Drill Powered Gear Pump

It seems like I'm always needing to transfer fluid from one place to another. For example, move water to water newly planted trees or plants, waste oil into another drum or hydraulic oil into a machine, etc. So I decided to try to build my own gear pump that runs off my cordless drill. You can buy drill powered pumps off Amazon or Ebay but what is the fun of that? And besides I don't think any of them will do 25psi and/or 8.5gpm!

I decided to try a gear pump because I wanted it to be able to supply higher pressures if I needed. A vane pump would also work but has more moving parts and a centrifugal pump won't build much pressure. This project is reasonably simple but tight tolerances are key to getting decent performance out of your pump. If you have too loose of tolerances it just won't pump as fast or as high of pressures.

I used Autodesk Fusion to design the parts first and then printed and fit together and changed the design as needed.

Note: Because this project took a few iterations to get perfected (no leaks, fixing breakage etc) you may notice that some of the parts are not the same. Most notably the main body in my final design has a flange for mounting to a board or other object. The changes make no difference in assembly.

Supplies

For Tools you will need a few basic tools like screwdriver, torch or heatgun, a knife, maybe a file or grinder and a 3D Printer. If you don't have a printer you can always get stuff custom printed or check out your local makerspace. If you have an electric screwdriver, impact or drill those would be handy but not really necessary.

For Supplies you will need:

3D Printing filament. either PLA or PETG will work fine, my final model has some of both in it. If you want to use TPU for gaskets you will also need that.

RTV silicone, gasket maker or similar sealant. It is sold at auto parts stores. Or Amazon.com: Dynatex 49203 Blue RTV Silicone Gasket Maker

8-32 screws. 1.1" long. 12pieces. Or optionally for more strength 2 at 1.1" long and 10 at 1.4" long. If they don't have washers attached it would not be a bad idea to have but are not essential.

608 Bearings. 4 pieces.

1/4" hex to 1/2" square socket driver. I used the 1/2" one out of this set. Amazon.com Milwaukee Socket Adapter

Short piece of heat shrink tubing.

Step 1: Print Your Parts!

For this project we are going after strength, so I used 7 wall loops and 60-70% infill. If you want you could go even higher on both of those numbers, and it won't hurt anything. The extra walls will help with strength and will help keep things watertight.

I like to use Ironing to keep the parts as smooth as possible. This is key for a project like this where the tighter your tolerances are the better it will pump.

I have attached pictures of the correct orientation to print the parts. Supports are required only on the main housing and the driven gear. The reason for these orientations is that we want the places where the gears rub the housing to be as smooth as possible.

Due to different printer settings, you may have to play with the exact sizes a little to get your parts to fit exactly. I scaled the drive gear and the driven gear down to 98% because they were just a little too tight. The rescaling didn't affect the bearing shaft size enough to make a difference.

I use Orcaslicer and one of the advantages is that it supports using .step files as well as the usual .stl files. The reason that I like that is that where there are curves a .step file will be perfectly round while a .stl will tend to have little facets all the way around. This isn't critical to this project but that is the reason that I included the .step files.

I also included the Fusion files so that you can make your own changes and mounting points to suit your needs.

Step 2: Prepare and Insert Steel Driver

I ground down the little lips at the back of the big part of the steel driver with the bench grinder. But this probably isn't necessary. Then clamp the driver in a bench vise, vise grips or pliers and use a small torch or heat gun to heat it up. It needs to be just hot enough to melt into the gear. Now take the driver in a pliers and carefully slide it down into the square hole in the drive gear. Try to keep it as straight and as square as possible. Now let it cool while being careful not to bump it out of square with the gear.

Step 3: Add Heat Shrink

Cut a short piece of heat shrink that is just bigger than the shaft and slide it over. Now heat it up with a torch or heat gun and then while it's still warm work one of the 608 bearings over it. The bearing to heat shrink joint should be a snug fit.

Step 4: Prepare Housings for Assmbly

I used PETG for the main housing and it leaves strings all over the place. (at least for me). So I used a Dremel tool and sanding wheel to clean them out. I also ran the side housing on a flat bench sander to make it really smooth. This is not necessary but will improve performance.

Step 5: Fit Gears to Housing

At this point you will want to put both gears into the main housing and check for fit. Ideally, they fit in tight but will rotate when the drill is attached. The pump will be fairly tight to begin with but will wear in after some use. But if it is too tight then chuck the drive gear with its adapter into your drill and insert it into the main housing and spin it for a few seconds in both sides of the housing. Then once it is spinning free set the other gear back in and test the fit again. If it still doesn't fit just repeat until it does.

Step 6: Press in Bearings

Press your bearings either onto the stub shafts coming out the sides of the gears or into the side housing. Use a hammer or a press if you have one. One tip is to use sockets to press them on if you want to press them on over a shaft or support them differently.

Now to be honest I only put a bearing around the input shaft/steel adapter because I ran out of bearings. (due to another project) It doesn't seem to be a big deal and the gears ride inside the housing fairly smoothly without the extra bearings. However I suspect that it would take less power to turn if they were in there.

Step 7: Apply Sealant

Now take the tube of rtv silicone gasket maker and squeeze it out onto the edge of the main housing. Then use your finger or popsicle stick and smooth it out so that it goes around all the holes. I tried printing a gasket out of TPU and Printing it single layer so that I could just vary the first layer height to adjust the thickness. (I tried 0.2mm and 0.3mm thick). It worked decently but I had a hard time getting it to seal 100%. I think if it were printed thicker yet it would work just fine. So, I included the gasket file in the zip folder.

Step 8: Put Gears In

Put the gears in and press into place. Make sure they are all the way down in.

Step 9: Attach Top/side

Carefully set the top/side on now and start all the screws. If you opted for the longer screws put the two shorter ones in the holes over the inlet and outlet. Tighten them just until the gasket maker starts to squeeze out the side just a little. At this point it might be a good idea just to make sure the gears turn with the drill. Now let it sit for an hour or whatever the instructions on the tube say. Then tighten the screws down fairly snug but don't strip them out if you are using the shorter screws. Once again check to make sure the gears turn. The gears will be fairly tight for the first while but that is fine because they will wear in and fit nice and tight then.

Running all those screws in is where it is handy to have a cordless impact driver or electric screwdriver because there are no metal inserts so the screws are stiff the whole way to the bottom.

Step 10: Attach a Hose

Now find a hose that will fit over the barbs. I used 3/4" garden hose, it was on the big side, but a hose clamp tightened it down quite nicely. A 5/8" or similar hose may also be used. If you are having a hard time getting it to fit on take a torch or heat gun and warm the end of the hose up and it will help a lot in getting the hose on. Then take a hose clamp and tighten the hose down. Be careful not to break off the inlet and outlet ports. (I dropped the pump and broke the inlet on a previous design) But do make sure that there is no leaks where the hose attaches or it will leak and/or the pump won't prime very well.

Step 11: Test!

Now go find some water and try it out! As you can see in the first picture in this step the water will shoot quite far (10-15ft) just straight out of the pump. I setup a basic test rig with a pressure gauge and a valve to restrict the flow. With no restriction it will empty a full 5 gallon pail in 35 seconds or about 8.5 gallon a minute. When I closed the valve all the way I could get it to go over 50Psi (even saw upper 50s) but then it started leaking out between the layers. So I consider 20-25psi to be a safe pressure without it leaking. (Guess I'll have to dial in my printer a bit more.)

Because it's a gear pump it is completely reversable and will pump equally well in both directions.

For all these tests I used a Milwaukee M18 drill. If your drill is having a hard time powering it just back off on the speed a little or switch to low gear. (My other drill had a harder time at full speed).

I think that if the outlet port was bigger it would take less power as I think it is restricting it a little. But I wanted to keep the outside diameter of the port small enough to fit a garden hose and also keep the wall thick enough to it wouldn't just break off.

Note: if you are having a hard time getting it to prime, lower it down closer to the water and make sure the hose is on tight on the inlet side so that it isn't sucking air.

Step 12: Put It to Work!

Now go water your trees or garden. Move oil from one drum to another or anything else you can think of. Hey! you could even build 2 and have a water fight!