When the Scott mentions a 2" computer fan, I believe he actually means a 60mm fan. The reason for this is that the 2" PVC coupler (which is the large diameter tube in the picture) itself has an Inside Diameter (ID) to take a 2" PVC pipe (since couplers are designed to join two sections of pipe), BUT by 2" pipe I mean that it adheres to a standard called "Nominal Pipe Size", used in the USA ;-
...which defines only the OUTSIDE diameter (OD) of the pipe. So the "2 inch pipe" actually has a fixed OD of 2.375" / 60.33mm, and the "2 inch" bit of the name actually refers to the INSIDE diameter of the pipe. With the usual "Schedule 40" standard that these plumbing parts tend to be, Schedule 40 defines the wall thickness of the pipe, so if we have a 2" Sch.40 pipe it therefore has a 0.154" / 3.912mm wall thickness (according to the data table in the above link) and therefore has an ID of 2.375 - (2 * 0.154) = 2.067" / 52.502mm, or about 2".
So if the "2 inch" PVC pipe (that goes in such a "2 inch coupler") has an OD of 2.375" / 60.33mm, then the 2" coupler must have an ID of 2.375" i.e. 60.33mm, so it can accept a 60mm computer case fan if you, as is mentioned, cut off the corners to make it round, then the fan with the now round surround / fan shroud will fit into the "2 inch" PVC coupler.
Also as confirmation of this, I believe that the fan that Scott has used is an IMC Micro Boxer fan. Since his pictures show such. I Googled and found this fan on Amazon ;-
http://www.amazon.co...micro boxer fan
...which appears to be an exact match. Item code is 2410PL-04W-B20. It is a 60mm x 60mm x 25mm thick cooling fan for a PC case or CPU etc. heatsink, it draws 0.08A, has a 5-blade plastic impeller, and Ball bearing. IMC Magnetics Corporation who made it where taken over by Curtiss-Wright, and it appears you can no longer buy this fan from IMC. So those on Amazon etc. appear to be New Old Stock. The fan isn't particularly highly specified for a 60mm 12V fan, at a mere 18 CFM ;-
The "2 inch to 1 1/4 inch PVC bushing" referred to in Scott's parts list is designed to be inserted as a push fit into FITTINGS that take pipes (in order to adapt a smaller diameter pipe to a fitting outlet), not into pipes themselves, so the "2 inch bushing" has the same OD as a "2 inch pipe" i.e. 2.375" / 60.33mm, and thus fits as a push fit into the "2 inch coupler". The other two reducing bushings are based on the same standards and principles and thus the two reducer bushings fit inside the large bushing with a push fit, the two smaller bushings fit into each other.
In the same way, ID of his "1 1/4 inch to 3/4 inch PVC bushing" has the same ID as the OD of a "3/4 inch pipe", i.e. 1.050" / 26.67mm, and the "3/4 inch pipe" actually has an OD of 1.050" / 26.67mm, and an ID of 1.050 - (2 * 0.113) = 0.824" / 20.93mm, which is close to 3/4 inch, and the pipes are named by their internal size not their external size.
Scott is using a thin walled pipe called Class 200, the only PVC part mentioned that is not Schedule 40. This is to allow greater air flow due to smaller wall thickness. A "3/4 inch PVC plug" would NOT go into the pipe, even if the pipe was Schedule 40 wall thickness. This is because a plug is designed to plug up an unused FITTING, not to plug up the end of a pipe. So the plug is the SAME OD and ID as the pipe of the same Schedule wall thickness. Hence a "3/4 inch plug" does NOT fit a "3/4 inch pipe". Scott seems to have made a mistake in his description when he refers to the 3/4 PVC plug. I believe he meant a "1/2 inch PVC plug MPT", see below.
I know this since my contact from New Mexico, Paul G. was immensely helpful in showing me how all these parts fit together, as he actually had bought some of these parts for his own SCT cooler. He also used a thin walled Silverline brand 3/4" PVC pipe also called Class 200. Class 200 refers to the pressure it will withstand, in PSI, so that pipe will withstand 200 PSI. That PVC pipe of Paul's is also refered to as SDR21 (Standard Dimension Ratio), which is a ratio based on the diameter versus the wall thickness ;-
...where, at least nominally, the OD of the pipe divided by it's wall thickness is 21.
The part that Paul bought to plug up the end of the pipe was called "1/2 inch PVC plug MPT", where MPT means Male Pipe Thread, which is defined by a standard called National Pipe Thread, a standard used in USA ;-
...which defines a pipe having a 1/2 tapered male NPT thread on it as having a maximum OD (measured just before the threads meet the continuous pipe, not at the very end of the threaded section at the end of the pipe) of 0.840" / 21.336mm.
A "3/4 inch PVC Schedule 40 pipe" has an OD of 1.050" / 26.67mm, and an ID of 1.050 - (2 * 0.113) = 0.824" / 20.93mm, and so the "1/2 inch NPT / MPT PVC plug" (0.840" / 21.336mm OD) should be a tight press fit into such a pipe since the plug's thread would be 16 thou / 0.406mm (or 8 thou either all around / either side) larger than the pipe (the "3/4 inch" pipe that we would use here has no internal matching thread of course) and would screw in tight simply because of the tapered thread gripping the plain internals of the pipe.
Paul and Scott have both used a thinner wall "3/4 inch" pipe where the threaded plug was actually a sloppy fit in the pipe, so Paul tells me. Paul showed me a receipt of the parts he bought to confirm all of this (had item codes, descriptions etc).
The Silverline "3/4 inch" PVC class 200 / SDR21 pipe actually has a slightly thicker wall thickness in reality. It should have a wall thickness of 1.050 / 21 = 0.050" i.e. 50 thou, but they actually manufacture it to 0.060" minimum wall thickness in reality;-
So the plug should be a slightly less sloppy fit than it otherwise would be.
Paul simply used the flange on the end of the plug to glue onto the "3/4 inch" pipe, and did not rely on the thread etc which as he said was a sloppy push fit.
What we are actually supposed to use on the end of a pipe is a CAP, not a plug, so the ideal part should be a "3/4 inch PVC cap" which has an ID of the pipe's OD.
So you can't just buy a "3/4 inch PVC plug with a plain Male Spigot end", and expect it to plug up the end of the "3/4 inch" pipe, since plugs are supposed to go into pipe fittings, not pipes, as aforementioned.
So all you do is push the 3/4" pipe into the 1 1/4" to 3/4" reducing bushing, then push those into the 1 1/2" to 1 1/4" reducing bushing, then push those into the 2" to 1 1/2" reducing bushing, then push those into the 2" coupling, then push the fan into the end of the coupling, then push the 1/2" MPT plug into the end of the 3/4" pipe (which is a sloppy fit, you need to glue the flange onto the end of the pipe to hold it in).
I hope that helps explain how the first items (mentioned on this picture shown above) go together, and what the actual real dimensions are of each of the parts.
Edited by Live_Steam_Mad, 07 October 2014 - 05:14 PM.