When using my Kobalt CMS, I notice a large spark from the motor compartment
when I turn off the saw. Sometimes it looks like it fills the whole
compartment. Is this a sign the brushes need replaced?

Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
rec.woodworking

To email me directly, send a message to puckdropper (at) fastmail.fm

"Puckdropper" wrote:

When using my Kobalt CMS, I notice a large spark from the motor
compartment
when I turn off the saw. Sometimes it looks like it fills the whole
compartment. Is this a sign the brushes need replaced?

Good place to start.

Might not be seated properly.

Lew

"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
When using my Kobalt CMS, I notice a large spark from the motor
compartment
when I turn off the saw. Sometimes it looks like it fills the whole
compartment. Is this a sign the brushes need replaced?

Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
rec.woodworking

To email me directly, send a message to puckdropper (at) fastmail.fm


Sounds like a normal condition when an electronic brake in engaged.

Read your owner's manual. Is this a saw with electric brake?

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
When using my Kobalt CMS, I notice a large spark from the motor
compartment
when I turn off the saw. Sometimes it looks like it fills the
whole
compartment. Is this a sign the brushes need replaced?

Puckdropper
--
"The potential difference between the top and bottom of a tree
is the
reason why all trees have to be grounded..." -- Bored Borg on
rec.woodworking

To email me directly, send a message to puckdropper (at)
fastmail.fm

"DanG" wrote in news:5opvm.443888$Ta5.188839
@newsfe15.iad:

Read your owner's manual. Is this a saw with electric brake?


The saw indeed has an electronic brake. If that's normal behavior, I'll
let it be.

Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
rec.woodworking

To email me directly, send a message to puckdropper (at) fastmail.fm

"Lew Hodgett" wrote in news:001c03e2$0$24199
:


"Puckdropper" wrote:

When using my Kobalt CMS, I notice a large spark from the motor
compartment
when I turn off the saw. Sometimes it looks like it fills the whole
compartment. Is this a sign the brushes need replaced?

Good place to start.

Might not be seated properly.

Lew


I took the brushes out, blew out the sawdust in the brush chambers and
put them back. The big spark is gone, and I think I picked up a little
missing speed.

I'll have to add that to the occasional maintenance list. It only takes
about 2 minutes.

Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
rec.woodworking

To email me directly, send a message to puckdropper (at) fastmail.fm

Electric brake shorts out the motor winding and it generates
current in the winding in reverse - generating voltage - and sparks
if the brushes are not smooth on. The short isn't hard, but soft
through a low resistance value.

Good find.
Martin

Leon wrote:
"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
When using my Kobalt CMS, I notice a large spark from the motor
compartment
when I turn off the saw. Sometimes it looks like it fills the whole
compartment. Is this a sign the brushes need replaced?

Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
rec.woodworking

To email me directly, send a message to puckdropper (at) fastmail.fm


Sounds like a normal condition when an electronic brake in engaged.

"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
"Lew Hodgett" wrote in news:001c03e2$0$24199
:



I took the brushes out, blew out the sawdust in the brush chambers and
put them back. The big spark is gone, and I think I picked up a little
missing speed.

I'll have to add that to the occasional maintenance list. It only takes
about 2 minutes.


I suspect that the fix will be short lived. I think you are trying to fix a
normal condition.

Leon wrote:
"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
"Lew Hodgett" wrote in news:001c03e2$0$24199
:

I took the brushes out, blew out the sawdust in the brush chambers and
put them back. The big spark is gone, and I think I picked up a little
missing speed.

I'll have to add that to the occasional maintenance list. It only takes
about 2 minutes.


I suspect that the fix will be short lived. I think you are trying to fix a
normal condition.


Sometimes my old Skil looks like one of those 4th of July sparklers
inside the case.
I don't know if it's normal or healthy... I just know I won't use it
around open cans lacquer or paint thinner. :-)


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

"-MIKE-" wrote in message
...


Sometimes my old Skil looks like one of those 4th of July sparklers inside
the case.
I don't know if it's normal or healthy... I just know I won't use it
around open cans lacquer or paint thinner. :-)


You would probably do well to not use any thing that sparks around flamable
vapors.
I am still in wonderment having retired from the automotive industry how GM
prevented gas tank explosions. They used submerged electric fuel pumps and
the gasoline literally went through the motor and brushes. No, gas tanks do
not always have gasoline in them so being constantly submerged is not the
answer.

Leon wrote:
"-MIKE-" wrote in message
...
Sometimes my old Skil looks like one of those 4th of July sparklers inside
the case.
I don't know if it's normal or healthy... I just know I won't use it
around open cans lacquer or paint thinner. :-)


You would probably do well to not use any thing that sparks around flamable
vapors.
I am still in wonderment having retired from the automotive industry how GM
prevented gas tank explosions. They used submerged electric fuel pumps and
the gasoline literally went through the motor and brushes. No, gas tanks do
not always have gasoline in them so being constantly submerged is not the
answer.


I'm guessing the pump was low enough as to always be submerged, even
when the tank was "empty?"

Reminds me of the Mythbusters episode in which they *could not* get a
gasoline trail to ignite with a burning cigarette, like you see in the
movies.
Apparently, smoldering tobacco embers are not hot enough to ignite
gasoline vapors.

Another interesting fact from my electrical engineer friend who works
for a huge electric producer...
Those giant electric turbine generators are cooled with direct water
immersion. Turns out pure H2O doesn't conduct electricity. It's all the
minerals and other stuff in water that does.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

On Sun, 27 Sep 2009 13:46:09 -0500, -MIKE-
wrote:

Leon wrote:
"-MIKE-" wrote in message
...
Sometimes my old Skil looks like one of those 4th of July sparklers inside
the case.
I don't know if it's normal or healthy... I just know I won't use it
around open cans lacquer or paint thinner. :-)


You would probably do well to not use any thing that sparks around flamable
vapors.
I am still in wonderment having retired from the automotive industry how GM
prevented gas tank explosions. They used submerged electric fuel pumps and
the gasoline literally went through the motor and brushes. No, gas tanks do
not always have gasoline in them so being constantly submerged is not the
answer.


I'm guessing the pump was low enough as to always be submerged, even
when the tank was "empty?"

Even when the tank is "empty" it's not empty. It's full of gasoline
fumes, which without air (oxygen) aren't dangerous at all. ...and
there isn't any air in there either.

Liquid-fueled rocket and jet engines commonly use the fuel and
oxidizer as a coolant.

Reminds me of the Mythbusters episode in which they *could not* get a
gasoline trail to ignite with a burning cigarette, like you see in the
movies.
Apparently, smoldering tobacco embers are not hot enough to ignite
gasoline vapors.

Another interesting fact from my electrical engineer friend who works
for a huge electric producer...
Those giant electric turbine generators are cooled with direct water
immersion. Turns out pure H2O doesn't conduct electricity. It's all the
minerals and other stuff in water that does.

The water going through turbines is hardly pure. I doubt water
touches the generator windings themselves.

"-MIKE-" wrote in message
...


No, gas tanks do
not always have gasoline in them so being constantly submerged is not the
answer.

I'm guessing the pump was low enough as to always be submerged, even when
the tank was "empty?"

Nope, mentioned that above, of millions each year built this way there had
to be a few thousand that went with out caps and the gas evaporated.



Reminds me of the Mythbusters episode in which they *could not* get a
gasoline trail to ignite with a burning cigarette, like you see in the
movies.
Apparently, smoldering tobacco embers are not hot enough to ignite
gasoline vapors.

Another interesting fact from my electrical engineer friend who works
for a huge electric producer...
Those giant electric turbine generators are cooled with direct water
immersion. Turns out pure H2O doesn't conduct electricity. It's all the
minerals and other stuff in water that does.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

krw wrote:
Another interesting fact from my electrical engineer friend who works
for a huge electric producer...
Those giant electric turbine generators are cooled with direct water
immersion. Turns out pure H2O doesn't conduct electricity. It's all the
minerals and other stuff in water that does.

The water going through turbines is hardly pure. I doubt water
touches the generator windings themselves.

I'm not talking about the water running through the tubes from a dam,
that spin the turbines.
He was specifically referring to steam powered generators, btw.

And yes, he said they use pure H2O.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

Leon wrote:
"-MIKE-" wrote in message
...


No, gas tanks do
not always have gasoline in them so being constantly submerged is not the
answer.
I'm guessing the pump was low enough as to always be submerged, even when
the tank was "empty?"

Nope, mentioned that above, of millions each year built this way there had
to be a few thousand that went with out caps and the gas evaporated.


"Had to be?" Sounds pretty speculative. :-)


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

---remove "DOT" ^^^^ to reply

"krw" wrote in message
...
On Sun, 27 Sep 2009 13:46:09 -0500, -MIKE-
wrote:

Even when the tank is "empty" it's not empty. It's full of gasoline
fumes, which without air (oxygen) aren't dangerous at all. ...and
there isn't any air in there either.

Yeah, there is oxygen/air in there, every time you open the tank some gets
in. Besides, the tank would collapse if it were totally sealed, Air has to
displace the disappearing gasoline.



The water going through turbines is hardly pure. I doubt water
touches the generator windings themselves.


But gasolinr does on a Gm electric fuel pump. My fuel pump in on my 1975
Olds failed. I dropped the tank and replaced the pump, it is attached to
the tank unit/gas gauge float assembly. I cut it open and the thing was
spottless inside but the brushes were totally worn out. Gasoline went in
one end of the motor and exited on the other. On one end of the motor was
the plastic pump.

On Sun, 27 Sep 2009 16:25:49 -0500, "Leon"
wrote:


"krw" wrote in message
.. .
On Sun, 27 Sep 2009 13:46:09 -0500, -MIKE-
wrote:

Even when the tank is "empty" it's not empty. It's full of gasoline
fumes, which without air (oxygen) aren't dangerous at all. ...and
there isn't any air in there either.

Yeah, there is oxygen/air in there, every time you open the tank some gets
in. Besides, the tank would collapse if it were totally sealed, Air has to
displace the disappearing gasoline.

Nope. Not any more. The engine controls recycle fumes back to the
tank. Tanks have been sealed for decades.

The water going through turbines is hardly pure. I doubt water
touches the generator windings themselves.


But gasolinr does on a Gm electric fuel pump. My fuel pump in on my 1975
Olds failed. I dropped the tank and replaced the pump, it is attached to
the tank unit/gas gauge float assembly. I cut it open and the thing was
spottless inside but the brushes were totally worn out. Gasoline went in
one end of the motor and exited on the other. On one end of the motor was
the plastic pump.

Sure. No one was arguing that point. It's hardly dangerous.

On Sun, 27 Sep 2009 16:23:51 -0500, -MIKE-
wrote:

krw wrote:
Another interesting fact from my electrical engineer friend who works
for a huge electric producer...
Those giant electric turbine generators are cooled with direct water
immersion. Turns out pure H2O doesn't conduct electricity. It's all the
minerals and other stuff in water that does.

The water going through turbines is hardly pure. I doubt water
touches the generator windings themselves.

I'm not talking about the water running through the tubes from a dam,
that spin the turbines.
He was specifically referring to steam powered generators, btw.

I was thinking more about hydro-electric turbines, which are also
water cooled.

And yes, he said they use pure H2O.

Nothing is pure. ;-) In this case it has to be as close as possible
because of the process. If there were any impurities they would be
deposited in the "boiler". Not a good thing in a nuke, either. ;-)

"krw" wrote in message
...

Nope. Not any more. The engine controls recycle fumes back to the
tank. Tanks have been sealed for decades.

Yes the engine compartment does recycle fumes back to the tank but there is
a lot of AIR that goes with it. Additionally there are lots of peole
driving around with lost gas caps, check engine lights and all. And again,
the tank is not sealed when you open it up to fill it with gas. There is
just way too much of a chance of the perfect combination for the electric
motor to set off an explosion if there was not a fool proof way to arrest
the spark. How that is accomplished even the Olds factory rep could not
explain when I was the service sales manager back in the 80's.




But gasolinr does on a Gm electric fuel pump. My fuel pump in on my 1975
Olds failed. I dropped the tank and replaced the pump, it is attached to
the tank unit/gas gauge float assembly. I cut it open and the thing was
spottless inside but the brushes were totally worn out. Gasoline went in
one end of the motor and exited on the other. On one end of the motor was
the plastic pump.

Sure. No one was arguing that point. It's hardly dangerous.

Obviousely but the simple explanation has not yet been explained to me.

"-MIKE-" wrote in message
...
Leon wrote:
"-MIKE-" wrote in message
...


No, gas tanks do
not always have gasoline in them so being constantly submerged is not
the answer.
I'm guessing the pump was low enough as to always be submerged, even
when the tank was "empty?"

Nope, mentioned that above, of millions each year built this way there
had to be a few thousand that went with out caps and the gas evaporated.


"Had to be?" Sounds pretty speculative. :-)

I was in the automotive service business from 1972 to 1995. I saw it all.

On Sun, 27 Sep 2009 17:10:33 -0500, "Leon"
wrote:


"krw" wrote in message
.. .

Nope. Not any more. The engine controls recycle fumes back to the
tank. Tanks have been sealed for decades.

Yes the engine compartment does recycle fumes back to the tank but there is
a lot of AIR that goes with it. Additionally there are lots of peole
driving around with lost gas caps, check engine lights and all. And again,
the tank is not sealed when you open it up to fill it with gas. There is
just way too much of a chance of the perfect combination for the electric
motor to set off an explosion if there was not a fool proof way to arrest
the spark. How that is accomplished even the Olds factory rep could not
explain when I was the service sales manager back in the 80's.

Nonsense. There is no air in there at all, even without a gas cap the
vapor pressure of the gas will push any out.


But gasolinr does on a Gm electric fuel pump. My fuel pump in on my 1975
Olds failed. I dropped the tank and replaced the pump, it is attached to
the tank unit/gas gauge float assembly. I cut it open and the thing was
spottless inside but the brushes were totally worn out. Gasoline went in
one end of the motor and exited on the other. On one end of the motor was
the plastic pump.

Sure. No one was arguing that point. It's hardly dangerous.

Obviousely but the simple explanation has not yet been explained to me.

Explanation for what?

krw wrote:

The water going through turbines is hardly pure. I doubt water
touches the generator windings themselves.

I've toured the Robert Moses power generation station in Niagara Falls a
number of times. The turbines are at the bottom of the dam to take
advantage of the water's pressure. The generators are on the top floor
of the structure to facilitate installation/replacement. The two are
connected by a massive shafts. You're correct, the water (hopefully)
doen't come near the generators.

--
Jack Novak
Buffalo, NY - USA

Nova wrote:
krw wrote:

The water going through turbines is hardly pure. I doubt water
touches the generator windings themselves.

I've toured the Robert Moses power generation station in Niagara Falls a
number of times. The turbines are at the bottom of the dam to take
advantage of the water's pressure. The generators are on the top floor
of the structure to facilitate installation/replacement. The two are
connected by a massive shafts. You're correct, the water (hopefully)
doen't come near the generators.

Actually, large-capacity turbine-generators are typically H cooled to
enhance conductivity. One does not smoke in the vicinity...

http://www.gepower.com/prod_serv/products/generators/en/hydrogen_cool.htm

--

"Leon" wrote in
:


"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
"Lew Hodgett" wrote in news:001c03e2$0$24199
:



I took the brushes out, blew out the sawdust in the brush chambers
and put them back. The big spark is gone, and I think I picked up a
little missing speed.

I'll have to add that to the occasional maintenance list. It only
takes about 2 minutes.


I suspect that the fix will be short lived. I think you are trying to
fix a normal condition.

I'll keep an eye on it. I expect some sparks (nature of the beast), but
this was a rather large one that filled the motor chamber. Now it only
does it when I let go of the switch before it's come up to speed. (I'm
curious now. If it starts again I'll have to put an ammeter on there,
take a few readings, then clean the brushes.)

Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
rec.woodworking

To email me directly, send a message to puckdropper (at) fastmail.fm

"krw" wrote in message
...
On Sun, 27 Sep 2009 17:10:33 -0500, "Leon"
wrote:


"krw" wrote in message
. ..

Nope. Not any more. The engine controls recycle fumes back to the
tank. Tanks have been sealed for decades.

Yes the engine compartment does recycle fumes back to the tank but there
is
a lot of AIR that goes with it. Additionally there are lots of peole
driving around with lost gas caps, check engine lights and all. And
again,
the tank is not sealed when you open it up to fill it with gas. There is
just way too much of a chance of the perfect combination for the electric
motor to set off an explosion if there was not a fool proof way to arrest
the spark. How that is accomplished even the Olds factory rep could not
explain when I was the service sales manager back in the 80's.

Nonsense. There is no air in there at all, even without a gas cap the
vapor pressure of the gas will push any out.


Obviousely clueless.

"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
"Leon" wrote in
:


"Puckdropper" puckdropper(at)yahoo(dot)com wrote in message
...
"Lew Hodgett" wrote in news:001c03e2$0$24199
:



I

I'll keep an eye on it. I expect some sparks (nature of the beast), but
this was a rather large one that filled the motor chamber. Now it only
does it when I let go of the switch before it's come up to speed. (I'm
curious now. If it starts again I'll have to put an ammeter on there,
take a few readings, then clean the brushes.)


My Delta does it, at night with a not so well lit garage the motor becomes
pretty lit up when I release the switch.

Leon wrote:
"krw" wrote in message
...
....
... There is no air in there at all, even without a gas cap the
vapor pressure of the gas will push any out.

Obviousely clueless.

Not quite, no...not _exactly_ "none" wrt to air but the high vapor
pressure (very low flash point) of gasoline _is_ the key. To save
having to dig up the flammability and explosive mixture data, the most
cogent explanation I found on the web quickly was at a site discussing
the Flight 800 explosion that went on to compare the situation w/ jet A
and an airline tank and the fuel pump in automobile tank and gasoline.
From that site--

Cars contain fuel pumps and wiring inside the fuel tanks - why
don't they blow up more often?

Gasoline tank vapor spaces are almost never flammable while Jet A
tanks in airplanes will always pass through a flammable regime during
normal flight operations.

The ullage of gasoline fuel tanks in automobiles is almost always too
rich to be flammable except at very low temperatures. This is due to the
much lower flash point (about -40 C) of gasoline in comparison to Jet A.
The vapor space in a partially-filled gasoline tank does not become
flammable until the temperature has dropped below about 10F and a
serious hazard will exist below 0 F down to about -40 F for a typical
gasoline (Reid Vapor Pressure (RVP) of 9.5 psi, flammability limits
between 1.4 and 7 % by volume). [See W.F. Marshall and G. A. Schoonveld,
SAE Transactions, Vol. 99, No. 4, 594-617, 1990]

For this reason, the probability that a fuel tank containing liquid
gasoline has a flammable vapor space is extremely small in most climates
except in the artic regions. The exception to this is when the tank is
removed for servicing and the fuel is drained from the tank. Since
gasoline has such a high vapor pressure, the tank can have a flammable
vapor space even if there is no liquid fuel visible inside that tank.
For example, the complete vaporization of about 1-2 tablespoons of
gasoline will result in a flammable mixture inside a 15-gallon capacity
automobile tank. This is the reason why welding on or near "empty" gas
tanks is extremely hazardous and thorough purging of the tank with
steam, carbon dioxide, nitrogen, or other inert gas is required before
repair work is started.

The in-tank fuel pumps in modern fuel-injected vehicles are designed
to run submerged in fuel, as are the fuel pumps in aircraft, and the
fuel circulates through the pump, including the sparking
brush-commutator system. Unless the gasoline tank is almost
completely emptied of fuel, this will not pose a hazard since there
will be only fuel and not a fuel-air mixture within the pump. So in
order for an in-tank fuel pump to pose an ignition hazard, the tank
must be "run dry" under very cold conditions so that flammable vapor
surrounds the commutator.

In short, the answer is that the high vapor pressure of gasoline does
create an atmosphere that is too rich for explosion even when the tank
is uncapped if there is any liquid fuel at all in the tank at anything
above very cold ambient temperature.

I will agree it _is_ something of a mental twist that the very
volatility of gasoline is in fact the property that mitigates the fire
hazard suppressant from the fuel pump when the tank is low (although I
presume the pumps are mounted in a well or at least at the lowest point
in the tanks in order to keep them submerged until absolutely all fuel
that can be picked up has been. I suppose one could even raise the
inlet pipe a little to ensure that; don't know if they do or not.)

hth....

-dpb

--

"dpb" wrote in message
...
Snip


I will agree it _is_ something of a mental twist that the very volatility
of gasoline is in fact the property that mitigates the fire hazard
suppressant from the fuel pump when the tank is low (although I presume
the pumps are mounted in a well or at least at the lowest point in the
tanks in order to keep them submerged until absolutely all fuel that can
be picked up has been. I suppose one could even raise the inlet pipe a
little to ensure that; don't know if they do or not.)

hth....

-dpb


While the explanation is valid and works for 99.999% of the time my question
is about the other .0001 percent of the time. When the lost gas cap is
never replaced and the car is parked and sits for several months with little
fuel. Eventually some one cranks it up and the tank has little fuel to
submerge the pump.
And if you think that is not common, repositions of abandoned cars filled
the bill at the dealerships and many were often stripped.



Because the fuel pump is relatively tiny and totally enclosed, IIRC there
was a check ball valve on the inlet side, perhaps in some instances of a low
fuel condition there is an actual flash when the pump motor in energized,
but the flash is contained with in the motor casing. I do recall the motor
housing being rather substantial compared to most electric motors found on
automobiles.

Thanks for the time spent gathering the information.

Leon wrote:
"dpb" wrote in message
...
Snip

I will agree it _is_ something of a mental twist that the very volatility
of gasoline is in fact the property that mitigates the fire hazard
suppressant from the fuel pump when the tank is low (although I presume
the pumps are mounted in a well or at least at the lowest point in the
tanks in order to keep them submerged until absolutely all fuel that can
be picked up has been. I suppose one could even raise the inlet pipe a
little to ensure that; don't know if they do or not.)

hth....

-dpb


While the explanation is valid and works for 99.999% of the time my question
is about the other .0001 percent of the time. When the lost gas cap is
never replaced and the car is parked and sits for several months with little
fuel. Eventually some one cranks it up and the tank has little fuel to
submerge the pump.
And if you think that is not common, repositions of abandoned cars filled
the bill at the dealerships and many were often stripped.

While perhaps it is relatively common, it's still highly unlikely to be
a problem. If there's enough fuel to crank and start the engine,
there's enough to suppress the spark and have high enough vapor pressure
to prevent flammability at any temperature above about -10F. Remember
the flashpoint of gasoline is -40C (which iirc is the magic point where
-40C=-40F???).

About the only time above about 0F one could get a real problem would be
an essentially dry tank w/ residual vapor and run the pump dry. I'd
think that if vehicles were so poor condition as to be left w/ empty
tanks and no lid there would be little likelihood of them being cranked
in any near-term time frame. Hence the evaporation over a period of
time would likely imo serve to remove even the vapors.

--

dpb wrote:
....

While perhaps it is relatively common, it's still highly unlikely to be
a problem. If there's enough fuel to crank and start the engine,
there's enough to suppress the spark and have high enough vapor pressure
to prevent flammability at any temperature above about -10F. Remember
the flashpoint of gasoline is -40C (which iirc is the magic point where
-40C=-40F???).

About the only time above about 0F one could get a real problem would be
an essentially dry tank w/ residual vapor and run the pump dry. I'd
think that if vehicles were so poor condition as to be left w/ empty
tanks and no lid there would be little likelihood of them being cranked
in any near-term time frame. Hence the evaporation over a period of
time would likely imo serve to remove even the vapors.

And if your contention is that it is _possible_ under specific
circumstances and there's no failsafe protection against that very
dilute vapor case that is in the flammability region then yes, it is
possible.

I hadn't actively thought about the Arctic conditions increasing risk, I
don't know if there's anything done for the really cold areas out of the
ordinary or not. I'd guess not; rely on folks in inclement weather
areas having enough sense to keep adequate fuel on hand I'd guess.

--

"dpb" wrote in message
...

While perhaps it is relatively common, it's still highly unlikely to be a
problem. If there's enough fuel to crank and start the engine, there's
enough to suppress the spark and have high enough vapor pressure to
prevent flammability at any temperature above about -10F. Remember the
flashpoint of gasoline is -40C (which iirc is the magic point
where -40C=-40F???).

The problem is though people run out of gas, people run over things on the
highway, Houston Freeways, that bounce up and puncture the bottoms of the
tanks. Tanks commonly run dry with the pump running.





About the only time above about 0F one could get a real problem would be
an essentially dry tank w/ residual vapor and run the pump dry. I'd think
that if vehicles were so poor condition as to be left w/ empty tanks and
no lid there would be little likelihood of them being cranked in any
near-term time frame. Hence the evaporation over a period of time would
likely imo serve to remove even the vapors.

That is possible but GM has been using a fuel tank pump since the "early
70's I worked directly and exclusively with GM vehicles for 17 years and
never ever heard of a problem. And I am not in doubt that what works,
"works" effectively. I was and still am curious as to exactly what makes
the set up "fool proof".

On Sep 28, 8:38*am, "Leon" wrote:
"krw" wrote in message

...



On Sun, 27 Sep 2009 17:10:33 -0500, "Leon"
wrote:

"krw" wrote in message
. ..

Nope. Not any more. *The engine controls recycle fumes back to the
tank. *Tanks have been sealed for decades.

Yes the engine compartment does recycle fumes back to the tank but there
is
a lot of AIR that goes with it. *Additionally there are lots of peole
driving around with lost gas caps, check engine lights and all. * And
again,
the tank is not sealed *when you open it up to fill it with gas. *There is
just way too much of a chance of the perfect combination for the electric
motor to set off an explosion if there was not a fool proof way to arrest
the spark. *How that is accomplished even the Olds factory rep could not
explain when I was the service sales manager back in the 80's.

Nonsense. *There is no air in there at all, even without a gas cap the
vapor pressure of the gas will push any out.

Obviousely clueless.

Wrong again. Unlike you, I'm not guessing.

Leon wrote:
"dpb" wrote in message
...
While perhaps it is relatively common, it's still highly unlikely to be a
problem. If there's enough fuel to crank and start the engine, there's
enough to suppress the spark and have high enough vapor pressure to
prevent flammability at any temperature above about -10F. Remember the
flashpoint of gasoline is -40C (which iirc is the magic point
where -40C=-40F???).

The problem is though people run out of gas, people run over things on the
highway, Houston Freeways, that bounce up and puncture the bottoms of the
tanks. Tanks commonly run dry with the pump running.




About the only time above about 0F one could get a real problem would be
an essentially dry tank w/ residual vapor and run the pump dry. I'd think
that if vehicles were so poor condition as to be left w/ empty tanks and
no lid there would be little likelihood of them being cranked in any
near-term time frame. Hence the evaporation over a period of time would
likely imo serve to remove even the vapors.

That is possible but GM has been using a fuel tank pump since the "early
70's I worked directly and exclusively with GM vehicles for 17 years and
never ever heard of a problem. And I am not in doubt that what works,
"works" effectively. I was and still am curious as to exactly what makes
the set up "fool proof".

I don't think it is totally fool-proof except that the conditions for
flammability are much more limited than you think owing to the high
vapor pressure that does, as another poster noted, keep positive
pressure in the tank as long as there's any fuel surface at all.

And, I'd venture that most of the cases you're talking about there's
still a residual of fuel in the tank, only that it is below the pickup
level.

Added to that that the brushes are undoubtedly built to be non-arcing so
that there really isn't a continuous ignition source, the conditions
just aren't satisfied.

--

"dpb" wrote in message
...
Leon wrote:
"dpb" wrote in message
...
While perhaps it is relatively common, it's still highly unlikely to be
a problem. If there's enough fuel to crank and start the engine,
there's enough to suppress the spark and have high enough vapor pressure
to prevent flammability at any temperature above about -10F. Remember
the flashpoint of gasoline is -40C (which iirc is the magic point
where -40C=-40F???).

The problem is though people run out of gas, people run over things on
the highway, Houston Freeways, that bounce up and puncture the bottoms of
the tanks. Tanks commonly run dry with the pump running.




About the only time above about 0F one could get a real problem would be
an essentially dry tank w/ residual vapor and run the pump dry. I'd
think that if vehicles were so poor condition as to be left w/ empty
tanks and no lid there would be little likelihood of them being cranked
in any near-term time frame. Hence the evaporation over a period of
time would likely imo serve to remove even the vapors.

That is possible but GM has been using a fuel tank pump since the "early
70's I worked directly and exclusively with GM vehicles for 17 years
and never ever heard of a problem. And I am not in doubt that what
works, "works" effectively. I was and still am curious as to exactly
what makes the set up "fool proof".

I don't think it is totally fool-proof except that the conditions for
flammability are much more limited than you think owing to the high vapor
pressure that does, as another poster noted, keep positive pressure in the
tank as long as there's any fuel surface at all.

And, I'd venture that most of the cases you're talking about there's still
a residual of fuel in the tank, only that it is below the pickup level.

Added to that that the brushes are undoubtedly built to be non-arcing so
that there really isn't a continuous ignition source, the conditions just
aren't satisfied.

--

That makes sense to me.

According to a table I have, for 100 octane gasoline vapor, when mixed with
air, the explosive (flammable) range is from 1.4% to 7.6%. vapor/air
mixture, - a condition which, as you say, would rarely be met.

"dpb" wrote in message
...

I don't think it is totally fool-proof except that the conditions for
flammability are much more limited than you think owing to the high vapor
pressure that does, as another poster noted, keep positive pressure in the
tank as long as there's any fuel surface at all.


Ok you and he are both missing the point. I realize that the with and
absence of air the possibility of an explosion is nil. I am specifically
looking at the situation where there is air present, ie. a rupture in the
tank where air absolutely will displace the gasoline that is leaking out.
We saw this all the time in the shop. Car died on the freeway, completely
empty tank.



And, I'd venture that most of the cases you're talking about there's still
a residual of fuel in the tank, only that it is below the pickup level.

If there is a hole in the bottom of the tank, it is absolutley below the
pick up level. Out of the millions of vehicles built with this
configuration you have to know that there will be a deviation that will
negate the situation that relies on the lack of air to prevent an explosion.
Because I have not ever heard of a tank explosion caused by an electronic
fuel pump I know that the system works under normal conditions but normal
conditions do not always exist.




Added to that that the brushes are undoubtedly built to be non-arcing so
that there really isn't a continuous ignition source, the conditions just
aren't satisfied.

That may be the case. Non arcing brushes and again the brushes were in a
strongly built contained steel enclosure behind a steel ball check ball.

"litteratuer" takenonotice@all wrote in message
...
--

That makes sense to me.

According to a table I have, for 100 octane gasoline vapor, when mixed
with air, the explosive (flammable) range is from 1.4% to 7.6%.
vapor/air mixture, - a condition which, as you say, would rarely be met.

And rarely is the event that I am talking about. Rarely does not equal
absolutley not, and with millions upon millions of these vehicled out there
you still don't hear of a problem. There has to be a stop gap safe guard
that takes care of those rare situations such as when there is an accident
with a ruptured tank and no explosion by fault of the fuel pump. There are
simply way too many conditions that can and do occour that would create the
right rare situation.

Leon wrote:
"litteratuer" takenonotice@all wrote in message
...
--
That makes sense to me.

According to a table I have, for 100 octane gasoline vapor, when mixed
with air, the explosive (flammable) range is from 1.4% to 7.6%.
vapor/air mixture, - a condition which, as you say, would rarely be met.

And rarely is the event that I am talking about. Rarely does not equal
absolutley not, and with millions upon millions of these vehicled out there
you still don't hear of a problem. There has to be a stop gap safe guard
that takes care of those rare situations such as when there is an accident
with a ruptured tank and no explosion by fault of the fuel pump. There are
simply way too many conditions that can and do occour that would create the
right rare situation.

I don't think there's any evidence to support that hypothesis that the
conditions can be made right so easily as you suppose--in fact, I think
the evidence clearly demonstrates the opposite--that is, despite the
number of vehicles, the conditions under which the fuel pump is an
ignition source _and_ the tank vapors are in an explosive mixture state
is simultaneously, are, simply not events that occur with any frequency
at all.

Again, all these scenarios you've brought up simply don't lead to
nothing but a dilute air:vapor mix in just the right
proportions--there's still far to much fuel.

Again, I don't think it is impossible, only highly improbable.

--




--

Leon wrote:
....

If there is a hole in the bottom of the tank, it is absolutley below the
pick up level. ...

But are the pumps mounted in a well? Are there not formed
hollows/ridges for structural rigidity in the tanks? Even if it leaks
to the point of not running, I'd expect there to be a little gas in
almost all cases left in such areas. If the tanks were a perfect sphere
and you punched a hole at the very bottom, all the liquid would run out,
yes. But there still wouldn't be air intrusion in most cases, only
almost pure vapor.


Added to that that the brushes are undoubtedly built to be non-arcing so
that there really isn't a continuous ignition source, the conditions just
aren't satisfied.

That may be the case. Non arcing brushes and again the brushes were in a
strongly built contained steel enclosure behind a steel ball check ball.

So, there's the design feature(s) you're after which are simply part of
the design. I'm not saying the pumps are built w/ no thought of
preventing an ignition source; only that I'm convinced there's no
secondary protective device or system other than the base design and the
physics of gasoline combustibility.

--

"dpb" wrote in message
...
Leon wrote:
...

If there is a hole in the bottom of the tank, it is absolutley below the
pick up level. ...

But are the pumps mounted in a well? Are there not formed hollows/ridges
for structural rigidity in the tanks? Even if it leaks to the point of
not running, I'd expect there to be a little gas in almost all cases left
in such areas. If the tanks were a perfect sphere and you punched a hole
at the very bottom, all the liquid would run out, yes. But there still
wouldn't be air intrusion in most cases, only almost pure vapor.


Added to that that the brushes are undoubtedly built to be non-arcing so
that there really isn't a continuous ignition source, the conditions
just aren't satisfied.

That may be the case. Non arcing brushes and again the brushes were in a
strongly built contained steel enclosure behind a steel ball check ball.

So, there's the design feature(s) you're after which are simply part of
the design. I'm not saying the pumps are built w/ no thought of
preventing an ignition source; only that I'm convinced there's no
secondary protective device or system other than the base design and the
physics of gasoline combustibility.

--


It may also be that even when the fuel/air ratio conditions for combustion
are met, the arcing from the brushes may not provide a high enough
temperature to instigate ignition. (The article in the url below gives an
ignition temperature of 600F for gasoline vapor.)

http://tinyurl.com/yanzowk

Subject

First liar doesn't have a chance.

Lew