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a solid base under the gate which will prevent it from rebounding 
when it is dropped into position. The slides are made of 5- by 
7-inch hardwood strips, 6 feet longer than the crib height. One 
slide is placed on each side of the sluice way in a notch 16 inches 
long and 5 inches deep which is cut into the side logs of the sluice. 
Each slide timber is solidly spiked to the sluice way on the down- 
stream side and provides a backing against which the gate works. 
The groove in the sluice tunbers is widened to 22 inches at the 
top and a slide similar to those placed in the downstream side is 
spiked in place in order to keep the gate in position. 
Bear-trap Gate. — This type of gate has been used frequently 
in Pennsylvania. It has two rectangular leaves each of which 
Fig. 135. — The Bear-trap Sluice Gate. 
has a length equal to the width of the sluice. They are fastened 
to the bottom of the sluice by hinges on which they turn. The 
upstream leaf overlaps the downstream one when the leaves 
are down and the gate open. 
The gate is raised by the pressure of water from the upper 
pool, which is conveyed in a channel, controlled by a sluice 
gate, to a chamber (A), Fig. 135, constructed under the gate. 
A second channel, also provided with a gate or stop cock, con- 
nects this chamber with the lower pool. When the connection 
with the upper pool is opened, while that with the lower pool 
is closed, water from the upper pool fills the chamber under 
the gate. This causes the downstream leaf to rise, first by 
flotation and then by the impulse from the flow of the water. 
The upper leaf is raised by the lower leaf which slides under it, 
the friction being reduced by rollers. The height to which the 
gate rises is limited either by stay chains, or by a wood cleat 
nailed on the under side of the upper leaf. In lowering the gates 
the operation is reversed, the connection with the upper pool 
