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  1. #1
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    Vacuum speed vs connection size

    Appion tells us that with a 1/4” connection on each side of a vacuum hose, a larger hose still makes a significant difference. I’m still wondering if anyone has tested the difference in speed between a 3/8 hose with 3/8 hooked up to pump and 1/4 on recovery cylinder vs 3/8 hose with 3/8 at pump and 3/8 at cylinder (drum adaptor compatible cylinder). I’m assuming the full 3/8 has to be faster. What about 1/2 hose with 3/8 at pump and 1/4 on cylinder? How does this hose compare to 3/8 on both connections? Thanks. If no one has actually timed this then I might have to set this up and try next weekend.

    Maybe this is obvious to some but I guess vacuum on a cylinder is preferable on the vapour port (if you only pull on one side) so that I’m not restricted by liquid dip tube?

  2. #2
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    It is really all academic. Lowering the pressure drop is what it is all about...to a point. Depending on vacuum pump size, system size and actual vacuum level, you will reach a point where the refrigeration systems internal restrictions are the greatest barrier to achieving a low evacuation level. The “outside restrictions” are the only thing we can change and lowering those as much as possible is what it is all about.
    "Right" is not the same as "Wise".

    Don't step on my favorite part of the Constitution just to point out your favorite part.

  3. #3
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    I think it is Appion who has a video on comparing hose sizes.

    A few months back I had to help an apprentice with a reversing valve. Good lord, seems like it took FOREVER to get any kind of a vacuum pulling through his charging manifold and tiny hoses.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  4. #4
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    Have the 1/2 inch Appion Hoses with 3/8 and 1/4 connections,didn't want to have to use a lot of reducing fittings. I like the Heavy Duty connections and Hoses seem tough! But pulling through a micro channel or core max shaders slows things down no matter.

  5. #5
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    Quote Originally Posted by jayguy View Post
    It is really all academic. Lowering the pressure drop is what it is all about...to a point. Depending on vacuum pump size, system size and actual vacuum level, you will reach a point where the refrigeration systems internal restrictions are the greatest barrier to achieving a low evacuation level. The “outside restrictions” are the only thing we can change and lowering those as much as possible is what it is all about.
    So I’m curious to see then which is less restriction, 3/8 hose with two 3/8 connections, or 1/2 hose with 3/8 and 1/4 connections

  6. #6
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    I'll bet the later. Here is a simple way to look at it:

    Let's say you have a restrictive orifice on a larger pipe. That orifice presents a specific restriction, mostly unrelated to the larger pipe size.

    Now imagine if you put 100 of those specific restrictions in series, regardless of pipe size, you just greatly slowed down the flow.

    I know I'm presenting the 'problem' from the other end of the spectrum, but I think you'll get what I'm trying to say. Besides, 99% of all A/C's out there only have 1/4" flare connections. So if you had a hose of any size with only 3/8's connections, you'd need a reducing adapter or need to cut in a larger access port.


    Quote Originally Posted by Shreadhead View Post
    So I’m curious to see then which is less restriction, 3/8 hose with two 3/8 connections, or 1/2 hose with 3/8 and 1/4 connections
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  7. Likes HVAC/R 19 liked this post
  8. #7
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    Quote Originally Posted by BBeerme View Post
    I'll bet the later. Here is a simple way to look at it:

    Let's say you have a restrictive orifice on a larger pipe. That orifice presents a specific restriction, mostly unrelated to the larger pipe size.

    Now imagine if you put 100 of those specific restrictions in series, regardless of pipe size, you just greatly slowed down the flow.

    I know I'm presenting the 'problem' from the other end of the spectrum, but I think you'll get what I'm trying to say. Besides, 99% of all A/C's out there only have 1/4" flare connections. So if you had a hose of any size with only 3/8's connections, you'd need a reducing adapter or need to cut in a larger access port.
    That makes sense to me. 100 3/8 sized restrictions vs 1 - 3/8 and 1 - 1/4” restriction and very little restriction between.
    I do a lot of chillers that have 3/8 or larger valves. I’ve been using straight 3/8 hose a lot of time but I started to question if my Appion 1/2 Hoses would actually be faster on 1/4” access’. I think I’ll test this when I get a chance to prove your hunch! Thanks for the insight!

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  10. #8
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    Talking to guys at the shop, the majority seemed to think that it would only be as fast as the smallest bottleneck, so most thought 3/8 would be faster.

  11. #9
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    It's cumulative.

    Every little thing you do adds to the benefit.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  12. #10
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    i have 5/8 hoses from the pump to gauge and then from gauge to unit. the ned of the hose is 1/4 inch. And I don't have any depressors in them. I use 1/4 inch ball valves on the end of the hoses when a depressor is needed. I typically work on larger equipment. It was a big difference. yes 5/8 is over kill but at the time i said what the heck.

    did a test once. same vacuum pump each time. my set the second time. another guys 3/8 vacuum and 1/4 after that. We sucked down an empty 50 lb recovery tank. night and day. I could do 2-3 tanks to his one. as long as there wasn't moisture... the speed could be a down fall.

  13. #11
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    From what I understand it's based more on volume so I'm not sure for what you have but the cfm through a 1/2" hose is much greater regardless of the bottleneck. Think of gas when you have a 3" gas line but you have a 1 1/2" gas meter. It doesn't affect the 3" gas flow greatly.

    Sent from my SM-G930V using Tapatalk

  14. #12
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    6’ of 1/4” hose has a greater pressure drop (loss of flow) than a 1/2” length of 1/4” opening.

    Blow through a washer with a 1/4” hole in the center. Now blow through a 1/4” hose 6’ long.

  15. Likes Cool breeze 38 liked this post
  16. #13
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    Bunch of smart fellas on here! I tested tonight with 125lb recovery cylinder. Evacuate to 500 microns, using Appion 1/2” hose 3/8 x 1/4” flares, and a Yj 3/8 x 3/8 flare hose. Pulled on the vapour port and the only thing that changed was the hose and drum adapter. 15 min 20 seconds for 3/8 hose, 10 min 45 seconds for 1/2”. That is substantial! Feel free to gloat and say you knew it! Haha

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