Local ventilation has been greatly improved in recent years, until now it seems difficult to understand how in its most perfect form it could be further improved upon. As it has generally been known in the past, the local or seat vent is a pipe connected to the water-closet principally, but also to the urinal and the slop sink, at such a point and in such a manner as to carry off into the outer atmosphere the odors incident to the use of the fixture to which it is attached. It may be stated that the local vent has no connection in any way with the back vent system, the purpose of the two forms of vents being entirely distinct. In Figs. 161 and 162 are shown the common methods of applying local ventilation to water-closets - the method first introduced.
It has been used mostly in connection with the water-closet, and is made of galvanized sheet iron or copper pipe, generally of 2 in. diameter. In its original form, the local vent was attached to the water-closet by a horn cast onto the side of the bowl and at a point above the water line.
The action of the local vent depends upon the fact that heated air rises. Whenever possible it should be connected into a heated flue, as in Figs. 161 and 162. The heat rising in such a flue creates a strong suction on the lines of local vent, usually powerful enough to draw into it all odors arising from the use of the fixtures connected to it.
These odors are carried up through the flue, and are discharged into the atmosphere at a point where they cannot become a nuisance. When it is impossible to connect the local vent into a heated flue, it may be carried through the roof, and a draught created by burning a small gas jet in it. A very important point is that the local vent pipe should always enter a flue above all openings into it. If otherwise connected, foul odors from the vent might escape through flue openings into rooms of the house.
In Figs. 1G1 and 162 are shown the two methods of constructing local vents, one consisting of a separate vent from each fixture to the flue, the other making use of one main pipe into which the separate vents are branched. The separate-vent system of Fig. 162 is by far the preferable.
Fig. 161. - Common Method of Constructing Local Vents.
Fig. 162. - Good Method of Constructing Local Vents.
Whenever local vents from several fixtures are connected into a main line of vent, the latter should be of an area equal to the combined areas of the individual vents. The venting of lines of water-closets, such as found in public toilet rooms, is illustrated in Fig. 163.
In this work, the individual vents are connected into a main horizontal line which is carried into a heated flue. There is not the objection to the use of a main local vent on public work that there is in residence- and dwelling-house work.
Fig. 163. - Local Venting for Line of Water-Closets.
Fig. 164. - A Common Method of Ventilating Public Toilet Rooms.
The use of the local vent system described above, is still common in dwellings, residences, etc., but for large toilet rooms or public toilet rooms, this system after a time, gave place largely to another system, which is illustrated in Fig. 164. It will be clearly seen that this method does not follow closely the definition of local vents, but the subject is not complete without a consideration of it.
The illustration shows a double line or battery of water-closets, each water-closet compartment being provided with a register communicating with the foul-air duct or flue at the rear of the battery. Also at intervals along the line of water-closets, registers are placed at the ceiling for the purpose of bringing into the room a supply of fresh air. Thus it would seem that with provision for exhausting the foul air, and for admission of fresh air, this system would give perfect results.
Fig. 165. - Water-Closet with Raised Rear Vent.
Its weak point, however, is the fact that in order to enter the foul-air duct through the register at the side of the fixture, the foul odors and gases must first be drawn out of the closet bowl, and this gives them an opportunity to become more or less diffused in the atmosphere of the room, which is a serious objection. It may be stated at this point that much appears in the author's work "Modern Plumbing Illustrated," concerning these two methods of toilet-room ventilation, which is not given here.
Figs. 166-167. - Raised Rear Vent Applied to Siphon and Siphon-Washdown.
There is a form or method of local ventilation which has neither the objectionable feature of diffusing the odors generated, nor the objectionable feature of the method first described, which is its inadequate size of vent. The method here alluded to is the method which calls for the use of water-closets having raised rear vents, a method which gives most excellent results.
In Fig. 165 is shown one of the modern types of water-closet with the raised rear vent attached. It will be seen that instead of being of only 2 in. diameter as was the form of local vent first described, this vent is 3 to 4 in. in diameter. Furthermore, the raised rear vent is in no way unsightly, but on the other hand really adds to the appearance of the fixture. In Figs. 166-169 are shown sectional views of the most common types of water-closets with the raised rear vent applied. This is to show that the principle is one that can be easily applied to any of the modern types of water-closets. The additional expense of such a fixture over the common type is very slight.