Double Acting Diaphragm Pump

We are Team Orca, a group of four second year Product Design Engineers, from Glasgow School of Art and Glasgow University. We got given the task of building a water pump to lift five litres of water through a height of approximately 600mm. The competition was judged on efficiency and all teams were supplied with a 24V DC motor. Out of 5 teams we came second!

Step 1: Material List

30mm Steel rods (6mm) (Driving rod)

Pvc-pipes and joints 21.5mm (for delivery and suction manifolds)

(At least two t-joints and two straight joints as these are required for check valves)

4 Marbles (check valves)

4 O-rings 10mm (check valves)

4 Nails (for the check valves)

Rubber 1mm (diaphragms)

Acrylic (check valves and sealing rings)

Bolts (securing diaphragm and chamber to pump body)

MDF (for vacuum forming the chamber and as a frame)

Two sheets of HIPS (for vacuum forming the chamber)

Big pipe that can be cut into pump bodies

4 Washers (Driving rod)

2 Nylon nuts (Driving rod)

2 Nuts (Driving rod)

Gearbox and scotch yoke mechanism , you can make this yourself but we used one from a cheap jigsaw

Step 2: Tools

Band saw (for plastic, metal)

Die (For threading the steel rod)

Tap (For threading the pump body)

Drill

Laser cutter (for diaphragms, sealing ring and check valves)

Vacuum former (For creating chamber)

Step 3: Creating Parts - Sealing Ring

Laser cut from the plastic sheet. A ring with eight evenly spaced 6mm holes.

Step 4: Creating Parts - Pump Body

Cut off 60mm from a large pipe. Drill holes using the sealing ring as a guide. Thread the holes using the dip. Make sure the dip and bolts you are using match up and that the holes are deep enough.

Step 5: Creating Parts - Diaphragm Chamber

Create a hole with the same diameter as the inner part of the pump body in a board of MDF. The board should fit inside the vacuum former and the hole should be in the center. Put your plastic sheet under the piece of MDF and switch the vacuum former to blowing. Try to get the dome at approximately 2cm deep. This is for the diaphragm to fill as much as possible of the chamber. It was 2cm in our case.
Use the sealing ring as a guide and cut off the outside of the chamber and drill holes.

Next, cut a curved section out of a straight bit of pipe, then cut the dome to match as shown in the pictures and use cement to get it rock solid.

Step 6: Creating Parts - Diaphragm

Laser cut a circle with holes that match up with the sealing ring out of the sheet of rubber. It should also have a hole in its center for the driving rod. To reduce the torque and make it easier to prime a more flexible rubber is desired, but if it is too flexible you won't be pumping anything. We tried some different ones before we ended up on the final molded silicon rubber.

Step 7: Creating Parts - Check Valves

Laser cut two rings 21.5mm wide and with a 12mm hole in the middle. Super glue an o-ring centrally on each of the two rings. This is the seat for the marbles and will go into the joints. The seat sits between the joint lip and the pvc pipe, this way the pvc cement is all the glue that is needed. To stop the marble from “escaping” we need to put a nail through the pipe that is connected to each valve joint. It’s important that the nail is perpendicular and through the center, it should be approximately one and a half marble diameter from the seat.
Above is our overview over joints and check valves. Water is sucked from the bottom of the picture and delivered in the top. Each valve seat can be very lightly coated in Vaseline.

Note! We had a design using t-joints for connecting the chamber to the manifold. We switched this to a straight bit of pipe so in the diagram above use four straight joints instead of the t-joints.

Step 8: Adapting the Scotch Yoke

A scotch yoke and gear mechanism was taken from a jigsaw. It needed to be adapted in order to drive the diaphragms and be driven by the motor. These were laser welded (we couldn't weld normally as the ventilation wasn't working there at the time) onto the scotch yoke as shown above.

Step 9: Putting It All Together

Create two aluminium guides for the driving rod as shown. Assemble the two pumps by putting bolts in the holes that have been tapped through all the parts (sealing ring on top, then diaphragm, chamber and last pump body). Use pipe cement to assemble the manifold to the desired length and shape. Lastly create a frame of mdf to keep it all together.

Step 10: Sealing the Pump

Prior to the final stage of sealing, the pump was tested several times and it was noted how each time vast volumes of water were lost due to leakage at the sides and centre of the diaphragm (where the driving rod was attached). By sealing well, it creates a vacuum and ensures that as much water as possible is conserved. It also enables the pump to prime better. Therefore this is a very important stage, which should include sealing between the sealing ring, rubber, screws and chamber. As well as between the driving rod, washers and rubber at the centre of the diaphragm.
We could probably have done with quite a bit less silicon for the looks, but we were running out of time and needed the pump working optimally.

Step 11: There You Have It, a Diaphram Pump!