What is a BCD and what are Dump Valves?
BCDs are critical dive gear used, primarily, to adjust the buoyancy of its wearer, hence the name; Buoyancy Control Device. While diving, a low pressure hose from the main regulator allows the user to press a button to fill the bladder and another to empty the bladder. In addition to this control method, most BCDs also contain several dump valves. These are spring-operated valves that are normally closed.
Depending on the physical orientation of the diver, getting the last bit of air out of the BCD may not be possible with the aforementioned "empty" button. Dump valves are placed usually at the top and bottom of the BCD so that the wearer can activate them to get the last bits of air out, no matter which end of their BCD is closer to the surface.
Dump valves consist of a spring, flat seal and pull cord. They thread onto a port on the dump valve and when the user pulls on the pull cord, the seal is moved away from the port and air can escape.
Salvaging a BCD
BCDs, like most dive gear, are not inexpensive. Fortunately, dive gear is designed to be incredibly rugged and usually lasts a very long time when properly maintained. When gear does fail, a lot of it can be repaired.
While new dump valves can be purchased, this is unfortunately not true for most BCD dump valve ports. If that plastic part, which is bonded to the BCD becomes damaged, the entire BCD is usually rendered useless.
The Solution
A sailor came to me in Tahiti with this exact problem and asked if I could help. BCDs are made out of a vinyl coated fabric, and have round holes cut into them where the ports will be added. The ports are inserted through this hole and usually bonded with a PVC cement or similar material to hold the port in place.
On this particular Scubapro BCD, the dump valve also helps secure the port by threading directly onto it.
Determining Dimensions
This sailor had was was left of the original port and the working dump valve. I retrieved these, determined the relevant dimensions and thread pitch and then created a version of this original that would solve the problem and also lend itself to easy 3D printing.
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| 3D printed tools used to determine thread pitch and radii |
The original was injection molded, so adjustments were needed to make the design compatible with FDM manufacturing.
Creating the Part in CAD
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| 2D shapes used to create the 3D object |
In this case, those closed shapes were "lathed" around a central axis to create two shapes, which were then added together. Finally, air evacuation channels were "removed" from the bottom and 2.0 mm-pitch threads were added to the top portion.
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| 3D Objects with extra operations performed |
The Printed Part
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| Replacement Part, Top side |
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| Replacement Part, Bottom side |
The printed part was tested against the dump valve and the thread pitch and size was perfect, allowing for a original-style fit.
The Fit Test
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| The replacement part inserted into the BCD |
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| With the dump valve re-installed |
