DC 300 question

JPG · Post by **JPG** » Sun Nov 03, 2013 12:59 am

Allow me to restate that!

Shop vacs have a greater static pressure difference between the inside and outside of the intake hose!;)

In your altimeters, the 'static pressure' is altitude dependent and needs to be motion independent to be accurate. i.e. the 'port' needs to be positioned so the flight motion does not affect the pressure at the port. Static in that case means the pressure with no motion contamination.

'Static pressure' is not always used consistently. Context means a great deal then.

skou · Post by **skou** » Sun Nov 03, 2013 2:06 am

[quote="JPG40504"]Allow me to restate that!

Shop vacs have a greater static pressure difference between the inside and outside of the intake hose!]

You know I was just pulling your chain, don't you?

steve

JPG · Post by **JPG** » Sun Nov 03, 2013 12:58 pm

skou wrote:You know I was just pulling your chain, don't you?

steve

When the subject is as nebulously defined and used as 'static pressure' is nothing is obviously said in jest.

Now that said, how can there be 'static pressure' in a pipe through which air(a fluid) and debris(hopefully only wood particles) is moving at a considerable velocity? Imaginary?:D

Annnnd since the velocity remains reasonably constant along the 'run' of the pipe(assuming constant cross sectional area), how can that 'imaginary' static pressure vary along that same 'run' of pipe?:D

Friction losses create pressure differences along the 'run' and across bends etc. Maximum pressure is at the sucking end(vacuum generator), and minimum pressure is at the intake end. Yes those 'pressures' are negative relative to atmospheric pressure and cannot be greater(in magnitude) than the current atmospheric pressure. Air compression is in the opposite direction(> atmospheric pressure) and can have far greater magnitude.

So your statements were not far fetched!;)

chris jay · Post by **chris jay** » Mon Nov 04, 2013 10:27 am

I'm used to a shop vac type flow. This unit doesn't seem to really have to much at the end of the hose when connected to a tool, and there seems to be quite a fair amount of chips on the floor. How about if I could figure out a way to use all three inlets at the collector, and run them into a 4 inch adapter, run 4 inch flex hose, then bush down the last 3 feet or so to connect to the machine? Or will using only one port from the vac do the same thing?

algale · Post by **algale** » Mon Nov 04, 2013 11:32 am

chris jay wrote:I'm used to a shop vac type flow. This unit doesn't seem to really have to much at the end of the hose when connected to a tool, and there seems to be quite a fair amount of chips on the floor. How about if I could figure out a way to use all three inlets at the collector, and run them into a 4 inch adapter, run 4 inch flex hose, then bush down the last 3 feet or so to connect to the machine? Or will using only one port from the vac do the same thing?

If you remove the piece that has the three inlet (held on with 4 screw I believe) you will find a single 4 inch inlet. What I don't know is whether if you run a 4 inch hose to the machine and step down to a 2.5 hose connection whether you would get more flow than just running one 2.5 hose all the way. I think so but I do not know. Also, with a 4 inch hose velocity drops so keep the run short.

Ed in Tampa · Post by **Ed in Tampa** » Mon Nov 04, 2013 12:40 pm

I have a shop vac that will nearly suck the dust from my SS Dust Collector, however it will choke when connected to a Plane or jointer.

One moves a lot of air and the other provides suction.

My shop vac will suck up a bolt and nut in a heart beat that my SS dust collector can't touch. But feed it a pile of saw dust and the SS acts like it is heaven, however if I slowly feed the shop vac the pile it will eat it up but it is sucking in all it can. The Dust Collector is also sucking in surrounding air and catching any dust in it also.

I find on my SS if I have a heavy amount of dust it seems to work better at dust collection if I keep a port open. Actual suction power is reduced but volume of air being moved seems to go up thus more dust is collected.

I will say the SS acts as a satifactory shop vac as I used mine for one for 20 or more years. However now I have a shop vac again I use it to clean up and the SS to keep the dust down.

chris jay · Post by **chris jay** » Mon Nov 04, 2013 9:43 pm

So I tried the 4 inch hose with a 2.5 bushing on the end, and the 2.5 inch hose (same length) in an experiment. I used 1/2 cup of corn meal as saw dust for each test. I put the pile on the ground and slowly scooted the hose towards it to see when it started pulling the corn meal in. There was small but noticeable difference between them. The 4 inch hose did preform better, but maybe by only 15% or so. The larger hose did "move" more air for sure