Understanding Well Pressure Tanks

A standard well system is designed to provide water to a home or business within a set pressure range. The low or “cut-in” pressure is the lowest intended water pressure when the pump is turned ON to add pressure to the system. The high or “cut-out” pressure is the maximum intended water pressure when the pump is turned OFF. Typical water system low/high pressure settings are 40/60 or 30/50 PSI.  The well pressure tank is what maintains these working pressures and continues the supply of pressurized water to the home or business when the pump is OFF. ​ The drawdown volume (working capacity) is the amount (in 

 gallons) of water the tank can supply between the pump cut-in and cut-out pressures.

Inside a well pressure tank there is a pre-charged compressed-air portion that is in the top of the tank that is separated by the water portion below by a water-tight rubberized bladder. To achieve the desired drawdown volume, the pre-charge pressure of the compressed air should be set to approximately 2 PSI below the pump cut-in pressure when the tank is empty of water. So, using a 40/60 system as an example, the pre-charge air pressure should be set to 38 PSI.

If the air pressure is either set or becomes too low, the bladder does not fully expand which means less water is stored in the tank. The tank will fill up and empty out more quickly, leading to the pump cycling (starting and stopping) more often. This rapid cycling can lead to increased energy consumption and more wear on the pump motor and other components.

If the air pressure is zero and/or water comes out at the air valve, this means that the bladder has completely failed, often described as a “water-logged” tank. A further symptom of a failed tank is that the pump is running almost constantly while water is being used, which can quickly lead to excessive wear and possible pump failure.

Bladders in pressure tanks can lose pressure and fail due to several reasons. Understanding these causes can help in maintaining the system better and potentially extending the life of the tank. Here are the main factors:

1. Natural Wear and Tear:
   • Material Fatigue: Over time, the repeated expansion and contraction of the bladder can cause the material to weaken and become less elastic, eventually leading to cracks or holes.
   • Age: As the tank ages, the materials naturally degrade, which can lead to failure.
     
     
2. Improper Pre-Charge Pressure:
   • Incorrect Initial Pressure: If the pre-charge pressure is not set correctly initially, it can cause the bladder to stretch too much or not enough, leading to premature failure.
   • Frequent Cycling: If the pump cycles on and off too frequently because of a low pre-charge pressure or an undersized tank, the bladder undergoes more stress, which can shorten its lifespan.
     
     
3. Water Quality:
   • Corrosive Water: High mineral content, acidity, or other corrosive elements in the water can weaken the bladder material over time.
   • Sediment: Sediment and debris in the water can cause abrasion or punctures in the bladder.
     
     
4. Mechanical Damage:
   • Improper Installation: Incorrect installation procedures can damage the bladder or cause it to operate improperly.
   • Physical Impact: External impacts or vibrations can damage the bladder, especially if the tank is not properly secured.
     
     
5. Pressure Surges:
   • High Pressure: Excessively high-water pressure can overstress the bladder, leading to tears or punctures.
   • Water Hammer: Sudden changes in water flow or pressure, known as water hammer, can cause significant stress on the bladder.
     
     
6. Manufacturing Defects:
   • Quality Issues: Defects in the bladder material or seams from the manufacturing process can cause premature failure.
     
     

In summary, low air pressure inside a well tank results in a reduced drawdown volume, shorter pump run times, and more frequent pump cycling. This occurs because the bladder cannot fully utilize the tank's volume, leading to inefficiencies and potential damage to the pump over time. Ensuring the pre-charge pressure is correctly set initially and maintained over time is crucial for optimal tank and pump performance.