I'm trying to understand what would be the end result of connecting a shop vac which is having a 2.5" diameter hose to the cyclone and using a 4" hose to connect to my tools.

Would this kill the CFM, pressure, etc ?

Is it better than having 2.5" hoses everywhere ?


  • What specifically is "the cyclone"? Also, what are you trying to accomplish with your shop vac? Do you also have a chip/dust collector in the mix (high air volume, low static pressure)?
    – scanny
    Jan 3, 2017 at 23:50
  • The cyclone is a Dust Deputy. No dust collector. Basically, I needed to know if it was ok/better to use bigger hose to go the my table saw which have a 4" port.
    – Stécy
    Jan 4, 2017 at 23:22

2 Answers 2


You definitely do not want to decrease your hose size as you get closer to the dust collector/vacuum. Just about every shop I have worked in has had confusion over dust collection piping, usually because they try to think of it like an HVAC system, or something that is pushing air. This is wrong, because you are pulling air, so if you think about it, when you step down from a 4" to 2.5" you are only able to pull as much air as fits in that 2.5" hose back to the vac, so in the 4" hose that same volume of air will be moving MUCH slower from the tool until it gets to the 2.5" portion.

Inversely if start smaller, say 1.25", then air flow moves faster until it gets to the larger hose. Think of this like pinching, or partially capping the end of a hose. You will notice a difference in the pressure, and thus the velocity.

Usually, you want to avoid changing sizes except when branching in another line, and then you need to increase the trunk line to accomodate the added CFM's.

Here is a good source of information for designing a system: Dust Collection Design

  • Ok, so having a 4" hose between the cyclone and the tool when a shopvac with 2.5" hose is not a good idea? Should I then have 2.5" all along and reduce at the tool ?
    – Stécy
    Jan 5, 2017 at 18:30
  • I think so. Is this for a tablesaw or a planer? Does your cyclone already have 2.5" ports? Jan 5, 2017 at 19:11
  • For a table saw. The cyclone already have 2.5" in/out ports.
    – Stécy
    Jan 5, 2017 at 19:41

Generally, folks use 2.5" hose for shop vacuums, which work at a high pressure differential but low volume, and 4" hose for dust collectors, which are designed to move more air but usually operate at a lower pressure differential. Tools for tasks...

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