i8S THK IMPROVEMENT OF RfVERS. 



into the masonry. The former supj>oses that the pin can be easily removed and 

 replaced when worn, which will occur sooner or later; luit in point of experience it is 

 usually very diflicult to do this, as the surfaces, even when greased, adhere so firmly 

 that steel wedges sometimes fail to separate them. As the bed-plate is cemented in, 

 the removal may finally necessitate coffering the lock, since it is difficult to do such 

 work under water. With pintles of other styles, which have proved equally and 

 sometimes more durable in practice, this objection does not exist, as they can be 

 replaced without difficulty. 



The surfaces of contact of a cast pintle and a cast shoe should always be chilled, 

 and if this is done they will wear longer than pintles of steel or shoes provided with 

 special bushings. 



Pintles for very small gates are usually about 4 inches in diameter at the top, and 

 for locks of 55 feet in width, altout 5$ or 6 inches in diameter. 



In concrete locks the pintles may be placed directly on the masonry, using a unit- 

 pressure of 200 Ibs. to the square inch, or special bearing-stones may be employed. 

 The former method is considerably cheaper, and is not less successful than the latter. 



The bonnet, or connection at the top of the heel, is sometimes formed in wooden 

 gates by using two iron straps bent to fit the heel, one at the top of the gate, the other 

 about a foot lower, with a small casting for the gudgeon-pin to which the anchor-bars 

 are connected. A more usual method is to employ a casting which fits over the top 

 of the heel, as shown on the drawings. It should always be provided with a movable 

 cap, so the anchor-bars can be removed and replaced when required during repairs to 

 the gate. In some of the older designs, where this was not done, it is necessary to raise 

 the entire gate when repairs have to be made which require a removal of the bars. 



The gudgeon-pins vary from about 2 to 6 inches in diameter, according to the size 

 of the gate. 



The center of rotation of the gate should be placed a little up-stream of the center 

 line, so the leaf will swing free of the quoin as soon as it begins to move. This dis- 

 tance may be from $ inch to several inches, according to circumstances. 



All the pins should have j w to jJ 8 of an inch clearance in the pin-holes so that they 

 can be removed easily. 



The diagonal straps used with wooden gates are sometimes made in one piece, 

 and sometimes in two, joined by a turnbuckle. In the former case the straps are made 

 a little short, from \" to jj ", and are put in place by being heated and shrunk on, and 

 in the latter they are put on as ordinary straps and screwed tight. This is the pref- 

 erable method, as should one become bent or broken by a boat or from other causes, 

 it is little trouble to remove and replace it. No strap or other iron should be placed 

 within 2 inches of the vertical surfaces of contact of the toes. 



The rollers on which the gate-spars travel (which may be two in number for each 

 spar, one on each edge of the wall) should be of ample diameter, to minimize the fric- 

 tion. Light and serviceable ones can be formed by taking a piece of 3$- or 4-inch gas- 



