GAMEWELL DIAPHONE Type B
Additional pictures and more information.
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Left: This is a side view of the diaphone cylinder assembly. It shows a 1/4" NPT pipe plug in the test port. For intial setting up, remove this plug and insert a 0-60 PSI gauge here. This picture also shows one of the two motor air exhaust ports just to the right of the test port. In operation, a small portion of the total air consumed drives the piston back and forth. This air exhausts here. As you can see, the resonator is made from rolled copper sheet, silver or hard soldered into a cast bronze front flange. The cylinder assembly and back cover are cast iron.
Right: Looking into the brass cylinder with piston re-moved. This picture shows the speaking slots in the smaller section of the cylinder, the motor air inlet ports just where the cylinder diameter increases, and also the three slots in the motor section as well as (around the outside edge) the ports that connect slots one and three of the motor section. Between the two studs is a recessed section of the outer cast iron hous-ing which becomes the exhaust port when the back cover is in place.
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Left: This picture shows the correct way to remove the diaphone piston, by inserting a 1/4 X 20 screw or bolt into the center tapped hole in the piston as a convenient handle. It is very important, as these pictures imply, that the air supplied to a diaphone should be clean and free of any metal chips or scale or other material which might score either the piston or the cylinder. The piston in this diaphone is aluminum.
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Left: Type B Diaphone dimensions.
To
sound this diaphone adequately, you will need at the very least a 60 gallon
receiver, and performance is better with a 120 gallon receiver. The typical
set up for type B diaphones when installed in fire stations calls for
a pair of 350 gallon high-pressure receivers and a high capacity regulator
after the solenoid valve to supply reduced pressure air to the horn. This
provides adequate reserve for sounding a number of coded fire alarm box
location signals in succession without losing pressure at the horn. When
setting up the diaphone, take a measurement of pressure at the test port
on the side of the cylinder assembly while it is operating, and if necessary,
adjust the regulator so that 40 PSI shows on the gauge. A 60 gallon receiver
will give you several good honks of a few seconds' duration. Receivers
smaller than 60 gallons will probably not give very satisfactory performance.
This is the classic fire station diaphone, used on
many fire stations and other public build-ings throughout the USA for
many years. It is exactly the same as the larger diaphone foghorns except
that it has one common air inlet port to supply both speaking and motor
air, whereas the foghorns have a separate motor air inlet. See article
on Gamewell diaphones elsewhere
on this website for detailed information about these horns. Slightly reducing
the pressure suddenly at the end of the blast will make this diaphone
terminate its signal with a grunt as does a type F foghorn. Sustaining
the lower pressure will cause a two-tone effect similar to that of an
F2T foghorn. The actual horn frequency is largely, (but not exclusively)
determined by the operating air pressure.
