CPI Waterproof Limit Switches – a Better Proximity Switch
In one of the largest non-combat ship procurements since WWII, Canadian shipbuilder SEASPAN was chosen to be Canada’s primary contractor for the Joint Support Ships (JSS) being built for the Royal Canadian Navy.
These purpose-built, multi-role vessels are tasked with a vital replenishment and resupply role that will allow the Canadian Navy to operate away from port for longer periods of time. They are also key for supporting training and humanitarian operations at home, and abroad.
Door Status On Ships is Critical
One of the key operational systems on the JSS (and indeed any ship) is the sealing of bulkhead doors and hatches. Watertight doors act as a fail-safe should sections of the ship be compromised, allowing the captain to control the flooding of compartments, keeping the ship balanced and afloat during a crisis.
Standard procedure for bulkhead door closed detection was to use a proximity switch. These magnetic indicators require active power through a 3 wire connection to determine door status at any point in time. The JSS program engineers quickly realized that running additional power to every door in the ship (there are hundreds) was not only inefficient and added complexity to wiring, but these proximity switches are also subject to other failure modes unrelated to the door status.
“They very much wanted a robust, passive sensing solution.” Notes John Crozier, CPI’s field application engineer for the project. When engineers approached CPI with the requirements, two key things stood out:
- The Switch needed to be extremely robust and completely water sealed as it might actually need to operate underwater.
- The mechanically actuated switch mounting required a form, fit, and function replacement into an existing door design.
The team at CPI quickly settled on the J4414 as the primary switch for this application. The all stainless steel J4 plunger switch actually has a long history of providing door closed detection for all kinds of military and commercial vehicles. In applications from engine hood lock detection to submarine hatch status sensors, the J4 is exactly the kind of small form factor, physically tough, yet precision engineered part these applications require. With a double exclusion seal the switch is all but immune to water and particulate ingress even during actuation, and parts can be qualified up to 100,000 cycles of electromechanical endurance.
In the case of the JSS program however there was even more. The position of the switch was already fixed by the existing door designs and so CPI would have to design a custom bracket that would provide mechanical actuation when the door was closed.
Using in-house 3D printing capabilities, CPI designed and printed several bracket designs eventually qualifying one prototype for use in the application. CPI’s well established 3D fast prototype printing process allowing for low-cost plastic mock units to be mounted within the application before committing to expensive dies or tooling. The process was both accurate and fast, saving the client much time and money on the qualification of the prototype.
Door Switch Field Performance
Production versions of the J4414 and the custom mounting bracket were installed on the JSS. The final design was so reliable that SEASPAN standardized the use of our design for all seaworthy doors and hatches on the JSS, and all active ship program door designs.
CPI’s J4 switches are truly made for seaworthy door seal detection and so much more. Call us today with your requirements and together we can create the perfect solution for your application.
This blog was originally published at https://www.cpi-nj.com/bulkhead-door-open-detection/
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