4 BULLETIN 115, II. S. DEPARTMENT OF AGRICULTURE. 
Practically all gates of this type are fitted with screw and wheel 
lift and locking devices. The locking device usually consists of some 
form of cast-iron nut turning on the thread of the gate stem under 
the crosshead. As the stem does not turn around but is lifted simply 
by the threads in the wheel it is necessary only to screw the loose 
nut to any desired point and lock it to a chain or bar connecting 
with one standard. This prevents it being turned in either direc- 
tion, and when the stem is raised until the nut reaches the crosshead. 
the shutter is locked as regards further opening, but may be closed 
partially or wholly by the consumer. Other devices used lock the 
gate so that it can not be either opened or closed except under 
action of the key. (See fig. 11. p. 42.) 
Most of the standards of this type of gate come in lengths of 6 
feet unless ordered otherwise, but the writer noticed many cases 
throughout the West where a material saving could have been exer- 
cised by ordering shorter lengths of standard. 
The standards may be made so that they will be at right angles 
to the connection for the pipe or at an angle of 60° or 75° with the 
pipe. In most cases the 75° angle probably will give better results, 
as the face then will be more nearly in conformity with the slope of 
the bank. One manufacturer even makes a type with a slope of 45° 
with the pipe. 
Most makers step up the gate sizes to conform to the sizes of stand- 
ard vitrified-clay pipe beginning at 6 inches and going to 24 inches. 
Some makers have gates for 30 and 36 inch pipe, but as a rule the type 
is changed. 
Gates with connections for rectangular openings are for use with 
timber or masonry tubes larger than standard sizes of pipes, as a rule. 
The standards, locking devices, etc., are the same as on the gates for 
pipes. These gates run in various sizes from 6 by 6 inches up to 
several feet in either dimension. The stems and lifts vary all the 
way from a simple handle and bar up to powerful geared rack-and- 
pinion or screw lifts. 
The third type of gates consists of sheet-steel or cast-iron slides with 
metal guides. They come in sizes up to about 12 feet wide and may 
be built up from a single panel to a battery of several openings. 
AVhere the masonry structure is divided into vents by masonry piers 
each gate is a unit independent of the others. They also are designed 
in batteries for installation as a metal unit in a gate structure with 
walls and floor of concrete or rubble masonry. This class has a struc- 
tural steel frame securely anchored by bolts to the floor and walls. 
An example of this type of gate is shown in Plate V, figure 2. 
The rack-and-pinion lift is the most common type for this class of 
gates. On the more simple ones the lever acts directly on the pinion, 
the gate being held by a pawl. More power is secured by inserting a 
train of gears between the lever and the rack. 
