Page 1 of 2 12 LastLast
Results 1 to 13 of 16
  1. #1
    Join Date
    Dec 2011
    Location
    Pinckney, MI
    Posts
    245

    Digital Gauges / Vacuum

    What are your thoughts on the use of Digital gauges during evacuation? I always had my analog's hooked up, but now that I use Digital, I'm more cautious based on my tool investment.

  2. #2
    Join Date
    Jun 2011
    Posts
    336
    Do you mean you use your manifold set as a vacuum micrometer gauge?

    Sent from my HTC One S using Tapatalk 2

  3. #3
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    873
    Your manifold shouldn't be used for evac. If you search on this forum you will see discussions about this.
    ckartson
    I didn't write the book I just read it!

  4. #4
    Join Date
    Dec 2011
    Location
    Pinckney, MI
    Posts
    245
    I'm not suggesting using my gauge as a measurement t of vacuum, but a junction point. I've been using a micron gauge for two decades to measure vacuum. If you don't use a manifold, digital or analog, where are you making the High/Low/micron gauge junction?


    Sent from my iPhone using Tapatalk 2

  5. #5
    Join Date
    Oct 2013
    Location
    SW Alabama
    Posts
    145
    The use or CRTs allow the connection of a micron gauge right at service valve and allow for the best blankoff test by isolating the hoses away from the gauge. That's how I do it. Plus my hoses go directly to the vac pump with a 3/8 tee.

    Sent from my DROID RAZR using Tapatalk 4

  6. #6
    Join Date
    May 2013
    Location
    STP, MN
    Posts
    96

  7. #7
    Join Date
    Jun 2011
    Posts
    336
    That's just the ticket I have been looking for. Just changed companies, the old one was not overly receptive to using micron gauges. Sounds like the new one is into them.

    Sent from my HTC One S using Tapatalk 2

  8. #8
    Join Date
    Jun 2011
    Posts
    336
    Quote Originally Posted by kuntrybumm View Post
    The use or CRTs allow the connection of a micron gauge right at service valve and allow for the best blankoff test by isolating the hoses away from the gauge. That's how I do it. Plus my hoses go directly to the vac pump with a 3/8 tee.

    Sent from my DROID RAZR using Tapatalk 4
    How much difference does it make separating the gauge from the pump for a blankoff test?

    Sent from my HTC One S using Tapatalk 2

  9. #9
    Join Date
    Dec 2011
    Location
    Pinckney, MI
    Posts
    245
    Very helpful. Thank you. I will use this set up from here forward.


    Sent from my iPhone using Tapatalk 2

  10. #10
    Join Date
    Aug 2010
    Posts
    1,747
    Quote Originally Posted by jpbhvac View Post
    If you don't use a manifold, digital or analog, where are you making the High/Low/micron gauge junction?
    So, use a flare tee or cross in place of the manifold. You can also change or permanently attach a convenient fitting to the pump itself.

    Ideally, you want a 3/8" swivel female to 1/2" male barbed fitting and a 1/2" line going from vacuum pump to Y, then two 6" 3/8" hoses to two 1/4 flare ends. Less connections in between the better. I would prefer Y over T if its available since the smoother bend is less restrictive.

    Any unnecessary sharp bends and connections are each a restriction and each connection is a possible leak point.

  11. #11
    I still use my gauges for evac on small units. It just doesn't make sense to pull out the CRTs and hook it all up on units that the charge is measured in ounces not pounds, plus I have the sman3s so there is a micron gauge built in. A little nylog on my hose and gauge connections and I can be at 500 microns before I could have the CRT hooked up and the cores pulled out. On residential split systems or big commercial units however its a HUGE time savor, unless I'm swapping a rusty txv power head and the system isn't open but for a second. Then I still pull thru the gauges cause it will pull down pretty fast.

  12. #12
    Join Date
    May 2009
    Location
    South of Heaven
    Posts
    1,089
    The only important issue is your micron reading of the system while ISOLATED from the pump. If you wanted to use a kitchen sink and the copper chrome plated piping connecting it to waste as your manifold there is nothing wrong with that ( although a dedicated vacuum rig may help out in regard to time ). There is nothing wrong with using a charging set as an evacuation means and it is only the end result that matters.

  13. #13
    Join Date
    Aug 2010
    Posts
    1,747
    Quote Originally Posted by tech45 View Post
    The only important issue is your micron reading of the system while ISOLATED from the pump.
    Thick walled or wire reinforced vinyl hose with barb fittings is perfectly fine. I would imagine that these have lower permeation coefficient and less tendency to out gas compared to charging hoses. This is what they use in analytical labs for applications such as pulling a vacuum for mass spectrometer and it is considered acceptable for vacuum down to 1 micron. For deep vacuum, which in the lab means something like 1/1000 to 1/100,000 of a micron (E-6 to E-9 torrs), they use flexible metal pipes, copper crush washers seated in place with knife edge fittings and such.

    You may even get away with a high quality pinch valve which seals by crushing down the vinyl hose enough to pinch it off. It is an externally mounted device with wing nuts, which in essence is a smooth edged locking vise-grip and no more. The advantage is that the entire valving is hermetically separated. If it ruins the hose by not making it rebound, oh well, cut off that section and go with traditional means. The hoses are cheap.

    Availability through the supply house or HVAC oriented marketing and packaging is not an indication of superiority. I believe some even expressed liability concerns associated with failure under pressure, but they don't seem to know that only pressures involved is simply not collapsing inward with 15psi acting against 0 psi inside.

    If you wanted to use a kitchen sink and the copper chrome plated piping connecting it to waste as your manifold there is nothing wrong with that ( although a dedicated vacuum rig may help out in regard to time ). There is nothing wrong with using a charging set as an evacuation means and it is only the end result that matters.
    Actually, it does matter. When there's an interruption in water line, you'll get air bubbles at faucets even after you've purged water at another faucet. That's because faucets are not meant to be gas-tight to an inward pressure or depend on outward pressure pressing out to maintain a good seal, so it loses the water column. The gaskets in manifolds are set with presumption of outer force so the outward pressures holds the gasket towards seating it.

    If you're inflating a playground ball to 1 psig, you can easily overcome the restrictions even inflating through a capillary hose since you can raise the source pressure without limit, even as much as 1,000 psi so long as you shut it off when the target teaches 1 psig.

    Disconnect the 1,000 psi source, then let it bleed out its own. Guess how long its going to take for it to naturally equalize to atmospheric pressure? Even if you pulled a perfect vacuum on the other end, you'll create a maximum of 15.7 psi of differential (14.7psia + 1psig = 15.7psia). It would equalize much faster by slitting the ball open compared to attaching the end to an infinite cfm vacuum pump.

    That's how you picture the last bit of a system evacuation. You're basically trying to deflate the ball of its last 1/10,000 of psig to equalize the atmospheric pressure through a capillary.

    The reason you hook up to both sides is just that. You'd be sucking through a tiny straw across the metering device. I believe you can demonstrate this by the difference in time it takes to evacuate by just the low side vs just the high side. Evacuating through high side will take much longer, because the large volume of low side has to get sucked through the capillary.

    Sharp surfaces, sharp turns, (i.e. 90 degree elbow), abrupt diameter changes, etc all adds flow resistance.

    1/4" flare fittings aren't truly 1/4" full flow. 1/4" ID tubes are 1/4" plus 2x wall thickness, yet you'll find that hole in 1/4" flare fittings are maybe 3/16. Measure it drill bits. You want as little of those in the way as possible. So, an F fitting at vacuum pump and two fatty hoses going to the system as directly as possible to the system is the most desirable.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event