Why residual water remains in the horizontal multistage pump after performance test?

Why residual water remains in pump after performance test?

It's normal for a horizontal multistage pump to retain some water after testing, mainly due to structural and physical reasons:

1. Complex internal flow passages: Multi‑stage impellers, guide vanes, and narrow chambers create many dead spots where water is trapped by surface tension and capillary action.

2. Horizontal installation & low points: The horizontal layout forms natural low‑lying areas at the bottom of each stage, where water accumulates and cannot drain completely by gravity alone.

3. Seal & cavity retention: Mechanical seal cavities, gasket grooves, and small balance holes can hold water after the test.

4. No full self‑drain design: Test drains are usually at the lowest point, but some residual film or droplets still cling to metal surfaces.

How to clean up before packing (anti‑rust)

Goal: completely drain → remove moisture → apply temporary rust protection → seal

1. Thorough draining (immediately after test)

• Open all drain plugs (bottom of pump casing, intermediate stages, seal chamber) and let gravity drain for ≥30 min.

• Tilt the pump slightly (if allowed) to help water flow out of low corners.

• Manually rotate the shaft several times to release water trapped around the impeller and seal.

2. Compressed air drying (key step)

• Use clean, dry compressed air (0.4–0.6 MPa) to blow through the pump from inlet to outlet, covering all stages.

• Focus on dead spots: seal cavities, bolt holes, and gaps between stages.

• Continue blowing until no water droplets come out and the inner surface is dry to the touch.

3. Interior cleaning & drying

• Wipe accessible internal surfaces with a clean, lint‑free cloth (avoid leaving fibers).

• For hard‑to‑reach areas, use a soft brush or swab dampened with isopropyl alcohol (evaporates quickly, leaves no residue).

• Ensure all surfaces are visibly dry before proceeding.

4. Temporary rust prevention

• Spray or brush a thin layer of water‑displacing anti‑rust oil on all internal metal surfaces (impellers, shaft, casing walls).

• Rotate the shaft by hand to distribute the oil evenly, forming a protective film.

• Do not use heavy grease; it’s hard to remove later and may affect performance.

5. Sealing & packing

• Seal inlet/outlet flanges with moisture‑proof blind flanges or heavy‑duty plastic caps.

• Place desiccant bags inside the pump casing before final sealing to absorb residual moisture.

• Wrap the entire pump in a VCI (volatile corrosion inhibitor) film or waterproof plastic sheeting.

• Store in a dry, well‑ventilated area before shipping.