Covering Bowl With Fingers While Drawing.

[torque]

dlattim wrote

What I believe is happening when one covers the bowl leaving a smaller opening for air to pass is that the velocity of the air increases across the ember. The draw pressure is the same so the volume of air going through the bowl is equal to the volume when the bowl is wide open. The partial covering of the bowl while drawing would increase the velocity of the air through the smaller opening, but in my opinion does not decrease the volume of air. I believe the higher velocity across the ember is what increases the heat of the ember. If one covers the bowl partially or completely while not drawing in through the stem then the result would less O2 to the ember and therefore a cooler ember. Our lungs are able to draw with sufficient pressure to overcome the resistance of a smaller opening when the bowl is partially covered. Again, the only effect is a higher velocity of air through the opening. The volume remains constant at the same draw pressure. I hope I made sense out of this.

This guy gives the best explanation of what elements of fluid mechanics actually come into play when using this technique. This simple application of Bernoulli's Law feeds air to the ember at a greater velocity helping to "revive" it. The two fingers over the bowl act as a form of orifice plate decreasing the pressure and increasing the velocity of the air flow into the bowl.

 

[mithridate]

I found this topic actually by googling, and read it with great interest. I have used a thumb to cover the bowl somewhat. Though I have noticed, as someone wrote that it is very good way to burn your finger if the bowl is too full. However, I haven't noticed very dramatic effect, so my thumb propably leaves too much way for air to go through. Need to try that "Bilbo technique".

 

[carolinachurchwarden]

Depends upon how much air you want to get to the ember, really. I usually hold my pipes, and my index finger typically does this tapping down effect on the draw, but if I need to restrict more air, I'll throw in my middle finger too. It definitely helps to keep it from going out if it's on the way out without drawing too much air and creating an ember that's too hot.

 

[briarbuck]

Wind (air) accelerates around corners. Air across fingers will do the same. Dlattim is correct.

 

[snowyowl]

I learned this technique when I started pipes at 16 in the Adirondacks.

Also tamping down a bowl that seems out will also revive the smoke.

 

[mso489]

The air velocity makes some sense. Another factor may be the air/fuel/heat proportions. When you partly cover the top of the bowl, you still have enough oxygen for a fire, but you contain more heat, which makes the ember burn more.

 

[nitemair13]

I noticed myself doing this when a pipe would start to die out. I didn't know it was a technique, I just sort of did it without thinking. I guess in the back of my mind I was trying to capture the heat and get it going again. I never notice a difference in flavor though.

 

[balkisobrains]

I do this to get whatever's burning to the "ideal temperature" & produce better flavor, but I am cupping a couple fingers over the bowl, and moving them around as required. Easy to over-cook it and miss the flavor-improvement doing this. Also, the some/more of of the smoke burning off is probably getting pulled back in, so that might have something to do with the flavor-improvement too.