How to find leaks in vacuum system? Vac vs DC?

[Doug Hobkirk]

My shop vac and my maybe 2HP Jet DC are in a shed on the side of my garage shop. I do not have the DC hooked up due to laziness running 220V and questions about whether I should bother. My shop vac hose runs to a Phil Thien separator. From there I run 2 1/2" or 1 1/2" or 1" to various tools, connecting only one at a time.



My first question is how can I discover any leaks in my vac connections? Is there any method that works great like testing for air leaks in a tire using soapy water? The suction at the end of the hose after the separator and the second hose is not as strong as the hose going into the separator. [Note: I suspect it's the lid on the separator, but I'd like to be sure and know exactly where to concentrate my efforts.]


My second question is why my 1" hookup works poorly? It is used for a Festool 6" ROS that only has a small fitting. I use a ribbed rubbery hose from a breathing machine I use to fight sleep apnea. It draws but weakly. The 1" hose fits around the Festool dust outlet tightly.
Third, should I bother hooking up the DC with the tools I have listed below?

The only tool I notice needing more flow for sure is the planer, and I don't use that very often enough to justify the DC just for it.
I also don't use the TS very often [I][I use the EZ guided saw system for big cuts]. The TS is a "portable" design saw, so I don't know if more flow would make much difference - the saw doesn't seem to generate huge quantities of sawdust in the type of sawing I usually do.



My "hook up" tools are:


(2/5" hose from separator) DeWalt 734 planer, Rigid 5" RO sander, Ryobi BT3000 table saw, router table underneath box (my current fence is a simple piece of wood with no DC fitting),
(1.5" hose) Rigid oscillating drum/belt sander, the circular saw on my Eureka-Zone guided saw system, and
(1" hose) Festool 6" RO sander.

[Alan Schaffter]

1. To check for leaks, connect the shopvac to the system so it blows into it , block off the end, and use a smoke candle or incense stick to check for leaks. In addition to the items I mention below, I suspect you might have leaks at fittings, around the barrel lid of your separator, etc.

2. See below.

3. See below.

Doug- you have discovered what many folks have found about a DC vs shopvac. The key to this is to understand the difference between static pressure (the suction provided by a shopvac) and flow measured in cubic feet per minute (CFM) provided by a DC.

While a shopvac can pick up material right in front of the nozzle or even support the weight of a bowling ball, it doesn't move a lot of air. Depending on the amount of pipe, bends, fittings, hose, filters, condition of the filter (clogged?), etc. which ALL impact and reduce the static pressure available, you may not even do good at that. Once you move the nozzle an inch or more away from the dust, you pick up next to nothing.

On the other hand, a dust collector is designed to move large volumes of air. It is designed to pick up dust from the machine and surrounding air, but like the shopvac, a DC is also hampered the same things that affect shopvacs and in many cases more so. DC's require much larger ducting and hose- 4" is the bare minimum and not even very good depending on the DC. Though not as much as a shopvac, DC's also provide a certain level of static pressure so they can pick up heavier chips. The performance of a DC blower can be illustrated with its "fan curve" like the one from Oneida below:

http://www.oneida-air.com/images/3hp-super-curve.jpg

At one end of the curve you have high static pressure but minimal CFM (this is the area where a shopvac operates. At the other end of the curve you have high CFM, but minimal static pressure. A DC operates best somewhere in the middle of the curve. If you load your DC up with resistance from small pipe, long runs, many bends, filters, flex hose, etc. you increase the the static pressure and seriously reduce CFM.

A simple example of why a DC vs shopvac for woodworking machines. Dust escapes from WW machines in all directions- outward making a cloud. Have a smoker with hefty lungs (good static pressure) blow a cloud of smoke- can do easy. The smoke coming out of his mouth quickly expands into a big cloud. Now have him try to suck it all back up- can't do it regardless of how strong his lungs are- he doesn't have the CFM.

There is one application suitable for shopvacs- picking up dust from hand power tools (routers, ROS, biscuit jointers, etc.) that have small dust ports. However, even in that case, if you reduce the size of the typical 2.5" shopvac hose to 1" at the tool, you are really handicapping the shopvac. Unfortunately few, if any, power hand tools have 2.5" dust ports.