What is the correct O-ring grease
to use with a submersible housing?
There are two basic configurations for O-ring seals; the `Piston' seal,
and the `Gasket', or compression seal. In the former, one
part of the assembly slides into the other, while in the latter, the
O-ring is squashed by a lid. The back doors of many compact
camera housings have piston seals.
The back doors of many SLR housings have gasket seals.
O-ring grease is not a sealant
it is a lubricant that enables piston seals to be assembled without
damage. Consequently, gasket seals do not need
grease, although a light coating may help to preserve the rubber and
may assist in cleaning.
If grease is
required, the type used is very important. In the past,
housing O-rings were nearly always made from Nitrile-Butadiene Rubber
(NBR), usually black, and the appropriate lubricant is either petroleum
gel (i.e., Vaseline), or preferably Silicone grease (e.g., Molycote
Silicone O-rings are common. These are often coloured, and
can be recognised by their textural similarity to silicone diving
masks. Petroleum gel can be used on some silicones, but
silicone grease will migrate slowly into the material, causing it to
swell and possibly disintegrate. The correct lubricant for
silicone rubber is fluorosilicone
It is also important to distinguish
between user seals (like the back
door of a housing and the battery cover of a flash unit) and control
shaft seals. User seals and static seals need only to be
greased before assembly, but control shafts need to be packed with
lubricant. If you simply grease a control shaft seal, it will soon dry
out and fail through abrasion.
grease should you use?
For O-rings, the grease helps to loosen dirt and acts as a
preservative. Put a small amount of grease on the O-ring,
spread it around, and then wipe off any excess with a lint-free cloth
towel. The O-ring will be left with a thin coating of grease.
This is generaly sufficient. Surplus grease simply acts to
Silicone grease can also be used on
screw threads, such as the camera
tray and flash arm fixings, to reduce corrosion and promote smooth
running. In that case a fairly generous amount is warranted.
should you service your housing?
User servicing should be done before and after every dive. It
is also advisable to do it as close to the dive as possible.
Before every dive; you should check and clean the main
back-door O-ring and the O-ring groove, and check that everything is
functioning correctly. After every dive; you should try to
rinse the housing and anything that has been attached to it in fresh
water as soon as you can.
different metals are in contact in salt water they form an
electro-chemical cell (like a battery), where an electrical current
flows and one of the metals dissolves. Severe corrosion
occurs in places where water remains trapped in contact with metals
when the equipment otherwise apears to be completly dry. For
example, a brass or stainless screw in an aluminium socket will have
water trapped in the threads. There are two ways to prevent
corrosion in this situation: either, take the screw out after diving;
or, cover the threads of the screw in silicone grease before putting it
in. The second choice is best when attaching, say, a mounting
ball to the top of a housing; since the need for repeated dismantling
of permanent fixtures is an inconvenience. Greasing the
screw-threads of hand-assembled parts (tripod screws, connector nuts,
etc.) is also a good idea. The first line of defence against
corrosion however, is to remove lighting trays from housings, dismantle
ball arms, unplug electrical cables and cap them off, etc, prior to