Summary: To prevent pump cavitation during burp drafting, pump operators must recognize the size of their tank fill plumbing. If the line is 2 inches, it cannot be fully opened while throttling up to 150 PSI without risking cavitation. Gating back the tank fill valve ensures efficient pump performance. If the line is 1.5 inches or smaller, full opening is usually safe. Understanding this distinction is key to smooth rural water supply operations.
During burp drafting — a technique for initiating rural water supply without priming — understanding your apparatus’s tank fill plumbing is critical. One overlooked but impactful detail is the diameter of the tank fill line and how it affects your ability to reach target pressures like 150 PSI without causing the pump to cavitate.
If the tank fill line is too large — typically 2 inches or more — the line can flow more water than the pump’s internal plumbing can supply. If you open the valve all the way and throttle up, you’ll see the pump start to cavity, leading to a sudden drop in performance and potential mechanical issues.
NFPA 1901 standards state that any apparatus with a 1,000-gallon tank or larger must have tank fill plumbing of at least 2 inches. This standard often sets up newer pumpers for potential cavitation if the pump operator isn’t prepared to manage the flow.
To stay in control, operators must know the size of their tank fill plumbing. If it’s 2 inches, slightly gate back the valve during recirculation. This restricts the flow just enough to allow the pump to reach 150 PSI safely. You’ll still be able to burp the air out of the pump through the tank fill line — you’ll just be doing it with finesse.
If your tank fill line is 1.5 inches or smaller, you're in the clear. These narrower lines naturally restrict flow enough to prevent cavitation, even when fully opened. That makes recirculating from your booster tank a more straightforward process.
Before jumping into burp drafting or any recirculation strategy, take five seconds to check your tank fill line size. This one detail can determine whether your draft setup runs smoothly or falls flat due to cavitation. Knowing when to gate back — and when you don’t have to — keeps your operation flowing and your apparatus protected.