Impulse sprinkler

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Revision as of 11:29, 3 February 2014

Executive Summary

Our group chose to look at an impulse water sprinkler for our dissection. The specific name of the product is the Melnor Pulsator Sprinkler. After taking the product apart and researching its use and customers' reviews, we performed a Design For Manufacturing and Assembly (DFMA) analysis, Failure Mode and Effects (FMEA) analysis, and Design for the Environment (DFE) analysis. Upon completing our analysis, we decided upon a few different ways that the product could be improved. In the realm of DFMA, we thought that the method of mounting the sprinkler to a metal stake could be adjusted, as the current method requires many parts and much manual assembly. Additionally, we thought that with minor tweaking to the largest part, the Main Frame, the custom made screws and clips on the sprinkler could be purchased off the shelf. In the realm of FMEA, we found that the product was most likely to fail because of a fracture in the main frame (caused by mistreatment or cold weather), the system not being properly aligned for the mechanism that sends the sprinkler in reverse to function, or a clog in the nozzle. These problems could be fixed by making the sprinkler of a hardier material to stop fractures, adjust the lengths of the components in the mechanism that sends the sprinkler in reverse, and to put a diffuser into the nozzle to prevent material from getting in. A majority of the complaints against the sprinkler were that the mechanism that causes that causes the rotation eventually stops working. We suggest preventing this by using a stronger material (to prevent deformation that causes the failure) or by using a better method of mounting the spring that can break due to mishandling. Finally, in the DFE realm, we found the greatest improvement could be made in the packaging. The sprinkler itself had little obvious room for improvement, but they were sold in pairs with large metal spikes. The packaging itself had a lot of room for recycling information or proper water conservation techniques, but it was not there. Additionally, by not selling them with the spikes, you could encourage users to reuse older spikes rather than tossing them out. Judging by the short lifespan on the product (around two years) a person could easily acquire plenty of metal spikes they don’t need that required effort to produce.

Stakeholder Needs

• What does the user need?

• • The user needs it to be easy to set up. It has to be easy to screw in to a hose without an excessive amount of water leakage.
  • There have to be easy to follow instructions.
  • It has to be portable, so that people with larger gardens can easily move it around.
  • It has to be durable since sometimes people just leave it in their yard.
  • It has to be reliable because the water distribution should be uniform.
  • It has to be able to water the lawn effectively while minimizing the amount of water that ends up on the sidewalk or driveway.
  • It has to work well with different water pressures.
  • It has to be easy to clean and maintain.

• What does the retailer need?

• • Inexpensive to produce and therefore inexpensive to acquire.
  • Lightweight so it is easy to ship.
  • Easy to explain to customers.
  • Durable, so customers will not need warranty replacements or repairs.
  • Compatibility with various mounts from various manufacturers.

• What does the manufacturer need?

• • Inexpensive to purchase materials
  • Inexpensive to create the pieces from the materials
  • Simple assembly to keep assembly costs down
  • Made of nontoxic materials (or have few toxic wastes) to save costs in preventative measures to protect workers or the environment
  • Design capable of having schematics clear enough for foremen to understand what needs to be made
  • Finished product not need to be maintained in any way to keep storage costs down while waiting for transport

• What does the transporter need?

• • Durable enough to not break during rough handling
  • Light enough to not over-encumber people or vehicles in the transportation sector
  • Compact enough to fit plenty into small spaces (maybe they interlock to be smaller and more can be fit in trucks or boxes)
  • Be able to withstand a variable range of temperatures likely to be experienced in transit
  • Inexpensive so that should they be broken in transit, there is less monetary loss

• What does the product have?

• • The product is easy to set up. All the user has to do is attach the sprinkler to the stake and put the stake in the ground and attach a hose
  • It can be adjusted to cover 360° or to just spray a specific region.
  • It has a sturdy build, but it has some plastic parts that may be prone to damage
  • It has maintenance and cleaning instructions included in the packaging.

• Comments/Observations

Home Depot Reviews

A stake is not always required since some places are equipped with an underground pipe system which the sprinkler can be directly screwed into. The maintenance instructions are easy to follow; furthermore, there is a clever color code: all the things that need to be adjusted are in green.

Steps to using the product

Step 1: Remove from packaging

The sprinkler is tied into a cardboard sheet using plastic ties, which are easily cut.

Packaging front

Packaging back and User Guide

Step 2: Make adjustments

The sprinkler head can be adjusted for the spray made, by using the built in deflector at the top or adjusting the diffusion of the spray. Furthermore, the plastic tabs at the bottom can be used to determine the angle of the spray, and can be restricted to a straight line or opened up to a 360° distribution.

360° Rotation with Metal Bracket Up

360° Rotation with Metal Bracket Down

180° Rotation with Metal Bracket Down

Step 3:Stick the stake into the ground

Make sure the stake is deep enough that the water pressure won’t displace the sprinkler(picture from Amazon^[2] since we couldn't actually test it because of the weather)

Impulse Sprinkler In Use

Step 4: Turn on Water Flow

Attach a hose to the open end on the stake, and turn on the water. The water pressure can be adjusted from the hose to affect the spray distance, as well as the knob on the top of the sprinkler

How the Product Works Mechanically

The water coming out of the nozzle goes into a S-shaped pipe from which the water goes out in the same direction it went in, but further to the left, allowing a higher torque to be generated. The reactive force to this torque is given by the acceleration of the inertia mass, such that the main frame remains almost immobile. When it then comes back toward the frame because of the spring and hits it, it gives its momentum to the main frame, which rotates a bit. But as it hits the frame, some water goes into the S-shaped pipe and the process begins again. If the spray arc is set to a 360 degree rotation, this rotation will continue indefinitely. However, if the spray arc is set to a limited range of motion, the metal bracket will trip on the clip after a few rotations, which will raise the interrupter. The interrupter stops the arm from rotating, so the force imparted to the S-shaped pipe is transferred back to the arm, and the rotation is reversed. While the first set of rotations described is choppy, with a small displacement each time the arm hits the main frame, this rotation is continuous. Eventually, the sprinkler will rotate back to its original position, where the metal bracket will hit the clip and lower the interrupter, and the process starts all over.

Interrupter in Position to Interrupt

Interrupter Down and Out of the Way

There are three different settings of the water spray that user input can affect. The first is how diffuse the spray is. The diffusion of the spray is controlled by the diffuser pin, which is the green screw seen in the picture above. If the screw is screwed in all the way, the water stream from the nozzle will hit the screw, causing the spray to diffuse. If the screw is unscrewed, the water stream will be uninterrupted, providing a more focused flow of water.

The second setting that can be adjusted is the distance of the spray. This is affected by the green adjuster knob at the top, which controls the slope of the distance adjuster. The water stream from the nozzle, after potentially hitting the diffuser pin, the hits the distance adjuster. At low distance settings, the distance adjuster is flatter, causing the water stream to deflect off it at a lower angle, and reducing the distance of the spray. At high distance settings, the distance adjuster becomes steeper, causing the water stream to come off at a higher angle, and increasing the distance of the spray.

The third setting that can be adjusted by the user is the angle of the spray, with two different modes. The two different modes (360 continuous/back and forth) are selected thanks to a lever, which can put a small plastic piece up or down each times it hits the metal parts setting the limits. When this piece of plastic is down, then the inertia mass will hit the main frame on it way back, pushing it counter-clockwise; when it is down, the inertia mass will hit the main frame before, just after being moved by the water going out of the s-shaped pipe, pushing it clockwise. That way you can go back and forth between two limits.

Videos testing a very similar model, from Rain Bird; between 04:00 and 05:30 on YouTube ^[3] Snapshots:

Part List

The impulse sprinkler examined consists of 19 parts, with 10 pieces being manufactured and 9 purchased off the shelf. The 10 manufactured pieces were all made of plastic, and produced via injection mold, while the off the shelf pieces consisted of 1 metal bracket, 4 metal springs, 3 rubber o-rings, and 1 Teflon ring. Part 13 (Clip), was used twice in the assembly, while each other part was used only once. There were no sub-assemblies identified in the product. The three parts that had to do with user adjustable settings were colored green, while all other plastic parts were made black.

Exploded view

Exploded View of Assembly

Bill of materials

Part Number	Name	Quantity	Mass (g)	Function	Material	Manufacturing Process	Image
1	Distance Adjuster	1	5	Adjusts distance of water stream	Plastic	Injection
2	High Adjuster Knob	1	3	Adjust the slope of part 1	Plastic	Injection
3	Axial Spring 1	1	<1	Keeps part 1 up	Metal	Off the shelf
4	Axle	1	<1	Allows the arm to rotate in the main frame	Plastic	Injection
5	Torsional Spring 1	1	1	Brings the arm back towards the main frame	Metal	Off the shelf
6	Arm	1	13	Inertia wheel/ Moves when hit by water and rotates the whole sprinkler when hit the frame	Plastic	Injection
7	Screw	1	<1	Disperses the water stream	Plastic	Injection
8	Main Frame	1	21	Base of the assembly that all parts attach to; also has a hollow section for water flow.	Plastic	Injection
9	Actuator	1	<1	Triggers the direction lock	Plastic	Injection
10	Interrupter	1	1	Changes the direction of rotation of the sprinkler	Plastic	Injection
11	Metal Bracket	1	<1	Hits the clips when it should change the direction of rotation and transmit the force to the actuator	Metal	Off the shelf
12	Torsional Spring 2	1	<1	Connects part 9 and 10 as an unstable triggering system	Metal	Off the shelf
13	Clips	2	1.5	Determine the range of motion	Plastic	Injection
14	Mount	1	6	Connect to the hose and allows the frame to rotate	Plastic	Injection
15	O-Ring 1	1	<1	Prevent leakage	Rubber	Off the shelf
16	O-Ring 2	1	<1	Prevent leakage	Rubber	Off the shelf
17	Ring	1	<1	Allows the frame to rotate inside the mount by reducing friction	Teflon	Off the shelf
18	O-Ring 3	1	<1	Holds the frame inside the mount and prevent leakage	Rubber	Off the shelf
19	Axial Spring 2	1	<1	Push down the mount to prevent leakage	Metal	Off the shelf

Design for Manufacture and Assembly (DFMA)

Design for Manufacturing

Design for Assembly

Numerous points (minimize Part Count, etc...) come both in DFM and DFA, so we will just add properties specific to the assembly in this table:

Failure Mode and Effects Analysis (FMEA)

Design for the Environment (DFE)

Eco-Manufacturing Design

The biggest way that the product could be designed better as far as eco-manufacturing is concerned deals with the packaging. The packaging is a large sheet of cardboard and it holds the two sprinklers with plastic zip ties. There is so much blank space in the packaging that could be used for including more information about the sprinkler, such as maintenance and recycling instructions. Also, since the majority of the product is made of plastic, the manufacturer could look into using recycled plastics with similar properties to the plastic currently being used. The packaging included two large and heavy metal stakes, which accounts for the bulk of the shipping weight and is undesirable for consumers who don't want to make a hole in their lawn.

Our most interesting new concept was a Roomba-like machine that goes around a yard and delivers the correct amount of water to each section of the lawn. It will drastically reduce over- and under-watering of lawns and it will make sure that the lawn is watered evenly as well. It will be ideal for the small sections of grass along the sidewalk and it can also have a mechanism to evenly distribute fertilizer as well. It would require some electronic software so that it would be able to detect edges of lawns and to monitor the amount of water being distributed to the grass.

Economic Input-Output Life-Cycle Assessment (EIOLCA)

For EIOLCA on the impulse sprinkler, it turns out that there were only two input factors that were relevant. In the production phase, there was only one relevant product, the entire sprinkler assembly, falling under the sector "Other Plastics Products Manufacturing". In the use phase, the only thing consumer uses during operation is water, under the "Water, Sewage, and Other Systems" sector. Over the two year lifetime of the sprinkler, the total carbon dioxide tax from the sprinkler was $3.11.

A number of assumptions about the lawn and environment, as well as about sprinkler operation had to be made in order to perform EIOLCA. Water use will vary greatly depending on the type of grass and size of the lawn, as well as the number of weeks per year that the lawn will be watered. It was assumed that the lawn would require 1" of water per week, and the lawn was 1000 square feet in surface area. By using 1" of water and 1000 square feet, it makes it easier to recalculate the CO₂ emissions, if given different lawn parameters. Furthermore, it was assumed that the lawn would be watered for 30 weeks of the year, with the other 22 weeks being in the late fall and winter months when it is too cold for grass to grow. Last, we had to assume that the sprinkler would spray the water uniformly over the desired area, and that leakage in the sprinkler was negligible, in order to calculate water use.

Team Roles

Team Leader: Tristan Greiner

DFMA Lead: Louis Dufour

FMEA Lead: William Bullard

DFE Lead (Eco-Manufacturing): Hira Ahmad

DFE Lead (Life-Cycle): Justin Hui Bon Hoa

Citations

[1] Home Depot Customer Reviews

[2] Amazon Rainbird Picture

[3] Impact Sprinklers Performance Review - Vigoro Vs. Rain Bird, by user Miguel Chavez