photographs and text by Jan Willem Bech

first published on
date: 25-05-2009

Here you see the rubber branche label on the counterlung. The unit was approved in 1938 by Siebe Gorman!
Here you see the complete unit. The oxygen cilinder was worn on the back.
The pressure regulator is fixed to a extended valve and fitted with a manual bypass membrane
The pressure regulator was fixed in position through the use of a hexagon axis.
The regulator side of the gas supply.
The oxygenbottle was equipped with heavy webbing
An additional smaller belt was added to prevent the large belt  to open unwantend
Here you see how the oxygen bottle was fixed in the webbing-holder
This is the bolt in open position. When it opens unwanted the bottle can not fall out.
This bottle was last hydro tested in 1962 !
BOC - Siebe bottle
This is the main valve of the oxygen bottle
This is the complete gas hose assembly. Reducing valve + hose to counterlung and Gaugehose
The valve to the gauge was to prevent total gas loss in case of a damaged gauge hose.
Protective cover for the gauge
This little device is a whistle. It starts when the pressure drops beneath a preset level to warn the user for the low pressure
Both pressure and minutes are on the gauge
The copper part looks like the scrubber but it is not! It is the Cooler! The cooler is a flat oval copper container having the filler on the side. The cooler has two connections, a female for connecting to the breathing bag / canister and a male at the top for connecting to the breathing tube. To ensure that the oxygen passes round the inner container a baffle plate is fitted in the outer container. (see picture below). Into the inner container is poured the cooling agent, approximately 10 oz. (284 grams)of sodium phosphate. In crystallised form at normal temperatures, sodium phosphate has the property of absorbing large amounts of heat before beginning to liquefy at about 86 degrees Fahrenheit ( 30 degrees Celsius). This container with its filling cap is placed inside and is integral with the outer container which has the two mentioned connections. The latter is on a swan neck and connects to the breathing bag, whilst the inhaling tube is attached to the male connection of the cooler. After use, cold water must be circulated around the outer container to revert the calcium chloride to its crystallised form. Under no circumstances should the cooler be polished since a polished surface attrackts exterior heat and this effect will obviously reduce the efficiency of the cooler!
The female connector to the breathing bag 
Filling opening for the coolant 
The Breathing tubes are made of corrugated vulcanised rubber, covered with stockinette (elastic fabric) for protection and measure one inch in diameter and approximately 7,5 "in length. The corrugation allows for flexibility, prevents collapsing and ensures that the wearer receives a volume of oxygen and not a jet. Two mica disc type valves, in cages are fitted to the lower ends of the breathing tubes and on inhalation both valves lift, the inhaling valve opening and the exhale valve closing
Siebe Gorman Vista Vision Breathing Mask 
Screwed on the female union is a spring-loaded relief valve which, on being depressed, permits excess pressure within the breathing bag to be released. 
Here the protective cover (blue) with the breathing bag inside 
Opening the entrance of the breathingbag assembly 
Protective cover 
When the breathing bag is taken out the cover, the closing clamp can be unscrewed to get inside the breathing bag and scrubber. 
The breathing bag-scrubber is sturdily constructed of vulcanised india-rubber and is divided into two compartments by a ribbed rubber curtain which extends from the top to within one inch of the bottom of the bag. At the top of the breathing bag are fitted three male and one female metal (brass) unions, the oxygen supply tub being connected to the smallest of the male unions. On the remaining male unions the cooler is connected to one on the left and the third is secured to the exhaling valve. Inside the breathing bag, immidiately beneath the oxygen supply tube male union, is a diffuser which causes the incoming oxygen be evenly distributed on the inhaling side of the bag and obviates the disturbance which a direct jet would cause on striking the absorbent situated in the bottom of the bag, creating irritating dust particles in the inhaled breath.
The Sofnolime or Protosorb is poored directly in the breathing bag.

To finish this article I would like inform you about a 45 page pdf with additional information and parts of this text that describes the Salvus and Proto rebreather used by firefighters and for mine rescue crews.
You can find the article here:
More Sources:

Pictures of the Proto in use:
Pictures of the Salvus:

Finally I would like to express my sincere gratitude to Mr Simon Lawler, for giving me the opportunity to carry out this Proto tear down, and all his work to scan the informative documents!

This information was supplied to me by J. Gompelman of Jeroen is a good friend and has a huge collection of diving books and information about everything that has a relation to diving......;))
thanks Jeroen!

The mark lll was in use in Wellington NZ until the mid 1970's Having a blue tereylene bag.  An inhalation tube and and exhalation tube.  both fitted with mika valves. The set used had small eye goggles and the nasal spring loaded clip. the inhalation tube and the exhalation tube were cloth covered.  The cylinder was of one hour duration.  But could be extended to 3-4 hours when using entrapped procedures.

The last use was to a chlorine spillage in Wellington.  They were withdrawn from service as they were to expensive to maintain. 
Auckland had up graded to the Mark IX set as a long duration unit but they were eventually were replaced by the Scott Airpack and other long duration CABA.

Gordon Sylvester.

additional information added 16-08-2009

I used to wear these sets in the early 1970's in the London Fire Brigade. As far as I can remember the oxygen cylinder Max. pressure was 132p.s.i and it contained 187 liters when full. Although the duration was 1 hour, we used to have a procedure called ' entrapped procedure ' where we could make the set last up to 8 hours. In fact the record stood at approx. 16 hours !  Our sets were equipped with mouthpieces and goggles. The coolers were painted black to reflect heat ! It brought back a lot of memories seeing pictures of it.

Trevor Mepham.

published 25-5-2009
Please sign my Guestbook

I was very fortunate to be able to buy me a Siebe Gorman Proto MK IV rebreather. Simon who sold me the unit was so kind to add all original papers in use with that unit. I offers a view on the training and background of the unit. I am very pleased to have this rebreather in my collection now. Please enjoy all the info on this great rebreather. There are really fantastic ideas applied in this design!

Menu reviews



Search page



Search this Website
 Information about RB
 Photo galleries
 Historical Information
 Links & Downloads
 Updates, speed menu
 Web shop
 Reviews SC rebreathers
 Reviews CC rebreathers
 RBís through the ages
 Inspiration rebreather
 Database Oxygen RBís
 Database Semiclosed RBís
 Speed menu
 Search this web