| 1. Disassemble the vacuum chamber. |
| 2. Remove the unilateral locking valve. |
| 3. Connect the vacuum pump, as is shown in drawing, create depression in the vacuum chamber and be convinced that depression remains. |
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4. Connect the vacuum pump to an opposite exit of the locking valve and be convinced that depression does not remain. |
| 5. If the unilateral locking valve does not correspond to requirements, replace it. |