Couch vacuum varying

1. First, it must be determined whether the source vacuum or sheet resistance is changing.
2. Check vacuum pumps and seal water, and check for slipping belts.
3. Check that consistency of mixed stock is steady.
4. Examine the basis weight profile.
— is it steady with time?
5. Check total head in headbox for variation. Variation in total head may be due to:
(a) malfunctioning of headbox control instrumentation.
(b) pressurized screens partially plugging, then unplugging.
(c) an oscillation in white water circuit.
6. Ensure that suction box is properly seated and that couch is true inside.
7. Do not let take-off line fall back to suction box zone as this will induce picking.
— check that draw-off curve is beyond suction box edge.
8. Ensure suction box is in correct rotational position.
See Consistency varying.