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[AMPS] Blowers for finned tubes

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Subject: [AMPS] Blowers for finned tubes
From: (Ian White, G3SEK)
Date: Wed, 11 Mar 1998 13:52:18 +0000
Rich Measures wrote:
>>For finned air cooled tubes, you need to supply the recommended CFM of air
>>volume through the anode fins which will give you a back pressure. Your
>>blower needs to be capable of supplying that CFM, into that pressure. 

>However, measuring cfm requires elaborate test equipment.  

Actually it's very easy using the method described by K6GT. Simply time
how long it takes for the outlet air to inflate a large, light plastic
bag. (To measure the inflated volume of the bag, suspend it in a part-
filled barrel of water, and pour in measured amounts of water into the
bag until it's just full. The water in the barrel outside of the bag
supports the weight.)

Accuracy: within a few percent. Cost: zero - you can still use the bag
for garbage afterwards.

>pressure in inches or cm of water column [using a manometer] is not 
>difficult.  It has been my experience that the mfg. ratings of blowers 
>tend to be enthusiastic.  There is no substitute for measuring the 
>pressure drop with a manometer.  I cut holes in a suitable cardboard 
>box., insert the tube, chimney and socket, and measure the pressure 
>differential produced by the blower in question.  

It's probably necessary to do both, but the volume flow rate comes
closer to being a fundamental measurement.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)

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