07 February 2005 M J Stanway a primer on dynamic sealing or, how to keep water from messing up all your cool moving contraptions

M J Stanway 07 February 2005 dynamic sealing STATICDYNAMIC

M J Stanway 07 February 2005 dynamic sealing O-ring (static seal) Specifications and help from Parker O-ring Handbook Specifications and help from Parker O-ring Handbook Male gland seals usually preferable Male gland seals usually preferable Easier to machine external groove Easier to machine external groove Less likely to damage seal during assembly Less likely to damage seal during assembly BUT prone to failure in rotating applications BUT prone to failure in rotating applications

M J Stanway 07 February 2005 dynamic sealing FlexiSeal Specifications and help from Parker Flexi-Seal Handbook Specifications and help from Parker Flexi-Seal Handbook “C” shaped open o-ring with enclosed spring “C” shaped open o-ring with enclosed spring Used by SeaGrant in thrusters and other reciprocating seals Used by SeaGrant in thrusters and other reciprocating seals Sold as “Spring-loaded PTFE seals” in McMaster (pg. 3244) Sold as “Spring-loaded PTFE seals” in McMaster (pg. 3244)

M J Stanway 07 February 2005 dynamic sealing FlexiSeal installation “heel first” 2-part gland seal advisable “heel first” 2-part gland seal advisable Open end of seal faces higher pressure Open end of seal faces higher pressure Easy to machine Easy to machine Easy to assemble without damaging seal Easy to assemble without damaging seal Other options include step-cut glands with/without snap ring retainer Other options include step-cut glands with/without snap ring retainer

M J Stanway 07 February 2005 dynamic sealing Magnetic Coupling Good for thrusters, not high enough accuracy for positioning actuators Good for thrusters, not high enough accuracy for positioning actuators Simple concept, potentially difficult design Simple concept, potentially difficult design COMPLETELY separated from fluid by casing material COMPLETELY separated from fluid by casing material

M J Stanway 07 February 2005 dynamic sealing Magnetic Coupling 2-3 manufacturers make something currently that MIGHT work 2-3 manufacturers make something currently that MIGHT work WHOI uses them for thrusters on something WHOI uses them for thrusters on something Might be able to design and fabricate our own at low cost Might be able to design and fabricate our own at low cost

M J Stanway 07 February 2005 dynamic sealing MC Design Considerations Use neodymium for high strength to volume ratio Use neodymium for high strength to volume ratio Possible source: K&J Magnetics - $7.50 for 100 (1/4 x 1/8 x 1/16) Possible source: K&J Magnetics - $7.50 for 100 (1/4 x 1/8 x 1/16) Even number of magnets, same on inner and outer rotor Even number of magnets, same on inner and outer rotor Alternate poles around rotors Alternate poles around rotors

M J Stanway 07 February 2005 dynamic sealing MC Design Considerations Rotor that sits inside in coupling would be wet side Rotor that sits inside in coupling would be wet side allows for thin wall thickness in endcap between magnets (that part is in tension) possible quick- disconnect props Endcap most likely Aluminum Endcap most likely Aluminum

M J Stanway 07 February 2005 dynamic sealing Other waterproofing Potting Potting Solid material Solid material Insulates Insulates Reduction in power Reduction in power Good for sensors, not actuators Good for sensors, not actuators Oil pressure compensation Oil pressure compensation Can have power loss Can have power loss System can be bulky & expensive System can be bulky & expensive

M J Stanway 07 February 2005 dynamic sealing Seals in our ROV questions? NOTE: pictures taken from Parker, Magnetic Technologies Ltd, Magnetic Materials and Components, and Bluefin Robotics