Gravity Zero MK II User Manual

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MK II Oxygen Rebreather

Closed Circuit System

User Manual

Definitions of Signal Word

Used in this Manual

Danger: This words indicates an imminently hazardous situation, which if not avoided, will

result in death or serious injury.

Warning: This words indicates a potentially hazardous situation, which if not avoided, could

result in death or serious injury.

Caution: This words indicates a potentially hazardous situation, which if not avoided, may

result in minor or moderate injury. It may also be used to alert against unsafe pratices.

1. INTRODUCTION

MK II is a new fully closed circuit oxygen rebreather designed by GRAVITY ZERO, Italy, for military and

technical use.

Oxygen Rebreather MK II is one of the most compact and lightest weight fully closed circuit oxygen rebreather

on the market.

A special version, called MK II pro is available on request; this version differs from the standard version MK II

in having an innovative soft shield composed of kevlar-cordura wich keeps and protects the polyurethane

rubber breathing bag from possible cutting and abrasion under special operating conditions.

Figure 1- Fully Closed Circuit Oxygen Rebreather MK II

2. TECHNICAL DATA

Manufacturer: GRAVITY ZERO

Order No 1

Working Principle: cyclic

Breathing Gas: pure oxygen

Cylinder (two type available):

 volume 2,0 litres 2,0 litres

 pressure: 200 bar 200 bar

 material: aluminium alloy steel

Breathing Bag Volume: 9,5 litres

Carbon Dioxide Scrubber : soda lime, about 1.30 kg

Duration: according to workload up to 3 hours

Maximum Depth: 6 metres, (ppO2 1,6 ATA)

Weight: 6 kg, ashore

Dimensions: L 400 mm x W 400 mm x H 110 mm

3. DESCRIPTION

MK II consists of the following main components (see figure 2):

1) Breathing bag. Made with poliurethane rubber sheets high frequency electronically welded. The

breathing bag has been placed in manner to give a small hydrostatic pressure difference as possible,

i.e. low inhalation and exhalation resistance.

2) Cylinder. Two cylinder type are available on request:

a) 1,5 litres/200 bar realized in aluminium alloy for decrease the magnetic level b) 2 litres/200 bar realized in steel alloy

3) Shut-off valve assembly. Open or close the gas flow from the cylinder, includes the manual actuating

type bypass, the pressure reducer and the safety valve

4) Pressure gauge. Test the internal cylinder pressure.

5) Canister. Contains the soda lime wich absorbs the carbon dioxide due to respiration acts. The

canister is made in such way that it becomes completely surrounded by a gas flow that prevents the

soda lime from being cooled down by surrounding water.

6) Hose connector. Carries the inhalation and exhalation hose gases in proper manner to and from soda

lime canister .

7) Inhalation and exhalation hose. Both hoses are provided with non return valves wich control in

proper manner the flow direction.

8) Mouthpiece. The mouthpiece contains a rotary valve wich isolates the circuit from the atmosphere

when it is in closed position. In the open position, the rotary valve supplies the oxygen to the diver.

9) Harness. The harness (neck strap and waist strap) are easy to adjust to desired lenghts.

MK II - Figure 2 , Main Components

MK II - Figure 3, Valve Assembly

4. FUNCTIONAL DESCRIPTION

Rebreather is a simply device that capture and recirculate the exaled breath, scrub out the carbon dioxide

produced by the respiratory functions and add oxygen to replenish what comsumed.

Oxygen Rebreather MK II is a cyclic type fully closed circuit oxygen rebreather.

Instead of a one-way gas circulation, to and from breathing bag as pendular type, the gas circulates in two

separate directions.

During the respiratory cycle the gas circuit is as in figure 4.

MK II - Figure 4, Breathing Loop

High pressure gas (see figure 5) passes from the oxygen cylinder through the bypass valve into the breathing

bag, expanding same and assuming the environmental pressure.

The diver inhales the oxygen from the breathing bag throuhg the inhalation hose and mouthpiece and exhales

the respiration gases throuhg the exalation hose into soda lime canister (the non-return valve contained in

each hose, controls in proper manner the flow direction).

The soda lime absorbs and fixes the carbon dioxide contained in the respiration gases and purifies fully the non

metabolized oxygen.

Therefore the oxygen passes in the breathing bag and the cycle start again.

Actuating the by-pass lever is possible to restore the oxygen metabolized or to inflate quickly the breathing

bag.

An high pressure gauge screwed on valve assembly shows the pressure rate of the cylinder.

MK II - Figure 5, Functional Diagram

5. PRE-DIVE PREPARATION

Before every dive with the rebreather MK II it is necessary to check the following points:

Checks and Refills Oxygen Cylinder.

Open the shut-off valve and verify the pressure value on the gauge; If the pressure value is less than 190 bar

refill the cylinder with pure oxygen as follows:

Warning: open slowly the shut-off valve; the high pressure oxygen flow may

burn or explode

 close the shut-off valve

 push down the bypass button to assure that the pressure discharge (make sure that high pressure gauge

indicates zero).

 unscrew the gauge hose nut with the spanner wrench size no 28, PN 400-900, and remove the gauge

complete fom the rebreather

 connect the high pressure refilling hose to refilling connection

 open the shut-off valve

 follows the relevant instructions to refilling the cylinder.

Warning: verify the cylinder test date; discharge and replace if necessary

Checks and Fill Soda Lime Canister

 unscrew the lock screw of the hose connector

 remove the hoses connector complete with corrugated hoses and mouthpiece from the breathing bag.

 remove the soda lime canister from the breather bag (to remove canister, take it firmly with the filler plug

in vertical position and rotating slowly the canister draw it.

Warning: make sure don’t damage the breathing bag torus gasket

 unscrew the canister plug and fill, using a funnel, with the appropriate soda lime (fill the canister a bit at

a time and tap the sides of the canister to ensure that it is packed with no gaps).

Caution: soda lime dust is caustic and can cause chemical burns

Warning: if the soda lime isn’t packed tightly in the canister this can lead to “channelling”, where the exaust

gas passes trough the scrubber without coming into full contact with the carbon dioxide absorbent.

Figure 6 a, Refilling Soda Lime

 screw the plug, verify the canister O ring (discharge and replace if necessary) and put the canister into

the rebreathing bag.

 verify the seating of canister, put down with care the canister and insert the torus gasket in the seating

 install the hoses connector complete and turning gently the same assuring that the gasket goes into filter

seating.

 lock with the screw

Final Check

Once you have completely assembled the rebreather, test it to ensure there are no leaks

 make sure that the four way valve is turned in closed position (lever in down position)

 slowly open the shut-off valve

 push down the bypass button and inflate moderately the breating bag

 submerge the rebreather in a tub of water and looking for leaks

 if a leak is detected, it is necessary locate and repair it before the dive

Leaks can occur any number of places; check the breathing bag and hoses for punctures; check all the fitting

and hoses connector to make sure they are properly closed.

6. DIVE

Donning the Rebreather

Figure 6 b, Tapping Soda Lime Canister

 insert the neck strap on the neck

 insert the waist strap

 adjust and put the breathing bag at the same height of diver’s counterlungs

On Surface

 open shut-off valve

 put the four way valve lever in up position

 inflate a little bit the breathing bag actuating the bypass button

 put mouthpiece and rotate the four way lever in down position

 inhale with mouth and exhale with nose within the breathing bag is empty

 rotate the four way valve lever in up position and leave mouthpiece.

This operation clean the bag from the other gases inside

Danger: it is very important to make properly this operations to make sure that no nitrogen gas is again in the

breathing bag.

Dive with Rebreather

 put mouthpiece with the four way valve lever in up position

 exhale all the air from the counterlungs trough the four way valve

 rotate the four way valve lever in down position

 inflate a little bit the breathing bag actuating the bypass button

 start the dive and during the first breath exhale from nose (in this manner the nitrogen gas into the

counterlungs is completely blow away)

 inflate when necessary, to compensate the oxygen usage, actuating the bypass button

Danger: it is very important to make properly this operations to make sure wich no nitrogen gas is again in

the respiratory circuit.

7. MAINTENANCE

Post Dive

 rinse with fresh water the rebreather with the four way valve lever in up position

 draw out the canister fom the breathing bag

 empty the canister from soda lime

 rinse the canister with fresh water and blow out residual soda lime granules from canister

 rinse with fresh water hoses connector complete of hoses and four way valve

 disinfect this assy with a bactericide solution and rinse again

 rinse into the breathing bag, disinfect with a bactericide solution and rinse again

 allow to dry all the components at a shady place before assembly

 lubricate ONLY with YNX grease, as illustrated in figure 7.

MK II - Figure 7, Lubrication Chart

Caution: all the components must be grease only with YNX grease. Any other kind of oils and greases may

burn or explode in contact with a pure oxygen flow

Biennial Maintenance

Test the cylinder

Overhaul the shut-off valve (manufacturer workshop)

Overhaul (Every Four Years)

Major overhaul of complete rebreather (manufacturer workshop)

Breathingh Bag Repair

Material and tools required:

 emery cloth grain size 100*

 Aquasure adhesive*

 brush*

 cleaning gasoline

 poliurethane rubber patch*

 punches and scissor

a) inflate the rebreathing bag, locate and mark the damaged area

b) roughen with emery cloth

c) clean with gasoline and let dry for fifteen minute about

d) roughen and clean the patch

e) coat with Aquasure adhesive the surfaces of patch and breathing bag

Caution: Aquasure adhesive contains toluene. Use only in well ventilated area. Avoid prolonged breathing of

vapors do not use near heat or flames. Do not ingest. If swallowed do not induce vomiting. Seek

medical aid immediately. Avoid contact with skin or eyes. Keep out of reach of children.

f) place patch in position and press on firmly

g) complete hardening takes place after one day.

h) test repair prior to use

Hoses Repair

Material and tools required:

 Aquasure adhesive*

 emery cloth grain size 100*

 brush*

 cleaning gasolin

a) locate the puncture on the damaged hose

b) roughen with emery cloth

c) clean with gasoline and let dry for fifteen minute about

d) coat with Aquasure adhesive the surface roughened with a thickness of about 1,5 mm

e) complete hardening takes place after one day.

f) test repair prior to use

Caution: Aquasure adhesive contains toluene. Use only in well ventilated area. Avoid prolonged breathing of

vapors do not use near heat or flames. Do not ingest. If swallowed do not induce vomiting. Seek medical aid

immediately. Avoid contact with skin or eyes. Keep out of reach of children

Gravity Zero MK II User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual