KP-21

Oxygen supply through the KP-21 system

The KP-21 supplies oxygen continuously, but the amount delivered to the mask is not fixed in a simple manual way. The device adjusts oxygen supply according to cabin altitude. At lower altitude, oxygen flow is limited. As altitude increases and atmospheric pressure drops, the internal altitude mechanism increases the supply. This makes the KP-21 different from a simple oxygen bottle with a shut-off valve. It is a regulated breathing device with its own pressure reduction and altitude-compensation system.

KP-21 pressure reduction stages

The oxygen inside the KP-21 is stored in a KB-2 cylinder. After the shut-off valve is opened, oxygen first enters the first-stage reducer, where the high cylinder pressure is reduced to an intermediate level. Then it passes to the second-stage reducer, which forms the final oxygen supply to the mask. The second stage works together with an aneroid-membrane mechanism. This mechanism reacts to cabin altitude and changes the oxygen flow accordingly. Such a two-stage layout gives more controlled supply than direct feeding from the cylinder.

KP-21 with KM-15I oxygen mask

The standard mask used with the KP-21 is the KM-15I oxygen mask. The mask line includes a flexible hose and a rubber economizer bag, which stores oxygen during the exhalation phase and makes supply more efficient during the next inhalation. The user breathes from the mask, while the KP-21 continues to maintain the required oxygen flow. The mask, hose, economizer, valves and fittings should be checked together with the device, because a serviceable oxygen unit will not work correctly if the connected mask assembly is damaged or leaking.

Control and monitoring on the KP-21 device

The KP-21 includes a shut-off valve, high-pressure gauge, oxygen flow indicator, reducers, altitude automatic mechanism and emergency manual supply valve. The pressure gauge allows the operator to check the cylinder charge before use. The flow indicator gives a visual sign that oxygen is moving through the system. The emergency supply valve provides manual increase of oxygen flow when required by aircraft procedures or when normal automatic regulation is not enough. These elements make the KP-21 practical as a portable unit rather than just a stored oxygen bottle.

Aircraft application of KP-21

The KP-21 is used on Soviet and Russian aircraft and helicopters, including applications on Mi-8 family helicopters depending on equipment configuration. It belongs to aircraft oxygen and life-support equipment and is intended for use up to high-altitude operating conditions defined by its technical documentation. The device may be carried for crew use, passenger support, or movement inside the aircraft during abnormal situations. Before installation or supply, the exact aircraft equipment list and oxygen system documentation should be checked.

Inspection and supply of KP-21

When ordering or replacing the KP-21, the full designation should be stated together with the required condition and completeness. It is important to clarify whether the request is for the oxygen device only or for a set with the KM-15I mask, hose, economizer, canvas bag and documents. Before use, the device should be checked for cylinder pressure, reducer condition, shut-off valve operation, flow indication, hose integrity, mask condition, leakage and documentation status. Oxygen equipment should also be inspected for cleanliness, storage condition and remaining service life.

Related system equipment: BKP-2-2-210, BKP-3-2-210, DKM-1M, MKM-250V2. These positions are grouped by system function and installation context, not as interchangeable replacements.