152 U. S. BUREAU OF FISHERIES 
minutes. When operating at capacity two trucks will be placed in one 
vestibule and two removed from the other about every 4 minutes. 
While doing this the door between the vestibule and the main tunnel 
must be kept closed, after which it should be opened and the outer 
door closed. The conveyer that carries the trucks is moved forward 
by compressed air or by some other means about one truck length 
at a time, instead of moving continuously. This method of handling 
gives plenty of opportunity for loading and unloading between the 
times when the trucks move. 
Several canners have raised this question: ‘‘Why not use two 
tunnels, emptying and filling one while fish are being prepared in the 
other? The air supply can then be shifted and the process repeated 
for the other tunnel.’’ This is impracticable; it is not possible to get 
uniform results in this way. If the air temperature is right for the 
fish in the first truck, each succeeding lot will be treated with cooler 
and cooler air. Much heat is removed from the air by each truck 
of fish. If the air temperature is raised sufficiently so that the last 
truck is treated with air at the right temperature, the fish on the 
RECIRCULATED AND WASTE AIR 
HATED AIR FROM BLOWER 


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£ 
Fic. 28.—Plan for cooker, using trucks 
aot 
first trucks will be greatly overcooked. For uniform results the 
trucks should pass progressively through the tunnel, so that all fish are 
subjected to the same range of temperature. 
The purpose of two doors on each vestibule is to prevent excessive 
loss of heat due to escaping air and to make it possible for a man to 
push the trucks into the vestibule. 
It will be noted that the tunnel is considerably wider than the 
trucks. This is necessary when more than three or four well-loaded 
trucks are used, to permit enough air to pass through the tunnel. 
Correctly designed and spaced air baffles are necessary at intervals 
in the free space on each side of the trucks to deflect the air, first 
from one side through the trucks and then back again; otherwise it 
would take the path of least resistance, and most of it would. go along 
the sides of the trucks. Baffles also are needed where the air enters, 
i deflect it in a straight path through the tunnel (not shown in the 
cure). 
Trucks should enter at the end where the hot air enters. In this 
way the fish will be heated to a high temperature where rapid moisture 
conveyor, 






LONGITUDINAL SECTION 
