[pure-silver] Re: Darkroom
- From: "richard l. gifford" <rlgif@xxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 12 Jan 2005 14:17:20 -0600
Georges Giralt wrote:
> Selon Ray Rogers <earthsoda@xxxxxxxxx>:
>
>>2.
>>
>>>I went for a high CFM number
>>
>>What does CFM stand for?
>>
>
> cubic foot per minute it serve as a measure of the amount of air a vent
> produce.
> Keep in mind that you need a complete change of air as often as possible
> (especially when toning with "nasty stuff" ) so calculate the CFM you need
> knowing your darkroom volume. Bear in mind that if you take air out of the
> room
> it must enter the same amount otherwise you will die with no air left ;-) (in
> other words, the motor will not have enough power to take air out if it pumps
> from a tightly closed room.
>
I passed up the original post, but this reminder about
replacement air seems like an appropriate time to
point out the advantage of pushing air in. This has
been discussed at length and should be in the archives.
As Georges says, air pushed out has to be replaced by
air coming in. Replacement air will take the path of
least resistance. If you use any kind of effective
filtration on an inlet opening, the easy path will be
around the door, baseboards, light switches, etc., not
your cleanest sources. Better to push filtered air in,
so any pressure differential is positive and air leaks
will be out rather than in.
Also, a CFM rating is specified at some pressure head.
If the fan rating doesn't mention pressure head, that
most likely means it is only intended for circulating
still air and therefore can't be expected to overcome
the resistance of a filter.
Regards... Dick Gifford
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