Understanding Pumps & Pump Curves
When looking for a pump we need to be certain its up for the job! Is it the right type of pump and can it handle what I need it to do?
For this we look at what we need to pump - is it rain water, sewage water, sludge, hot water, sea water etc. All these have an affect on what type of pump we should buy.
Also to look at the pumps intake, will your water have small items like silt or large items like nappies going through it? This will look at the solids handling (size of solids it can handle)
Flow rates - Can the pump keep up with the flow. If you have a pump rated at 1,000lph but you have 5,000lph of rainwater gushing in then things are going to get wet!
Pump curves - This will tie in with flow rate. The higher and further you pump the higher you go on the pump curve which will show the lower flow rates.
eg. you see a pump rated at 20,000lph 10m lift (this flow is based on zero lift and zero distance) lets say you need to pump 2m up and 30m away we need to find the dynamic lift of the pump (lift + distance friction loss = dynamic lift) 30m will take roughly 1.5m lift off the pump lift plus the 2m lift you need it to pump. now look at the pump curve at 3.5m and see its flow rates. This is now the actual flow rate at final discharge point.
Calculating Storm Water
To calculate the runoff from any given rainfall:
(This is an example of 1" of rainfall in 1 hour)
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. (In this example, 600" x 240" x 1" = 144,000 cubic inches of water.)
Divide by 231 to get the number of gallons (because 1 gallon = 231 cubic inches). (144,000/231 = 623.38).
Equating to 623 gallons for the hour.