A pressure differential hydro test on an exchanger is one

• A. Identical to a standard hydro test
• B. Only used for shell side
• C. Not applicable
• D. That is different when fire water is used on the shell and a hydro pump is used on the tubes

Answer: (D)

A pressure differential hydro test on a shell-and-tube exchanger is about checking integrity under a controlled difference in pressure between the two sides, using different media. A standard hydro test usually floods both sides with the same fluid and applies uniform pressure to both sides to look for leaks. When the shell side is filled with fire water and the tube side is pressurized with a hydro pump, you’re not just testing wall strength; you’re testing how gaskets, seals, and tube sheets behave under different fluids and a deliberate pressure difference. This setup requires separate pressurization paths, careful venting, and management of potential cross-contamination, because the two sides are treated differently and pressures aren’t identical. That nuance—the need to manage independent pressurization and fluids on each side—makes this differential test distinctly different from a standard hydro test.