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Doug C
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Joined: January 07, 2013
Posts: 255
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 Posted: Thu Jun 29, 2017 12:46 pm Post subject: Hose fittings vs air consumption |
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Some time ago I installed 3/8" fittings on all my air hoses and spray guns because I'd read that it's the set up most pro's use. But I was wondering if switching back to 1/4" fittings would give me more time between when the compressor cycles on? My compressor is on the small side and I've purchased a low air consumption gun for paint (not primer), and every little bit of air savings would help. But do the fittings make a difference in that regard?
Doug C |
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Evil_Fiz
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Joined: May 06, 2011
Posts: 1113
Location: Jacksonville, FL
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| Posted: Thu Jun 29, 2017 1:53 pm Post subject: Re: Hose fittings vs air consumption |
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See this thread for information on air flow and compressor related maters: Sandblasting - Harbor Freight Compressor
Short summation
A smaller size connector, or a more restrictive connector design of the same size, will restrict airflow but it may not have any impact on consumption because the flow rates are going to exceed the SCFM output of smaller compressors. The amount of air needed for a task is a fixed variable. If you are flowing 30 SCFM it does not matter what size connector you use. Larger connectors and more airflow are beneficial for things such as media blasting and running high consumption tools like grinders and impact wrenches. For painting, you need a steady, fixed amount of air for the paint to atomize properly. What may help you is cooling the air BEFORE it hits the tank. This will increase the air density in the tank effectively giving you more air to work with per cycle. This can be accomplished with an aftercooler between the pump and the tank.
(Taken from the Milton Industries web site: http://www.miltonindustries.com/couplers-and-plugs.html)
- Milton M-Style connectors flow 34 SCFM for both 1/4" and 3/8" (Most common connector type)
- Milton V-Style connectors flow 74 SCFM for both 1/4" and 3/8"
(Taken from the Dixon Valve US Website: https://www.dixonvalve.com/search/products?facet-f...isconnects)
- Dixon DCP103 1/4" body(male)/DC223 (female) flow 37 SCFM @100 PSI
- Dixon DCP5 3/8" body (male)//DC6 (female) body flow 70 SCFM @ 100 PSI
(The Dixon numbers bring the Milton numbers into question.)
- Drop to a 1/4" hose instead of 3/8". CAUTION, this my prove to be too restrictive.
_________________
“…It's not just about what's interesting. It's also about what's helpful, and it's helpful even if it helps just one other guy working on a Ghia.”
kiwighia68
See my build on TheSamba at:
The K_R_A_K_E_N_N : a 70 Ghia Convertible reinterpreted |
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heimlich 
VWNOS.com
Joined: November 20, 2016
Posts: 7566
Location: Houston, Texas
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| Posted: Thu Jun 29, 2017 7:44 pm Post subject: Re: Hose fittings vs air consumption |
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| What may help you understand is how water travels down a pipe. Your local water authority brings in a fairly big line to the road. From that line a series of lines and reducers are involved to bring the water to your home and also to increase the pressure. At the point of reducing the size of the line the pressure increases. I am sure there is an equation out there somewhere based on CFM/etc and hose size which will give you exact numbers. |
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Doug C
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Joined: January 07, 2013
Posts: 255
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| Posted: Thu Jun 29, 2017 8:26 pm Post subject: Re: Hose fittings vs air consumption |
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Wow, I appreciate all the info on this subject guys! It's very helpful.
Doesn't sound like there's any advantage to changing to smaller fittings. Though I do have a full set of 1/4" already and may put a stop watch on both sets to see what happens with my compressor, just for giggles.
I've heard of an ice bucket after the compressor to help dry the air but have no idea how to cool it before the tank, are there small add-ons to get this done?
My gun = 4.25cfm @ 30psi
AU paint (single/non-metallic) = 8-10psi @ cap
my compressor = 8.8scfm @ 40psi (21gal/3hp)
DougC |
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Evil_Fiz
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Joined: May 06, 2011
Posts: 1113
Location: Jacksonville, FL
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| Posted: Fri Jun 30, 2017 5:40 pm Post subject: Re: Hose fittings vs air consumption |
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| Doug C wrote: |
...I've heard of an ice bucket after the compressor to help dry the air but have no idea how to cool it before the tank, are there small add-ons to get this done?
DougC |
Here are some examples of aftercoolers:
http://blog.cnccookbook.com/2011/09/06/aftercooling-a-compressor-to-cut-down-on-moisture/
https://www.youtube.com/results?search_query=compressor+aftercooler
I went the transmission oil cooler route since after researching the different approaches I found it to be the most efficient from both a thermal transfer and airflow perspective. Rather than the B&M cooler I went with the Long Industries Tru-Cool H7B ENGINE OIL COOLER. Long is a division of DANA and they actually make the B&M coolers. The
Tru-Cool H7B is larger than the B&M referenced in the first link, has more plates, has a higher BTU rating, and is about $30US cheaper. Rather than using a $$$$ 220v 10" radial fan (my compressor is 220V,) I am experimenting with building a tapered box and using a 20" box fan to draw air through the cooler. I have not finished the build yet so I have no data to report.
The guy who built his aftercooler with the B&M cooler reports an almost 200*F drop in temperature. For his application, this drop in temperature results in a 38% denser air charge. If you are the math type, here are the formulas for calculating gas compression: http://www.engineeringtoolbox.com/compressed-air-storage-volume-d_843.html
Formula to substantiate above statement found HERE and an explanation HERE http://www.brighthubengineering.com/hvac/24491-what-is-charles-law/
"Using Charles' law (V2/V1 = T2/T1), the increased volume based on my temperature measurements will be:
427.59°K / 308.70°K = 1.38.
Meaning there's a 38% increase in air molecules stored in the tank under best case/worst case scenarios. Of course, it's a 60 gallon tank and it's going to contain 60 gallons of air no matter what. The "increased" storage capacity will be realized by the pressure in the tank not dropping considerably once the air cools down."
There is also anecdotal evidence that suggests the compressor will run cooler with an aftercooler.
GEEKY Stuff alert
Charles' law is only one part of the solution. You also have to take Boyle's Law into account. https://www.boundless.com/chemistry/textbooks/boun...-254-8360/
If that is not enough you have to unify the two laws into the Ideal Gas Law. https://www.easycalculation.com/chemistry/learn-ideal-gas.php
if you want to figure out the air density at a given pressure and temperature, The following two charts make it simple to arrive at a conclusion
Based on this information, and if I did not completely FUBR my math, your numbers should be:
Data for a 21 Gal Compressor
NOTE:
21 Gal = 2.807291667 Cubic Feet (CuFt)
1 Lb. of air = 13.35 CF @ STP (32*f/0*C/273*K) @ (1 Atmosphere)
STP = Standard Temperature and Pressure
Formula: <Density value from chart>*13.35*2.807291667
Density of air (lb/ft3)
70*F/0psi------------------------------------300*F/120psi-------------------100*F/120psi
-------------------------------------------------------------------------------------------------------
0.075 (lb/ft3)--------------------------------1.34 (lb/ft3)---------------------1.82 (lb/ft3)
which equates to: CuFt for a for 21 Gal Compressor at the above Temp. and PSI
2.810800782 CuFt-----------------------50.21964063 CuFt-----------68.20876563 CuFt
68.20876563 / 50.21964063 = 1.35
Cool the air charge from ~300*F to ~100*F and you can achieve a ~35% bump in air capacity/run time between compressor cycles.
...we're all in this together.
Emil
_________________
“…It's not just about what's interesting. It's also about what's helpful, and it's helpful even if it helps just one other guy working on a Ghia.”
kiwighia68
See my build on TheSamba at:
The K_R_A_K_E_N_N : a 70 Ghia Convertible reinterpreted |
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Doug C
Samba Member
Joined: January 07, 2013
Posts: 255
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| Posted: Fri Jun 30, 2017 9:35 pm Post subject: Re: Hose fittings vs air consumption |
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man that's some info right there!! Huge thank you! I got some things to consider. I actually was considering adding a transmission cooler (to my XC70) - maybe that would work for an after cooler before I install on the car.
Doug C |
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Doug C
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Joined: January 07, 2013
Posts: 255
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| Posted: Sat Jul 01, 2017 10:27 am Post subject: Re: Hose fittings vs air consumption |
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If I could make this transmission cooler work, I can kill two birds with one stone. It's the one that has been recommended for aggressively driving my '04 volvo xc70 and is dirt cheap at $37 and free shipping. I'd use it on compressor to paint my project car, then mount it to my daily driver afterwards. Need to look into plumbing the compressor.
https://www.amazon.com/Hayden-Automotive-676-Rapid-Cool-Transmission/dp/B000C39CL8
Doug C |
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Evil_Fiz
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Joined: May 06, 2011
Posts: 1113
Location: Jacksonville, FL
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| Posted: Sat Jul 01, 2017 12:22 pm Post subject: Re: Hose fittings vs air consumption |
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| Doug C wrote: |
If I could make this transmission cooler work, I can kill two birds with one stone. It's the one that has been recommended for aggressively driving my '04 volvo xc70 and is dirt cheap at $37 and free shipping. I'd use it on compressor to paint my project car, then mount it to my daily driver afterwards. Need to look into plumbing the compressor.
https://www.amazon.com/Hayden-Automotive-676-Rapid-Cool-Transmission/dp/B000C39CL8
Doug C |
I second your thinking  but want to add some details to consider.
- I was looking at the Hayden coolers and went as far a going to the local FLAPS that carried them a physically inspecting one. I was looking at the Hayden 689 which is 3/4” x 11-5/8” x 11” and has 9/16”-18, 37° JIC MALE FLARE (-6). This is the closest to the B&M/Long that Hayden makes. While researching coolers I consistently found good reviews of the Hayden products. Ultimately I went the B&M/Long route because it was proven to work and I had a ready made recipe I could follow.
-The 676 is much smaller and has 3/8 OD push-on connectors, not barbed. Those might not stand up to the pressure of the compressor and would probably restrict air flow. Compressor run time would probably increase due to lower air flow between the pump and the tank.
- The 676 WILL cool your air charge and help remove moisture, but not as much as the larger ones.
- The Hayden 687 may be worth considering because it is only slightly larger than the 676 but has screw-on fittings.
- No matter which way you go, you will still need a high CFM radial fan. (EDIT: AXIAL Fan, not radial.) The higher the CFM the better; somewhere in the 1500 CFM range is good.
- Match the fan voltage to that of your compressor so can wire it in parallel tot he compressor motor. This way the fan will run only when the compressor is running.
- A BOX FAN WILL NOT WORK. I mocked up a prototype this morning and it will not move nearly enough air to effectively cool the air charge.
-Since you are thinking of using the cooler in your car, you may want to consider a 12V fan and a 110 VAC to 12 VDC power supply such as the AC to DC Switching Open Frame Power Supply 12 Volts 10 Amps 120 Watt - $19.30. The fan can serve a dual purpose along with the cooler. Consider that you will need a 220 VAC relay to power the AC to DC power supply if your compressor is 220 VAC.
I am sharing this information, not because I know what I am talking about, but because these are the conclusions I have reached after spending quite a bit of time researching the subject. I hope this information saves someone time and effort in the future.
...we're all in this together.
Emil
_________________
“…It's not just about what's interesting. It's also about what's helpful, and it's helpful even if it helps just one other guy working on a Ghia.”
kiwighia68
See my build on TheSamba at:
The K_R_A_K_E_N_N : a 70 Ghia Convertible reinterpreted |
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