Maximator ROB-22 Oxygen booster

Maximator ROB: Rebreather Oxygen Booster
Finally: a small and affordable CE approved booster
By Steevke


Introduction

As most rebreather diver will tell you: “having a booster is not a luxury, it is an essential piece of diving equipment.”

Having a booster allows you to start your dive day with a full oxygen cylinder. If you don’t have one, you can transfill from a big J cylinder, but with every fill the available feed pressure drops, and after some fills you’ll end up with a half full J and maybe 100 bar in your small O2 rebreather cylinder, (in my opinion) not enough to do 2 long dives safely.

You can off course cascade 2 or 3 J cylinders, but you can only do this if you have the space available. It is also more expensive to rent 3 cylinders instead of one.

A booster is an alternative: it allows you to boost your gas to say 180 bar, so you have more than enough O2 to do 2 long dives and maybe have enough left for a shallow fresh water rinse dive on a week night.

There are a number of boosters on the market. The best boosters available are undoubtedly those made by Haskel. Quality comes with a price, unfortunately, so a genuine Haskel was out of the question for me. I then looked at the other offerings that I could afford, namely the baby booster from Jetsam, the Hydraulics International, the MPS C3 and the Maximator.


After a lot of consideration I decided to buy the new ROB booster from Maximator. I chose the ROB booster for a number of reasons:

1. It’s built in Germany from quality materials, and usually German engineering is worth its price.
2. It was designed as a real oxygen booster with decent separation between drive and boost cylinders and O2 compatible seals.
3. It is CE-approved for boosting oxygen.
4. Easy to find spares, as Maximator has sales offices all over the world.
5. It has an optional hand lever, so if you run out of drive gas in Farawayistan you finally get a chance to muscle up your other arm.
6. It is small and easy enough to transport.
7. Large compression ratio so easy to drive with an oil-less compressor that only has 7 to 8 bars available.
8. And finally: I was able to buy it very cheap !

“Well, this sounds to good to be through, so where’s the catch?” I hear you all say. Biggest disadvantage is the displacement. It is only 4.6 cm³, so boosting takes some time. I would not use it to boost an AL80 from 50 to 180 bar, unless you really have to. The recommended boost ratio is also quite small: 3.5. This makes sense though, as boosting takes more and more time when the pressure difference between supply gas and boosted augments.

And guess what: it arrived last week and I’m about to share my first experiences with it!


First impressions

The unit was decently packed and came together with drawing, certificate of compliance (CE-certificate) and manual. The manual was not really helpful, but better than nothing.

In a small bag 3 small particle filters get supplied, they need to be screwed in at the appropriate locations.

There are no whips included so before using the thing I needed to call Undersea, the best source of filling whips and other voodoo gas accessories.


Filling Whip: Supply Side

Basically the supply side whip consists of a bullnose adapter, a one-way valve, a needle valve a bleed valve, some hose and a BSP 1/3 connector. The needle valve is great as it allows to increase the pressure (and hence the flow) gradually. The slower we can fill, the less chance we have that something will spontaneously burst in flames, so you really need one to safeguard your investment. The one-way valve is useful as it prevents gas flowing in the wrong direction. The bleed we need to disconnect everything – just as with a regulator the pressure has to go of if you want to remove the whips.


Filling Whip: Discharge Side

On the discharge side we have a BSP ¼ fitting, a hose, an SPG, a bleed and a din fitting. Unfortunately the SPG was damaged during transport. I called Undersea and Collin promised to send a replacement by post – how’s that for excellent service! Luckily I still had a Wika Oxygen SPG lying here, so I can at least test the booster while I wait for the replacement to arrive.



Air Drive Side

For the air drive side I just used a standard BCD inflator nipple, so I can attach a standard stage bottle regulator (most of my stage regs have a drysuit hose attached). I plan to change this to a small run of hose with the addition of a Swagelock needle valve so I can precisely regulate the output of the stage reg.


The Real Test: How Will It Perform?

The proof of the pudding is in the eating, so a real world test was necessary. As I hate working I removed the hand lever and just used the air drive to boost my O2 cylinder.

In the picture you see:

• The 45 liter O2 bottle
• Fire extinguisher
• stage cylinder used as drive gas
• rebreather oxygen cylinder

Before putting everything on the greasy table I (more or less) cleaned it with pure Tramos Oxygen Cleaner.

Then I located everything right next to the door so I could roll it to my neighbours’ house if I suddenly had a fire problem.

In order to get a decent comparison I had both oxygen cylinders at 95 bar.

First I purged the filling whips, connected everything, prayed to God, held my breath and SLOWLY opened the drive gas cylinder (I was expecting a noisy booster like the Hydraulics International). And then…

This is great; it is much quieter than the hydraulics international.

I slowly increase the drive pressure so the booster cycle speed somewhat matched 1/3 of my heart rate and evened out at about 1 stroke per second. Slowly but steadily the pressure in the O2 cylinder started to rise.

After a couple of minutes I had to increase the drive pressure (by slowly turning the pillar valve on the stage cylinder) as the cycle speed started to slow.

After about 10 minutes the rebreather cylinder was nearly full (190 bar), the stage (which was about 60% full when I started) empty, and everything was still fairly cool. I decided to quickly connect a 15 cylinder because I wanted to fill the O2 cylinder completely to take some temperature measurements.


The booster was still pretty cool, running at 38°C (100°F) after boosting oxygen from 95 to 205 bar. Boosting this took about 15 minutes, a bit slower than you would have with a larger booster such as the Jetsam or the Hydraulics International. The O2 cylinder ran at 31°C (88°F).

Conclusion

Am I happy with what I bought? Yes, I am.

• I love the fact that the booster is small and not that heavy.
• I just love the build quality, which is on a par with the HI.
• I like the fact that you get a decent drawing when you buy it and that you can get spare parts easily in most parts of the world.
• I like the fact that is fairly silent. A bit noisier than the Jetsam, but at least you can talk when standing next to it (which you can not do with the HI).
• I like the manual hand lever, even if it is not that useful unless in the most dire circumstances.
• And finally I love the fact that I got it real cheap, so it left me with more money to invest in other dive equipment.

The only disadvantage I see is that it has a small displacement. If you need to fill all rebreather cylinders for a group of 12, you may be better of with a larger booster. For personal use on the other hand it is perfect.


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