We fabricated our first PVC prototype with the plastic venturi device last week. Using various endmills we created the slotted holes in both a cut pipe cap and an elbow joint.
The size and shape of our aspirator is significantly different than that in the DrinkWell design. While the DrinkWell aspirator has a constant diameter tube attachment that feeds out of the aspirator body, our plastic model has a tiered-width pipe, that connects to a double-ended conical stopper. This presented issues because the width between the middle block of the stopper and the aspirator tube end was too small for two widths of PVC piping. We experimented with different sized endmill slats, so that the elbow hit at the conical narrowing, while the pipecap hit at the wider aspirator diameter. This, however, applied skewed pressure to the aspirator, offsetting it from the central resting position.
Our laser cut aspirator ring holder also needs modifications. If we have the pipecap and pipe grip the aspirator at the wide part of the aspirator pipe, the aspirator will not be centered in the pipe. We are unsure if the uneven pressure on the aspirator ring-stop will be problematic. We will also experiment with the cut outs to allow the appropriate amount of water through.
This week we have cut and milled PVC for three new models. One involves the original size elbow joint and pipecap, but with two large slats, such that they both will grip the wide part of the aspirator input tube. We also have a set that instead uses a smaller pipe and cap, so that the aspirator will be more central and therefore have a better pressure balance. Our third involves two straight pieces, that would insert straight into the pump pipe.
We are preparing to replicate the DrinkWell regulator tank design as well as consider some other designs. The DrinkWell design uses a constant volume tank to maintain a constant pressure for the venturi device. This constant volume tank uses a ballcock valve and operates similar to a toilet tank. We have bought two ballcock valves to experiment with next week. We are also considering another design to maintain constant pressure for the venturi device – a constant head device. Thirdly, it has been brought to our attention that a device manufactured in India uses yet another mechanism and we are looking into the details of this design.