A pump according to Dictionary.com is “an apparatus or machine for raising, driving, exhausting, or compressing fluids or gases by means of a piston, plunger, or set of rotating vanes.” Sounds pretty simple right? Wrong, pumps have many options and must be sized not only to the size of your pool or spa, but also to the size of the filter you are using.
We are first going to go to the basics, moving water. How much water do you need to move? This will depend on what type of pool you have; commercial or residential?
If you have a commercial pool (a pool that is open to the public) by health department requirements you must turn the volume of water in the pool over every six hours. Let’s say for example you have a 100,000 gallon commercial pool, you will need a pump that will turn over 16,667 gallons an hour. We need to break this down into minutes for comparison purposes, so we need a pump that will move 278 gallons a minute. Now you can begin your search for the correct size pump. Let me tell you that will be one huge pump! A residential pool needs the same type of calculation but the size is much smaller. Let’s say you have a pool that is 20,000 gallons using the formula we used in our commercial pool example, but our required turnover time for a residential pool is ten hours. So, we need to turn over 2,000 gallons an hour or 33 gallons a minute. Once we determine the size of pump we are going to employ we need to make sure the filter we have will accommodate the designed flow rate of the pump, otherwise you will have a problem with water clarity or you could possibly cause damage to the filter trying to push too much water through too small a filter.
Let’s now talk about the different types of pumps. Most people do not realize that there are really three classifications of swimming pools; commercial, in ground residential and above ground residential. Each of these swimming pools requires a specific type of pump. Some commercial and residential in ground pools use the same type of pump depending on the number of gallons in the pool. But above ground pool pumps are a completely different animal. Commercial and in ground residential pumps are designed to lift water from below ground, where above ground pool pumps are designed to be fed water from above the ground. If you tried to put an above ground pool pump on a in ground pool you would struggle to get the pump moving water. So when you are shopping for a new pump make sure you purchase the correct pump for your type of pool.
The balance of this class we are going to talk about residential pool pumps. There are four types of motors; single speed (most common), two speed, variable speed, and variable flow.
Single Speed Motors- The shaft of these motors only turn at one speed usually 3,450 rpm.
Two Speed Motors– These motors will operate at high speed (3450 rpm) and can shift to a lower speed, usually a fraction of the high speed. These pumps have been historically used on spas; however they have been showing up more frequently on both in ground and above ground pools. The advantage here is that you will save money operating the pump at a lower rpm, however to make up for the slower volume of water you have to run the pump longer.
Variable Speed Motors– These motors have several preset speeds they will operate at, and will sometimes have a timer function and possibly even freeze protection. The advantage with this motor is you have some preset speeds you can perform various activities with like operate a water feature, clean the pool or filter, and save money on daily operation.
Variable Flow Motors– These motors are the premium motors because they allow you to set the flow rate in gallons per minute of the pump to whatever you want the flow rate to be up to the maximum designed flow rate of the pump. You can usually program several different flow rates to be whatever you want them to be, they are not preset, and this gives you maximum flexibility in operating special features on your pool. These motor may also have a timer and freeze protection built into them.
A little known fact about pool pumps is that not all similar horsepower pumps are created equal. This seems odd I know, however the ability to move water lies not with the motor’s horsepower, but lies with the internal design of the pump housing, impeller and diffuser inside the pump. So when you go to compare pumps you should consider horsepower, but don’t forget to consider the most important function, how much water the pump will move.
When it comes to caring for you pump one of the most important things is your shaft seal. The shaft seal keeps water from leaking out of the back of the pump (where the water is moving) and into the motor. This shaft seal is a two part item and it rotates against itself with the rotation of the motor. Remember the motor is rotating 3450 times in one minute! So in one hour the seal has rotated against itself 207,000 times! So if you operate your pump 12 hours a day the shaft seal will have rotated 2,484,000 times! Now do that for six months you are now at 447,120,000 times. So in two years you have rotated the shaft seal almost one billion times! That shaft seal will be pretty worn out and if you don’t replace it water will leak into the motor and ruin the motor in very short order. So we recommend you replace your shaft seal every two years to extend the life of your motor.
Another key issue with pumps are the gaskets; the gaskets perform two different functions. First, they keep air from getting into the strainer on the vacuum side of the pump; if the strainer lid gasket fails then you will have difficulty getting the pump to move water. Second, they keep water inside the pump from leaking out of the pump and from bypassing the impeller. It is wise to replace the lid gasket or O-Ring every two years and the other gaskets three to five years.
One last issue with a pump is the strainer basket. This basket is a strainer that will catch large debris before it reaches the impeller. If large debris were to reach the impeller it would clog it up blocking the flow of water. So it is important that this basket be in place while the pump is running. You should inspect the basket every year for cracks, and if the basket is cracked replace it as soon as possible. The best way to check a basket for cracks is to give it the Charmin test, what you do is gently squeeze the basket to see if any of the plastic grid separates from itself. If it does open up you will need to replace the basket. The way most baskets get cracked is people will bang them to empty the debris out of the basket, as the basket gets older it becomes more brittle and susceptible to cracking when you bang it. The best way to empty a strainer basket is to empty the bulk of the debris that will fall out into a trash can, then get a five gallon bucket of water fill it with water then take the basket turn it upside down in the bucket swish it around a little then lift it out. Most of the debris that would not come out in the trashcan will float off in the bucket and you haven’t banged the basket against anything. Basket life extended!
Ok, it is a beautiful day outside and time to go out and enjoy your pool! Class dismissed!