Pump It Up! Squid Inc's Positive Displacement Pump

As part of our University course at the Glasgow School of Art, we were set the challenge in teams of 4 to produce an efficient pump, and all we were provided with was a 24V 3500RPM DC motor.

The Brief was simple - to design and build a pump to lift 5 litres of water, through a height of 60 cm in under 5 minutes. The team who could make the most efficient pump would win.

This is how Team Squid created their positive displacement pump.

Step 1: The Piston & Piston Chamber

Through evaluation we decided we wanted to make a piston and cylinder pump. This meant we got to try out a number of pumps. Most of the ones that we tried were air pumps, and required a large amount of force to move when water was used.

Then we realised how easy it should be to make our own piston and cylinder. It was made a lot easier by the availability of the Uni workshop!

• Piston chamber was made from diameter 32mm PVC tube, cut to length roughly 100mm
• Plumbing pipe clips used to secure piston
• Piston head made from aluminum- turned on lathe to a diameter of 29.5 mm and width 10mm
• Groove in outer rim of piston head for rubber o-ring, takes diameter to 31mm & creates better seal between piston and chamber
• Piston head bolted onto rod roughly 150 mm long, which is threaded at both ends, secured with nut at either side

Having lubricated this with oil, it ran very smoothly.

Step 2: Crosshead & Clevis

• The most crucial aspect of running our piston pump, is keeping the piston and the crank aligned thus keeping friction minimal, allowing for a smooth pumping action and making sure our crank wheel/gears are not ruined.
• Crosshead was used to keep the piston straight in the piston chamber, we made our from scrap MDF we found in the workshop although could be made from say, aluminum, to prevent wear and tear. A hole was measured and drilled at a height the same distance from the board to the center of the piston. A lot of care was taken to make sure this was exactly right. Diameter of hole was slightly wider than the diameter of the rod, giving a clearance of roughly 0.5 mm
• Crosshead was secured to board using 4 metal brackets which we made very easily by drilling holes in, and bending sheet metal.
• When the crosshead was being secured to the board, we made sure to leave a small gap between the end of the piston chamber and the crosshead, so that there was no pressure build up when the pump is on
• We used a clevis to connect the piston to the crank rod which was again very easy to make from a strip of metal. The metal was bent round a small block of wood, and then, using a piller drill to keep the the holes perfectly aligned, we drilled straight through the metal & wood, giving us two perfectly aligned holes on either side. A bolt was secured between these two holes which the crank rod could rotate on. A third hole was drilled in the centre of the clevis, which the piston rod was bolted onto (hence the need for both ends of the rod to be threaded)

Step 3: The Valves

The valves we decided to use are very simple.

Materials:
21.5mm tube
1x T plumbing connector
1x straight plumbing connector
2x O-Ring
2x Acrylic seat (cut on laser cutter)
2x Marble
2x Nail

• Firstly we attached the O-rings to the seats, and then they sat on the ridge in the plumbing connectors. (The first time we didn't glue the seats down, and that caused a large amount of remaking).
• We then glued the seats into the ridges, placed the marbles on the O-ring and seat, then measured 1.5x the diameter of the marble up the connecting tubes and drilled holes for a nail to sit through. These were then held in place with tape and prevents the marble flying out of our valves when the water is pumped through
• We placed one of these valves at each side of a T-bar plumbing connector, thus the water is sucked through the bottom valve, and pushed out of the top valve

Easy as that! A functioning set of valves! (the valves can be easily tested by fitting a pipe to the T bar, and mimicking the piston by sucking/blowing into the pipe)

Step 4: The Gearbox

• The gear box is made from a selection of Meccano truss', plates, gears and shafts and held together using nuts and bolts. Ours was REALLY OLD, was of our team members grandfather played with it as a child!
• There are 4 gears, made of brass, two large and two small with a gear ratio of 49 to 1. This supplies the torque required to drive the piston.
• The piston is driven directly from the final gear using another piece of meccano as the crankshaft, which already had multiple holes along it for us to easily attatch the crankshaft to the gear/crank. This arrangement also allowed us to test various stroke lengths by changing the point at which the crankshaft is connected, allowing us to optimise efficiency.
• Cross sectional truss' make the gear box stiffer and improve the efficiency. Because of the way Meccano is designed the gears are easy to align and fit together.
• One issue with using Meccano is that the diameter of the holes and the shafts on the Meccano are 4mm however the output shaft for the motor is 3mm. To solve this problem, we had to make a 3mm to 4mm bush to fit the gears to the motor. We also drilled a 13mm hole in the Meccano to allow the give the motor a better fit and improve the rigidity of the structure.

Step 5: Alignment & Mounting

• The trickiest part of making the piston pump run smoothly is getting it all perfectly aligned. This took plenty of trial and error, but we eventually got it bang on, by drawing a centre line on our board and doing out best with our eyes to align everything to that.
• The board is designed so it can easily sit atop the opening of the tank, and so can easily be made to suit any dimensions of tank, making sure a section is cut out in order for the pipe to go down the the water.
• We used various pipe connecters and PVC piping to make our pipe system (taking out water up the height of 60cm as from the design brief), which were all sealed and made airtight

Now we have our finished pump! In testing, we managed to achieve 5.88% efficiency which we thought was not bad seeing as parts of out pump were over triple our ages!

The winning pump came in the form of a rope(elephant) pump, which managed an efficiency rating of 12%, with a diaphragm pump coming in second, and a radial piston pump in third place.

But none of them made as satisfying a sound as our vintage Meccano!