[Steam-engine] boiler feedwater injector conection

[EJHottel at aol.com]

Here is some info that may be pertinent. It is exerpted from the 2002  Pawnee 
Steam School Text. It refers to Traction & Portable boilers, but I  can't see 
why it would not be applicable to Stationary also. There is lots more  good 
advice. You might want to obtain a copy.
 
 
•RossStaggs instructor
Boiler Piping continued:

We will now  discuss a fitting you must make if you need an extension nipple, 
It is a nipple  with an extension, usually about one (1) inch long with a 
diameter that will  just slide inside the threaded pipe hole the nipple is to 
screw into. This  special nipple is used where the feed water enters the boiler, 
Using a lathe,  chuck a coupling and screw about a 3 or 3 1/2 inch long nipple 
into this  coupling. Bring your tailstock up to support the outer end of the 
nipple and  turn off the threads to about .015 to .020 below the roots of 
threads. You might  check here to see if it will pass through the threads in your 
boiler. Next set  your lathe up and cut the threads. Set the center line of 
the threading tool at  right angles to the center line of the pipe and not to 
the taper of the thread.  This makes a nice looking job.
These extension nipples can also be made  without a lathe. You will need 
either a nipple chuck or I use old or dull hand  expansion reamers for a nipple 
chuck. They work better than the regular tool  and, being centered on both ends, 
can be used to an advantage with a lathe. Even  with a broken or missing 
blade, these old reamers work good. With the reamer now  turned into a nipple 
chuck and tight in the nipple, put the square drive end in  a vise and you are 
ready to cut threads fhrther up the nipple. Your die should  be set for a 
standard thread and the dies advanced until they are beyond the end  of the nipple to 
a distance of 1/8 inch less than the distance you wish the  extension to 
protrude into the boiler. Extension nipples should only be made  from schedule 80 
pipe.
Piping a Traction or Portable Engine
We will start  our piping at the point where the feed water enters the 
boiler. Remove the old  fittings and inspect the threads. They should be sharp and 
at least three (3)  continuous threads. The curvature of the boiler will reduce 
the number of  continuous threads available for sealing, but this will not 
materially reduce  strength or “shear” as the partial threads are still 
effective.
At the point  where the feed water nipple enters the boiler we often see 
leaks. This is caused  by cold or even warm water being used as feed water. This 
contracts the nipple  and even with all precautions it will leak. This is where 
the extension nipple  comes in, but cannot be used in every case. ‘Where the 
nipple will come in  between two rows of tubes or the row of tubes is on a 
level with the nipple, but  inside the boiler shell by at least 1 1/2 inches an 
extension nipple can be  used. Do not make the extension of such a length as 
will put the discharge point  closer than about 1 inch from a boiler tube 
directly opposite.
The principle  of the extension nipple is that the extension projecting into 
the boiler will  carry heat to the threaded portion of the nipple and keep it 
from contracting to  a point where it will leak. Any amount of extension will 
help but there is no  advantage to making it longer than one pipe diameter. 
Beyond this point the  solids in the water will form incrustations (lime up) and 
choke  delivery.
With the nipple in the boiler we are now ready for our first  fitting. Screw 
the run of a forged steel tee on the outside end of the nipple.  The branch 
should beheaded toward the source of water feed. The outer end  of the tee 
should be plugged with a brass pipe plug having the square wrench  pad. This plug 
is essential for cleaning out the nipple as it tends to lime up.  This is 
especially true where an extension nipple is used.