In order to achieve correct air flow a balance between valve setting and pump output is necessary. The ideal setting is obtained by minimum back pressure or non-restriction of flow of air. Never physically restrict the output of the pump. Restriction causes damage to the diaphragm.
(SEE BACK PRESSURE)
Adjust air valve output as required. Use extra valve outlet for excess air, bleed over production to atmosphere. This protects against back pressure and mature diaphragm wear.