Flush valves are used in place of tanks in the flushing of water closets, urinals, and slop sinks. They may be placed directly back of and above the fixtures which they serve, or may be concealed behind partitions, as shown in Figs. C and D of Plate 42.

Flush valves may be operated either under direct pressure, as in Fig. B, or under tank pressure, as in Fig. A. The operation of flush valves under tank pressure is generally the more satisfactory method, as there is always a storage of water in the event of an interruption of the public supply, and the pressure is more positive and reliable. The tank pressure is always uniform, while direct pressure is extremely variable, which is an undesirable feature in not only this work, but in all branches of supply work. When a storage tank is used, the height of the tank above the highest flush valve should not be less than 10 ft. if good service is to be expected.

Plate XLII. The Use Of Flushing Valves

Plate 42.

Use of Flushing l/alves

Flush valves may be obtained that are to be connected with the supply pipe coming directly through the wall back of the valve, or for either right- or left-hand side connection.

The operation of most flush valves is similar in its general features. This action is as follows: When the handle is released after flushing, the valve is closed automatically by a jet of water discharged from the pressure side of the valve into and through a by-pass to the valve chamber beyond the piston head, which it gradually forces onto its seat. This by-pass is one of the sources of trouble, as any sand or other solid substance will clog up the passage and stop the passage of the water jet into the valve chamber. Some valves are provided with a device for holding back any such harmful solids.

It is difficult to state definitely proper sizes of pipes and connections for flush valves, as this information, given by manufacturers of different forms of flush valves, varies greatly, depending upon the different forms and construction of valves and upon the pressures that they are designed to work under. Some manufacturers advertise flush valves which work under pressures between 10 and 200 pounds, and are not affected in their operation by a variation between these two points.

Other makes of flush valves, however, are made in different styles, for different pressures. Owing to inability to give absolutely definite data which will cover all makes of flush valves, the following information is given in general, and may or may not be correct in the case of certain makes. Generally a pressure of 8 to 10 pounds is required for the operation of flush valves under direct pressure, and supply pipes serving buildings in which flush valves are used should be of such sizes and so installed that the drawing of water at fixtures will not reduce the pressure at any flush valve below the amount named.

In general, the size of service pipe for flush valves is from 1 1/4 to 1 1/2 in., when operated by direct pressure, for valves up to four in number, and these sizes should be increased for larger numbers.

When working under tank pressure, a main line of supply pipe is run down to the several floors, branches being taken to the different fixtures to be supplied.

A 1 1/2-in. main is ample for from one to four fixtures. If there is more than this number of fixtures, it is well in ordinary buildings to carry a 2-in. supply down from the tank 10 or 15 ft., reducing to 1 1/2 in. for the rest of the distance, and if the building is ten stories or more in height, the lower floors may be reduced to 1 1/4 and 1 in.

Flush valves for urinal use are often smaller in size than those designed for water-closet use, and have smaller supply connections. For low pressures a 1 1/2-in. connection to the flush valve is used, and for ordinary pressures 1 1/4 in. is the general size.

The storage tank for use in connection with flush valves should have a capacity, whenever possible, of about 6 gallons per fixture. This capacity is the requirement when a small number of flush valves are installed. On large systems, where a large number of valves are used, it is not necessary to provide such liberal storage, as the amount named per fixture allows for two successive flushes, and in large work it is almost impossible that all, or anywhere near all, of the fixtures served will be flushed at the same time. Therefore the size of the tank may be reduced from the capacity named, as may be correct for each separate system. A liberal capacity of storage is always desirable, however.