The rubber valve is necessary — although the system will work with it removed. Under normal operation, both check valves working, Air comes in through the top valve, and exits through the bottom. This allow single breathing of the air in the reservoir, and the reservoir will last between 10 and 15 minutes for a normal user.
When the intake valve is trapped, or that saliva is sticking the rubber valve to the seat. Use a match or other blunt item to correct the rubber intake valve.
- Top valve connected to the respirator tube is the intake valve.
- Bottom, larger valve is the exhaust valve.
Conceivably either valve can be stuck open or stuck closed.
There are three issues that can occur:
- Intake valve stuck shut
- Intake stuck open
- Exhaust stuck open
- Exhaust stuck shut
- Mask not sealed to face
- Various Combinations
It sounds like the intake valve is getting stuck shut and the mask is not secure. This occurs when the rubber valve gets trapped behind the plastic backstop assembly, or from adhesion. This limits oxygen intake — and allows room air to dilute incoming oxygen from leakage.
To test & fix the mask:
1) Remove plastic breather assembly from neoprene holder
2) Hold mask to face (no hose attached)
3) Breathe in/out. Intake should be clear and from intake port (top).
4) Exhaust should be clear (very low resistance) and from bottom exhaust port.
5) If either path has resistance — use a wooden match or other blunt item to gently open the rubber valve.
6) Test again for clear air flow
If you remove the top rubber valve (fix the intake open), exhaled air, will return with CO2 will re-enter the reservoir. This allows rebreathing CO2, which is sometimes helpful, but is not by design — but only when the exhaust port works properly.
The problem is that if you remove the intake valve, with the exhaust valve stuck shut, then ALL of the exhaust air will continuously re-cycle into the reservoir — and CO2 will accumulate. If this occurs the user will absolutely be tired when at finish. The reservoir will be nearly full.
If the intake valve is stuck shut, then the vacuum will pull room air into the mask. This means the user will be exercising with only the extra oxygen that enters the unstuck half of the intake valve. This will be 1/2 or less of normal oxygen. The user will be tired if this occurs and the reservoir will be about half inflated when finished.