How to Print-in-Place Watertight Water Pump

3D printed pumps have a reputation for leaking. The layer lines in FDM printing create porous surfaces that water easily penetrates. This project demonstrates how to overcome that challenge by printing an entire functional water pump—impeller and casing—in a single, print-in-place (PiP) design.

The secret lies in two parts: a specific CAD technique to define the gap, and a slicer hack that allows you to use dissolvable supports on a standard, single-nozzle 3D printer. The result is an airtight pump capable of generating a genuine suction head.

Materials and Tools

Materials

1. 3D Printer: Any FDM printer capable of manual filament changes.
2. Primary Filament: PLA (or another material compatible with your soluble support).
3. Soluble Support Filament: BVOH, PVA, or similar (must be compatible with your primary filament).
4. Epoxy Resin: Two-part clear epoxy for sealing the final print.
5. Bearings, O-rings, and Motor: Components needed for the pump's mechanical assembly (specific to your chosen pump design).
6. Water bath: A container of warm water for dissolving supports. (Optional: Ultrasonic Cleaner for faster dissolution).

Software

1. CAD Software: Fusion 360, SolidWorks, etc.
2. Slicer Software: PrusaSlicer, SuperSlicer, or any PrusaSlicer-based slicer.

CAD files

1. A slightly modified print and assemble version of the pump that you can have a go at printing yourself can be found on my Patreon Site for free here along with all the different impeller designs.

The first step is to design your pump with a specific gap between the impeller and the casing.

All the step by step slicer screen walkthroughs are in the following video

1. Select Impeller Design: For this project, a high-performing 10-vane axial and radial impeller was chosen for its useful pumping characteristics. Check out this video if you want to see how a range of impeller designs performed
2. Define Separation: In your CAD program, place the impeller and casing together. The gap between all moving parts must be an exact multiple of your print layer height.
3. Recommendation: Use a separation distance equal to two times your layer height (e.g. 0.4 mm for a 0.2 mm layer height).
4. Create the Interface Body: Create a new component called "Interface." This is a solid body that precisely fills the gap you defined in Step 2. This interface body will become the soluble support structure.
5. (Note: This pump design required two separate interface contact areas at two different heights.)
6. Export Models:
7. Export all components excluding the Interface component (This is your main part, e.g., pump-parts.stl).
8. Export only the Interface component (This is your support part, e.g., interface-support.stl).

All the step by step slicer screen walkthroughs are in the following video

You will now trick your single-nozzle printer into performing a manual filament change whenever it needs to switch from the main material (PLA) to the support material (BVOH).

1. Set Up Dual Extruders: Open your slicer (PrusaSlicer is used here). Navigate to Print Settings and change the number of extruders from 1 to two.
2. Adjust Retraction: Click on each extruder's settings and set the retraction length to a conservative 1 mm.
3. Add Tool Change G-Code: Go to the Custom G-code tab and find the Tool change G-code block. Add the following command(s) to force a pause/change:
4. M0 (Generic pause command)
5. M600 (Assisted filament change command, if supported by your firmware)
6. Enable Wipe Tower and Interface Shell: Under Print Settings > Multiple Extruders, check these two boxes:
7. Wipe tower enable
8. Interface shell (This is critical—it generates a solid boundary between the two materials, ensuring a smooth, closed surface once the support is dissolved).

Now you will load the two STL files and assign them to the different material extruders.

1. Import Models: Import both the pump-parts.stl and the interface-support.stl files into the slicer platter.
2. Assign Extruders:
3. Assign Extruder 1 (your main material, e.g., PLA) to the pump-parts model.
4. Assign Extruder 2 (your soluble material, e.g., BVOH) to the interface-support model.
5. Slice: Slice the model. The slicer will automatically plan filament changes where the interface material is printed.
6. (Note: Because the slicer prints both interface layers back-to-back, a design with two separate interface levels will result in four total filament changes.)

Perform the print, ensuring you swap filaments as prompted by the M0/M600 commands.

1. Mechanical Assembly: Once the print is complete, insert the bearings, O-rings, and a small amount of grease into their respective positions.
2. Soak: Submerge the print in warm water. For BBO, the dissolution process can take up to 3 days to completely free the impeller.
3. Release Check: Once the supports are dissolved, the impeller should spin freely, and the surface finish of the interior should be smooth.
4. (Tip: Use an ultrasonic bath to speed this process up significantly).

The final step is to seal the inherently porous FDM surface to ensure it is watertight and airtight.

1. Apply Epoxy: Thoroughly coat the entire exterior of the pump with two-part epoxy resin. This creates a tough, impermeable layer that lacquer or paint cannot match. Allow it to cure completely.
2. Performance Test: Connect the pump to a power source and tubing.
3. Test 1 (Flow Rate): Measure the time it takes to pump 1 liter of water when the inlet and outlet are at the same height (0 m head). (Result for my version: Approx. 16.9 seconds).
4. Test 2 (Flow Rate): Measure the time it takes to pump 1 liter of water when the inlet and outlet are at 1 m difference in height (1 m head). (Result for my version: Approx. 20.0 seconds).
5. Test 3 (Suction Head): Measure the maximum vertical distance the pump can be lifted above the water source while still running. (Result for my version: An average of 41 cm!)

Congratulations! You have successfully printed a watertight, functional water pump in one piece that can generate a useful suction head, all using a clever slicer hack on a standard 3D printer.