty, one needs to replace the whole (electronical) part.

There are 3 triple redundant main batteries. These can be replaced by qualified dealers or the factory. The secondary handset has its own independent power and deco computer and it is isolated from the main system. In fact damage or loss of any of the displays will not affect the core life support/PO2 control.

One always needs some power source to charge the Sentinel: this can be an issue on remote locations.

VR can supply solar chargers, 12v chargers or mains chargers. I have managed to charge my sentinel everywhere on the planet.

The primary HUD also has a buzzer. This is a vibration motor. Tactile alarms are the most recognisable especially in a hypoxia scenario.

The computer controls every aspect of the rebreather: gas pressures, PO2, breathing rates, scrubber temperature, batteries, O2 sensors, deco, etc., etc., etc.).

The handsets are (now) OLED full colour. I still have the old LCD. The computer has a lot of colourful screens. It requires a lot of training to find your way in the menus. Switching between screens takes some time: the response time of the computer is (too) long. I’m told that the response is much faster on new system The switches are on the side of the computer and difficult to manipulate with cold fingers or dry gloves. The number of hoses and optical fibers are difficult to align nicely under the hood: it can look very messy. The tanks are kept in place with Velcro strips. A “strange” manifold is dangling on the bottom of the CCR. This is for additional inflator feeds. It is not fixed to allow for the larger diluent cylinder when the foot of the case is extended. Before the dive the Sentinel requires that the diver follows a computerized pre-dive checklist. Pre-breathing is part of this checklist. When the scrubber is warm enough the pre-dive check is continued. The pre-dive sometimes requires 10 minutes to warm up the scrubber. I’m told this is because I have old software. VR has improved this for a wider range of climates. Also with the CO2 sensor fitted it should be quicker. Assembling and preparing the Sentinel requires more time then on other CCR’s (putting the lungs, canister, tanks and doing the pre-dive checks).

2. Buoyancy/trim

3 stars

Trim is good, when the top weights are in place.

3. WOB

4 stars

The Sentinel has only one transparent lung (I ripped two of them) in the top of the CCR. Placing the lung requires some exercise. The canister is huge: the thick “gaslayer” between the scrubber and the environment gives a good insulation. This is what makes it the most efficient canister on the market and is also why it ‘cares’ for the oxygen sensors so well.

The diameter of the breathing hose is enormous which has a positive effect on the WOB, but a negative effect on diving comfort. The BOV of the Sentinel is the only one (sofar) with a CE rating. To get that CE rating, they had to make the BOV very big. Also to allow it to be neutral in the water.

4. Travel (modularity)

1 star

One cannot take the Sentinel apart easily. VR’s philosophy is that some things just shouldn’t be taken apart by the user.

It is an expensive experience: the Sentinel has to travel as odd sized luggage. At Technology in Depth they recognized this problem and “invented” a travel kit. With this kit you can leave the case at home and fit different tank sizes. The Travel Sentinel is 800 EUR more expensive than the Sentinel Expedition Rebreather Optocon. OK thanks for saying something about this. See comments earlier.

5. Safety

4 stars (was 2 stars)

It has all the necessary safety features like a HUD, independent back up display, ADV, tempstick, CO2 monitor, gas pressure sensors, breathing detection (auto on), etc. The electrical wiring has been replaced by optical wiring. Optical wiring cannot rust and has far more redundancy.. The number of checks and alarms is maybe getting at a point that it decreases safety: the diver ignores the alarms during the dive and the pre-dive checks.

Once I experienced an “optic transmission” problem from the O2 sensors. I had no PO2 readings anymore on the primary and back up display. The design is one that could earn 5 stars. VR told me that most of the issues were solved.

6. Price

1 star

Prices start at 8500 EUR. The most expensive Sentinel is about 11.500 EUR, making it one of the most expensive units on the market.

7. Service/after sales/availability parts

2 stars

Spare parts are quickly available with the manufacturer.

8. Build quality

3 stars (was 2 stars)

A lot of plastic and Velcro, sharp edges, etc. Many Sentinel owners had to return their unit to the factory more than one time. Problems with pressure sensors, O2 cells transmitter, etc. VR has told me that they are over this now.

9. Cave diving

2 stars

The unit is very big. But size should be balanced against performance/trim? The Sentinel made a nice appearance in the movie Sanctum from James Cameron (about cave diving).

10. Deep and X-treme diving

2 stars

The unit is CE rated until 100 mtr. Because of the many problems I experienced with the unit, I wouldn’t take my unit very deep. But other people have done deep dives on the unit.