The swimming pool pump fulfills the function of drawing water from your pool, pushing it through the filtration equipment, and then returning it to the pool. The majority of pool pumps on the market are an integral unit housing an electric motor and a mechanical pump sealed in heavy duty molded plastic. They are available in a variety of horsepower sizes, starter system configurations and casing materials, but the basic design does not vary too much.
A typical pool pump consists of an electric motor which turns a shaft at high speed; most are single speed, though dual speed motors are installed on some pumps. The motor shaft is attached in turn to an impeller, a disc with raised vanes that throws water out from it’s center as it spins, thus doing the actual pumping action.
The water travels through an inlet port in the pump, passes through a leaf strainer which catches debris like leaves, hair, lint and other large foreign particles, then to the impeller and passes finally through an outlet port.
Pool Pump Types
Pumps come in a somewhat confusing mix of types; above ground, in ground, up rated, single speed or 2 speed, high head vs. medium head, high efficiency, variable speed, programmable speed and all the permutations and combinations. To pick out the right type for your pool, you need to know what this all means.
Pumps for above ground pools have a lower pressure rating, since above ground pools have shorter pipe runs and less equipment than in-ground pools, so the pressure of the system is less. The flow rate for a given size of pool will be the same, however. As pumps are designated as either in ground or above ground, you just need to select the right type for the kind of pool you have.
A two speed pump allows the pool owner to save money on energy bills by running at lower speeds the majority of the time; the higher speed operation is only used when vacuuming or backwashing is being done. It also has the advantage of being quieter, since the more water is flowing through a pump and filtration system piping, the noisier it is. Note that dual speed pumps are not suitable for a solar heated pool, due to the higher lift requirements for pumping the water through roof mounted solar panel systems.
Variable speed pumps take the concept of dual speed pumps to the next level, by incorporating digitally pre-programmed speeds for different tasks such as filtration, heating, cleaning and so on. The energy savings with this type of pump can be even greater than with a 2 speed pump, up to 90% over a single speed pump.
High or medium head refers to the Total Dynamic Head (TDH), a hydraulics term measuring the pressure in the system created by friction in the pipes, valves, fittings, filtration equipment, chlorinator, and heater, which the pump needs to overcome to move water through it. As mentioned before, an above ground pool will have less pressure, or TDH, so a low or medium head pump will suffice. An inground pool with a spa would require a high head pump.
High efficiency pumps are available; they use a motor that is more efficient than standard pump motors and can mean an energy savings of up to 20%. The variable speed and programmable pumps would also fall in this category.
There are many brands of pool pumps on the market, but you should stick to one of the proven major manufacturers, such as:
- Jandy – http://www.jandy.com/
Hayward – http://www.haywardnet.com/
Pentair – http://www.pentairpool.com
these brands all have good track records of reliability, energy efficiency and parts availability.
Pool Pump Sizing
The most important part of selecting a pool pump or replacement pump is to get the sizing right. Too small of a pump, and the filter will not work effectively; too large of a pump and you can damage your filter. In order to choose a pump that matches the requirements for your pool, there are several calculations needed.
1. You first have to determine your pool’s capacity in total gallons. Find the surface area in square feet by multiplying the width by length, then multiply the surface area by the average depth, which will give you the volume of the pool in cubic feet. Take the volume and multiply it by 7.5; the resulting figure is the total volume of your pool in gallons.
2. The second step is to find the flow rate required. The Turnover Rate is the amount of time required to circulate the entire volume of your pool once to meet safe, clean water standards. Check wit your local authorities to find out the minimum required turnover rate. Once you know the turnover rate, you can calculate the needed Flow Rate in gallons per minute as follows; divide the pool capacity (total volume from the last step) by the turnover rate in hours, then divide that result by 60 to give the flow rate in gallons per minute. For example, if your pool is 30,000 gallons and the turnover rate required is once per 8 hours, then 30,000/8 = 3750 3750/60 = 62.5 gallons per minute flow rate.
3. You also need to calculate the Maximum flow rate, based on recommended maximum water velocity. Again, check local regulations for recommendations’ typical max velocity is 10 feet per second for vacuum lines, 8 feet per second for suctions lines. Maximum flow rates for various pipe diameter sizes and flow speeds can be calculated from tables and charts in hydraulics reference books or pump manufacturers catalogs. For example, the max flow rate for 2 inch dia. pipe at 8 feet per second is 84 gallons per minute. Therefore, with a pool of the size in step 2, your pump should be rated for a flow rate somewhere between 62.5 and 84 gpm.
4. The final step is to factor in the friction loss from piping, fittings, filters and other parts of the pumping system, or Total Dynamic Head. This is probably the most difficult thing to calculate accurately. You need to find out the friction loss for all equipment in the lines the pump is connected to, as provided in the manufacturer’s documentation; this includes the heater, chlorination equipment, and filter. Friction loss for piping and fittings can be calculated from the number of fittings and elbows used, diameter and length of feet of straight pipe, as shown on the blueprints for your pool system.
Once you have determined the flow rate and total dynamic head required for your pool pump, select the proper pump size based on the performance curves or tables in the manufacturer’s catalog. The point representing the intersection of the flow in gpm and the TDH in feet of water should lie on the curve somewhere towards it’s middle, rather than the ends of the curve.
Once you have sized your pump, then you should size your filter to the pump, not vice versa.