There are about three reasons.
First, the water in the pressure air tank is so full that the water spills out along with the air flow, reaching the powder. This occurrence is common.Generally, the user does not think of water in the air tank.
Countermeasure: Drain away water in the air tank.
Second, there is water on either polisher connector or hose connector. The water will be enclosed in the air pipe during fixing connectors. Then the pressure air blows water into powder.
Countermeasure: drain water away from both polisher connector and hose connector before coupling connectors.
The third, the rubber sealing O-rings at the joint are broken.
Countermeasure: Replace the fault O-rings.