Pool Pumps – How To

I have written about a lot of different topics relating to swimming pools.  Mainly due to the fact that the purpose of this blog is to inform you, the reader of all things related to swimming pools.  I have geared the posts toward the pool owner rather than the pool professional.  This is due to the fact that as a pool professional they are more than likely already aware of everything that I am trying to relay in this blog.  Keeping that in mind, today I want to discuss the pool pump.  I know that in the past I have touched on certain aspects of these things but today I will approach it from a different perspective and that is through the eyes of the swimming pool owner.  A homeowner that is getting their first pool will often times start to feel a bit overwhelmed by all the new information they get regarding their pool.  It is almost like watching a baby see something amazing like fire works for the first time.  They are not sure what it is or does for sure but they know that they like it.  Hopefully with today’s post I can alleviate some of the fear that a new pool owner may be feeling in regard to their pool equipment.  So being that the pump is the first step to the system I will start there.

The pool pump is the device that brings the water from the pool and sends it through the filter and heater/heat pump.  It is also the thing that is generally making the most noise.  Take a look at the diagram to the left.  You will see that the pump consists of several different parts.  Those parts are pretty much standard on all pumps regardless of brand.  This particular pump has two or three inch inlet/outlets.  This is ideal in that the pump will not have to work as hard to draw the water from the pool.  Think of it as if you were drinking through a straw.  If you drink through a really narrow straw like one of those coffee stir sticks you will have to suck rather hard to get any fluid to your mouth.  Conversely, if you drink through a large straw like one of those you might get with a fountain drink at the gas station you will find that you do not have to put much effort into it to get very good results.  It is the same for pool pumps, well pool plumbing in general.  The larger the pipes, the easier it is for your equipment to work.  This will increase the flow and cut down on noise and vibrations from your pump.  Anyway notice that the pump has two main parts to it, the pump body and the motor.  These are separated by the seal plate.  The two parts are also considered the dry end and the wet end.  Basically the motor is what draws the water from the pool into the pump body.  The seal plate is what keeps the water from entering the motor.  The motor is powered by electricity and obviously water and electricity don’t mix, so the seal plate is a very important component to the pump.  There are some other things going on internally as well that you should know about.

The picture to the right shows the element known as the diffuser.  What this does is controls the characteristics of the water by decreasing the speed and increasing the pressure.  This allows the pump to send the water through the filter and the heater/heat pump more easily.

This next picture on the left shows both the wear ring and the impeller.  The impeller is attached to the motor shaft which spins when the pump is running.  This spinning is what creates the suction and draws the water from the pool.  The wear ring is basically a barrier between the impeller and the diffuser.  This protects both the diffuser and impeller from premature failure due to friction and heat.  Without it you would likely have to frequently replace the impeller or diffuser.

Next we have the picture on the right which shows the motor shaft and what is known as the mechanical seal.  These are located behind the impeller which is located behind the diffuser.  As I said before the motor shaft is connected to the impeller.  The seal goes around the motor shaft and is what keeps the water from entering the “dry end” of the pump.  The item in my hand in this picture is another seal which also goes around the motor shaft and aids in keeping water out of the motor.  Without these two seals in place you would have water entering the motor and causing damage.  These seals will need to replaced from time to time.  Extended dry runs of the pump will increase the potential for damage to the seals.  You will know that the seals need replaced if you see water coming from the motor end of the pump.  The motor has bearing in it that need to be kept dry.  If you get water through the motor of the pump then the bearings will be susceptible to corrosion.  You will know that the bearings are going out by the fact that the pump will become much louder than before.

Now these motors come in several different sizes.  Commonly pool pumps will range from 1HP to 2HP. (1 horsepower and 2 horsepower)  There are others available but most residential pools will use 1, 1.5, or 2HP pumps.  Typically the more HP you have in your pump, the more expensive it will be.  Figuring out what size pump you will need on your pool gets kind of tricky, and in my opinion is best left up to the builder to decide.  This is another reason why it is important to use a trustworthy builder from a highly regarded company to build your pool.

Most pool pumps will give you a gpm rating or gallons per minute.  To figure out how many gpm your pump must be capable of producing you will have to do some math.  You need to figure out your approximate pool volume in gallons.  Use the equation length X width X depth.  Most modern in ground pools have a shallow and a deep end if this is the case then you will first have to determine the average depth of the pool.  For that you simply have to take the deep end measurement and add it to the shallow end measurement and then divide the result by 2.

For instance if your pool has an 8′ deep end and a 4′ shallow end then you add 8+4 which = 12 and divide by 2 which gives you 6.  6 is would be the average depth of the pool, so to figure out the total approximate volume you take the length X the width X the average depth.  For example if your pool is 20′ wide X 40′ Long then you would take 40 X 20 X 6 = 48,000gal.

To get the gpm of the pump you will need for a pool that size you need to take the pool volume and divide it by the turnover time.  A turnover as it relates to pools is when the pump has successfully pumped out all the water in the pool and put it back.  Typically you want this to happen every eight or ten hours.  So to get the gpm you take the 48,000gal divided by 8 = 6,000 then take the 6,000 and divide by 60 = 100.  So you will need a pump capable of pumping at a rate of 100 gallons minimum per minute to achieve a turnover every 8 hours.

But we can’t stop there we now need to figure out the maximum flow rate for the plumbing.  The maximum flow rated is determined by the size of the plumbing used.  For instance the maximum flow through a 1.5″ pvc pipe is 44 gallons per minute.  So you will need to count the number of intake lines to determine the maximum flow rate.  For each 2″ intake you will get a maximum flow of 73 gpm to the pump.  For a 1.5″ intake you will get a maximum flow of 42 gpm.

This will give you a good idea as to if the pump you have is sufficient for the size of pool or if it is over kill.  In all honesty there are a few other things that come into play when sizing pumps but to keep from overloading anyone today I am going to leave it at this.  If you want more information on pump sizing you can find a lot of information on line.  I found some of this information at http://www.poolplaza.com

For other information pertaining to in ground swimming pools and specifically vinyl liner in ground swimming pools please check out my other posts.  I have written about many different topics.  If there is a topic I have not yet covered that you would like me to discuss please feel free to let me know.