The low Bb vent pad is a very important part of the making the oboe function well. Having it seal well helps with the resonance of the whole oboe. It also makes the 3rd register notes functional.
Every-so-often, it may be good to make sure that the low Bb vent pad is sealing. You can do this with a feeler gauge and by examining the movement of the keys.
Testing for leaks
When all keys are at rest, the low Bb vent key, on the bell of the instrument, must close completely. Test for closure using a feeler gauge. If the pad is barely touching the tone hole, or not touching at all, you will need to check the alignment of the bell-to-body sections. This alignment might need to be adjusted.
Another way to test is to simply press gently on the B-key touchpiece. There should be a tiny bit of free movement at the bell-to-body connection point, before the bell vent key begins to open.
If the bell vent is not connecting with its tone hole and/or there is no gap at the B-to-Bb-vent connection point, then we need to fix it.
If the vent pad is sealing the tone adequately, then scroll down this page a little to learn why it may fail from time to time.
How to Correct the Low Bb-vent Placement
If the low Bb-vent pad is not closing fully, the B-key is most likely lifting the low B connection. To test this, watch the connection point at the body-to-bell joint while you are pressing down the Low B touchpiece. The B-key must move a fractional amount (at the least), before it begins to push up on the bell’s vent key.
To add space between the connection points, turn the adjusting screw anti-clockwise.
To reduce the amount of space between the connection points, turn the adjusting screw clockwise.