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RAINTROL® FLOW CONTROL DRAIN
The RAINTROL® roof drain was developed to offer certain advantageous features. Drains, leaders, storm sewers, etc., can be economically sized by controlling the flow of water. This will reflect in significant cost savings, both in material and labor. In addition, by controlling the drain rate, existing facilities can be utilized without overloading, thus, new construction can be undertaken and tied into the present storm drains.

To accomplish the above, the RAINTROL® drain retains water on the roof. The water is allowed to build up to a predetermined height while the excess is drained off at a known maximum rate. The amount of net build-up is a function of rainfall intensity, time, roof area and drain flow rate. Also note that the flow rate is a function of the build-up or head of water, and not the height of the weir. As an example, water at a 2" depth will flow through either the three inch high or six inch high weir at the same rate.		 The area rating, flow rate and drain down time are given for various locations, consistent with the rainfall data for the localities. The data has been established for over 200 localities. Use of this data and tables will allow the engineer to lay out an efficient roof drainage system which will result in significant economies. Local codes must be observed to avoid conflict and approval problems.

THE AREA RATING IS THE MAXIMUM AREA WHICH CAN BE HANDLED BY ONE WEIR OPENING. The corresponding flow rate and drain down time are also given. Data is presented for four conditions of roof slope and four return periods. This provides data for sixteen conditions for each locality. In cases where the area rating would exceed 25,000 sq. ft., the rating is limited to 25,000 sq. ft. with a resulting lower flow rate and drain down time. Depth or build-up, the other limit upon which the table data is based, is as follows: 3" depth for flat roof, 4" for 2" rise, 5" for 4" rise and 6" for 6" rise.
DATA DERIVATIONS
The data presented on Table 1 is the result of extensive computer processing. Rainfall information obtained from isopluvial maps was computer matched with the flow characteristics of the weir. The results were computer plotted and tabulated in the final pages of tables.

The Weather Bureau Technical Bulletin No. 40, contains the isopluvials which provide the information for the Weiss Equations of Rainfall Intensity. This is more representative than other data available for design purposes. It also covers all areas, not just point locations. The weir equations were developed from test data. When the two equations are solved simultaneously, the area ratings in the tables are produced. Because of the methods employed, extreme accuracy was realized. Fig. 1 is an example of an isopluvial map. Cities along the same isopluvial will have similar rainfall. This allows use of the data for locations which are not listed.
100-Year 1-Hour Rainfall (inches)
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