By Mike Fowler
The biggest fear of any aquatic facility manager is a pool shutdown. Unfortunate events such as a fecal incident are impossible to control; however, a pump or filter should never be the cause of a facility closure. There are, in fact, several best practices one can follow to avoid some of the most common causes of pump and filter failure. The following guidelines, which have been developed in the field over many years, should be included in any aquatic facility maintenance plan. From daily checks to keeping specific spare parts on hand, aquatic facility managers can avoid a pump or filter failure from causing an aquatic facility to shut down.
It is important to remember all of the reasons that could cause a pool pump to fail. In many cases, there are simple recommendations that can be followed to ensure pumps do not stop operating.
Pump runs dry
It may seem obvious, but one of the main reasons for a pump to fail is because it has been allowed to run dry. When this happens, it could cause a loss of pressure, which can result in damage to the casing, impeller, and seal. When the seal fails the pump will seize, bringing it to a halt. This is not the case for all situations, however, as some pumps will run but the faulty seal will cause the unit to leak.
One of the most common reasons for a pump to run dry is because it has been improperly sized, resulting in cavitation. This means the pump is too large for the pool application. For example, a 283,905-L (75,000-gal) pool running 787 litres per minute (lpm) (208 gallons per minute [gpm]), can be handled by a 5-hp pump. However, a pool of this size is often equipped with a 7.5-hp pump, which is not using the valves or a variable frequency drive (VFD) to bring the flowrate to the proper level.
A consequence of over-sizing the pump will more than likely result in cavitation or possibly even seeing the unit run dry and fail. The best way to avoid a failure caused by improper pump sizing is to install a VFD that is capable of bringing the flowrate up to where it needs to be to prevent the pump from running dry.
The same thing can happen if the pump has an air leak, if the pump’s strainer basket is full, and/or has not been cleaned out properly. That said, the pump’s strainer basket should be visually inspected at least once a week. Dirty strainer baskets reduce filter and heater efficiency and put abnormal stress on the pump motor. In addition, sometimes, if the valve on the suction side of the plumbing is closed off, it can also cause the pump to run dry and shutdown.
Similarly, a pump can run dry as a result of a loss of prime. Essentially, this means the pump does not have enough water coming into the suction side and, as a result, it does not work properly because it will not prime. When troubleshooting this problem, check the suction piping and valve on any suction gate valves for any issues. The lid on the pump strainer pot should also be secured, while at the same time making sure the lid gasket is in place.
It is also important to check the pool’s water level to make sure the skimmer is not drawing air. The suction lines, pump strainer, and pump volute (the casing that receives the fluid being pumped by the impeller, slowing down the fluid’s rate of flow) must be full of water. The valve on the suction line must also be working and open (some systems do not have valves).
Pump runs backwards
This may sound ridiculous, but it is quite common for pumps to fail when they ‘run backwards.’ For some technicians, it is not unusual to receive a call from the field with a report that a pump is not, in fact, pumping the proper amount of water, resulting in the motor running hot and at higher amperage.
These symptoms could point to the fact the motor is ‘wired backwards.’ Essentially, the wiring of the pump is such that the motor is not rotating in the proper direction that it is designed, which not only affects the rotation of the impeller, but also the flow of water through the pump.
Pump damage from improper water chemistry
Improper water chemistry can also lead to pump failure. Often, when the pool’s water chemistry has a low pH, the bronze cast impeller within the pump motor can begin to deteriorate from corrosion.
Anytime water chemistry is not balanced, especially for a prolonged period, pool pumps suffer the effects of corrosion. When chlorine levels reach between 1 and 3 parts per million (ppm) and the pH reaches between 7.2 and 7.6, there is a high probability corrosion will affect the life of the pump. It will also affect the flowrate, as the water coming out of the pump will be reduced.
In addition to corrosion, pump impellers can fail as a result of cavitation, which means the pump is pushing, or trying to push, much more water than what it was designed to do. If the failure is cavitation, the pump will start to make a loud rattling sound when the impeller is deteriorating.
To avoid deterioration of the bronze impeller, it is important to keep pool water chemistry properly balanced, keeping a particularly close eye on chlorine and pH levels. The best way to do this is to use an automatic chemical controller. If an automatic controller is not present, daily testing of the water can also help to protect against imbalanced water chemistry.
In addition, when dealing with non-plastic pumps, or those with bronze impellers, aquatic facilities should keep an extra impeller on-site for quick replacement. As a best practice, aquatic facilities should also have an extra motor on hand to avoid having to shut down the pool.