Some additional info to those that have written good material thus far:
Washout plugs
1. There were two different tapers used on fine thread W/O plugs - 1-1/4" & 3/4" TPF.
The former gave quick take up, the later gave better tightness.
2. If your going to maintain the use of fine thread plugs, it is worth while to obtain the
necessary taps to clean up the threads. This also includes square or Acme thread Huron,
Prime or TZ plugs/cap styles.
3. Do not make the mistake of adding more than one or two wraps of thread tape to a fine
thread plug.because of poor thread condition - it can still blow out.
I have never had to "Tape" a square thread plug. Reseating the sleeve is necessary.
Coat with lubricant, but tape?
4. The steeper 1-1/4 tpf plugs demand better thread condition.
5. When firing up a boiler after inspections or being stored, ALWAYS check washout plugs
for leakage during the 1st 5lbs. Generally, you can still tighten leakers if threads are good.
NEVER tighten any plug beyond that pressure. Better to blow the steam off.
A better practice is shown below (5a).
A foreman at BHM told me a story of climbing up into a cab of a 1500 being fired up after
an inspection only to find a boiler washer and helper trying to tighten an arch tube plug with
the boiler having 125psi on the gauge. The helper was leaning on the wrench to add pressure
to the plug while the boiler washer was tightening the plug/wrench. The foreman told them to
STOP in no uncertain terms.
When that happened once in a great while, they would move the engine out unto the table and
turn it so the plug, if it blew out would not injure anyone. Then someone would reach in and gently
tap the plug with a hammer, if it blew out, would blow out into clear ground. Some times it would stop,
if not it was back into the 'house and blow the steam off the boiler. Then tighten the plug. That is what
happened in this case.
5a. A good practice before fire up is to use 'house water pressure or with water in glass, charge with
air to pressurize the boiler, then check the plugs for leakage.
All these will work IF, threads are in good shape.
6. Fine thread W/O plugs were generally 12 tpi, Canadian Pacific were 11 tpi and Baldwin used a 14
thread pitch on their own power. It is not impossible to find pipe thread on industrial or farm boiler
but not on locomotives.
So be careful. It is a good practice during shopping or storing over an off season (if there is/are plugs
that are suspect poor condition are that require excessive tightening to keep tight) to tap out the hole and
chase the threads on the plug or apply a new plug.
7. While not seen much today, years ago using graphite & valve oil for plug lubricant, after a period of time
the plug would develop a hard ring of baked on graphite at the outside face of the plate W/O hole. If you
should have this problem, the hard ring must be cleaned off and the thread form should be free of any baked
on material before applying the W/O plug.. Plugs with this condition were known to leak and blow out because
the baked on ring would prevent the plug from being tightened correctly.
8. Needless to say, as has been mentioned, be sure not to cross thread the plug into the hole when applying.
Easy to do when threads are poor and too much thread tape has been applied.
Arch tubes
9. When many other points could be made, one additional problem is the lack of "rattling" arch tubes at monthly
washouts. Many instances of arch tube failure happened because of scale build up on the inside surface of the
arch tube causing overheating.
Generally, arch brick were removed, arch tubes checked by feel for condition and hammer tested for thinness.
Beware of areas where arch tubes are bent as if the bend isn't smooth and a "kink" is noted over a period of
time the tube on the inside can wear away interior surface leading to failure. Arch tubes have a very strong
flow of water due to boiler water circulation and violent steam generation.
Smooth bends, proper application (in door & throat/flue sheets) and keeping inside surfaces clean are the best
practice to insure long life and good condition.
Chris A..
