British Aerial Spray Tank, SCI, 1000 lb.
Smoke Curtain Installations (SCIs) may be pressure or gravity flow types. If the tank was gravity flow, it was called Type G. If it was a pressure type, it was called Type H (for high pressure) or Type L (for low pressure). When the spray tank was used for chemical purposes, it was called a Type S/G, the S denoting Secret, and the G denoting gravity feed.
The tank generally consisted of a tank or body, of cylindrical shape, with either domed or flat ends. On the upper surface of the body was a filling hole, an air inlet assembly at the forward end, an externally mounted box containing electrical connections, etc., and a suspension lug. The outlet assembly was on the underside of the body with the emission pipe and nozzle connected.
The body was streamlined by the addition of nose and tail fairings. A tail fairing was normally fitted on all SCIs when carried externally on an aircraft. Later versions of SCI, which were carried externally, had a domed nose, therefore, a nose fairing was not essential, although it did improve the aerodynamics of the system.
The body was lagged with insulating material to prevent extreme cooling of the charging. This was done on tanks that were stored outside, and on internally stored ones when used from a great height or in cold weather.
The emission pipe was normally 8.89 centimeters (3.5 inches) in diameter with a 6.35- centimeter (2.5-inch) emission orifice. In the case of externally stored systems (250- and 500- pound versions) the emission pipe is a short pipe turned at a right angle so the emission orifice pointed to the rear. In the case of internally stored SCI, the pipe was longer and was faired. This pipe extended through the belly of the aircraft.
Operating mechanisms were fitted inside the air inlet and emission assemblies. These consisted essentially of a Bakelite sealing disk in each assembly, with an electric detonator attached. These detonators were connected to the aircraft electrical system, which was used to arm aircraft bombs. The detonators broke up the Bakelite disks, and the fill was emptied by gravity flow alone. Earlier marks (versions) used an electric-fired cartridge to break the disk.
The air inlet assembly in earlier versions was baffled to prevent splash and vapor from coming out after firing, but in later models a spring-loaded valve proved more effective.
Mark numbers were also assigned to each weight category to indicate whether the tank was configured for external or internal use on the aircraft. Mark numbers for each weight class could be Mk I, II, III, or IV. The MK number was changed when modifications were made.
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