Swimming Pool Flow Meters
Residential swimming pools are not closely regulated for things like water quality, filtration times or other safety issues. No city inspector is going to stop by your home and take a look around for anything that might be amiss. In the world of commercial swimming pools a visit from your local city inspector is a certainty, and they will want to take a look at your water quality and testing logs.
Nothing is left to chance in the world of commercial swimming pools. Water filtration and chemical balance is checked and recorded up to every hour depending on the type of commercial facility the pool is located in. The volume of the pool is known, as is the rate of water filtration, such that a fairly accurate turnover rate of the water can be calculated. Perhaps this level of monitoring is unwarranted in the average backyard swimming pool, however some benefits can be derived from borrowing from the commercial world.
In order to keep a swimming pool filtered properly you should filter the water up to three times every 24 hour period. This commercial standard is often reduced down to as little as a single turnover per day in residential pools that do not get much in the way of swimming traffic or debris load. This means that whaterver the volume of your pool is, this is the amount you need to filter your pool every day at a minimum, or in an ideal sense you should triple this value every day. Simply take the volume of your pool and divide that by the number of hours per day that you run your pump. This will give you the hourly flow rate you need to maintain your water for your pool. Then divide this by 60 to give you the gallons per minute value that you need to maintain in order to meet a single turnover of your pool volume. All of this is covered in the turnover rate calculation that you can find in this article about matching pump and filter sizes.
If you understand everything in the above paragraph then you are already well ahead of the curve with how you maintain your pool water. The only problem is that the above calculation only works in theory. You might have a 25,000 gallon pool, and you run your pump 12 hours per day, so this means you know that you need just over 2000 gallons of water filtered per hour for each of the 12 hours you are running your filtration system. This works out to about 34.7 gallons per minute in flow through your system...the only problem is how do you know how much flow your pump is actually realizing in your system?
Why A Flow Meter Is Better Than Calculating Flow Rates
While it may be possible to calculate pool volume and hourly flow rates for your system, one thing that is not able to be calculated is how much flow your pump will be able to put out. If you can imagine an example with two identical pools except that one pool has the pump located 100' away from the pool location, while the other has the pump and filter located directly adjacent to the pool. As you might imagine even though the pools and filtration systems are otherwise identical, the longer distance from the pool to the pump location adds extra friction losses and resistance to flow. This means that the flow rate for the pumps will be different even though they are the same pump with the same flow ratings. Now again, picture two identical pools, except this time one of them has the pump and filter installed on a hill that is adjacent to the pool, and raised 10' above the elevation of the water level in the pool. Again, despite being otherwise identical pools and equipment, the flow rates for these systems will be completely different.
It is possible to be able to calculate the total dynamic head for a pool system, in theory. In practice this is not something that the average pool owner (or even the average pool technician) would be able to do. Even if you did go through the process of measuring the head resistance and calculating flow rates, this would only give you a snapshot of the system as it exists right now. Any change in valve settings, return eyelets, pump speeds, or even the difference between a clean filter and a dirty filter will change your calculated values so much as to invalidate them completely. In total, it is not practical to be able to use calculated values for actual flow rates in a pool system. An educated guess could give you a reasonable estimate based on pipe size, flow restrictions, and pump performance curves, however this would still have a margin of error too great to rely on for determining filtration schedules.
The solution to this complicated calculation for flow rates is simple, and something that is borrowed from the commercial swimming pool industry. A city inspector for a commercial pool will need to verify that the turnover rate is at least three times the volume of the pool every 24 hours. In order to facilitate checking this, flow meters are required to be installed on all commercial pools so that the flow rate through the lines can be verified. A flow meter completely skips the requirement for a calculation by mechanically measuring the actual flow moving through the pipes. While the flow value can still change in the system with changing conditions such as a dirty filter, any changes in flow can be easily noted and recorded to make sure that the flow rate is sufficient for the filtration needs of the pool.
Benefits Of Flow Meters For Pools
In addition to filtration schedules, a very important reason to know actual flow rates is due to flow requirements for certain pieces of pool equipment. For example, all pool filters have a maximum designed flow rate, which is the maximum flow volume that the filter can handle before you risk damaging the filter or filter media. While this used to be less of an issue, newer pool pumps are more powerful than ever and many of the larger variable speed pumps are near to three horsepower and plenty capable of exceeding maximum designed flow rates for some filters.
Click here to see maximum flow rates for all filter models
Pool heaters also have minimum flow rates, as well as optimal flow rates which you would need a flow meter in order to dial in. While some very new high end variable speed pumps come equipped with an onboard flow meter for dialing exact flow rates, the vast majority of residential pools would benefit greatly from the addition of a flow meter to their plumbing system. As variable speed pumps become more and more common (and required by law by 2020), the need for the average pool to have a flow meter installed increases. Running a variable speed pump at either too low or too high of RPM speed could cause your pool to be chronically underfiltered, or potentially exceed the maximum designed flow rates for your other pieces of equipment.
Flow meter for 1.25" plumbing
This is an analog flow meter for horizontal pipe installation on 1.25" PVC plumbing. The flow range is 9 - 50 GPM
Flow meter for 1.5" plumbing
This is an analog flow meter for horizontal pipe installation on 1.5" PVC plumbing. The flow range is 10 - 70 GPM
Flow meter for 2" plumbing
This is an analog flow meter for horizontal pipe installation on 2" PVC plumbing. The flow range is 20 - 120 GPM
Flow meter for 2.5" plumbing
This is an analog flow meter for horizontal pipe installation on 2.5" PVC plumbing. The flow range is 25 - 150 GPM
Flow meter for 3" plumbing
This is an analog flow meter for horizontal pipe installation on 3" PVC plumbing. The flow range is 45 - 240 GPM
Flow meter for 4" plumbing
This is an analog flow meter for horizontal pipe installation on 4" PVC plumbing. The flow range is 125 - 500 GPM
Flow meter for 6" plumbing
This is an analog flow meter for horizontal pipe installation on 6" PVC plumbing. The flow range is 250 - 1050 GPM
Flow meter & check valve for 2" - 2.5" plumbing
This is an analog flow meter and check valve combo for installation on 2" or 2.5" PVC plumbing. Flow range 20 - 110 GPM. Not all pools need a check valve however if you need a check valve to protect your heater from a chlorine erosion feeder or salt water chlorinator cell then this flow meter and check valve combo is the best option. If you have a pump that is located above the water level of your pool then you can locate this check valve on your suction intake to prevent the water in the suction lines from draining back to the pool every time you open the pump and clean out the strainer basket.
If you add a flow meter to your plumbing system then you can take all of the guesswork out of your filtration schedule and turnover rates. You will also be able to dial in the most efficient flow rates for your filter or heater as well as monitor for the difference in flow rates as your system changes like from a dirty filter or changes in your plumbing orientation. While you can locate a flow meter anywhere in your plumbing system it would be best to locate these flow meters on a horizontal section of pipe directly before or directly after the filter. It is ideal to have a straight section of pipe that is 10x the pipe diameter before the meter, and 4x the pipe diameter after the meter. As an example for 2" plumbing this would be 20" of straight, unobstructed pipe before the meter, and 8" after the flow meter.
Swimming pool blog
How to calculate pool volume and turnover rates
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Variable speed pool pump reviews
Proof of variable speed pump savings
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