Designing a Seawater Pump
Highlighted Skills
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Onshape (CAD)
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DFMA
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aPriori: choosing most cost effective manufacturing process
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Granta: material selection
In teams of three, we were then tasked to design a rotary vane pump that theoretically pumps filtered seawater for the New England Aquarium. The water pump had design flaws that were improved on in this seawater iteration.
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Given Requirements:
Temperature (F): 35-120
Inlet Pressure (atm): 1
Outlet Pressure (atm): 5
Speed (RPM): 3600
MTBF: 50% duty cycle over a 1 year period; on 10 min, off 10 min
Units per Year: 1,000
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Taking into account the corrosive nature of seawater, we considered using 316L stainless steel for parts that touched the seawater. Furthermore, we factored in galling, galvanized corrosion, shear stress analysis, and thermal expansion due to the temperature requirements. Besides keeping in mind DFMA, the goal was to also factor in the cost of manufacturing-- for that, we used aPriori to estimate the cost of using specific manufacturing processes such as machining from stock versus sand casting and then machining.
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Each custom component was designed using Onshape and we created GD&T drawings for each part. The retaining ring, shaft seal, o-ring, ball bearing, bolts, and washers were all purchased from McMaster-Carr.
Fig 1. Isometric view of final design.
Section view of final design.
Exploded view of final assembly.
Here are all of the custom parts and notable design features.
Back housing. 316L stainless steel. Sand casted + milling.
Notable features:
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o-ring groove for sealing back front plate
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clocking nubbin
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check diameter for front plate
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tattletale for seal failure notification
Front plate. 316L stainless steel. Machined.
Notable features:
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Tattletale for seal failure notification
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Teardrops funnel water in and out of pump to avoid water corralling in internal housing
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Entry and exit ports on face for easy removal of burrs and sharp edges-- different from the water pump manufactured above!n-- di
Rotor + shaft. 316L stainless steel. Sand casted + machining.
Notable features:
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Combined rotor and shaft for minimization of parts
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Groove for retaining ring
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Shaft diameter differs on fixed and free side to account for movement of rotor+shaft due to thermal expansion
Anti-poke washer. Stainless steel sheet metal. Sheet metal stamping.
Notable features:
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extra safety feature so nobody loses a finger
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holes for thermal breathability
Vane. Delrin. Machined.
Notable features:
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Shape to reduce friction of vanes against housing
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radius on top for better contact without friction housing
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"shelf" allows small amount of force to push vane down
Rotor/shaft combination drawing for casted part.
Parting line drawing for rotor/shaft combination for casting.
Rotor/shaft combination GD&T drawing for machining after casting.
Bearing housing GD&T drawing.
Exploded view.
