Do Different PVC Fittings Really Make a Difference in Water Flow?

Published on September 12, 2009

An overall shot of the test system at the AES facilities in Apopka, FL
An overall shot of the test system at the AES facilities in Apopka, FL

Consumer Report

We always hear about the efficiencies of some pipe fittings over others, and most often see them in writings or in some graph. Writings and graphs are great, but we wanted to find out exactly what the graphs would look like in a real-world situation.

I contacted our friends at Aquatic Eco-Systems (AES) and spoke with Bob Heideman about putting together a comparison test. After a little back and forth on how the test would be done, AES came up with a test fixture that would show us exactly what happens in relation to our flow rates by using one 90º configuration over another.

Understanding it All

The name of the game is “low friction loss.” When you select a low-head, high-efficiency koi pond pump from one of the koi dealers, you will probably get a state-of-the-art, quiet, very low amp draw pump that will last for many years. In order to get the most out of that low-head pump, you will need to have a low-head plumbing system.

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 Let’s face it, with today’s energy costs, we need to be concerned with conserving energy, and you can get that little bit extra just by selecting the right pipe fittings. By selecting the correct elbows when you build your piping system, you can use a smaller pump than you otherwise would, thereby saving energy. Even if you can’t find a smaller pump with lower energy consumption, you will still benefit by getting more water flow from the same pump. And who doesn’t want more water flowing over their waterfall?


Get This Through Your Head

The term “head” as it pertains to pumps has two parts to it. The one that most people know is the “actual head,” or “vertical head.” This is a measurement in inches, feet or meters that specifies how high the water is being lifted above the pond’s water level. In the case of a koi pond, “vertical head” is most likely going to be the distance from the surface of the pond water to the top of a waterfall.

The gauge for the bead filter at six psi.
The gauge for the bead filter at six psi.

At a higher pressure, the pump is moving less water, so it is doing less work. It is also the weight of the water that causes so much head loss when it is forced to change directions.

Another part of the term “head” is commonly called “dynamic head.” Dynamic head is a total of all the things that resist water flow in the piping system. It includes the friction loss from the pipes themselves, the loss due to the water changing direction, and the restriction of filter devices, ball valves and any other components in the plumbing system.

“Total head” is the sum of both “actual head” and “dynamic head.” You must use your “total head” as a guide when selecting a pump. Water is heavy. That is why most pumps use more energy when pumping at low pressure than they do when pumping at high pressure. The weight of the water being moved is more of a burden on the motor than the pressure, or “head,” it is being lifted to.

To illustrate this, just picture yourself carrying a heavy rock, moving in one direction, and then trying to change direction 90º in a short distance. You will almost have to stop, which takes energy, and then restart in the other direction, taking more energy. If you could make the turn over a longer distance, it would not take as much energy.

Where, What And How

The test took place at the Aquatic Eco-Systems facility in Apopka, FL. In the test, we compared 90º PVC elbows to two 45º elbows and 90º sweeps. Trying to keep the test as realistic as possible short of building an actual pond, a 500US/416UK gallon show tank was used as our pond.

The Short, Common, 90º Elbows
The Short, Common, 90º Elbows

For the plumbing, 3ft/91.4cm of 1.5in/40mm PVC pipe with two 90º elbows that lead from a 1/4hp SHE 2.4 pump to a bead filter running at 6psi was used. For the rest of the test 46ft/14m of 2in/50mm PVC pipe was used with eight 90º directional changes, as well as a 4ft/1.2m vertical rise to simulate a waterfall.

Bob did not want to rely strictly on a flow meter, so the flow was also measured by catching the pumped water in a 45US/37UK gallon tank over a timed period. Each test was run six times and then averaged to get the final numbers in gallons per minute.

Just a quick note here; do not get caught up in what equipment was used for the test. We are not testing equipment we are testing the turning options we have with different pipe configurations. The equipment used is just a means to an end.

The Results

The Short, Common, 90º Elbows

35.5US/29.5UK gallons/min, which is 2130US/ 1773UK gallons/hr.

Two 45º Elbows next to each other

Two 45º Elbows next to each other
Two 45º Elbows next to each other

38.5US/32UK gallons/min, which is 2310US/1923UK gallons/hr.

The 90º Long Sweep

39.8US/33UK gallons/min, which is 2388US/1988UK gallons/hr.

Just Some Thoughts

I must be honest, I was expecting a larger difference between the pipes, as probably many of you were, and as Bob pointed out, “At first glance, that may not look like much of a difference—hardly enough to worry about. But when you realize that you can get as much as 12% improvement in your pump’s output simply by using different elbows, you’d have to be crazy not to do it!”

Here are some points I would like to make as food for thought. The difference between the common 90 and the sweep 90 is 4.3US gallons/min, which works out to 258US/215UK gallons/hr. As Bob mentioned, it doesn’t look like much, but let’s go just a bit further with it. 258US gallons/hr is 6192US/5155UK gallons in a 24-hour period.

The 90º Long Sweep
The 90º Long Sweep

If you have a pond that size, you will get one more pass through your filter each day. If your pond is half that size, you’ll get two more passes through your filters per day. I think you can agree that is a pretty good trade off for just changing some elbows. Keep in mind we only used a few turns; in an actual pond you could have quite a few more than that hindering your flow even more.

Even if you think the 12% increase is not worth your time and a few extra pennies think about it this way: If you wanted a targeted gallon/hr flow, you could very easily get it from a bigger pump than needed, or you can plumb your system more efficiently and buy the smaller pump and get the same targeted flow rate. The bigger pump will get the job done; however, the smaller pump will cost you less to purchase and less in annual operating costs.

~ Bob Heideman (deceased) and Ryan Chatterson of Aquatic Eco-Systems, Inc. contributed to this article.

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6 thoughts on “Do Different PVC Fittings Really Make a Difference in Water Flow?”

  1. I use a lot of PVC pipes in leisure industry applications (pools, spa’s, hot tub applications) and I have never noticed a difference in water flow, having said that we operate at fairly low pressure so I am guessing that the actual system pressure would be a huge contributing factor to this, as well as the heat of the water through the system. Thanks for the article though, very interesting and will share this with my team.

  2. Long time ago, but I just read this and found it intriguing. As I thought, it will benefit my pool to use sweeps, even if they are slightly more expensive. I have very limited ‘return’ capacity, so everything I can do to improve it is on the upside. Thanks!!

    Cap’ nJan

  3. Also, if you have many such connection, the reduced friction (head) adds up. This test was for only a single 90.

  4. Great test thank you. It does however seem that you used a DWV (drain waste vent) type PVC for the long sweep, which I don’t think is really proper for a pressurized system. So maybe just go with the schedule 40 45’s. I’m also wondering about the impact of someone absentmindedly (to be kind) installing, in the middle of a completely 2″ PVC pool system, reducers and a 1.5″ 3-way valve. Ignore the 3-way, it can be set for “straight through” – but wondering about the impact of that short run of reduced pipe diameter.

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