GATE STRUCTURES FOR IRRIGATION CANALS. 6 



TYPES OF GATE SHUTTERS. 



The openings or vents in gate structures generally are regulated 

 by either slot shutters, comprising flashboards and wooden and metal 

 slide gates ; radial gates; or shear gates. There are also several styles 

 of collapsible gates, roller curtains, needles, butterfly gates, and other 

 devices, but their use is very limited in this country, and for that 

 reason they are omitted from this publication. 



SLOT SHUTTERS. 



The type of slot shutters in most common use is a wood or metal 

 shutter sliding in grooves or slots. This arrangement does very 

 well for small gates, but where the opening is so large that there is 

 any great amount of pressure against the gate the friction becomes 

 so great as to render the operation of the shutter difficult. Some- 

 times this sliding friction is reduced by inserting a roller bearing 

 between the shutter and the guide. 



Wooden gate shutters are the most common of all types. Various 

 types of wooden shutters are shown in Plate I. Slides for openings 

 up to about 4 feet wide are made wholly of wood, as a rule. Larger 

 shutters are usually braced with iron, and those 8 to 12 feet in width 

 commonly are furnished with a metal shoe which slides against the 

 guide. Small gates are usually nailed together, but it is better to 

 use bolts freely on gates wider than 3 feet. 



If redwood lumber is used gates up to 3 feet wide may be made of 

 1-inch stuff single thickness, but above that it is recommended that 

 at least 2-inch stuff be used, or, better still, double 1 or 11 inch, with 

 the two layers at right angles to each other. Tightness may be 

 secured by placing a layer of tar paper between the two layers of 

 wood. Gates of pine and of any timber other than redwood, except 

 very small ones, should not be made less than 2 inches in thickness. 

 If built of double material they will be more nearly water-tight and 

 stiffer than if built of a single thickness. 



Most of the much-used metal slide gates are made by foundries 

 and machine shops that specialize in this work and issue very com- 

 plete catalogues that describe in detail each kind of gate. Most of 

 them are included in one of three types: Grates for pipe deliveries 

 through the banks, gates for rectangular tubes of wood or masonry 

 through the banks, or gates for open channels. The first type consists 

 of a sheet-steel or cast-iron slide over a cast-iron face orifice with 

 angle iron or steel standards and the necessary lugs to attach the 

 gate to the bell, and of a cast-iron, vitrified-clay, cement, or corru- 

 gated-iron pipe. In the trade nomenclature the size of the gate 

 agrees with the size of the pipe to which the gate is to be attached ; 

 that is, an 8 -inch gate is ordered to fit a pipe 8 inches inside 

 diameter. 



