place one hammer arrestor on the hot water line & a second one on the cold water line just before the thermostatic valve and that will be sufficient.

In regard to your use of two 45's instead of a 90, unless you really think you need the additional soldering practice, there is nothing to really be gained by that.

Thanks for the reply lazypup. I didn't realize I could place the arresters before the thermostatic. that makes it much easier since that area isn't as congested.

Funny you should mention it, I think I do need the additional practice. I enjoy soldering (I'm weird I guess) and if I didn't do the 45's I would always wonder if my flow would have been better if I did.

Thanks again.

If you enjoy soldering never let it be said that I stood in your way because I too enjoy soldering however let us examine what the differences in flow would be.

When computing pipe friction we must first compute the "Total Developed Length of Pipe (TDLP)". TDLP is the physical length of the actual pipe + the additional friction losses introduced by fittings, which is know as "Fitting Insertion Loss (FIL)".

The Fitting Insertion loss is different for each type and size of fitting however it is always expressed as an equivalent length of straight pipe that would introduce the same amount of friction.

The FIL does vary considerably from one type of fitting to another and it also varies by the diameter of the fittings so it is important to check the actual fitting insertion loss tables,

You will no doubt be using 1/2" copper for these lines so let us examine the FIL for 1/2" 45deg elbows and 1/2" 90deg elbows.

The 1/2" 90 elbow FIL is 1Â of pipe.
The 1/2" 45 elbow FIL is 0.5' of pipe.

You would be using two 45deg elbows in place of a 90deg elbow therefore the FIL with two 45elbows would be 2x 0.5' = 1ft of pipe. Therefore to answer your quandary, there would be no difference in flow in which case I personally would use the 90Âs to minimize the number of joints that could possibly fail in future, and if I felt I still needed to play with the torch I would just go to the bench and solder up a little high chair for my nieces doll babies.

In some instances your reasoning is correct however, as I stated previously the fitting insertion loss varies greatly from one size of fitting to another.

By example;

I am listing a small sample of the Fitting Insertion Losses for copper pipe fittings taken from the Fitting Insertion Loss table published on pg.32 of "The Copper Tube Handbook" published by Copper.org

1/2"-90=1ft 1/2"-45=0.5' In this case using two 45's would be the same as one 90

A 1"-90=2.5' while a 1"-45=1' so in this case two 45's would equal 2' which is less than the 90el

A 4"-90=12.5' while a 4"-45=5' thus using two 4' 45's would be 10 feet which is much less than the 12.5' for the 90,

If you would like to see the complete friction loss tables, Fitting insertion loss tables as well as a complete guide to all your questions about copper pipe & tube you could download the complete Copper Tube Handbook in PDF format free at:

http://www.copper.org/applications/plumbing/techref/cth/download.html

Hi Lazypup. I checked out the copper handbook even though my knowledge was limited on some of the technical aspects. If you don't mind, I have one more (and I promise that this is the last one) question. I'm assuming that the fitting insertion loss for the 45's are based on a couple of standard 45's. Now if I use street 45's, would the friction be less if I oriented it in a manner so that they were in a "bell and spigot" type of configuration?

If you insist that it definitely isn't worth it to use the 45's then I'll stick with the 90's. I think you already did, but just in case I managed to sway your opinion somehow.

Also, do you have a picture of the high chair for your neices doll's? My daughter's would freak out if I did that.

Generally the Insertion loss is the same for a street fitting as a regular fitting however in some instances the fitting allowance for street fittings is actually higher than the conventional fitting, especially at higher flow velocities. The problem is that as the fluid changes directions in the first fitting the flow does not have time to stabilize before changing again in the second fitting. This results in an internal vortex current that increases resistance.

I currently don't have any of the copper chairs or even pictures of them here, but I do have the original prototypes that were made by my GF's stepfather with CPVC. When I first saw those I was really impressed, so much so, that I decided to use the design as a class project in an apprenticeship class. I found that not only is it a fun project, the apprenticeship students seemed much more intent on getting the project finished and having something to take home instead of just soldering or gluing a bunch of fittings into an assorted mess of scrap.

Send me an email and i will be glad to send you back a couple pics as well as a simple line drawing and cut sheet.

What would others say about using vertical air columns instead ? I put a couple of vertical air columns using a tee just where the hot and cold run to my washer, it seems to have worked as there's virtually no thump when the washer runs; I know they will eventually lose their water, but the bathroom sink supply valves are right underneath and are the lowest taps in the house, periodically I can disconnect one from the tap and drain the system, and replenish the air (in theory)