In the system of plumbing shown on Plate 29, the venting of the several lines of water closets is accomplished by extending the horizontal soil line beyond the last fixture, and connecting this extension into a main vertical line of vent at a point higher than the top of the fixtures.

The main vent stack may be at either end of the line of fixtures, but when placed at the end opposite the soil stack the connection of the horizontal lines into the vent stack is usually much shorter and more direct, and installed with the use of less pipe. When placed at the same end as the soil line, the running back to this point of a long line of large-sized pipe would often be a difficult or impossible matter.

Plate XXIX. Continuous Venting Of Water Closets - Circuit Vents - Loop Vents

Continuous Venting of Water Closets Plate 29

Continuous Venting Of Water Closets Circuit Vents  83

This form of venting is not strictly on the continuous-vent principle as shown in the three preceding plates, but being along somewhat the same general lines is often alluded to as continuous venting.

This method is also known as circuit venting.

The system of circuit vents, as prescribed by certain plumbing ordinances, consists in the extension of the horizontal branch soil or waste lines and the connection of these extensions into a main vertical vent stack, the entire system including both main soil or waste stack, main vent stack, and branch soil or waste lines, providing for each line of fixtures a complete air circulation through the branch which serves them.

The advantages derived from this system, as applied to water-closet lines, may also be obtained for other fixtures.

Fixtures of other character, such as the lavatory located on the second floor in Plate 29, are vented as shown in the case of this lavatory. The use of the circuit-vent system is of special value when applied to lines of water closets, such as are very common in public toilet rooms, for the reason that the free circulation of air through the horizontal lines does away with the necessity of venting the individual fixtures in the ordinary manner, that is, from the lead bend. A water closet, however. connected to a horizontal soil line served by a circuit vent, and located 5 ft. or more from that line, should be vented in the usual manner.

It will thus be seen that the continuous venting of lines of water closets by means of circuit vents, provides ample protection to the fixtures against siphonage, and effects a great saving in avoiding the outlay incident to installing a separate vent for each water closet.

The common method of venting lines of water closets is shown in Fig. D, Plate 40. Any branch line of soil or waste pipe serving a line of two or more fixtures may be provided with a circuit vent to the advantage of the system.

When the horizontal soil branch is of not more than 20 ft. in length, measuring from the main soil stack, and the line is not entered by more than four water closets, the vent extension may be reduced to 3 in. from the end of the branch into the main vent stack. When a larger number than four water closets enter the horizontal soil branch, the vent extension should not be reduced in diameter, but should continue of the same size as the soil branch, into the main vent stack.

While not allowable to use quarter-bends on any part of the drainage system, they may be used on circuit vents, as shown in Plate 29. While much used on this work, a better form of practice is seen in the use of a T-Y or Y and eighth-bend, in place of the quarter-bend, thus allowing the use of an end cleanout, by means of which the entire horizontal branch could be controlled in the event of stoppage.

In addition to the circuit vent, there is also what is known as the loop vent. The loop vent is a modified form of the circuit vent, used when a line or group of fixtures on a single floor is to be circuit-vented, and there are no fixtures on the floors above.

In this case the soil or waste branch is extended beyond the line of fixtures, and run up as in the case of the circuit vent, and then looped over the line of fixtures into the soil or waste vent of the stack into which the branch soil or waste pipe connects.

, The loop vent may be used for a single line of fixtures, on a floor above which are other fixtures emptying into the same soil or waste stack, by connecting the loop into the main vent stack above the highest fixture of the group.

The loop vent for a 4-in. soil branch may be 3 in. in diameter.

For 5 and 6-in. soil branches, the loop vent should be 5 in. in diameter, and for larger sizes 6 in.