Plastic PVC Pipe Friction Loss
The following information is technical information for those of you using large pumps for water features in your pond. This information doesn't affect the typical homeowner and their pond set up. This information is used primarily for landscapers and pond professionals who need to calculate the friction loss and size of hose to use with their pump for a given water feature. If you have questions, please ask us and we'll be happy to help you.
Often times pond owners use too small of a hose on their pump. Always use the same size of hose or even one size larger as the discharge port on the pump. For example: a pump with a 1 1/2" ID discharge would need a 1 1/2" ID or 2" ID hose.
Each fitting in your plumbing system creates resistance and can slow your water flow. We recommend using our flexible PVC pipe which eliminates most fittings.
As a reminder, the DEPTH of the pond where the pump is located does not count toward the 'head' or 'lift' of the pump. The 'head' or 'lift' of the pump is determined by the distance ABOVE the water's surface.
Feet of head is typically measured in terms of vertical lift and horizontal distance. However, the diameter and length of pipe can have a significant effect on the performance of the pump as well, especially if the pipe diameter is too small.
A pump must have power to not only push the water up to the vertical height of the waterfall and the horizontal distance to the waterfall but also overcome the friction loss created by the pipe.
Total Dynamic Head is the feet of head (lift) added to the friction loss created by the pipe. In most small ponds with short pipe runs, friction loss is typically not a problem. However, in a feature with long streams or high flow rates, friction loss can have a big impact on the performance of the pump.
To determine Total Dynamic Head you would add the feet of head and the friction loss. The chart below lists the feet of head equivalent created by flow and pipe diameter. These figures are shown based on a 100' length of pipe.
Example: We are pumping 70 GPM (4200 GPH). The chart shows that 70 GPM (gallons per minute) through 100' of 2" pipe equals 8.83' of head while a 3" pipe only equals to 1.24' of head. If you waterfall is 10' high and 100' away, you will have a total head of 18.83' using 2" pipe but only 11.24' using a 3" pipe.
What does this mean? It means that your water flow will be different based on the size of pipe you choose. How you determine the water flow is to check the GPH or GPM of the pump at a given height. This information is typically shown on our website, on the manufacturer's box or from the manufacturer. For example, say you have a 4200 GPH. The '4200 GPH' refers to the GPH at 0' or 1' of lift. As you continue to increase the 'lift', the water pressure decreases. By calculating the Total Dynamic Head by using the formula below you will see that if you use a 2" pipe versus a 3" pipe, you will see a significant difference in the amount of lifts. What you then do is take that number (in this case, the 8.83 for 2" pipe and the 1.24 for the 3" pipe) and then look on the pump chart to see what the water flow is at that lift. That water flow would be the flow that you would have at that particular lift.
To explain further, let's make up a chart for the 70 GPM (4200 GPH) pump. It may look like this (this by no way indicates the performance of our pumps, it is purely a made up example):
|GPH @ 1' lift||GPH @ 5' lift||GPH @ 8' lift||GPH @ 10' lift||GPH @ 15' lift|
|4200 GPH||3500 GPH||3000 GPH||2200 GPH||1200 GPH|
As you will see from the above, the GPH @ a 1' lift is 4200 GPH. The GPH @ 8' lift is only 3000 GPH. Now, looking at our Friction Loss Chart below, you will see that a 70 GPM pump connected with a 2" pipe will provide a 8.83' head and a 1.24' head for a 3" pipe. When we check out the pump performance chart we see that at 8' head the pump will only push 3000 GPH and at 1' of lift the pump will push 4200 GPH. This difference is quite significant. Why? Your waterfall or filter at the top of the pond may need 4200 GPH in order for it to have the flow you want. You may also have a filter that needs to filter the pond water at a certain rate in order to keep the pond clean. If you don't have enough water flow, your water feature or filter will not perform the way you want it to. And of course, you paid good money and put forth a lot of effort to have the look you want. So, be sure to choose the right size of pipe when planning your next waterfall feature. Always be sure to use the same size of pipe as the pump discharge requires or the next largest size. When you go up to the next largest size, be sure to check the friction loss chart below to see what the Total Dynamic Head will be and then essentially, what your GPH will be at that head.
I hope this helps. :o)
Friction Loss Chart
|GPM||GPH||1"||1 1/4"||1 1/2"||2"||3"||4"||6"||8"|