Quick Answer
During rapid drawdown in pressure tanks, the water level drops more quickly than the pump can replenish it, causing a sudden loss of pressure. This can lead to decreased water flow rates and potentially damage plumbing fixtures. Pressure gauges may also malfunction or give false readings.
Rapid Drawdown Causes
Rapid drawdown in pressure tanks is often caused by a sudden increase in demand, such as when multiple sinks or showers are used simultaneously. This can happen in households with high water usage, particularly in areas with multiple bathrooms or a large family. In these situations, the pressure tank’s ability to maintain a consistent water pressure is compromised.
Pressure Tank Sizing Considerations
When sizing a pressure tank, it’s essential to consider the total drawdown time and the corresponding pressure drop. A general rule of thumb is to size the tank based on the total gallons per minute (GPM) of the plumbing fixtures and appliances. For example, a household with 2-3 bathrooms may require a tank with a capacity of at least 50-75 gallons to handle simultaneous drawdowns. It’s also crucial to consider the pump’s ability to refill the tank, as well as any additional factors such as elevation changes or pipe friction losses.
Mitigating Rapid Drawdown
To mitigate rapid drawdown in pressure tanks, it’s recommended to install a larger pressure tank or upgrade to a more powerful pump. Additionally, using a pressure tank with a “floating” bladder or a " diaphragm" style tank can help to maintain a consistent water pressure. In some cases, installing a separate pressure tank for each bathroom or a separate tank for the well pump can also help to alleviate rapid drawdown issues.
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