Printable seal kit for Chapin open-head style metal pump sprayers (SCAD + STL)

Printed seals aren't ideal due to porosity and surface roughness, but TPU has decent chemical resistance.   Consider also that a seal kit costs about $30 (plus shipping, since nobody local is going to have them).  A 70% quality part isn't that bad when it's available the same day at 4% of the cost.

I have no idea what model numbers my sprayers are. They're old steel sprayers with brass pumps.  They're late 70's to mid-1980's vintage -- old enough that they had leather cups.

This is likely closest to the parts from the 6-4627 kit, but I'm not sure. The head designs have changed slightly over the last 40 years, so some of the dimensions may have changed slightly.

Printed in SUNLU 90A TPU, 4-5 shells, 20% infill. Ironing should be enabled to help make sure the top face of the valve is smooth enough to seal well. Printing on a smooth bed may be preferred for the same reason.  It may be better to print solid to avoid the risk of leaks by permeation.

The static seals (the lid and tube seals) can be seated with a non-drying sealant (e.g. Hylomar Universal Blue, Permatex Permashield, or something as simple as Rectorseal or just beeswax). All that's needed is something non-drying and viscous enough to seal the textured face of the printed part without being extruded by gas pressure.  Using a sealant helps make up for the inferior as-printed surface. It's not 100% effective, but it's an improvement.

The moving seals (the cup and valve) can be installed dry or with silicone grease. If you have issues with the cup wanting to stick or chatter in certain fluids, the traditional hack is to wrap one or two layers of thin teflon tape around the cup skirt. No thickness is needed here; we're just forming a chemically inert and lubric barrier between the TPU and the pump tube. During the pull stroke, the cup moves down and air is drawn between the cup and the flat backing washer. If you apply tape, make sure to not tape over this joint.  Likewise, the flat face of the cup should be as smooth as possible, as it is a moving seal surface.

At least on the two pumps I just rebuilt, the mouth of the pump tube had some rough burrs. I smoothed the tube mouth with some cratex to make it easier to insert the piston assembly. A smooth entry is doubly important if you're using teflon tape.