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There is a website describing how to use a discarded 'fridge compressor
for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. I do not have the website address. I was browsing on a computer at the public library at the time and did not write it down. However you can find it by going to www.boat-links.com, clicking on "The Mother of All Boat Links", clicking on the first box "amateur boatbuildign and repair" and scrolling down untill you find the link about vacuum bagging. Nowadays all discarded 'fridges go to a recyling depot where they "vacuum bag" the freon gas to protect the ozone layer of the atmosphere. It should be easy to get a compressor by telephoning the miniciapl garbage department. Since compressors do wear out it would be a good idea to look for ones off later model 'fridges (the date of manufacure should be on a label on the 'fridge) bring home 2 or 3 to try. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
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On Sun, 19 Oct 2003 19:23:55 -0400, "sour (max camirand)"
wrote: On 18 Oct 2003 14:47:14 GMT, (William R. Watt) wrote: There is a website describing how to use a discarded 'fridge compressor for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. I remember reading about this, too. Seems very feasible. If I ever have any vacuum bagging to do, I'll give it a shot. Has anyone tried it? -m Fridge compressors blow out their oil then seize up in 1 to 10 hours, in my experience. If you trap the oil, or keep adding it, I hear you can keep 'em running. Brian Whatcott |
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If you can find an old, and I mean REALLY old, compressor with single
intake and output ports and maybe cooling fins it will last an acceptable time but anything built after they changed from latches to magnetic sealing strips will crap out very quickly. William R. Watt wrote: There is a website describing how to use a discarded 'fridge compressor for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. I do not have the website address. I was browsing on a computer at the public library at the time and did not write it down. However you can find it by going to www.boat-links.com, clicking on "The Mother of All Boat Links", clicking on the first box "amateur boatbuildign and repair" and scrolling down untill you find the link about vacuum bagging. Nowadays all discarded 'fridges go to a recyling depot where they "vacuum bag" the freon gas to protect the ozone layer of the atmosphere. It should be easy to get a compressor by telephoning the miniciapl garbage department. Since compressors do wear out it would be a good idea to look for ones off later model 'fridges (the date of manufacure should be on a label on the 'fridge) bring home 2 or 3 to try. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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"William R. Watt" wrote in message ... There is a website describing how to use a discarded 'fridge compressor for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. hahaha.. good one. he claims he got 25 psi vacuum..... do not pass go, do not collect $200. go to jail. hugh p.s. my old engineering profs would fail you the whole year for saying somthing like that in any individual exam.... |
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I see that mistake so often that I just automatically think inches Hg.
Any decent vacuum pump should be able to reach 25 to 28" Hg in a really well sealed bag but a perfect seal is very hard to get. While laminating plywood requires as much vacuum as you can get most glass bagging is done below 15" so pump volume is usually a lot more important than ultimate pressure. hugh wrote: "William R. Watt" wrote in message ... There is a website describing how to use a discarded 'fridge compressor for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. hahaha.. good one. he claims he got 25 psi vacuum..... do not pass go, do not collect $200. go to jail. hugh p.s. my old engineering profs would fail you the whole year for saying somthing like that in any individual exam.... -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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"Glenn Ashmore" wrote in message
news:oMQkb.80431$sp2.38130@lakeread04... I see that mistake so often that I just automatically think inches Hg. Any decent vacuum pump should be able to reach 25 to 28" Hg in a really well sealed bag but a perfect seal is very hard to get. While laminating plywood requires as much vacuum as you can get most glass bagging is done below 15" so pump volume is usually a lot more important than ultimate pressure. true. the mercury thing can confuse people. i'm living in SI-land so a unit like psi is already wierd enough. if you started talking about inches of mercury here people would start looking up the address and phone number of the nearest loony-bin. 'twould be like using a unit like a furlong per fortnight or a slug/acre or something.... just unbelievably arcane and difficult. ah well. us SI people owe the french for something.... still, every time i see that mistake i laugh because our engineering profs did have a habit of trying it out on students and if you went for it you were in BIG trouble. hugh p.s. i also always wonder if maybe people are vacuum bagging composites on venus or half way down the atmosphere of jupiter. |
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William R. Watt ) writes:
claims he got 25 psi vacuum for his right. change "psi" to "lb". -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
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Hugh,
How about laughing to yourself next time and explain to the guys that didn't go to engineering school why it's wrong. No need to be rude. Regards, Ron |
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Standard atmospheric pressure is a bit over 14 PSI so that is as much
pressure as a vacuum can produce. The first proven vacuum was produced by Evalgelista Torricelli, Galileo's assistant, by filling a glass tube with mercury and turning it upside down. The mercury dropped until the weight of the mercury in the tube equalled the pressure of the air outside. That was about 30". Torricelli almost got in a lot of trouble about this because the Pope had decreed that there was no such thing as a vacuum so he sent the idea to a Frenchman named Pascal to work on. For many years we have happily used the height of the mercury to describe a vacuum. We and the English used inches and everyone else used milimeters. Then the French and Itallians conspired to change everything at an international standards conference and we ended up with Torr as the official measure. Being Itallian the unit had to be totally irrational so a Torr is 1/760th of an atmosphere. To add to the confusion the "Bar", (short for barometer) was used to describe one standard unit of atmospheric pressure so vacuums are measured in fractions of a bar called millibars. Also the French did not like for an Itallian to get any credit so in an evil pact with the British, they came up with the Pascal to describe one atmosphere of pressure. To get the British to go along the Pascal was based on a unit named after an Englishman, the Newton, but to keep the English in their proper place they made the Pascal equal to a million Newtons. The thing is, the measurement of "standard Atomspheric pressure" that they used to set the actual values was off a bit so all of these units are not quite accurate. That is why I still use inches of Mercury. :-) Ron Thornton wrote: Hugh, How about laughing to yourself next time and explain to the guys that didn't go to engineering school why it's wrong. No need to be rude. Regards, Ron -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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let's see. vacuum is an absence of atmosphere, or a presence of nothing but
room for there to be something. the earth's atmosphere applies a pressure of approx 14.5 psi at sea level, with the pressure varying a little depending on the weather. thus, an absolute vacuum has approx 14.5psi less pressure than one feels at the surface of the earth. a vacuum bag with zero pressure inside is 14.5psi lower than outside. thus it is impossible - in earth terms at least - to talk of 25psi of vacuum. if one lived on jupiter, one could talk about 25psi of vacuum and if the guy with the claim lives on jupiter and is making composites there then i'll stop laughing and be amazed. as for laughing, the reason the engineering school profs got so upset with this mistake is that they regarded it as something fundamental that should have been learned at high school. so do i. it's kinda like wandering around the world without knowing that light travels faster than sound or that shakespeare was english. you know - basic stuff. hugh p.s. and i wasn't rude. i was laughing. "Ron Thornton" wrote in message ... Hugh, How about laughing to yourself next time and explain to the guys that didn't go to engineering school why it's wrong. No need to be rude. Regards, Ron |
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Thanks Glenn,
I already knew, but obviously others did not. I have never ever seen Glenn intentionally post anything in the least bit "rude." Unfortunately others would most likely not say the same for me :-) Fred "Glenn Ashmore" wrote in message news:zeSkb.80436$sp2.58104@lakeread04... Standard atmospheric pressure is a bit over 14 PSI so that is as much pressure as a vacuum can produce. The first proven vacuum was produced by Evalgelista Torricelli, Galileo's assistant, by filling a glass tube with mercury and turning it upside down. The mercury dropped until the weight of the mercury in the tube equalled the pressure of the air outside. That was about 30". Torricelli almost got in a lot of trouble about this because the Pope had decreed that there was no such thing as a vacuum so he sent the idea to a Frenchman named Pascal to work on. For many years we have happily used the height of the mercury to describe a vacuum. We and the English used inches and everyone else used milimeters. Then the French and Itallians conspired to change everything at an international standards conference and we ended up with Torr as the official measure. Being Itallian the unit had to be totally irrational so a Torr is 1/760th of an atmosphere. To add to the confusion the "Bar", (short for barometer) was used to describe one standard unit of atmospheric pressure so vacuums are measured in fractions of a bar called millibars. Also the French did not like for an Itallian to get any credit so in an evil pact with the British, they came up with the Pascal to describe one atmosphere of pressure. To get the British to go along the Pascal was based on a unit named after an Englishman, the Newton, but to keep the English in their proper place they made the Pascal equal to a million Newtons. The thing is, the measurement of "standard Atomspheric pressure" that they used to set the actual values was off a bit so all of these units are not quite accurate. That is why I still use inches of Mercury. :-) Ron Thornton wrote: Hugh, How about laughing to yourself next time and explain to the guys that didn't go to engineering school why it's wrong. No need to be rude. Regards, Ron -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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hugh wrote: if one lived on jupiter, one could talk about 25psi of vacuum and if the guy with the claim lives on jupiter and is making composites there then i'll stop laughing and be amazed. I would think that post curing would be a lot easier on Jupiter. :-) -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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From what GA wrote it would be better to look for an older unit than a
later one as I assumed. It could be tested with a car vacuum guage. A vaccum guage costs about $15 at Canadian Tire. I found one at a garage sale last summer for $4 which included a timing light and a remote starter switch. As for burnout maybe the compressor doesn't have to run at full power. Perhaps a light dimmer switch could be used to set it at the speed needed to maintain the vacuum for the particular application. Or 2-3 compressors could be hooked up together and run at lower power off the same dimmer switch. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
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The problem is lubrication. Refrigerators circulate oil with the
refrigerant to keep the compressor lubricated. When you use it as a vacuum pump there is no oil. You can extend the life a little by squirting a little WD40 in the intake before each session but that is of limited value when the compressor runs 4 or 5 hours at a time. I suspect that the older compressors last longer because they are built "looser". As refrigerators got more energy efficient the compressors have been built to closer and closer tolerances so constant lubrication became more critical. I made a high vacuum system back in science fair days out of an old pre-WWII Kenvinator compressor and used it for several projects. When I started doing woodwork I used it to bag veneers for several years. When it finally died I tried several newer compressors but none lasted more than a couple of sessions. They would run for 10 or 15 minutes and then the thermal switch would kick them off. Ruined a lot of expensive veneer trying to figure a way to keep them running. There are at least 50 vacuum pumps on eBay right now that would be ideal for vacuum bagging. All under $100 and many under $50. Not a bad price considering that if a refrigerator compressor craps out in the middle of a session you could ruin that much material or more. Here are a few that would work. http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=11 773 http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=26 236 http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=26 236 http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=46 547 http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=46 548 Here is a perfect setup complete with flow guages and tank: http://cgi.ebay.com/ws/eBayISAPI.dll...ategory=73 21 William R. Watt wrote: From what GA wrote it would be better to look for an older unit than a later one as I assumed. It could be tested with a car vacuum guage. A vaccum guage costs about $15 at Canadian Tire. I found one at a garage sale last summer for $4 which included a timing light and a remote starter switch. As for burnout maybe the compressor doesn't have to run at full power. Perhaps a light dimmer switch could be used to set it at the speed needed to maintain the vacuum for the particular application. Or 2-3 compressors could be hooked up together and run at lower power off the same dimmer switch. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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The other problem is cooling. The freon and oil charge carry heat away
from the compressor which is probably why Glenn's tripped the thermal switch. Before I got a "real" vacuum pump I used refrigeration compressors successfully by cooling with a fan and constantly lubricating thru a bleeder on the vacuum side with one of those air line oilers made for lubing air tools. WD40 is not a very good lubricant for this, I used light oil and sometimes even thinned motor oil with kerosine. I also had an old airbrake compressor off a bus that I drove with a 1 hp electric motor. I spite of the physics, I believe I could have pulled 25 psi with it (maybe thru a worm hole from Jupiter). On the output side she would put out 300 psi. All of this was back when vacuum pumps were a lot more than $50 on Ebay. Regards, Ron PS. Fred, re-read my earlier post please. You will find it was not directed at Glenn. |
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Ron Thornton ) writes:
... I spite of the physics, I believe I could have pulled 25 psi with it (maybe thru a worm hole from Jupiter). On the output side she would put out 300 psi. All of this was back when vacuum pumps were a lot more than $50 on Ebay. another PSI supporter, "Pressure Scale Inches" (of mercury). -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
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William R. Watt wrote: Ron Thornton ) writes: ... I spite of the physics, I believe I could have pulled 25 psi with it (maybe thru a worm hole from Jupiter). On the output side she would put out 300 psi. All of this was back when vacuum pumps were a lot more than $50 on Ebay. another PSI supporter, "Pressure Scale Inches" (of mercury). Oh, NO! Not another measure! We have enough already! ;-) -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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"Glenn Ashmore" wrote in message news:rr0lb.80765$sp2.32669@lakeread04... Oh, NO! Not another measure! We have enough already! ;-) Yes, but how many barnyard atmospheres would that be? (both are recognized as official measurements) |
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"Ron Thornton" wrote in message
... I spite of the physics, I believe I could have pulled 25 psi with it (maybe thru a worm hole from Jupiter). no ron, you couldn't pull 25psi with it, no matter what you believe. the amount it put out on the high pressure side won't help you there. hugh p.s. having worked on a bunch of different projects over the years i'm surprised to see people going to so much trouble trying to make - as they say - a silk purse out of a sow's ear. experience has told me many times (and keeps doing so whenever i try to cheat it) that the cheapest way of doing something is to buy the right equipment for the job rather than trying to "make do" with something else. as glenn already said, it's also a good way to ruin a lot of expensive materials. |
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Glenn Ashmore wrote:
The problem is lubrication. Refrigerators circulate oil with the refrigerant to keep the compressor lubricated. When you use it as a vacuum pump there is no oil. You can extend the life a little by squirting a little WD40 in the intake before each session but that is of limited value when the compressor runs 4 or 5 hours at a time. If you're using WD-40 as a lubricant, that's a major part of the problem. WD-40 is a good water-displacer, but its performance as a lubricant is abysmal. From perusing the sites for DIY vacuum systems, it appears that the preferred lubricant for refrigeration pumps is ATF (automatic transmission fluid). All things considered, $50 or so for a Gast vacuum pump on Ebay seems like a better way to go. -- Regards Brian |
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Check out Harbor Freight. They sell a vacuum pump driven off
an air compressor for about $10. It is probably listed on the web site as an automotive A/C part. I was in one of their stores, it is packaged as an A/C evacuation pump. John "William R. Watt" wrote in message ... William R. Watt ) writes: claims he got 25 psi vacuum for his right. change "psi" to "lb". -- ---------------------------------------------------------- -------------------- William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
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Those will work on a small bag for a few short sessions but they are
hard on a small air compressor when you need to hold a vacuum for several hours. You would need to add a resin trap, tank, check valve, solenoid and vacuum switch to save the compressor. jcassara wrote: Check out Harbor Freight. They sell a vacuum pump driven off an air compressor for about $10. It is probably listed on the web site as an automotive A/C part. I was in one of their stores, it is packaged as an A/C evacuation pump. John "William R. Watt" wrote in message ... William R. Watt ) writes: claims he got 25 psi vacuum for his right. change "psi" to "lb". -- ---------------------------------------------------------- -------------------- William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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"Matt/Meribeth Pedersen" ) writes:
"Glenn Ashmore" wrote in message news:rr0lb.80765$sp2.32669@lakeread04... Oh, NO! Not another measure! We have enough already! ;-) Yes, but how many barnyard atmospheres would that be? (both are recognized as official measurements) the barnyard atmosphere on my grandfather's farm was usually pretty high due to a combination of barnyard manure and barnyard language -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
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The motors of most shop vacuums are cooled by the air that flows through the vacuum parts. If there's no
flow of air through the hose, there's none through the motor and the motors burn out quickly. A very few shop vacuums (Fein and ?) have 'bypass' fans which cool the motor even if there's no flow through the hose. Ed Askew wrote: I just use 2 shop vacuums. Actually, one is a vacuum cleaner for cleaning out pellet stoves. I've done small things with just one regular shop vac I bought at Wal-Mart. The thing is to get a good seal from your bag. You need lots of duct tape. Ed. (William R. Watt) wrote in message ... There is a website describing how to use a discarded 'fridge compressor for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. I do not have the website address. I was browsing on a computer at the public library at the time and did not write it down. However you can find it by going to www.boat-links.com, clicking on "The Mother of All Boat Links", clicking on the first box "amateur boatbuildign and repair" and scrolling down untill you find the link about vacuum bagging. Nowadays all discarded 'fridges go to a recyling depot where they "vacuum bag" the freon gas to protect the ozone layer of the atmosphere. It should be easy to get a compressor by telephoning the miniciapl garbage department. Since compressors do wear out it would be a good idea to look for ones off later model 'fridges (the date of manufacure should be on a label on the 'fridge) bring home 2 or 3 to try. |
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On Mon, 20 Oct 2003 07:57:08 -0400, Glenn Ashmore
wrote: If you can find an old, and I mean REALLY old, compressor with single intake and output ports and maybe cooling fins it will last an acceptable time but anything built after they changed from latches to magnetic sealing strips will crap out very quickly. William R. Watt wrote: Maybe he means 25 inches of vacuum, now is it inches of water or mercury (big difference between the two)? Since atmospheric pressure at sea level is 14.7 psi there is know way he is pulling 25 psi vacuum unless he has it in a tank pressurized to 10 psi above atmospheric. JJ There is a website describing how to use a discarded 'fridge compressor for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. I do not have the website address. I was browsing on a computer at the public library at the time and did not write it down. However you can find it by going to www.boat-links.com, clicking on "The Mother of All Boat Links", clicking on the first box "amateur boatbuildign and repair" and scrolling down untill you find the link about vacuum bagging. Nowadays all discarded 'fridges go to a recyling depot where they "vacuum bag" the freon gas to protect the ozone layer of the atmosphere. It should be easy to get a compressor by telephoning the miniciapl garbage department. Since compressors do wear out it would be a good idea to look for ones off later model 'fridges (the date of manufacure should be on a label on the 'fridge) bring home 2 or 3 to try. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned James Johnson remove the "dot" from after sail in email address to reply |
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I've done it several times, and so have a lot of other guys. Mine
don't overheat. They're not even all that warm. I worried about that the first couple of times I did it. (I've used 2 different vacuum cleaners.) I've never heard of anyone's overheating while vacuum bagging. There's quite of bit of air moving out of the vacuum cleaner exhaust while they're on. I leave them on about 6 hours. Some guys leave them on all night. How are people vacuum bagging without using vacuum cleaners? Ed. Jim Conlin wrote in message ... The motors of most shop vacuums are cooled by the air that flows through the vacuum parts. If there's no flow of air through the hose, there's none through the motor and the motors burn out quickly. A very few shop vacuums (Fein and ?) have 'bypass' fans which cool the motor even if there's no flow through the hose. Ed Askew wrote: I just use 2 shop vacuums. Actually, one is a vacuum cleaner for cleaning out pellet stoves. I've done small things with just one regular shop vac I bought at Wal-Mart. The thing is to get a good seal from your bag. You need lots of duct tape. Ed. (William R. Watt) wrote in message ... There is a website describing how to use a discarded 'fridge compressor for vacuum bagging. The fellow who tried it used a vaccum gauge from an automobile in his configuration and claims he got 25 psi vacuum for his project. He just used standard plumbing fittings to connect the vacuum bag. I do not have the website address. I was browsing on a computer at the public library at the time and did not write it down. However you can find it by going to www.boat-links.com, clicking on "The Mother of All Boat Links", clicking on the first box "amateur boatbuildign and repair" and scrolling down untill you find the link about vacuum bagging. Nowadays all discarded 'fridges go to a recyling depot where they "vacuum bag" the freon gas to protect the ozone layer of the atmosphere. It should be easy to get a compressor by telephoning the miniciapl garbage department. Since compressors do wear out it would be a good idea to look for ones off later model 'fridges (the date of manufacure should be on a label on the 'fridge) bring home 2 or 3 to try. |
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What are you using for a bag? Sounds like you don't have a very good
seal. There should be no air if the bag is sealed properly. Ed Askew wrote: I've done it several times, and so have a lot of other guys. Mine don't overheat. They're not even all that warm. I worried about that the first couple of times I did it. (I've used 2 different vacuum cleaners.) I've never heard of anyone's overheating while vacuum bagging. There's quite of bit of air moving out of the vacuum cleaner exhaust while they're on. I leave them on about 6 hours. Some guys leave them on all night. How are people vacuum bagging without using vacuum cleaners? Ed. Jim Conlin wrote in message ... The motors of most shop vacuums are cooled by the air that flows through the vacuum parts. If there's no flow of air through the hose, there's none through the motor and the motors burn out quickly. A very few shop vacuums (Fein and ?) have 'bypass' fans which cool the motor even if there's no flow through the hose. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
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James Johnson ) writes:
Maybe he means 25 inches of vacuum, now is it inches of water or mercury (big difference between the two)? Since atmospheric pressure at sea level is 14.7 psi there is know way he is pulling 25 psi vacuum unless he has it in a tank pressurized to 10 psi above atmospheric. yes, that would 25 inches of mercury. that is what is measured by the car engine vacuum guage. if you car engine vacuum guage is 14.7 you have some expensive engine work in your immediate future. still the vacuum on the suction side of a vacuum pump is not limited by atmospheric pressure, even when connected to a vacuum bag set up for resin curing. all it means is the pump is creating a vacuum greater than atmospheric pressure and could be run at a lower speed. imagine a vacuum pump strong enough to suck the resin, hull, and all right into the pump. can't do that at atmopheric prssure. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-freenet email must have "notspam" in subject or it's returned |
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William R. Watt wrote: still the vacuum on the suction side of a vacuum pump is not limited by atmospheric pressure, even when connected to a vacuum bag set up for resin curing. all it means is the pump is creating a vacuum greater than atmospheric pressure and could be run at a lower speed. imagine a vacuum pump strong enough to suck the resin, hull, and all right into the pump. can't do that at atmopheric prssure. That is why a lot of carbon spars are vacuum bagged inside a pressureized and heated autoclave. Supprising how much you can squish a carbon fiber layup at 100 psi. :-) -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
cheap vacuum bagging
William R. Watt wrote:
still the vacuum on the suction side of a vacuum pump is not limited by atmospheric pressure, even when connected to a vacuum bag set up for resin curing. Well, actually it *is* limited by atmospheric pressure unless you have the bag in a pressurized environment. Evacuate the bag to 0 psia/bara/mm hg/pa/torr/microns (whatever absolute units you want to use) and the pressure differential between the bag interior and exterior is simply the ambient pressure. In open air, that's atmospheric pressure. all it means is the pump is creating a vacuum greater than atmospheric pressure and could be run at a lower speed. imagine a vacuum pump strong enough to suck the resin, hull, and all right into the pump. Imagine is all you *can* do unless you find an alternate motive force besides the atmospheric pressure. Sans such motive force (e.g. pressurized chamber), 14.7 psia is all you have to work with, on a good day (well, you *do* have bag mass and acceleration due to gravity, but that works for you on the top side, and against you on the "bottom" side). can't do that at atmopheric prssure. Exactly. Keith Hughes |
cheap vacuum bagging
"William R. Watt" wrote: James Johnson ) writes: Maybe he means 25 inches of vacuum, now is it inches of water or mercury (big difference between the two)? Since atmospheric pressure at sea level is 14.7 psi there is know way he is pulling 25 psi vacuum unless he has it in a tank pressurized to 10 psi above atmospheric. yes, that would 25 inches of mercury. that is what is measured by the car engine vacuum guage. if you car engine vacuum guage is 14.7 you have some expensive engine work in your immediate future. still the vacuum on the suction side of a vacuum pump is not limited by atmospheric pressure, even when connected to a vacuum bag set up for resin curing. all it means is the pump is creating a vacuum greater than atmospheric pressure and could be run at a lower speed. imagine a vacuum pump strong enough to suck the resin, hull, and all right into the pump. can't do that at atmopheric prssure. William R Watt Can't do that with even a perfect vacuum. All you get is one atmosphere of 'suction', which cannot ever actually exist in a pneumatic system. Now, an hydraulic system, where the pump evacuates a liquid, can pull harder than an air pump, up to the point where the liquid boils, providing there is not one tiny bit of gas in the system, which would cause the vacuum 'suction' to max out at less than one atmosphere. No such system is possible. In a mercury tube barometer, a little dissolved gas released by the vacuum from it's imprisonment as a solute in the mercury, if there is any fills the 31" space at the top of the tube at some low pressure, low enough that the barometeric pressure outside the tube presses hard enough to suspend the mercury. So, pressure forming is used in applications where more than one atmosphere of 'squish' is required. Explosive pressure forming can provide hundreds of atmospheres of 'squish.' -- Terry K - My email address is MY PROPERTY, and is protected by copyright legislation. Permission to reproduce it is specifically denied for mass mailing and unrequested solicitations. Reproduction or conveyance for any unauthorised purpose is THEFT and PLAGIARISM. Abuse is Invasion of privacy and harassment. Abusers may be prosecuted. -This notice footer released to public domain. Spamspoof salad by spamchock - SofDevCo |
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