I want to use a 2.5 CFM vacuum pump (from Pittsburgh Automotive... http://www.harborfreight.com/25-cfm-vacuum-pump-98076.html) to pull a vacuum on a system in my house. I am a bit confused, though, as to how the pump works since there is only an inlet valve but no outlet? I will suck the gas into the pump to create vacuum in the system, but where does that gas then go?

  • Yea 2.5 cfm is not much volume, so don't expect fan like volume... This type of vacuum pump is usually pretty slow (and noisey)
    – Tyson
    Nov 18, 2016 at 0:16
  • @Tyson would this outlet be connectable to a line? Or it is just like general exhaust that is put into the room that the pump is sitting in?
    – Runeaway3
    Nov 18, 2016 at 0:21
  • Passive.. Its not meant to contain. Whatevdoes the red knob do? It may be associated with that... 2.5 cfm could leak out around it
    – Tyson
    Nov 18, 2016 at 0:26
  • @Tyson is there a way to contain this leaking? Whether it is the red or black knob, do you know of anyway of perhaps enclosing that and connecting it to a line?
    – Runeaway3
    Nov 18, 2016 at 1:18
  • I don't think it works that way, but I could be wrong as I've never used that model.
    – Tyson
    Nov 18, 2016 at 1:26

1 Answer 1


My pump has a small outlet that is covered to capture the oil that may spray out if the pump is turned on without a load, or when first pumping down a system so the oil doesn't get blown out of the pump but is drained back into the pump. Most mechanical high vacuum pumps are rotary vane these use a fiber plate and the oil to make the seal. If there is no load the pump pulls more oil in and pushes it out the exhaust (some pumps do make big oil messes if not loaded for long or allowed full flow at the start of a pump down. Some less expensive pumps have a port to direct the oil into a container (vacuum pump oil can get expensive). There should be a warning if the pump doesn't have an oil reclaim system because it can be very messy.

  • it turns out my pump has that same type of cover to separate the oil and the air. Is it possible to remove this and instead put a fitting onto it, and connect this fitting to an exhaust line (so that I may contain the exhaust)? Perhaps putting some type of filter to prevent the oil from being put into the line?
    – Runeaway3
    Nov 18, 2016 at 23:12
  • 1
    I am not sure on your model if a filter would work. Any back pressure on the exhaust will affect your pumping speed and possibly the base pressure. Even the best mechanical vacuum pumps only creat a vacuum equivalent to 14.7 psi if you think about it as a pressure so it doesn't take much to affect the pumping speed and or base pressure.
    – Ed Beal
    Nov 20, 2016 at 8:07

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