Aluminum Pressure Tanks

Aluminum pressure tanks store and deliver pressurized water or air in municipal treatment systems, utilizing compressed air cushions to maintain system pressure and provide surge protection. These vessels operate by compressing air above the liquid level, creating a pneumatic spring that absorbs pressure fluctuations and maintains steady downstream pressure without pump cycling. Typical municipal installations achieve pressure ratings of 150-300 PSI with capacities ranging from 80 to 2,000 gallons. The key trade-off is aluminum's lighter weight and corrosion resistance versus higher initial cost compared to steel alternatives, plus potential for galvanic corrosion when coupled with dissimilar metals in piping systems.

• Chemical Feed Systems (Sodium Hypochlorite Storage): Aluminum tanks store 12.5% sodium hypochlorite solution at 15-35 PSI, feeding downstream injection points. Selected for corrosion resistance to chlorine compounds and lighter weight versus steel. Typical sizes: 500-5,000 gallons for 1-25 MGD plants

• Potable Water Storage/Hydropneumatic Systems: Maintains system pressure (40-80 PSI) during low-demand periods, reducing pump cycling. Aluminum resists internal corrosion from treated water. Common in smaller plants (0.5-5 MGD) with 1,000-10,000 gallon capacities

• Backwash Water Storage: Stores filtered water at 20-50 PSI for filter backwashing operations. Aluminum's corrosion resistance suits potable water contact. Typical: 2,000-15,000 gallons for 2-20 MGD plants

Daily Operations: Monitor tank pressure via local gauges or SCADA, typically 40-80 PSI range. Check for proper cycling during demand fluctuations - tanks should show 10-20 PSI pressure swing. Verify no external leakage at connections and observe air compressor runtime for pre-charge maintenance needs.

​

Maintenance: Inspect external surfaces monthly for corrosion or damage. Annual internal inspection when possible, checking bladder condition and sediment accumulation. Replace bladders every 5-7 years. Requires confined space entry procedures, atmospheric monitoring, and mechanical ventilation. Basic mechanical skills sufficient for routine maintenance.

​

Troubleshooting: Rapid pressure loss indicates bladder failure or air leakage - check pre-charge pressure first. Waterlogged tanks show minimal pressure variation and require bladder replacement. Excessive cycling suggests undersized tank or control valve issues. External corrosion at welds indicates coating failure. Expected service life: 15-25 years with proper maintenance.

• Pressure Vessel Shell: 5000-series aluminum alloy construction, ASME Section VIII certified. Wall thickness 0.25"-0.75" depending on pressure rating (150-300 PSI typical). Municipal sizes: 48"-144" diameter, 8'-20' length

• Bladder/Diaphragm Assembly: EPDM or butyl rubber membrane separating water and air chambers. Replaceable design with 5-7 year service life. Sized for 25-40% tank volume at operating pressure

• Inlet/Outlet Connections: ANSI 150# flanged nozzles, typically 4"-12" diameter. 316 stainless steel wetted components

• Pressure Control Valve: Pilot-operated pressure reducing valve maintaining downstream pressure ±5 PSI. Bronze or stainless construction, 2"-8" sizes typical

• Air Charging System: Schrader valve or compressor connection for pre-charge adjustment (typically 2/3 operating pressure). Includes pressure gauge and relief valve

• Operating Pressure Range: 150-300 psi working pressure for typical municipal distribution systems, with 1.5-2.0 safety factor yielding 225-600 psi tank ratings

• Volume Sizing: 10-15 gallons per GPM of pump capacity for standard cycling; 20-30 gallons per GPM for reduced cycling applications. Typical municipal ranges: 80-5,000 gallon capacity for 0.5-50 MGD systems

• Drawdown Volume: 25-35% of total tank volume at standard pre-charge (30% below cut-in pressure)

• Pre-charge Pressure: Set at 2-5 psi below pump cut-in pressure. Typical municipal range: 35-65 psi pre-charge for 40-70 psi cut-in systems

• Connection Sizing: 2-8 inch flanged or threaded connections based on system flow. Minimum 4-inch for systems >500 GPM

• Cycling Rate: Design for maximum 6-10 starts per hour per pump to prevent premature equipment failure

• Temperature Range: -10°F to 180°F for standard butyl bladders; EPDM bladders for higher temperatures

• Flow Velocity: Limit inlet velocity to <10 fps to prevent bladder damage and water hammer

• What tank volume is required for acceptable pump cycling? Calculate based on system flow variation and acceptable starts per hour. Undersized tanks cause excessive pump cycling (>10 starts/hour), reducing pump life and increasing energy costs

• Should single large tank or multiple smaller tanks be specified? Single tanks >2,000 gallons become difficult to transport and install. Multiple tanks provide redundancy but increase complexity

• What pre-charge pressure and bladder material optimize performance? Incorrect pre-charge reduces effective drawdown volume by 40-60%. Standard butyl works to 180°F; EPDM required for higher temperatures but costs 15-20% more

• How does tank location affect sizing and performance? Elevated installations require higher working pressures, affecting tank selection and costs. Ground-level placement may require larger volumes for equivalent performance

• Primary: Division 40-05-23 - Packaged Water Storage Equipment

• Secondary: Division 33-11-00 - Water Utility Distribution Piping (when part of distribution system upgrades)

• Material/Equipment Verification: ASME certification and nameplate verification, bladder material compatibility with local water chemistry, pressure rating confirmation (typically 150-300 PSI municipal)

• Installation Requirements: Concrete pad sizing for seismic and wind loads, piping connections sized for peak flow (avoid velocity >8 fps), electrical coordination for pressure switches and level controls

• Field Challenges: Access for bladder replacement (plan 8-foot clearance minimum), freeze protection in northern climates

• Coordination Issues: Lead times: 6-12 weeks standard, 16-20 weeks for custom ASME vessels

• Pentair Codeline - Model PTA series (100-15,000 gallon range), strong municipal presence with pre-engineered packages

• Wessels Company - WellMate and Hydro-Pro lines (20-10,000 gallons), known for reliable bladder systems

• Amtrol - Well-X-Trol and BoilerMate series (2-2,000 gallons), popular for smaller municipal applications

• Highland Tank - Custom fabricated units (500+ gallons), specializes in large municipal installations with ASME certification

• Concrete/Steel Elevated Tanks: Preferred for systems >2 MGD, 3-5x higher capital cost but lower O&M

• Variable Frequency Drive (VFD) Systems: Eliminate pressure tanks entirely, 10-15% higher energy costs but precise pressure control

• Composite Pressure Vessels: 20-30% cost premium over aluminum but corrosion-free, gaining popularity in aggressive water chemistry applications like coastal municipalities

Establish relationships with local manufacturer reps early - they often provide free on-site commissioning and troubleshooting support. Size tanks 20% larger than calculated to accommodate future demand growth and reduce cycling frequency. Specify redundant pressure switches from different manufacturers (Dwyer + Square D) to avoid single-point failures. Consider factory pre-piped skid packages for installations under 1,000 gallons - typically saves 15-25% on total installed cost.