Water Flow (GPM) Capacity Based on ID Size and Pressure
| PRESSURE | FLOW IN GPM THROUGH PIPE ID IN INCHES |
|---|
| PSI | 1" | 1.5" |
| 20 | 26 | 76 |
| 30 | 32 | 94 |
| 40 | 38 | 110 |
To calculate the runoff from any given rainfall:
- Take the dimensions of the footprint of your roof and convert them to inches. (So, a 50' x 20' roof is 600" x 240".)
- Multiply the roof dimensions by the number of inches of rainfall.
- Divide by 231 to get the number of gallons (because 1 gallon = 231 cubic inches).
- In order to size a trench drain system (lenght and width), the following information is needed: 1 Total lenght of the trench drain (feet or meters).
- trench (feet or meters).
- area where the trench drain will be installed.
- drain run.
- Please contact FILCOTEN sales of engineering for any help you may require.
Water Flow Capacity in Steel Pipes (sch 40)
| Pipe Size | Maximum Flow (gal/min) | Head Loss (ft/100 ft) |
|---|
| 12" | 4,700 | 4.0 |
| 14" | 6,000 | 4.0 |
| 16" | 8,000 | 3.5 |
| 18" | 10,000 | 3.0 |
Take the roof's total square footage and divide by the total square footage handled by one drain. The result is the number of drains needed. For example: 50,000 / 4,400 = 11.36; or 12 drains required.
DESIGN OF SUB-SURFACE DRAINAGE SYSTEMS Sub-surface drainage is the removal of excess groundwater below the soil surface. It aims at increasing the rate at which water will drain from the soil, and so lowering the water table, thus increasing the depth of drier soil above the water table.
A 110mm foul drain taking the discharge of less than 1 l/s should be laid at a 1:40 (25mm per metre) fall. A foul drain taking the discharge from a minimum of one WC can be laid at 1:80 (12.5mm per metre). Gullies incorporating in foul water or combined drainage systems must have a 50mm minimum water seal.
Regardless of surface characteristics, when it comes to surface drainage, slope is the most important issue to consider. For efficient drainage, paved surfaces should have a minimum 1-percent slope. Turf or landscaped areas should have a minimum slope of 2 percent. "Shoot" the grade.
The highest point of a manhole (or other access chamber) is the cover level (CL), which is the height of the cover above a benchmark level, and the difference between Cover Level (CL) and Invert level (IL) is the overall depth of the chamber.
FALL = GRADIENT X DISTANCE
For example, calculate the fall in a 50 metre section of foul water pipework if the gradient is to be 1 in 80. A gradient of 1 in 80 is converted to a number instead of a ratio. 1 / 80 = 0.0125.A gradient of 1:60 means that there will be 1 unit of fall for every 60 units of patio width. The patio is to be 4.2m wide, so if that distance (the run) is divided by 60, the result is the 1 unit of fall.
A 110mm foul drain taking the discharge of less than 1 l/s should be laid at a 1:40 (25mm per metre) fall. A foul drain taking the discharge from a minimum of one WC can be laid at 1:80 (12.5mm per metre). Gullies incorporating in foul water or combined drainage systems must have a 50mm minimum water seal.
For 4-inch PVC piping and a building sewer less than 50 feet long, the minimum slope is 1 inch in 8 feet, or 1/8-inch per foot, and the maximum is 1/4-inch per foot. For sewers longer than 50 feet, the slope should be 1/4-inch per foot.
Pipe Size. Some older sinks may have drains that connect to a 1 1/4-inch tailpiece, but most modern drains have a 1 1/2-inch outlet. All the pipes that connect to the tailpiece, including the P-trap assembly and all the horizontal extensions, are either 1 1/4 or 1 1/2 inches in diameter.
All above ground and below ground horizontal drainage pipes should be laid to an adequate gradient. Gradients from 1 in 40 to 1 in 110 will normally give adequate flow velocities. A gradient of 1 in 80 is suitable for commencing calculations for pipe schemes.
4 Common Types of Drainage Patterns. Drainage patterns are classified on the basis of their form and texture. Read on to learn some common types of drainage patterns, such as: dendritic, deranged, centripetal and trellised.
A trench drain (also channel drain, line drain, slot drain, linear drain or strip drain) is a specific type of floor drain containing a dominant trough- or channel-shaped body. It is used for the rapid evacuation of surface water or for the containment of utility lines or chemical spills.
How does channel drainage work? Linear drainage systems drain water along their entire length, rather than at one point like a gully does. They are made up of an enclosed channel with some form of grating over the top. The main purpose of a channel drain is to remove surface water away from a selected area.
