The H-Factor

Using the ATTSYNC Command to Update Blocks with Attributes

I stumbled across this AutoCAD command today while looking for a solution to another problem:

"ATTSYNC - Updates block references with new and changed attributes from a specified block definition.

Use this command to update all instances of a block containing attributes that was redefined using the BLOCK or BEDIT commands. ATTSYNC does not change any values assigned to attributes in existing blocks."

I am sure many of have run across this problem: The background has blocks with attributes and you want to get rid of one, or add one. You could use ATTSYNC to update each block with the added attribute or have it remove the extra one. The change can be made by creating a new block (BLOCK command) or by editing the existing one (BEDIT command).

The BEDIT editor is pretty cool. Say, the background drawing has a light fixture, door or window with pieces in seven layers. You can use BEDIT to change all items to one layer. Upon closing the editor, all blocks on the drawing will be updated with the changes. You should check it out.

Determining OS, IP and System Information

This little link does a lot - click it to determine all kinds of things about your computer. Try it.

Support Details

Creating Your Own Hanger Details

In V50/V51 we consolidated all the hanger details (and fittings, riser details, etc) into group drawings. To create your own hanger detail it is probably best to modify one we already have. From the CLEANUP toolbar, select the second button (which is a flyout) and select Hanger Details. This will open a drawing containing all the details we have.

Lets say you want to use a Hilti HDI-P fasteners. Since HydraCAD does not have a hanger with that fastener, find one that is close. The fifth hanger uses a Hilti Shield. This looks close enough, so it will be easy to modify it. Change the text to say Hilti HDI-P (you may need to explode the hanger block, first). Then SAVE this drawing. It is a good idea to make a backup of this drawing as well, in case we update it. Next time you pick the Hanger Details command, your version will come up. Add your hanger number in between the 'Typical' and 'Hanger' words.

Note - To insert these hanger details into your drawing, select what you want, pick the Edit->Copy with Basepoint command and select the base point you want. In your target drawing, pick the Edit->Paste command.

Using the Viewport Label Menu to View 3D Fittings in AutoCAD 2012

In my opinion, probably the best new feature in AutoCAD 2012 is the Viewport Label Menu. This is in the upper left of the drawing area:

Especially when it comes to 3D fittings. Lets say you created a 3D riser and you want to display the SW Isometric View and have the Visual Style of Conceptual applied to it. Just pick the [TOP] part of the menu and select SW Isometric.

Then pick the [2D Wireframe] part of the menu and select Conceptual.

Nice and easy.

Why Fitting Equivalent Length Modifiers Work

This was written by a coworker - Steve Downing - for a customer who had to have an answer for the AHJ as to why the equivalent lengths for C100 piping are less than those for C140:

'The fitting equivalent length modifiers were intended to keep the friction loss (Pf) thru a given size fitting as a constant for any given flow regardless of what kind of pipe it is attached to or what the C-factor of that pipe is when calculated with the Hazen- Williams formula.  It is done by altering the fitting length based on the internal diameter and C-factor of the pipe it is attached to.  This is because the loss thru a fitting is not dependant on the type of pipe attached to it or that pipes C-factor, but in fact is a constant based on flow and caused because the water is forced to make a turn.

 

These two modifiers are found detailed in paragraph 22.4.3.1.3.1,  paragraph 22.4.3.2, and paragraph 22.4.3.2.1 of NFPA 13 (2010 Edition) and apply to all fittings except copper and plastic for which different equivalent length tables are provide by the manufactures.

Let's take an example and see how this works.  Let's assume a 1" Tee with 40 gallons running thru it that's attached to a 1" piece of Schedule 40 with an internal diameter of 1.049 and a C-factor of 120.  Based on the equivalent length of 5 feet from table 22.4.3.1.1, the Pf for such a fitting would be 2.3456

Now, let’s make the C-factor be 100 and redo the calculation.  Our 5 foot fitting now becomes 3.568 based on a modifier of .713 from table 22.4.3.2.1.  This results in a Pf of 2.343.  So, the C-factor portion of the modification does in fact hold the Pf's the same for all practical purposes.

Now, let’s return to a C-factor of 120, but make the pipe be Schedule 10, which has an internal diameter of 1.097.  The fitting modifier from paragraph 22.4.3.1.3.1 is 1.243 which makes our 5 foot fitting into a 6.217 foot fitting.  Now plugging that into the 

Hazen-Williams formula results in a Pf of 2.3455.  So again, the Pf remains essentially the same.

Finally, let's use both Schedule 10 and a C-Factor of 100.  The new equivalent length is 4.4329 based on using both modifiers and the Pf is 2.343, which is again essentially the  same.

The very small difference in the second and forth calculation is attributable to the modifier of .713 listed in NFPA 13.  This number should actually be .713698 or .7137 when rounded based on the formula (Cnew / 120)^1.85 power.  If .7137 was used the two resultant Pf's would be 2.3456 and 2.3456 which would bring them in line with the others.

However, even with this discrepancy, the NFPA modifiers do in fact result in essentially the same Pf thru a fitting regardless of what kind of pipe it is attached to or what C-factor it is used with even though the fitting equivalent lengths will appear to vary from that used with Schedule 40 and a C-factor of 120"

Unable to See Sprinkler Head Previews in AutoCAD 2012

AutoCAD 2012 has a different background color than earlier releases, and believe it or not, this causes the following problem - when setting up sprinkler heads, you are unable to see what heads look like when selecting a head symbol.

The Solution:

1. Go into Options
2. Pick on the Display tab
3. Pick the Colors button
4. Set the 2D model space - Uniform background color to Black