OT Vacuum pump maintenance / repair

the following:


Right, imaginative in a pushy way, just like steampunk. ;)

http://en.wikipedia.org/wiki/List_of_photo_sharing_websites
I hope you have lots of pics of that one. I'd love to see it.

Cool. Have someone _else_ post pics (both of the building and of your charred body) after the next cumulonimbic display day, OK?
-- The great thing about getting older is that you don't lose all the other ages you've been. -- Madeleine L'Engle
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On Wed, 19 May 2010 06:29:31 -0700, Larry Jaques

Thanks
I'll get some shots this weekend; it can't rain forever, can it?

OK, both you and Mike (Michael?) have posted rather dire commentary about the lack of grounding on metal roofs. That has made me wonder if there are any real guidelines for such. Metal roofs (here I'm referring to galvanized steel types, from standing-seam to v-crimp and the more modern variations, applied to wood-frame structures) have been around for at least a century. I question that they would be more prone to attracting strikes than any other roof covering, but I readily admit that I've not looked very deeply into the issue.
Bonding and grounding would be a significant and problematic matter, though. The burst of current from a lightning strike would require an assload of bonding points, as I doubt that the roof itself would be sufficient to drain away all the juice from the point of the discharge to a single cable (no matter how thick the cable might be). Another problem with most lightning rod schemes is that ground (soil) conductivity is not always good enough to conduct the full current of the discharge from any single point, so there is a lot of ancillary discharge through all sorts of unplanned pathways (viz, lots of your house structure). A direct strike on any house would necessitate a distributed grounding "grid" to carry away the current before it could do real damage. That's a lot more bucks than most people are willing to spend.
The military used to (still does?) protect sensitive areas, such as ammo dumps, by erecting a tall, well-grounded tower nearby. There is a cone of protection (don't remember the angle) that extends around such a structure.
There is also the matter of whether it is best to ground a high point on a house if there are other tall objects nearby. "Well, I was going to go to that tree, but the spike on the top of that house looks so much more attractive to me; I think I'll hit it" (Apologies for anthropomorphizing an electrical discharge.)
Anyway, I'd like to hear thoughts on the matter of grounding a metal roof (on a wood frame building) as opposed to treatment of other types of roofing material. Lightning protection is a very interesting, complex, and poorly understood subject. Maybe a separate thread?
Joe
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[snip]

Metal roofs are no more a problem than metal plumbing, like the drain stack vent that must protrude above the roof ridgeline. Or a TV antenna attached to the chimney.

The top of the tower is called an air terminal. Tall thin metal poles are often used. Such poles are usually seen in electric power switchyards in substations.
The half-angle of the cone is 45 degrees. In other words, the protection footprint is a circle on the ground of radius equal to the tower height.

All of this is well understood. There is a MIL Standard (I don't recall the number, but it's publicly available) that is widely used for figuring out how best to protect structures from lightning.
Joe Gwinn
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I think it is Mil-hdbk- 419a that you can't remember . I also think they revised the method used to calculate the lightning protection from a grounded pole.
Dan
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The cheap Delavel-type compressed air powered pumps easily pull 29". HF has one for $10 or so. JR Dweller in the cellar
On Tue, 11 May 2010 07:53:34 -0700 (PDT), snipped-for-privacy@c3net.net wrote:

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The better pumps will turn liquid water into vapor, and draw the vapor out. A dry system is essential to running properly.
The HF air thing is better than no vacuum, but not any where near as good as a real vacuum pump.
--
Christopher A. Young
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Thank you all.
To the poster that mentioned the air compressor veturi type of vac gage - I used one of those a few years ago when I serviced the A/C on my wife's car. A poorly positioned clip chaffed thru a tube on the condensor. I found that the pump effectiveness was very dependant on ambient (or engine compartment temp). If I ran the engine to temp and then used the venturi vac pump, I could hear as moisture droplets were pulled out (I had replaced the filter along with the condensor). I never felt confident that I pulled adequate vacuum (never saw 29 in of Hg on the gage), but after 2 seasons, the A/C is still functioning well in her Saturn.
So what is considered an inexpensive micron / thermistor vacuum gage? After a quick search most of these gages run between $200 to $450. These would appear to be gages for daily professional use. I found one gage for $137 http://www.testersandtools.com/Robinair-14010A-Thermistor-Vacuum-Gauge.php?page=product&Department 5&Category=7&product=QVT-2008051214350087963. I expect to use this equipment once every 2 to 3 years.
Are there lower cost gages out there? I am a bit leary of a used gage - concered about a used gage calibration / function. Would a dedicated vacuum gage such as this: http://www.valuetesters.com/Yellow-Jacket-69044-Vacuum-Gauge.php be better than relying on the manifold gage? If so, I would need to plumb it into the R134 manifold or connect it to my old R12/R22 manifold gage set and connect that to the other port on the A/C system during drawn down. With all the money that I will be spending on A/C parts, I do not have a lot of money left over for additional tools.
FWIW, my '91 F150 has suffered "black death". This Saturday I am going to play around with flushing the Condenser and Evap (presuming that I can get the broken off orifice tube out of the evaporator - was using an orifice removal tool and the end broke off anyway) but realistically I anticipate replacing condensor, evaporator and suction/ pressure hose (with integral muffler) along with the accumultor and compressor; so I would be pulling a vacuum on virtually a new A/C circuit.
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snipped-for-privacy@c3net.net fired this volley in

I got the Robinaire model you cited for $97 from Network Tool Warehouse -- http://www.ntxtools.com . They frequently have really hot deals on refrigeration equipment. Apparently, they buy new stuff from factories, but also do large buys from distress sales, and offer the materials at pretty spectacular prices.
LLoyd
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On May 12, 10:29am, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

Right now the least expensive micron/thermistor gage at Network Tool Warehouse is $157. I'm thinking that I'll have to take the risk and do without (doing a long evacuation and changing the vac pump oil once during the process), knowing that the accumulator/dryer will be new. Thanks for the link - I did order an inexpensive flush gun, a few extra qts of vacuum pump oil and a 134A fitting for my vac pump.
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On May 12, 7:21am, snipped-for-privacy@c3net.net wrote:

Don't overlook a U-Pullit joint as a source of used parts. I've gotten a lot of A/C related parts for cheap, whole compressors for $7 when all I needed was clutch parts, clips, clamps and other hardware. If you like living dangerously, you can salvage condensors and evaporators and flush those instead of your original contaminated parts. Very, very cheap compared with the cost of new. Also you can learn how-to on wrecks instead of messing up on your own stuff. I've rebuilt the compressors with new gaskets and seals and come out way ahead.
Stan
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