The importance of the use of DDT water suspensions, as contrasted with emulsions or solutions, is outlined from the point of view of logistics of supply, economy, and superior results obtained on earthen wall surfaces commonly encountered in Latin America and elsewhere in the tropics. The need in this area for a simple hand-operated apparatus to dispense water suspensions of DDT, rather than motor-driven equipment, is justified.
The development of a knapsack-type hand-pumped sprayer for use with DDT water suspensions is reported. The basic unit modified for this purpose is the Army item of issue, “Sprayer, Insect, Knapsack Type, Lofstrand Model.”
The important feature of the new unit is the large capacity filter of #40 wire-screen placed on the end of the outlet pipe where it is protected inside the body of the tank, yet available for cleaning each time the tank is opened for refilling with insecticide. The filter is constructed so that no particles can enter the hose which will either plug the nozzle or cause the gun valve to stick; yet the filter has sufficient capacity not to become plugged itself in evacuating a tankful of DDT mixture.
The sprayer is fitted with interchangeable air-relief valves, one of which may also be used to secure pressure in the tank from a compressed air source, where such is available.
With each group of sprayers used by a field crew there is a combination standpipe, funnel, and preliminary filter. This provides for the filling of sprayers to a standard level, and reduces wastage in filling the tanks.