Hard drives are hermetically sealed

[Timothy Daniels]

Just for the record:

http://www.tbwt.com/interaction/pcparts/html/1a.htm
"... If smoke, dust or hair got trapped between the head and the platter, the
hard drive would be ruined. That is why the hard drive is hermetically sealed
against dust, smoke and moisture."

http://www.allaboutcircuits.com/vol_4/chpt_15/6.html
"If the hermetically-sealed environment inside a hard disk drive is contaminated
with outside air, the hard drive will be rendered useless. Dust will lodge
between the heads and the platters, causing damage to the surface of the media."

http://www.atarimagazines.com/startv3n4/stcare.html
"Finally, never, ever open up your hard disk to clean its heads. Hard drives are
hermetically sealed and need no head cleaning"

http://www.wsd1.org/kelvin/Departments/teched/TUTORIAL/harddrv.htm
"The container is open in this illustration; however, it is normally
hermetically sealed to keep out dust."

http://www.microscopy-uk.org.uk/mag...ww.microscopy-uk.org.uk/mag/art98/hdrive.html
"The very close working tolerances is partly why the hard drive has to be
hermetically sealed, as tiny dust particles or any hint of condensation would
interfere with its reliable operation. When I dismantled the drive there was a
small woven pad enclosed, possibly a drying agent, to remove last traces of
moisture."


*TimDaniels

 

[Alien Zord]

Just for the record:

http://www.tbwt.com/interaction/pcparts/html/1a.htm
http://www.allaboutcircuits.com/vol_4/chpt_15/6.html
http://www.atarimagazines.com/startv3n4/stcare.html
http://www.wsd1.org/kelvin/Departments/teched/TUTORIAL/harddrv.htm
http://www.microscopy-uk.org.uk/mag...ww.microscopy-uk.org.uk/mag/art98/hdrive.html

*TimDaniels

No they are NOT! They are sealed against dust but they do have filtered
breathing holes to allow air inside to expand and contract with temperature
and atmospheric pressure. Over the years I've dismantled many failed drives
and saw the filters and breathing holes for myself. Some drives even have
warning labels on the outside showing where the hole is and warning not to
cover it (Hitachi DK23FB notebook drive and I've seen others).

Internet is a wonderful medium for gathering information but do not always
believe everything you read because there are frequently errors,
inaccuracies and sometimes utter rubbish too.

 

[kony]

No they are NOT! They are sealed against dust but they do have filtered
breathing holes to allow air inside to expand and contract with temperature
and atmospheric pressure. Over the years I've dismantled many failed drives
and saw the filters and breathing holes for myself. Some drives even have
warning labels on the outside showing where the hole is and warning not to
cover it (Hitachi DK23FB notebook drive and I've seen others).

Internet is a wonderful medium for gathering information but do not always
believe everything you read because there are frequently errors,
inaccuracies and sometimes utter rubbish too.

I too have dismantled many drives, and saw those filters & holes.
However, some of the more recent drives I've opened, did not have any
filter or vent I could find.

 

[Alien Zord]

I too have dismantled many drives, and saw those filters & holes.
However, some of the more recent drives I've opened, did not have any
filter or vent I could find.

Neither could I on some of them but then I came across this Seagate patent:
"Breather vent assembly formed in a sealed disk drive housing"
http://www.priorartdatabase.com/IPCOM/000001062/

Also for more interesting reading just type
hard+disk+drive+air+vent
into Google.

 

[Noozer]

Just for the record:

http://www.tbwt.com/interaction/pcparts/html/1a.htm
"... If smoke, dust or hair got trapped between the head and the platter, the
hard drive would be ruined. That is why the hard drive is hermetically sealed
against dust, smoke and moisture."

Wrong... Some drives may be sealed, but not all!!!

I'm looking at a drive right now with a hole that specifically says DO NOT
COVER!

 

[Timothy Daniels]

"Alien Zord" shared:

Neither could I on some of them but then I came across this
Seagate patent:
"Breather vent assembly formed in a sealed disk drive housing"
http://www.priorartdatabase.com/IPCOM/000001062/

Evidently, Seagate thought it was worth patenting, and the
patent office granted it in June of 1992, but did they or anyone
else ever use it?

I called Maxtor and spoke to their senior tech support supervisor,
asking if Maxtor currently makes a HD with a vent hole that would
allow at least equilization of air pressure between the platter chamber
and the environment. He said no, but that he recalls one a vent hole
that allowed air to get behind the circuit board for cooling. He stressed
that the HDs are assembled inside a class 10 clean room and that
even a smoke particle would be a problem for a HD, much less
condensation. The following link is to Maxtor's tech manual for their
DiamondMax Plus 9 line of HDs, which you may find interesting,
but I couldn't find any mention of a vent hole or hermetic seal:
http://maxtor.com/en/documentation/manuals/diamondmax_plus_9_manual.pdf

*TimDaniels*

 

[Timothy Daniels]

I'm looking at a drive right now with a hole that specifically
says DO NOT COVER!

So? That hole may not go through to the platter chamber
but merely ventilate the back of the circuit board. Would
you care to give the make and model no. of that hard drive?

*TimDaniels*

 

[R. Anton Rave]

Neither could I on some of them but then I came across this
Seagate patent:
"Breather vent assembly formed in a sealed disk drive housing"
http://www.priorartdatabase.com/IPCOM/000001062/

Also for more interesting reading just type
hard+disk+drive+air+vent
into Google.

So the vent can be a groove molded or machined into the casting?

If there wasn't any vent, could the liquid magnetic shaft seal blow
out? Are liquid magnetic seals still even used in hard drives?

 

[jamarno]

I called Maxtor and spoke to their senior tech support
supervisor, asking if Maxtor currently makes a HD with a
vent hole that would allow at least equilization of air
pressure between the platter chamber and the environment.
He said no, but that he recalls one a vent hole that
allowed air to get behind the circuit board for cooling.

What were his qualifications? Most tech support people simply
memorize a very basic training manual and have no understanding of its
contents and unwittingly give out completely wrong information at
times. For example I once spoke with a Panasonic monitor "technician"
who didn't even know about convergence - "I don't know what
convergence are." (sic), yet he was described by his manager as being
one of the best "technicians." Another time I called CTX, another
monitor maker but one that had been known for staffing its tech
support with real technicians, to ask about what changes should be
made when the horizontal output transistor was replaced (CTX had
issued a bulletin about them), and a person who proudly referred to
herself as a "technician" was clueless about this, and when I doubted
her qualifications she pouted, "What makes you think that I'm not a
technician?" It turned out that CTX had laid off all the real
technicians from tech support.

He stressed that the HDs are assembled inside a class 10
clean room and that even a smoke particle would be a problem
for a HD, much less condensation.

It's common for manual memorizers to embelish their words with
irrelevant facts like that. I once asked Maxtor about their motor and
voice coil driver chips running at 70 deg. Celcius. The tech support
person said that it was exceeding the maximum allowed 55C and wanted
to replace the drive, proof that he cared about customers but didn't
understand the difference between maximum allowed ambient temperature
and maximum allowed device temperature. I had to speak to 3 people
before someone seemed to know about the chips themselves.

 

[Timothy Daniels]

What were his qualifications? Most tech support people simply
memorize a very basic training manual...

In view of the qualifications presented on Usenet or the Web,
how could his have been any worse? He said he was a direct
employee of Maxtor, had access to the engineering department
to ask questions, and that he had been around the longest
among the tech support personnel. Admittedly, he may not
know proprietary information, and if he did, he wouldn't
divulge it if it would harm his employer, but who else here has
presented anyone as a more convincing authority? As for
an hermetic seal being possible, why not? I'd think that
14.5 lbs/sq. in. is pretty easy pressure to seal against given
the casting and there being no need for shaft seals. In most
situations, the inside pressure and the outside pressure would
be nearly equal. And just think about it - why would there be
any need for pressure equalization at all?

*TimDaniels*

 

[kony]

In view of the qualifications presented on Usenet or the Web,
how could his have been any worse? He said he was a direct
employee of Maxtor, had access to the engineering department
to ask questions, and that he had been around the longest
among the tech support personnel. Admittedly, he may not
know proprietary information, and if he did, he wouldn't
divulge it if it would harm his employer, but who else here has
presented anyone as a more convincing authority?

One would hope a maxtor employee has accurate info, and futher that the
tech conveys this accurate info instead of pulling something out of the
ass.

On the other hand, consider phone tech support personnel for what they
are- entry level employees. They may be brillant at (something) but if it
were hard drives you'd think maxtor would have them doing something more
useful than talking to end-users.

As for
an hermetic seal being possible, why not? I'd think that
14.5 lbs/sq. in. is pretty easy pressure to seal against given
the casting and there being no need for shaft seals.

Irrelevant. The bearing IS sealed.

In most
situations, the inside pressure and the outside pressure would
be nearly equal.

No, they'll never be equal unless the drive is at room temp, OR if it has
a vent.

And just think about it - why would there be
any need for pressure equalization at all?

Now you're trying to both oversimplify and outguess the engineers, who
obvously did think there was a need for pressure equalization since drives
have had them. Clearly the air pressure can affect the heigh of the head
over the platters... the only remaining question is whether drives are now
engineered to overcome a pressure difference without that vent (which it
apears likely), and if so, how?

 

[Timothy Daniels]

Irrelevant. The bearing IS sealed.

Therefore, there is no need for any motion to be communicated
between inside and outside. All communication can be
electrical - for both power and information. Why would there
be a need for a vent hole on current hard drives?

No, they'll never be equal unless the drive is at room temp,
OR if it has a vent.

Play it again, Sam: "In most situations.... .... be nearly equal".
Most situations would involve room temp, right?
And what you mean is "temp of the room at the time of assembly".

But I ask again, why does the pressure inside have to equal
the ambient pressure?

Now you're trying to both oversimplify and outguess the engineers,
who obvously did think there was a need for pressure equalization
since drives have had them.

Is it really more complex than I envision? If so, how do you know?
Maybe drive casings were larger and more flexible in the old days.

Clearly the air pressure can affect the heigh of the head over the platters...

Good point! Maybe that's why Maxtor HDs are hermetically sealed -
to maintain the internal air pressure, that is, to keep in enough air
so the heads can be held off the platter - i.e. "fly".

the only remaining question is whether drives are now
engineered to overcome a pressure difference without that vent
(which it apears likely), and if so, how?

By having a small internal volume and a rigid casing.

*TimDaniels*

 

[kony]

Play it again, Sam: "In most situations.... .... be nearly equal".
Most situations would involve room temp, right?
And what you mean is "temp of the room at the time of assembly".

Most situations would not involve room temp, to the extent that the air
inside the hard drive will not be at that temp.

I did not mean "temp of the room at time of assembly", and while they
could try to estimate the operational temp of the air inside the drive, it
could not be considered a constant.

But I ask again, why does the pressure inside have to equal
the ambient pressure?

It doesn't, but can you not see why it might need to remain constant even
though the drive temp changes from cold/off to warm/on?

Is it really more complex than I envision? If so, how do you know?
Maybe drive casings were larger and more flexible in the old days.




Good point! Maybe that's why Maxtor HDs are hermetically sealed -
to maintain the internal air pressure, that is, to keep in enough air
so the heads can be held off the platter - i.e. "fly".

No, you're getting it backwards. The head height would be calibrated,
would be at a precise height at a certain air pressure. That air pressue
will change in a sealed drive when it heats or cools, and thus the head
height, distance from the platter, might be (apparently was) expected to
change.

The issue is then, how to counteract that mechanically or electronically.

By having a small internal volume and a rigid casing.

No.

 

[Timothy Daniels]

It doesn't, but can you not see why it might need to
remain constant even though the drive temp changes
from cold/off to warm/on?

No, it's the density that has to remain a constant
to provide a constant "flyability" for the heads.
Any pilot knows that it's *density* of the air that
gives the wings their lift and the prop its thrust,
and that temperature and pressure effects have
their primary aerodynamic significance in their
effects on air density (and to lesser extents, on
air viscosity and drag). Remember that wings
don't care how much pressure there is all around
them, but they *do* react to the pressure
*differential* created by air flow to give them lift.
And the effects of air flow are a function of the
air's density.

No, you're getting it backwards. The head height would be calibrated,
would be at a precise height at a certain air pressure.

We both got it backwards. It's not pressure that's important,
it's air *density*, and a sealed platter chamber would provide
the constant density for a controlled head "altitude" above the
platter. And this density would be maintained by a rigid case.
Take a look at a modern hard drive. Notice the webbing
around the motor "can"? It provides stiffness and strength to
keep the chamber from flexing in or out. If air were allowed to
flow into and out of the chamber, such rigidity wouldn't be
needed. But given a constant volume and a constant mass
afforded by sealing and riditity, the air will have a constant
*density*.

*TimDaniels*

 

[kony]

We both got it backwards. It's not pressure that's important,
it's air *density*, and a sealed platter chamber would provide
the constant density for a controlled head "altitude" above the
platter. And this density would be maintained by a rigid case.
Take a look at a modern hard drive. Notice the webbing
around the motor "can"? It provides stiffness and strength to
keep the chamber from flexing in or out. If air were allowed to
flow into and out of the chamber, such rigidity wouldn't be
needed. But given a constant volume and a constant mass
afforded by sealing and riditity, the air will have a constant
*density*.

Then why did/do some drives have the air vents?

You're right that the air density is an issue, but not the issue you're
claiming. When a drive casing heats up, it expands, and the internal
volume of that casing increases, moreso when the drive is very rigid.
Rigidity would have a negative effect in this regard, but still important
since it houses rapidly moving mechanisms.

If it's flexible, perhaps the TOP of the drive, then it can flex inward
to counteract that frame expansion and retain the density, except that I
don't know if it's THAT flexible, and the heating of the air increases the
pressure against that top panel if the drive is sealed. The pressure
would increase but the density may drop. Perhaps this is countered by
a precision machining that results in a precise internal volume, a
machining that wasn't cost-effective prior to a technological advance.
Possibly those thin metallic stickers on the drive(s) are flexing enough
to get the density to the needed level.

The "webbing' around the bottom is simply a structural support for the
bearing.

 

[Timothy Daniels]

Then why did/do some drives have the air vents?

I don't know. But I suspect that the allowed
operational environment was more restrictive (i.e. not
as high as 10,000 feet as Maxtor currently allows).

*TimDaniels*

 

[Guest]

It's not pressure that's important, it's air *density*, and
a sealed platter chamber would provide the constant density
for a controlled head "altitude" above the platter. And
this density would be maintained by a rigid case. Take a
look at a modern hard drive. Notice the webbing around the
motor "can"? It provides stiffness and strength to keep the
chamber from flexing in or out. If air were allowed to flow
into and out of the chamber, such rigidity wouldn't be needed.
But given a constant volume and a constant mass afforded by
sealing and riditity, the air will have a constant *density*.

I'd think that the thin steel cover on top would flex far more than
the aluminum casting, and changes in temperature would cause greater
changes in air density than any flexing would. My guess is that drive
castings are made rigid simply to reduce acoustical resonances and
reduce vibration during head seeks that would require longer settling
times before the track can be read or written.

While I'm hardly an authority, I know of only one case where lack of
body rigidity caused problems, and that was with the old 5.25" Seagate
ST-225/238 drives, where overly long mounting screw pressing against
the domed cast aluminum top could bend it enough to upset the
alignment between the platters and the head arms pivot enough to cause
the index track to be erased during low level formatting. This drive
positioned its heads with a stepper motor and no servo, unless you
include the outer index track that was read during head
recalibrations, and I believe Seagate tried to further reduce flexing
by putting a plastic washer under one of the circuit board mounting
screws.

 

[Guest]

I don't know. But I suspect that the allowed
operational environment was more restrictive (i.e. not
as high as 10,000 feet as Maxtor currently allows).

The old Western Digital drives that were vented to the atmosphere were
rated for operation from -1,000 to +10,000 feet.

 

[Manny]

So? That hole may not go through to the platter chamber
but merely ventilate the back of the circuit board.

Why do you need a hole in the aluminum to ventilate
the PCB? They're not sealed to one another, and any
additional ventilation could simply be molded into
the aluminum or better yet, holes could be drilled
in the PCB.

 

[Timothy Daniels]

Why do you need a hole in the aluminum to ventilate
the PCB? They're not sealed to one another, and any
additional ventilation could simply be molded into
the aluminum or better yet, holes could be drilled
in the PCB.

I have no idea. It was merely a theory offerred by
a Maxtor support tech to explain such a hole which he
had seen in older hard drives (which Maxtor no longer
makes). His term was "ventilation" of the back of the
PCB. Perhaps it was to allow component cooling or
release of air heated by hot components on the board.

*TimDaniels*