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Project Summary

We are designing a urinal that decreases the amount of splash-back.



Urinals, as they exist today, do not adequately serve their function which is to be a sanitary means of unsanitary-fluid disposal. Frankly, one of the most simple and logical inventions since the origination of plumbing has only ever been improved marginally. 



The back-splash that occurs in urinals is a problem for two main reasons: the unsanitary mess it creates for the patron as well as the facility owner (qualitatively observable) and micro-biological dissemination via micro-droplets suspended in the air, which can be a major health concern [1].


Many existing products, both fully functional urinals (figure 1) and inserts (figure 2) claim to reduce splash, but if you want real sanitation none of these solutions are adequate because none address the fundamental issue: fluid flow making contact with a surface at a certain normal velocity will cause splash. 


Figure 1- "Virtually Splash Free"          Figure 2- Anti-Splash Backguard


Urinal manufacturers have not strayed far from the original "seatless toilet" design from which the modern urinal originated, although there have been some changes. The first major difference was privacy: urinals got smaller and flatter so as to be more easily separated by dividers. The second- and most recent- major step was water conservation. Internationally, the IAPMO (International Association of Plumbing and Mechanical Officials), which has existed for about 80 years, has established guidelines by which plumbing fixtures are developed including water usage and materials. The EPA (Environmental Protection Agency) also sets guidelines for conservation purposes.


However, as conservation development has surged forward to the point of zero water usage, development in the way of actual sanitation has remained at a relative stand-still.


Existing solutions to the splash problem are mostly afterthoughts (Table 1). The basic urinal is completely ineffective, the basic bee solution does not adequately address the problem, and expensive designs avoid the issue by promising a "virtually splash free surface" which leaves a lot of room for interpretation. The companies that make these expensive urinals do not substantiate the claim at all.


"Reduced Splash"



Doesn't work

     This is your standard urinal

"Pee Bee"



Slight improvement

User reliant

Only slight improvement if used perfectly

"Virtually Splash Free Surface" May reduce splash beyond standard urinal

Extremely expensive

No evidence to back up the claim

Table 1- Existing solutions


The reason these solutions are insufficient is actually relatively simple (to diagnose, not to cure): A stream of water either will or won't splash when it hits a surface depending on whether it is respectively above or below a calculable threshold normal velocity (Figure 3). As the male experience shows, an average stream of urine is well above that threshold. Even as the angle of attack is decreased, by the time the normal velocity would be below the threshold, the stream is encountering the geometric irregularities at the base of the urinal as well as water-on-water splash in the basin.


Figure 3 - Splash/spread velocity threshold [2] - This is a graph of droplet velocity in the normal direction versus velocity in the tangential direction. The dotted line is the splash/spread velocity threshold, above the line the droplet will splash and below it the droplet will simply spread out. 


Intellectual Property

There are several proposed solutions that are patented or have patents pending. Several are tabulated below along with some relevant description. However, our approach to the problem differs so drastically from the existing intellectual property that very little can even be drawn on except for material properties.


United States Patent 1379206, O'Hara May, 1921


United States Patent 7398565, Chou July 2008




We intend to construct a urinal such that no stream of urine ever hits a surface in a manner such that splash occurs. Due to the difficulty of mathematically modeling such an irregular stream, our process has involved using qualitative understanding of the nature of splash and combining that knowledge with the numerical data obtained from Professor Shreyas Mandre.


Our proposed solution is a series of curved, thin, sharp blades. By orienting them such that the leading edge is always tangent to the stream of urine, we hypothetically eliminate splash as long as the leading edge is thin enough (See Figure 4). And if the stream travels between stators (as it statistically will most often), we will orient the blades such that the stream never contacts the blade with a normal velocity above the splash threshold. Furthermore, because at some point the fluid will run off the smooth blade, we will ensure that the fluid decelerates via friction sufficiently to prevent splash at that point. In this way, we hope to completely eliminate splash.


Figure 4 - Sharp, thin blade under stream of water


Due to the irregular nature of the phenomenon we are handling, our optimization will result from quantitative and qualitative analysis of each iteration (call it informed trial and error).


Our first iteration will be a partial manifestation of what we have brain-stormed to be the logical solution. It will be a portion of the blade section of the design (enough to test its effectiveness) constructed of thin aluminum. Using Pro-E CAD modeling, we have developed a digital blueprint of our idea and what we think the final product will look like. See Figure 5 for the Pro-E model. 



Figure 5 - CAD conceptual modeling


The second iteration will be an optimization of first design. Primarily, we will determine the best number of blades for the design. We will also be sharpening the edge of the stators to eliminate their normal component and further improve the urinal's resistance to splash. Finally, we will optimize the scale of the urinal to be most space and water efficient while still maintaining a comfortable and ergonomic design for the user.


The third and final iteration will also be an optimization of second iteration. The main facet of this phase will be to choose the best material for the design; one that will further improve fluid mobility and decrease rinse water consumption. Most importantly, this iteration will be a full and complete urinal that we hope will achieve our goals.


These goals are summarized in our list of requirements as of 3/17. It is possible that our requirements could change significantly as our testing progresses depending on our findings.


First Iteration

Splash is a product of two factors in the fluid flow; the first being the velocity of the flow and the second being the geometry of the surface which the fluid impacts. Knowing that fluid velocity is a variable with each user and cannot be controlled, we decided to focus on the geometry of our design. In our design, stators tangent to the direction of flow work to gently redirect the path of the fluid and prevent splash.


As well as having a circular curve to redirect the flow, the stators are also angled in varying degrees. This ensures that when used properly (i.e. fluid is directed from the center of the device) no fluid will impact the urinal at a normal direction and result in splash-back. Please see Figure 6.



Figure 6 - Cross Sectional view of first iteration - This diagram is a cross sectional view of the first iteration. It shows the blades used for a single side of the urinal. With the left side at the top of the arc as center, our model was design so that any stream from this center point will not create a splash when it impacts any point on the stator design.  


The dimensions for our design were extrapolated from both current models and human features. The scale and dimensions of the design have not been solidified yet and are to be optimized with the second iteration.


To model our design, we used the CAD program Pro-E. This allowed us to easily change the design and adapt new features, a benefit that will also be seen in optimization for the second and third iterations. This also allowed us to precisely map out the proper dimensions and easily transfer them to the physical model we built. Taking the dimensions for each blade from the CAD modeling, we cut each piece of sheet metal to the proper width and the uniform height of 12 inches. Next we needed to bend each sheet to its own unique curve, the critical aspect of the design. Again, using the dimensions from the CAD model, we made our own large-scale protractor and used a sheet metal slip roll to gently form each stator to the necessary radius. Please see Figures 7, 8 and 9. 




Figure 7 - Our homemade protractor                     Figure 8 - Using the slip-roll to curve the stators        Figure 9 - Protractor with stators on curves  



After creating each stator, we used the dimensions from our Pro-E model to create a grid on paper and transfer the angles for each stator onto the Styrofoam frame we created to hold the blades for this iteration. The final result for this first iteration is a Styrofoam casing containing our stators, please see Figure 10. This iteration was built solely for splash testing purposes and for proof of concept. It was not built as a fully functioning prototype.



Figure 10 - First iteration design


Testing Procedure 

For our testing, we made a few assumptions. We assumed that the stream would always originate from essentially the same point, that the stream velocity is within a certain range, and that the stream can be modeled by water forced out of the tip of a syringe.


The point of origin is located 3 inches in front of the center of the urinal. One of our design considerations was controlling where the user is standing, and our research shows that we can control this variable fairly consistently.

The stream velocity (on average) was determined to be about 2.5 m/s.


Our testing procedure was multi-faceted: it consisted of setting up white blotting paper in front of the apparatus and spraying a dyed stream continuously while rotating the source, and then repeating this procedure while keeping the source steady at a number of different angles. In this way, we could observe the overall effectiveness of the apparatus as well as the effectiveness of individual parts. While the testing is not quantitative, it sufficiently demonstrates the function of our apparatus.



**NOTE** During our week hiatus from studies, the phone/camera containing the photographic records of our first tests was stolen . We have continued to move forward with our second iteration but we will re-record our first iteration tests for your viewing pleasure when we do the tests on our second iteration for comparison purposes.


We observed zero splash-back. Even when we drastically altered the point of origin and drastically increased the velocity of the stream, there was still no observable splash-back.

However, a significant deflection of the flow was observed and because of our understanding of the phenomenon of splash there is likely micro-splash that is unobservable with our current testing procedure.



Obviously the observed results indicate that our prototype is headed in the right direction. However, several improvements need to be considered.


1) The leading edge of each stator could be sharpened. The advantage of this would be minimized normal impact. While qualitatively the current design, via conservation of momentum and other fluid principles, appears to eliminate the splash-back caused by the normal leading edge, we suspect that there could be unsanitary micro-splash that needs to be minimized. The major concern with sharpening the leading edge is user safety.


2) Material considerations: We observed that aluminum allows for droplets to remain on the stator surfaces. Many waterless urinal designs boast sanitary, self-cleaning surfaces, so perhaps such materials could be considered for our design. The advantages would include sanitation and reduced water usage. The disadvantages would include increased cost of production and durability.

It is also worth noting that this phenomenon of fluid friction on the aluminum surface helps decelerate the flow.


3) There is one stream trajectory possible (when flow is not originating from near the intended point) which misses the stators entirely. This design flaw needs to be fixed either by adding a stator (if this would leave enough room for cleaning) or by adjusting the radii of the stators (which, based on our testing, should not decrease the effectiveness of the urinal).


4) Size: Our design is very big (too big).

With our current design, the full urinal would be about 2 feet wide and 1 foot deep. The thought behind this was to ensure that the apparatus would sufficiently accomplish our goals (significant deceleration of fluid, trapping all splash that might occur in the back of the urinal, wide margin of user error, etc). However, since our first iteration seems to be drastically more effective than even we anticipated, we may be able to decrease the size of the urinal.

The amount the depth can be decreased will depend on the material we choose because enough deceleration must occur to eliminate splash in the back of the urinal.

The width can be decreased to the extent that the user still feels comfortable standing at the designed point of origin. The current design is meant to allow the user almost 180 degrees of range. This is probably excessive. We will do further market research to find the minimum acceptable width.


Second Iteration


Our second iteration aims to address several of what we determined to be the 4 major issues with the 1st iteration: leading edge, materials, stator orientation, and size. Specifically, we intend to address leading edge, stator orientation, and size while leaving material considerations for our 3rd iteration.


In addition to addressing the above issues, we also intend our second iteration to be a full-scale mock-up so that we can determine the right scale and do some market testing to determine what the consumer wants and how we can adjust parameters to best suit the consumer's needs.


Essentially, we would like our 2nd iteration to be a proven viable mock-up while in our 3rd iteration we can focus on methods of construction/cleaning and making our product fully functional and easily reproduce-able.


The second iteration will be tested in a manner similar to the first in order to determine its effectiveness. We would like to be able to demonstrate that this design, with whatever tweaking is necessary, is ready to be produced in its full form (actual desired materials, drainage, etc) in our third iteration.




Updated Requirements


Because our first iteration functioned extremely effectively, our basic design will remain the same: stators with leading edges tangential to the flow. However, one of our major changes was re-scaling the design.Our new design sacrifices approximately 25 degrees of horizontal range for 8 inches decreased width and 2 inches decreased depth. This makes the design lighter and smaller without sacrificing much in the way of usability. While the overall width decreased 8 inches, the actual opening width only decreased 4 inches and the horizontal range remains an extremely generous 125 degrees.


Figures 11, 12 & 13 - A CAD rendering and full-scale model of our 2nd iteration design. Note that amongst subtler changes this design has 1 fewer stator and is thinner.


Construction methods of this design are similar to those of the 1st iteration: Styrofoam frame holding the metal stators in place. This is a quick and cost-effective way to solidify our design before moving to the more expensive materials and complicated methods that our final iteration will entail.


The major difference between the prototypes (other than design considerations) is that this one will be a full-scale mock-up and will be, aside from a flush mechanism, complete and functional. We left the top effectively open and the back made of clear plastic so we can more carefully observe the nature of the flow using a strobe.


We used a slightly thicker stator (.03 inches) because we anticipate needing thicker stators for structural reasons. Our testing did not show a significant change in performance with the thicker stator.


Since our second iteration is geometrically what we were intending for our final prototype, we were able to perform more comparative tests on it, the most important of which was comparing the splash pattern off our prototype versus splash pattern off a piece of ceramic (perpendicular flow). The test was performed by spraying a constant turbulent stream of water (via pump) at our prototype from a variety of angles and by spraying the same stream of water at a ceramic surface (tile), each for 20 seconds. Blotting paper was laid out 13 inches in front of the back wall of the prototype and 13 inches in front of the tile. We could then observe the extent to which the blotting paper got wet.

While this test was largely qualitative, the results were striking. The tile alone showed an even layer of tiny droplets mixed with an even but less dense layer of visible droplets. On our prototype, the density of microdroplets was notable decreased but we noticed slightly more visible droplets that in our previous tests when we sprayed at a high velocity with certain nozzles. The source of the splash is not entirely clear and our observation has led us to believe that the most likely source of these droplets is irregularity in the nozzle itself cause rogue spray.


We also used our second iteration for a small amount of market research. We asked a number of random male subjects how they would stand in front of the prototype if they were using it and measured the distances that they stood from it. Within 2 inches, the origin of stream was determined to be 6 inches from the face of the urinal, precisely as it had been designed.


The 2nd iteration seems to be a success which allows us to move on to manufacturability.


Third Iteration


For our third iteration, we aimed to optimize manufacturing method and cleanability. Having determined that functionally our design more than satisfied our set requirements, we can focus on making the prototype a feasible reality.


Three main factors were considered:

1) Ease of production (number of components, method of construction)

2) Price of production

3) Ease of cleaning


The third iteration actually went through a number of iterations itself:


Our first design constructed much like our more rudimentary prototypes. The metal stators were to be held in place by the clamping force of a top flush unit and a bottom drain unit. This allowed for relatively easy assembly (just line up the stators on the bottom unit, place the top unit on top, and bolt into place) and could be kept reasonably sanitary my minimizing the contact area between the stators and the base (less area for bacteria to get trapped).

However, this iteration had several flaws:

1) Not sanitary enough

2) Too many components

3) Not easily cleanable enough ( no way to easily access blades)

4) High price of production (while material costs are low, there are components of several different materials that require varying types of manufacturing)

5) Does not allow for exploring different materials later


It was suggested by Prof. Bradford that we could make a design where the stators did not need to touch the bottom trough. Also, if we designed the top of the urinal in such a way that the stators could slide in and out of a top piece, then each blade would be significantly more easily accessible and thus more easily cleaned. This design also allowed for the parts to be either extruded or injection molded, opening the doors to other materials.


BUT the design suffered 2 major flaws:

1) Although the extent of our designs did not cover flush mechanism, it seemed that creating an effective and efficient flushing system that could work around these movable stators might be difficult. While this would be an obstacle but COULD potentially be worked around, the 2nd flaw was the knockout punch.

2) Because of the curvature of the stators, they could not be put in place or removed. Their length and curvature cause the stators to curve around and make contact with the front surface of the urinal. At first we did not think this was a huge deal since it would still make the blade significantly easier to clean, but then we realized that this curvature would not even allow us to slide the stators in in the first place.


Also taken into consideration during this time were the material possibilities for our urinal. In line with the sanitary nature of our stator design, we also want them to be as water repellent as possible, thus we need a very hydrophobic material. This means that upon contact with the surface of the stators, the fluid would bead up with a very large angle tangent to the surface, as seen below in Figure 14.A.



Figure 14 - Hydrophobicity [3] - this figure demonstrates the effect on a droplet of liquid that is on the surface of both [A] a very hydrophobic material as well as [B] a non-hydrophobic material. 


Through our research we found numerous materials that have been developed and would be ideal for our requirements. Among these is a very strong and cheap plastic called Lexan that is called "ultra-hydrophobic" and is used in many buildings for its strength and resistance to weathering. Another possibility is a material called PETG, which is a type of plastic used in processing such things as soda bottles, thus demonstrating its hydrophobicity. Another benefit of PETG is its ease of production thanks to injection moulding. These two are possibilities for effective production in a future commercial product.


Our third iteration sacrificed ease of cleaning for ease and price of production. Ultimately, we have a prototype to show that with a 50 cent toilet brush this design is really quite easy to clean. This final iteration consists of only 2 main pieces and 12 bits of hardware (4 threaded rods, 8 nuts) to hold it together. It is sanitary, extremely easy to manufacture and extremely effective.




We would like to thank Shreyas Mandre and Joseph Liu for their helpful discussions and tips with our project.



[1] Bruce Lighthart, Jinwon Kim, 1989, Simulation of Airborne Microbial Droplet Transport, Applied and Environmental Microbiology, Vol. 55, No. 9 

[2] James C Bird, Scott S H Tsai and Howard A Stone, 2009, Inclined to splash: triggering and inhibiting a splash with tangential velocity, New J. Phys. 11 (2009) 063017

[3] Mohammad Amin, Mohammad Akbar and Salman Amin, 2007, Hydrophobicity of Silicone Rubber Used For Outdoor Insulation (An Overview), Advanced Study Science Center Co. Ltd. Rev. Adv. Mater. Sci.16







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