I like using a pump sack as a pack liner. One of us takes the pump sack. The other takes a trash compactor bag.

The pump sack works well to inflate an air mattress – and the Exped nozzle fits Toothless’ Sea to Summit pad as well.

Only problem is – all of the Exped pump sacks that we have ever gotten eventually soak through in heavy rain. This results in our quilt, sleep clothes and pad getting wet. And defeats the point of using a pack liner…

I’ve given pack liners a lot of thought this year for our PCT LASH with the kids.

I have some nylofume bags, trash bags and trash compactor bags. All of these are fine options (although, despite using nylofume on day hikes I don’t feel confident with it for such a long trip), but I keep going back to the pump sack. How am I going to solve my leaking pump sack problem?

Concept

I decided to make a nozzle that I can attach to any plastic bag and use as a pump sack.

If I use a nylofume pack liner or a regular trash bag I can potentially have a pack liner / pump sack combo that’s lighter than the Exped pump sack.

I have a 3D printer so I can make one out of plastic or TPU and do a lot of prototyping easily.

I measured the Exped pump sack nozzle dimensions, and made my own cap design that could be sealed with o-rings to keep the water from leaking past the interface.

Testing and Prototyping

I 3D printed the nozzle out of PETG for prototyping. I kept testing the fit into the sleeping pad valve.

Eventually I made a prototype out of TPU. Since 3D printed parts are porous and can leak water through the extrusion lines and layers, I needed to test this to ensure it would not leak. I printed a version out of TPU that didn’t have a hole and filled the nozzle with water, placed it on paper, and looked for evidence of water leaking.

No water leaked over several days.

So I moved forward and added some features to add o-rings.

I tested attaching the TPU to a plastic bag with the worlds best tape – Tuck Tape. This stuck to the TPU very well and I have been fidgeting with it for months, so I determined the tuck tape would hold up long term.

Then I designed a cap. I printed the prototype out of PLA.

Final Design

The final design has the TPU nozzle Tuck Taped to a trash compactor bag.

The cap is made of purple PETG (the colour is for visibility).

The cap and nozzle are attached with scrap round elastic looped through some holes.

There are two o-rings.

The entire thing weighs close to 8 grams including the tape. This is on par with a pad pal inflator but doesn’t require a battery to operate.

Download the files

You can download the files here https://makerworld.com/en/models/1103617

So does it work?

Is it water proof?

I have filled the bag full of air, then squeezed it. The nozzle and cap seal air when I apply as much pressure on the bag as I feel comfortable doing without damaging the bag itself. I bear hug it. No leak.

If it fails on trail, I can tie a knot in the bag to tie off the hole I created and inflate using my breath.

Does it inflate a pad?

The nozzle fits, and it inflates a sleeping pad. Again, both my Exped and Sea to Summit pads.