Fog Signal-Diaphone

The following is based on operation at Douglas Head Lighthouse pre-1976 when the F-Type Diaphone was discontinued.The engine room remains virtually untouched,but the diaphone and associated coder have long since disappeared.

Diaphone Piston 2004 __ Diaphone Piston 2004
Cylinder liner and piston were gunmetal castings,accurately machined to allow about two thousandth of an inch play between liner and piston.
Diaphone Diagram 2004 _ Diaphone Piston 2004

Simplified Diagram ___________________ "F" Type Diaphone Piston

Air was supplied to the "Motor" section of the diaphone,which caused the piston to reciprocate at aproximately 90 cycles per second,this meant that the slits in the piston and cylinder liner, lined up twice per cycle allowing the "Sounding" air through,giving a tone of 180 cycles per second.
The "Motor" air was stopped before the "Sounding" air,which as the piston slowed down gave the characteristic "Grunt" for which the diaphone was known.
Many American and Canadian diaphones were Two-Tone giving a "Beee-Ooooh" sound,but British ones were generally single tone.


Engine/Compressor 2004 Receiver 2004
Engine/Compressor (2004) ____________________ Air Receiver (2004) ______

There were two Lister CS 18/2 (18 horsepower/two cylinder) diesel engines (Built 1938) run on a paraffin/oil mix (4 gallons paraffin to pint of oil) with belt drive to Reavell compressors,the four yellow tanks behind the engine were cooling water tanks for the individual engines and compressors.
Air was fed to the Receiver which incorporated various safety valves,valves and pressure gauges,behind the valve to the right is a fog signal chart recorder by James Ritchie of Edinburgh,which gave a 24 hour record of operation.
When new engines etc installed in 1938,the opportunity was taken to re-site the fog signal (in the square outbuilding)

Diaphone-Position 2003

All photographs Copyright Fred Fox