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HP boxes: direction of air flow
开云体育Hello Tom,
Normally outside in as far as I know. The fan will not blow against a dust filter, will it? Cheers, Harke On 14/11/2023 15:48, tom_iphi via
groups.io wrote:
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开云体育It is quite common for the casing to have ‘positive’ pressure in order to keep any foreign bodies out unless they are filtered through Any grille/filter foam mesh etc. ? HIH Regards Nigel ? From: [email protected] <[email protected]> On Behalf Of Harke Smits via groups.io
Sent: Tuesday, November 14, 2023 3:15 PM To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP boxes: direction of air flow ? Hello Tom, ? Normally outside in as far as I know. The fan will not blow against a dust filter, will it? Cheers, Harke On 14/11/2023 15:48, tom_iphi via groups.io wrote:
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开云体育Probably because the filter material degraded with age and fell apart; then was not replaced. Can’t suggest where to get it or what alternatives there might be. It may also have a slight benefit in reducing the jet engine noise typical of HP fans. ? Tom, N8ZM ? From: [email protected] <[email protected]> On Behalf Of tom_iphi via groups.io
Sent: Tuesday, November 14, 2023 11:57 AM To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP boxes: direction of air flow ? Indeed, the dust filter is a good argument. |
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You can buy it on Ebay, and from industrial suppliers. On Tue, Nov 14, 2023 at 12:12?PM Tom via Metronet <n8zmTWH@...> wrote:
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The filter foam is called reticulated foam. It's sometimes sold as fish filter foam (even though that's filtering water) but it doesn't follow that all fish filter foam is usable for air filters. It's also sometimes used to face loudspeakers.
I found a wide selection of it in the Bauhaus store in Berlin a few years ago. Unfortunately I've used up my stocks. If any reader is near there, they could do a great service to us all by putting some on ebay - what's there is mostly unsuitable. |
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The filter foam is called reticulated foam. It's sometimes sold as fish filter foam (even though that's filtering water) but it doesn't follow that all fish filter foam is usable for air filters. It's also sometimes used to face loudspeakers.
I found a wide selection of it in the Bauhaus store in Berlin a few years ago. Unfortunately I've used up my stocks. If any reader is near there, they could do a great service to us all by putting some on ebay - what's there is mostly unsuitable. |
开云体育I went to a local foam supplier that has different types of open cell foam...cut thickness desired..or use a sharp serrated bread knife and slice off what is needed from a block....trim to size....other option is the aluminum filter material used above stoves to collect grease fumes...again trim to size搁别苍é别 On 11/14/23 9:58 AM, Michael A. Terrell
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Is it a different material than heating vent filter (or activated carbon vent filter for black color) ?
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Ozan On Tue, Nov 14, 2023 at 10:04 AM, Adrian Godwin wrote: The filter foam is called reticulated foam. It's sometimes sold as fish filter foam (even though that's filtering water) but it doesn't follow that all fish filter foam is usable for air filters. It's also sometimes used to face loudspeakers. |
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Your average big box store (around here) or pet supply store has filters for air systems or litterboxes.? Those filters are granulated carbon and relatively inexpensive.? Air filters for HVAC systems can be trimmed, depending on type.
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Harvey On 11/14/2023 1:05 PM, 搁别苍é别 wrote:
I went to a local foam supplier that has different types of open cell foam...cut thickness desired..or use a sharp serrated bread knife and slice off what is needed from a block....trim to size....other option is the aluminum filter material used above stoves to collect grease fumes...again trim to size |
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In the general case, higher velocity air will drag more dust with it so if no dust filter, then fan should exhaust the enclosure. On Tue, Nov 14, 2023, 9:15 AM Harke Smits via <yrrah=[email protected]> wrote:
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I've built a lot of large electrical equipment enclosures for the chemical processing industry...
From a common sense perspective I always thought the fan & filter should draw air into the cabinet for two reasons: 1. This maintains a positive pressure which keeps dirt etc from entering in through gaps or cable entry holes - this also means air has to come through the filter. 2. The positive pressure means there's more air particles to cool down the equipment inside. This is also done in (for example) tube transmitters where the anode is cooled with a blower to remove more heat than ambient pressure could remove. Cheers, Matthew |
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It depends on how the engineer was feeling on the day he
designed the cooling... Basically, if you suck through a filter and blow into the cabinet, you will need to spend a bit of effort making sure the air gets to all parts of the instrument that need cooling. If air hits the power supply first, the rest of the instrument will be baked by power supply heat. On the other hand, if you suck on the case, you can open up holes in the panels adjacent anything that needs cooling, and it will get fresh cool air right on it. Power supply heat will go straight out the back and not on the sensitive electronics... It can be a little hard on the fan's bearings, though... The other clue is inter baffling and ducting. That usually means a pressurized case. -Chuck Harris On Tue, 14 Nov 2023 06:48:48 -0800 "tom_iphi via groups.io" <iphi@...> wrote: Hi folks, |
开云体育Yes, but...‘On the other hand, if you suck on the case, you can open up holes in the panels adjacent anything that needs cooling, and it will get fresh cool air right on it. ‘ Then what about screening? Some instruments require a good screened casing... There’s always a trade off... screening/cooling/keeping dust and dirt out... Surely easier to clean a filter than a whole instrument. Regards Nigel by banging a nail into a piece of wood... On 14 Nov 2023, at 22:57, Chuck Harris <cfharris@...> wrote:
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开云体育Yep.? I don't understand why you would even consider sucking dirty air through the vents and gaps.? ? ? ? ? Jim Ford? Sent from my T-Mobile 4G LTE Device -------- Original message -------- From: Matthew C <matthew.curlis@...> Date: 11/14/23 2:23 PM (GMT-08:00) Subject: Re: [HP-Agilent-Keysight-equipment] HP boxes: direction of air flow From a common sense perspective I always thought the fan & filter should draw air into the cabinet for two reasons: 1. This maintains a positive pressure which keeps dirt etc from entering in through gaps or cable entry holes - this also means air has to come through the filter. 2. The positive pressure means there's more air particles to cool down the equipment inside. This is also done in (for example) tube transmitters where the anode is cooled with a blower to remove more heat than ambient pressure could remove. Cheers, Matthew |
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Ask the manufacturers of virtually all PC's.
They find it is cheaper and easier to use the DVD player as a dust filter... If you pressurize the case, you have to study the air flow and install baffles and ducting to make sure that air gets to everywhere cooling is needed, and the air is actually cooler than what you are cooling. If you suck on the case, you can get your cool fresh air simply by opening a few holes in the case. As to dust, it generally takes a lot longer for an instrument that sucks on the case to get so stuffed up with dirt that it burns up. A filter, that actually works, will get clogged much sooner than no filter. And, since most people put off periodic maintenance until some fictitious "tomorrow" that never comes, a clogged filter will never be noticed until the instrument fails... Usually long before the warranty is up... I am not recommending one method over the other, just simply explaining why each method is used. -Chuck Harris On Tue, 14 Nov 2023 20:42:53 -0800 "Jim Ford" <james.ford@...> wrote: Yep.? I don't understand why you would even consider sucking dirty |
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I don't think there ever was a "corporate standard" about whether air pressure within an instrument should be positive or negative. The issue was largely left to R&D teams, as a function of the specific requirements of every product (power dissipation, noise level requirements, mechanical constraints, cost, MTBF, maintainability, to name a few).
There's an example of the cooling system used in the 54600 oscilloscope series in the February 1992 issue of HP Journal, pages 37 and 38. Simple concept, and interesting reading. Cheers, Joel |
Michael A. Terrell
Anders