J. Phil Thien's Projects

I got some HF dust bags to put in my Craftsman Shop Vac. They fit just fine.
WHen I turned on the vac, the air flow was inadequate immediately. I checked to be sure no kinks in the bag material etc. None.
I gave up on the bags, Was I doing something wrong? Is the problem inferior quality HF bags?
Jerry

Hi

I was just doing the math...

A one inch round hole has a cross sectional area of 0.785 sq inch
Six 3/8" holes have a total of 0.662 sq inch.
A 3/4" hole has 0.44 sq inch.
A half inch hole has 0.196 sq inch area.

A two inch tube has an area of 3.14 SQ inch.
A 2.5 inch vacuum tube has a cross sectional area of nearly 5 sq inches!!

So if you use a 3/4 inch hole in your can lid, you are asking 0.44 sq inches to absorb the volume being sucked through at least 3 to 5 sq inches of vacuum tube.

Secondly, I think that the force pushing/pulling the valve open would be related to the area over which the force is applied.  (Force = Pressure X Area)
Vacuum and pressure are really the same thing (the vacuum created just lowers the pressure inside the tube or can,
the outisde atmospheric pressure remains the same, and is what is crushing the can.

The idea is that a rather large disk would need a stronger spring to keep it closed.

So if you increase the size of your washer and hole in the can, your weak spring will succumb to the vacuum in the can (pressure from outside the can).
The tension on the spring could be adjusted to just keep the valve closed under normal operation, then a skosh more.
When a blockage occurs the valve would open allowing air in to buffer the collapsing force.

I am making a 20 gal tank, I could do some experiments with different sized holes to see when the can no longer bows in with hole wide open.
It seems to me you would want that size, and then add a little more, to get a relief valve which would be adjustable.
Maybe the bigger the better... you can always add more spring power. This would allow finer adjustment and control.

Jerry

Re: 31.6 degrees

I am not sure how precision these units are made.
I did notice there is a rolled lip on the center of the cone.  If not taken into account I got close to 32 degrees. If the protractor was not allowed to contact the lip, the angle I measured was 30 degrees.

Not sure what is right for any given unit, but just check to be sure you are taking the lip into account when measuring prior to cutting.
;)
Jerry

Hi

Im new,

I got HF DC and proceeded to install baffle while 35A filter is on order.
Someone said they didnt know the angle of the cone inside the HF midsection.
It is 30-60-90 degree triangle.  If you cut the dowels at 90 degrees, then trim off an end at a 30 degree cut, you end up with a compatable wedge shaped piece that you cut off.  I used this piece on the other side of the cone, so the screw goes straight in, Quick diagram below.