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Plumbing Basics

Basic information about plumbing and water flow.

If you take a 1.0 HP pump off your pool and replace it with a 2.0 HP pump, you will get a lot better flow, right?  Not so fast.  It may actually work a lot worse than the original pump if your piping will not support the additional flow.


At 7 IPS, here are your maximum flow rates through different piping

  • 1.5″ PVC pipe can carry a maximum flow rate of 45 gallons per minute
  • 2.0″ PVC pipe can carry a maximum flow rate of 87 gallons per minute
  • 2.5″ PVC pipe can carry a maximum flow rate of 105 gallons per minute

3.0″ PVC pipe can carry a maximum flow rate of 165 gallons per minuteBasic fact: You can only push so much water through a pipe, and the amount of water is directly related to the size of the pipe.

The maximum optimal velocity of water in pool system piping is 7 inches per second (IPS). There are actually safety regulations that are driving this down toward the 5 IPS level, but the 7 IPS standard applies to most systems.

So . . . if you try to put a 1.5 HP pump on a system that has only one 1.5 inch pipe on the suction side of the pump, you are in for trouble. Your 1.5 HP pump wants to move 75-90 gallons per minute, but the intake pipe is only capable of moving 45 gallons per minute.

This creates an excessive amount of vacuum on the suction side of the pump and causes what is known as cavitation.  You will see a lot of air bubbles in the pump pot and the pump will probably be very noisy as well.


Every foot of piping adds a certain amount of resistance to the system and results in pressure loss.  If you have ever hooked several garden hoses together, you know that the pressure at the end of hose is a lot lower than it is at the faucet.

  • 1.5 inch pipe – every 100′ of pipe reduces pressure by 4.5 psi
  • 2.0 inch pipe – every 100′ of pipe reduces pressure by 3.5 psi
  • 2.5 inch pipe – every 100′ of pipe reduces pressure by 2.9 psi
  • 3.0 inch pipe – every 100′ of pipe reduces pressure by 2.25 psi

If your equipment is a long way from the pool, it does impact your total flow.


Every pipe fitting adds to the total pressure loss (otherwise known as head loss or friction loss) in the system.

  • 2.0″ 90 degree elbow – equivalent to 4 extra feet of pipe
  • 2.0″ 45 degree elbow – equivalent to 2 extra feet of pipe

You get the general idea.  If you have a bunch of elbows in a system you reduce the flow.  If you put them all in a row, you reduce the flow even more because of the turbulence that you create.  This is why it is always best to separate elbows by 6-12″ of pipe if possible (but on tight equipment pads it is not always possible).


Your pump, filter, backwash valve, heater, chlorinator, skimmers, return inlets and intake and return valves all create a certain amount of friction loss that reduces the flow and pressure in the system.

Many people don’t give any of this a thought, but it does matter.

Here is the bottom line . . .

At Pool Stop we understand hydraulics and water flow.  This means that when we recommend a solution for your pool, it will work guaranteed! Properly sizing all the plumbing and equipment makes for a quieter, more energy efficient pool and saves you money in the long run.

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