Originally Posted by Bob Dodge
DC's like the Kraemers, use a completely different system from the consumer machines. Most industrial dc manufacturers use the same system. They are NOT showing you "AT WHAT" static pressure the dc is operating at, they are showing you the effect of adding "external static resistance".
Every Kraemer chart you look at, starts with the volume the dc is pulling, with 1" of static resistance added to the dc, then 2", then 3" etc. THAT'S why they all start at 1" sp. They're showing you what you'll get as you add ducting. 1", is NOT the operating point of the dc. That might be something like 800 cfm AT 3.7"sp for example, and with 1" sp added, your operating point will now be 4.7" sp.
With consumer dc's, you have to figure that out yourself. You have to take into consideration the inlet pipe for example, and calculate a new entry-loss if you're going to use smaller diameter drops. Then, from there, you have to calculate the effect of adding your pipe.
Bob