By Tom Stephan
Booster pump systems are critical to maintaining the pressure and flow demands in modern high-rise buildings such as hotels and office structures so water pressure on the top floors is as good as that on the ground level. Given the importance of booster pumps in multi-storey buildings, it’s essential to keep these systems in good working order. There are many different things that can go wrong with booster pumps, from leaks to motor breakdowns. Here are some guidelines for troubleshooting pump performance and steps to take to ensure maximum performance and avoid future problems.
Booster pumps vary in terms of how much power they need, depending on the head and flow conditions required to meet the application. Ensuring a booster pump system operates within the minimum and maximum flow rate as close to the best efficiency point as possible will provide the longest product life. With regard to incoming power supply, most motors are rated to handle +/- 10 per cent of the motor nameplate voltage. In some cases, such as with the use of a variable frequency drive (VFD), up to 15 per cent voltage variation may be possible, depending on the VFD. However, if the voltage is outside of the product’s recommended range, you risk excessive heating of the motor windings, which can greatly reduce the life of the motor. Both high voltage and low voltage to the motor tend to increase amperage. High amperage means high heat which is one of the most common failure modes in motors. Proper training and use of a meter for troubleshooting are beneficial, as is an understanding of key properties such as voltage, amperage, frequency, resistance and capacitance.
A common mechanical issue is malfunctioning pressure switches. When low or inconsistent water pressure occurs, the solution often involves adjusting or replacing the pressure switch, as well as ensuring there is no blockage in the pressure line to the switch. The switch signals the system to start or stop pumping, depending on the pressure in the water system.
Another common mechanical problem is check valve failures. When the check valve is stuck open, the pump can spin backward causing additional wear and significant stress on the pump and motor if it was energized while spinning backward. The empty pipe and zero-pressure differential between the suction and discharge can lead to an upthrust condition on startup, causing considerable damage. When the check valve is stuck in the closed position, the pump will deadhead, adding significant energy to the water inside the pump. The result is excessive heat and no cooling flow for the motor, which can damage both the motor and the pump.
Other warning signs
Sometimes, problems can be attributed to improper system sizing, rather than a defective or broken component. Pumps equipped with VFDs are designed to operate within a range of speed, and operate close to the best efficiency point which tends to be near the centre of the curve. With optimum conditions, pumps can operate trouble-free for decades. But indicators of a booster pump that has been improperly sized or incorrectly installed can appear sooner than that. These warning signs typically arise as deterioration increases.
Noise: Pump performance problems in the form of noise, humming or rattling may be due to insufficient water supply (possibly caused by suction issues). It may also be internal parts causing the problem, or the need for motor maintenance, such as lubrication, new bearings or cleaning.
Vibration: Feeling a pump during maintenance inspections can detect minor vibrations before the situation escalates. Make sure the mounting is sufficient, and if possible, reinforce the attachment. Additionally, booster pump systems can be equipped with sensors to automatically feed vibration data to condition monitoring equipment.
Heat: Whether coming from the motor housing or the pump itself, heat is another sign of friction, wear, pressure or out-of-tolerance issues. Sensors are also available to monitor temperature.
Low water pressure: Low water pressure can be attributed to many different issues. But, most of the time, it’s an issue with the suction. Suction issues on booster pumps are often due to clogged filters if pumps are not properly maintained and filters are cleaned infrequently. Another issue that can cause suction problems is a leak somewhere in the system. Or, it could simply be that a valve isn’t opened completely.
Pressure is too high: Booster pumps are meant to boost pressure, but they should stay within the maximum working pressure of the pump. Since most booster pumps are centrifugal pumps, any pressure on the suction is added to the pressure from the pump itself. It’s critical to keep this in mind when sizing the proper pump.
Short cycling: The phenomenon of booster pumps turning off and on within seconds or minutes is known as short cycling. Frequently, this is due to a leak in the system somewhere that needs repair. It could also be due to a waterlogged hydropneumatic tank in the system. Recognizing the symptoms of common problems in booster pump systems can ultimately help contractors identify their causes and select the appropriate course of action before significant damage to the booster pump and motor occurs.
Troubleshooting tips at a glance
Most problems with booster pump systems can be divided into two categories: electrical or mechanical.
- Ensuring a booster pump system operates within the minimum and maximum flow rate as close to the best efficiency point will provide the longest product life
- If the voltage is outside of the product’s recommended range, you risk excessive heating of the motor windings, which can greatly reduce the life of the motor
- Low-voltage conditions may result in a no-start situation
- Low or inconsistent water pressure could be the result of a malfunctioning switch or blockage in the pressure line to the switch
- Water pressure problems can also mean a bad check valve, which can cause additional wear and significant stress on the pump and motor
- Improper sizing or incorrect installation can also cause problems in booster pump systems
- Warning signs such as noise, vibration, excessive heat, unusually low or high water pressure, or short cycling all point to the need to determine the root cause prior to failure