In a message dated 10/7/2007 11:13:11 P.M. Eastern Daylight Time,
atlasyts@bellsouth.net writes:
Maybe this is one of those things that isn't terribly obvious,
> but -
> having used a variety of screw type clamps - I'm
wondering why
> plain old spring clamps aren't suitable for this
application. I can't
> ever remember having one fail in
service. (photos below)
>
> Dale R.
> COZY MkIV
#0497
> Ch.12; Ch's 13, 16, 19 & 23 in-progress
One of my jobs for uncle sugar was to evaluate price overcharging and
cost cutting suggestions. Since award money and free time off was involved, I
was supposed to be deadly accurate, soothing, diplomatic, generous and
answer all submissions within hours.
No problem, I developed a collection of boiler plate paragraphs, and
some whole responses that were used when hundreds of people would see the same
thing and write in about that.
I once did a special on hose clamps, because so many people complained
about the ordinary looking worm screw style clamp found in any hardware and
home store. The main cause was Taiwan and Chinese built replicants that
were flooding the auto parts stores.
The are a number of methods used in controlling the quality of products
used by the military.
We have MS or Military Standard drawings, that depict the item to the
extent desired by the producer of the drawing. The minimum required features
sizes and materials to be used in construction and in some cases colors may be
called out. Sizes will be in accordance with the normal system of adding up
whole sizes in 1/16" the same as AN hose fittings. A dash 16 would be one inch
(16 1/16"ths) one half inch is (8 1/16"ths)
and so on. There may or may not be a performance listed, such as
holding power, or maximum torque.........
Normally this is describing a good quality clamp in common service on
production equipment, suitable for a wide range of applications and produced by
a number of US and NATO companies. No in process inspections or visits by
Government inspectors are required. No Mil-I-45208 called out.
These are the ones least likely to get me any action, because these are
consumed by the Government by the thousands each month and is a good bread and
butter product for the manufacturers. Costs average
about $0.20 each.
At the other end of the scale is the NAS or National Aerospace standard
worm clamp. Done to drawings as above but with a MIL-I-45208 or later quality
control system requirement with the additional requirement that
sources of supply for materials are called out. Samples of production
lots are tested to destruction, in the presence of a Government inspector.
Samples of each lot are kept on hand by the manufacturer for a specified length
of time up to 40 years. Torques required to produce a specified clamping power
may be called out. Drawings for each component site additional requirements.
Safety wire features on the worm hex are required. This is one spicy clamp and
no doubt, many have found their way onto a Chevy in the parking lot behind the
barracks. Low buy quantities and a small number of manufacturers interested in
bidding, make prices in the $3.00 to $4.00 area normal. This is a big
source of complaints.
The best clamps are used on submarines, and may look the same as above
with all of those features and the addition of a material traceable to the ore
where the material was mined, and a number of requirements for record keeping. I
forgot the MIL for Mercury Free, but it involves the certified absence of
mercury from production facilities, tooling , mining, transport and
packaging. There may be a serialization identification with NSN/Cage
Code and date of manufacture in the marking spec. This clamp comes with a
box of paper work that has its pedigree. Some of its brothers are never used but
stored for the life of the boat as evidence of quality. The cost of one of
these clamps is astounding, and I had no access to the data or sources
involved
but it was a US company. These I had to send on the Navy
for resolution.
A fire involving even a tiny amount of mercury produces a gas that can
reduce your IQ to a dismal number in a few hours. Imagine 100 10 year olds with
a 500 megaton capability.
If a worm style Name brand clamp junction comes off, it's because
you didn't tighten it. Generally you can tighten one until it cuts the end off
of the hose. You can drill the worm hex for safety wire on your own.
You can lubricate the worm and the thrust flange on the worm before
tightening. You loop a short piece of wire under the clamp prior to tightening.
Then one end goes through the wire hole and twist. There should never be a
failure at a properly designed hose clamped junction.
Spring clams? Shame on you.
Lynn E. Hanover