air lines and valve flow rate - North Carolina Woodworker

	» Upcoming Events Welcome New Member Chat! Every Thursday evening at 7:30pm Click here for more. Mid-West Tool Collectors Tool Meet Click here! Saturday January 14th in Hillsborough Lie-Nielsen Toolworks Hand Tool Event Click here! Friday January 20th 10-6 and Saturday January 21st 10-5 at the Cratfs Center in Raleigh 12-29-2011, 11:49 AM   #1 air lines and valve flow rate   DQ Qualified Corporate Member ChrisM from Raleigh, NC Posts: 1,202 12-29-2011, 11:49 AM I'm considering putting a solenoid-actuated valve on my air tank, so I can turn that on/off remotely from the shop. My lines leak a little, so I'd prefer to only have the compressor run when I'm actually using it. The flow specification for the valve says "cv 7". The valve has 3/4" fittings which, I think, will be correct for my compressor. Anyone know what effect that flow spec will have in effective flow rate? IIRC, my compressor is rated for ~10 CFM at 135 psi - I do not foresee every using more than one tool at a time, but do hope to try my hand at spraying with an HVLP system. TIA! Chris __________________ Turning beautiful wood into scraps...one board at a time. Go Boilermakers! Views: 198 12-29-2011, 05:25 PM   #2     DQ Qualified Chris from Windsor, VA Posts: 386 Re: air lines and valve flow rate Chris - The CV rating refers to liquid service. It is the number of gallons of water the valve will pass with a pressure differential of 1 psi. With a 3/4 NPT fittings, my guess is that this valve should be plenty for your needs. Maybe Ethan will pipe in with a much more technical evaluation . C. __________________ "Remember - If the women don't find ya handsome, they should at least find ya handy!" - Red Green "Always take hold of things by the smooth handle." - Thomas Jefferson   12-29-2011, 06:32 PM   #3   DQ Qualified Corporate Member Alan Schaffter from Washington, NC Posts: 2,398 Re: air lines and valve flow rate Chris, I've researched this issue on and off for a few months now and haven't been able to find a simple answer, or at least one I can wrap my brain around without getting a headache! The best so far is the example for "Gas Applications" on page L27 of this pdf. The valve in the sample problem has a flow factor (Cv) of .58 with a flow of 500 SCFH (8 CFM) at 35 psi and a pressure drop of 5 psi. Unless I am missing something, looking at the equation, Cv varies directly with Q (flow) so with the same flow, temp, pressure, and pressure drop, a valve with a 7 Cv should flow 12 times as much in that situation, although I think the main purpose is to calculate the pressure drop. Using 10 CFM (600 CFH) flow, 55 deg. 135 psi inlet, assuming a 100 psi outlet I get a required Cv of .84. So either a Cv of 7 is way more than enough, a decimal is missing and it should be .7, or I'm doing something else wrong. Come on, somebody with a little Fluid Dynamics background, please weigh in! Originally Posted by merrill77 I'm considering putting a solenoid-actuated valve on my air tank, so I can turn that on/off remotely from the shop. My lines leak a little, so I'd prefer to only have the compressor run when I'm actually using it. The flow specification for the valve says "cv 7". The valve has 3/4" fittings which, I think, will be correct for my compressor. Anyone know what effect that flow spec will have in effective flow rate? IIRC, my compressor is rated for ~10 CFM at 135 psi - I do not foresee every using more than one tool at a time, but do hope to try my hand at spraying with an HVLP system. TIA! Chris __________________   12-29-2011, 06:47 PM   #4     DQ Qualified Corporate Member Scott Smith from New Hill, NC Posts: 3,452 Re: air lines and valve flow rate Unless that 3/4" valve has some type of small orfice inside it, it will flow way in excess of your needs - probably 10X if not more.   12-29-2011, 08:58 PM   #5     DQ Qualified Corporate Member Bryan from Burlington, NC Posts: 1,493 Re: air lines and valve flow rate Originally Posted by Alan in Little Washington Come on, somebody with a little Fluid Dynamics background, please weigh in! While I would love to speak eloquently on the subject, and impress you with a highly knowledgable technical explination, but that was a long time ago, so I will not try. It is true that the valve is a restiction in the piping, but in your case, I expect that will be negligeble. I agree with Scott that the valve will flow far more cfm than you will need. Remember you have 2 other restrictions, the capacity of the compressor pump itself and the 3/8, or even 1/4 hose from your piping to the tool. The hose is a far greater restriction than the 3/4 inch valve and you should not have any trouble at all. __________________ He is your partner, your defender, your friend, your dog. You are his love, his life, his leader. He will be yours, faithful and true to the very last beat of his heart. You owe it to him to be worthy of such devotion   12-29-2011, 09:01 PM   #6     DQ Qualified Corporate Member Mark from Goldsboro, NC Posts: 2,302 Re: air lines and valve flow rate As long as the opening on the solenoid is as large or larger than the inside diameter of the air hose connected to the tool, you should not have a problem. Most air flow problems occur from using too small of an air hose. If using a 1/4 id hose, you want it to be short (preferably less than 12') for most conventional tools. If going to HVLP, you want to use a minimum 3/8" id hose with the hi-volume air fittings on the hose and gun (the hi-volume quick disconnects have almost a 3/8" id where the normal ones are about 1/4"). A 50' length of 1/4" air hose can drastically reduce the volume of air delivered to the tool. Although not noticed with short duration air tools like impact wrenches, etc, it will definitely starve a spray gun or pneumatic sander. Go __________________ Practicing at practical woodworking   12-30-2011, 10:47 AM   #7     DQ Qualified Corporate Member ChrisM from Raleigh, NC Posts: 1,202 Re: air lines and valve flow rate Thanks for the responses! Now I just need to figure out how to control it from my shop (30' away). Perhaps I'll look into one of those X10 remote control units. __________________ Turning beautiful wood into scraps...one board at a time. Go Boilermakers!   12-30-2011, 01:15 PM   #8     DQ Qualified Chris from Windsor, VA Posts: 386 Re: air lines and valve flow rate Chris - Beware the unit you posted requires 1.5 amps at 12 volts DC for the coil. That's a fairly hefty wall-wart to supply that much current. The wall wart would have to plug in to the X10. C. __________________ "Remember - If the women don't find ya handsome, they should at least find ya handy!" - Red Green "Always take hold of things by the smooth handle." - Thomas Jefferson   12-30-2011, 02:29 PM   #9   DQ Qualified Dave from Raleigh, NC Posts: 423 Re: air lines and valve flow rate Didn't I notice that they have the same valves with 120V solenoids?   12-30-2011, 02:31 PM   #10     DQ Qualified Corporate Member ChrisM from Raleigh, NC Posts: 1,202 Re: air lines and valve flow rate Originally Posted by CDPeters Beware the unit you posted requires 1.5 amps at 12 volts DC for the coil. That's a fairly hefty wall-wart to supply that much current. The wall wart would have to plug in to the X10. I had no trouble finding 12V 2A converters, such as this one. Most of the X10 Modules are rated to handle 100W light bulbs - this adapter would draw less than 24W. Am I missing something? __________________ Turning beautiful wood into scraps...one board at a time. Go Boilermakers!   12-30-2011, 05:41 PM   #11   DQ Qualified Corporate Member Alan Schaffter from Washington, NC Posts: 2,398 Re: air lines and valve flow rate Wire an outlet to your shop lighting circuit for the 12V transformer so the valve will be closed whenever the lights are off and open when you are in the shop with the lights on. That is what I had planned to do, but with my numerous leaks, the piping would bleed down which is ok for my second story shop, but I wouldn't be able to use my garage level drop. __________________     North Carolina Woodworker > Tools, Equipment, and Techniques > Power Tools and Their Use Tags air , flow , lines , rate , valve « Previous Thread | Next Thread » Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts HTML code is Off Similar Threads Thread Thread Starter Forum Replies Last Post Compressed Air Lines rcflyer23 Workshops 31 08-28-2011 06:07 PM DC 'Relief Valve' Gotcha6 Safety & Health 3 02-23-2010 08:29 AM	» 2012 NCWW Calendar » Stats Members: 5,937 Threads: 38,463 Posts: 381,389 Top Poster: DaveO (15,287) Welcome to our newest member, DavidM » Today's Birthdays weekenderlady
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