SELECTING A PUMP
SELECTING A PUMP
Excerpt found at https://www.marquisgardens.ca
Posted by Marquis Gardens Team on June 13, 2016
Choosing the proper pump will provide you with:
There are a few key elements that you need to know in order to choose the correct pump:
APPLICATION: WHERE WILL YOUR PUMP BE?
In the pond at the bottom: look for a solids handling pump (great for pumping waste into filtration units)
In pond – In the skimmer:look for a skimmer/high volume pump (skimmer pumps do not need to handle solids as there is usually a filter basket or net prior to the pump
Require a lot of head height:(ie: a water feature with falls 20ft or higher): Direct Drive pump – delivers a large amount of head height
Require volume but minimal head height:(ie: most pond applications) Asynchronous/Mag drive – high efficiency pump with high volume, but less head height than direct drive.
HOW MUCH VOLUME DO YOU NEED?
LIGHT FLOW = 100 gph per inch of spillway
AVERAGE FLOW = 150 gph per inch of spillway
HIGH FLOW = 200 gph per inch of spillway
WIDTH OF SPILLWAY X DESIRED FLOW RATE = TOTAL GPH
3ft wide spillway
Examples for waterfalls with a 36” wide spillway:
LIGHT FLOW: 36” Spillway x 100 GPH = 3,600 gph
AVERAGE FLOW: 36” Spillway x 150 GPH = 5,400 gph
HIGH FLOW: 36” Spillway x 200 GPH = 7,200 gph
Every pump has a chart/graph available to determine at each head height, the amount of gallons outputted.
As head height increases gallons outputted decreases
DETERMINING WHAT PUMP YOU NEED ACCORDING TO HEAD HEIGHT
- Add 1 ft of head height for every 10 ft of hose you are using
- Add 1 ft of head height for every 90 degree angle you are using
You have a waterfall that requires 4500 gallons and is 5 ft above the waterline, has 20 ft of hose and utilizes 3 elbows.
Therefore, your head height is
5ft (height of waterfall) + 2 ft (hose) + 3 ft (3 elbows)
= 10 ft of head height
You will need a pump that pumps out 4500gph at 10 ft which in the above graph would be the SP5300 (Pink Line)
Important Pump Info: Back Pressure
The life of any pump is directly related to the operating conditions it works under. One of the most common causes of premature pump failure is LOW head.
Pumps are designed to work under a certain amount of load. In low head applications not enough back pressure is put on the pump and it spins too freely. This causes the motors to run hot and shortens their life considerably.
In every plumbing system you should incorporate a valve somewhere in the discharge line. This valve can then be closed part way to simulate back pressure if not enough natural pressure is created.