Dryer, Projector Let Class See Sprinkler Head Fuse
Few people witness the action of a sprinkler head fusing in a fire, but while preparing a classroom presentation on automatic sprinklers a thought struck me that it would be interesting and educational if it could be shown in detail.
I came up with the idea of using an ordinary blowing hair dryer to generate the necessary heat to cause the head to pop off. The next thought was, how would this work on an overhead projector? I tried it and the result was impressive.
For the full presentation I use a commercial set of overhead transparencies. Starting with water supplies, I progress through the various pieces of equipment up to the riser and alarm valve. Then I go on to describe the different mains and branch lines and head spacing required for different occupancies. We then discuss the various types of sprinkler heads.
Fusing starts in 30 seconds
At this point, I set up the overhead projector for the demonstration and explain that I am going to show them exactly how a sprinkler head operates when it’s fused by a fire. This always creates an air of expectancy. Within about 30 seconds after applying the heat from the dryer, the fusible element can actually be seen to start moving. A few moments later the solder can be seen melting. All the action is magnified by being projected on the screen, yet seemingly slowed down at the same time.
Soon the head pops. The pieces fly apart and land scattered on the glass. The head is left open, just as it would be if it were flowing water during a fire. It brought the students right up out of their seats. I looked up and found eight or nine of them gathered around the projector, pointing at the different parts and trying to pick them up to see what they were like.
I was convinced that this was a worthwhile project that should be shared with other instructors. As with any project, however, there are some details and considerations that must be worked out. These included:
- Which is the best sprinkler head to use for the demonstration?
- How to keep the head steady on the projector (the hot air from the dryer pushed the head to the side).
- How to protect students, instructor and projector from the effects of the flying parts and hot solder during the demonstration.
This works best
Of those heads I tried, the 165-degree Grinnell Duraspeed not only fused dependably, but popped apart with such vigor that it provided a most effective display. It should be noted that whatever head is chosen, the demonstration should be tried ahead of time to assure success.
Keeping the head steady on the projector was accomplished by the simple task of screwing the head into an elbow which was attached to a short length of pipe. The extra weight of the elbow and pipe did the trick. Some small rubber pads placed under the piping might be even better.
Obviously the most important consideration is safety: the protection of the eyes of all those present and, to a lesser extent, preventing damage to the projector during the demonstration. A trip to the local glass dealer produced two pieces of safety glass approximately 12 inches square and a strip of Plexiglas 4X20 inches. The Plexiglas was bent to a 90-degree angle by heating the center area over the flame of a top burner on a kitchen stove. When it’s at the proper angle it can be cooled under cold tap water and it will hold its shape and return to its original hardness.
No chance of damage
One of the pieces of the safety glass is placed directly on the lens of the overhead projector to protect its surface. The bent piece of Plexiglas is set on edge on the safety glass on the audience side of the projector. The second piece of safety glass is then placed on the top edge of the Plexiglas which supports it. The sprinkler head is placed between the two pieces of safety glass and within the corner created by the Plexiglas. Now with the instructor looking through the top piece of glass and the class looking at the screen, all should be effectively shielded from flying parts. There is no chance of damaging the lens of the projector.
This graphic training demonstration provides the student with a learning experience that will make your class one of the remembered ones.
