1. What is a Pressure Tank Size Calculator?

Definition: This calculator determines the minimum size of a pressure tank needed for a water system based on pump flow rate and pressure settings.

Purpose: It helps plumbers, well installers, and homeowners properly size pressure tanks to prevent pump short-cycling and ensure system efficiency.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( V \) — Required tank size (gallons)
• \( Q \) — Pump flow rate (gallons per minute)
• \( P_{on} \) — Cut-in pressure (pump turns on, psi)
• \( P_{off} \) — Cut-out pressure (pump turns off, psi)
• \( P_{precharge} \) — Tank precharge pressure (psi)

Explanation: The formula calculates the tank volume needed to provide adequate water drawdown between pump cycles.

3. Importance of Proper Tank Sizing

Details: Correct tank sizing prevents pump short-cycling (frequent starts/stops), extends pump life, maintains consistent water pressure, and improves system efficiency.

4. Using the Calculator

Tips: Enter the pump flow rate (gpm), cut-in and cut-out pressures (psi), and tank precharge pressure (typically 2 psi below cut-in). All values must be > 0 and P_off > P_precharge.

5. Frequently Asked Questions (FAQ)

Q1: What is drawdown capacity?
A: The amount of water the tank can deliver between pump cycles (between cut-out and cut-in pressures).

Q2: Why is precharge important?
A: The air precharge ensures proper operation and should be set to 2 psi below the cut-in pressure when the tank is empty.

Q3: What's a typical pressure switch setting?
A: Common settings are 40/60 psi (cut-in/cut-out) or 30/50 psi, but this depends on system requirements.

Q4: How do I find my pump's flow rate?
A: Check pump specifications or measure flow by timing how long it takes to fill a known volume.

Q5: Should I round up the tank size?
A: Yes, always select the next standard tank size larger than your calculation to provide margin.