Bee vac--- negative pressure

[nella]

What is the maximum number in inches on a vacuum gauge(or fraction of an inch) that a bee vac can be operated at without hurting the bees?

[chad]

7 inches. :-D Just kidding,I don't really understand your question.Wish I could help.I just adjust mine with vents until it just pulls them off gently.I adjust it because I will use anywhere from 10 to 50 foot of hose.

[NasalSponge]

Would that be inches of water or inches of mercury?

[nella]

Because pressure was once commonly measured by its ability to displace a column of liquid in a manometer, pressures are often expressed as a depth of a particular fluid (e.g. inches of water). The most common choices are mercury (Hg) and water; water is nontoxic and readily available, while mercury's density allows for a shorter column (and so a smaller manometer) to measure a given pressure.

[Ross]

Just enough pressure that a bee can hang on for a few seconds before giving up and being sucked in.  It helps to reduce the hose at the nozzle to produce a higher flow for the first few inches, then a larger bore hose the rest of the way to reduce injuries.