Re: [Killietalk] Washers, O-rings & homemade bulkhead fittings

["Koran, David HQ02" <David_Koran at hq02.usace.army.mil>]

Almost 20 years ago I purchased a large number of used, pre-drilled 1/4"
plate glass 20 gallon tanks.  I was able to find flat rubber washers to
accommodate homemade bulkhead fittings constructed with 1/2" PVC/CPVC
fittings.  I have looked for a supplier of them on the internet since then
but I did not find anything but on the other I haven't looked recently.  I
purchased them at a "full service" hardware store in Cincinnati
(Aufdenkampfes, if they are still in business in the Over-the-Rhine section
of town).  Your home supply stores today like Home Depot or Lowes only seem
to handle stock that turns over quickly and flat rubber washers in odd sizes
don't seem to be one of those items.

About 10 years ago I purchased some bulkhead fittings at a local farm supply
store, Central Tractor Farm and Family (store) which operated from the Mid
Atlantic into New England but they have become a casualty of suburban sprawl.
They were cheaper than the same bulkhead fittings I saw at the Home Depots
and Lowes and definitely cheaper than the aquarium suppliers and some
aquaculture on-line sites.  I haven't checked to see what Tractor Supply or
Southern States stocks.

Lowes offers a fairly good selection of O-rings in the 1/16" and 1/8" size of
various diameters but only a few sizes at the upper end work with the PVC
fittings.  Your cost is about $1.15 - $2.00 for a box of 10.  At Home Depot,
with Spring coming, look in the section with garden hoses for replacement
washers.  Previously they sold a ring of 10 1/8" O-rings for uses as hose
washers but last year they were packaged as a combo pack of O-rings and
washers (5 each).

The problem with using O-rings with the PVC fittings is that when you tighten
down the couple too tight the O-ring will stretch and unless you have a large
"collar" the O becomes distorted and you might not get the greatest seal.  In
general, the grey conduit fittings from the electrical department are the
same pipe thread size but have the advantage of larger collars.  You will
also find that in a separate section (many at Lowes) where they have nipples
and coupler they also carry "plastic"/PVC fittings/couplers.  They are more
expensive than the plumbing white PVC or grey electric fittings but have the
benefit of the thickest collars.

The other problem is that the plumbing fittings are tapered in the thread
whereas the electrical are not, hence you can close the bulkhead down so the
collar meets the seal.  You can get around this with the plumbing fittings if
you purchase a NPS 1/2" tap and tap out the fitting so it will close down
further.  It is always a good idea to use the Teflon tape to also seal your
joints.

Another trick if you are working with a plastic container taking the homemade
bulkhead fitting is to drill your hole slightly smaller than the thread of
your fitting and tap a thread into the hole so you also screw in the male
portion of the fitting.  In using O-rings for these bulkhead applications I
slip on an O-ring onto the male portion, screw it through the plastic, place
a second O-ring on the exposed male fitting and then screw down the female
fitting.  The PVC fittings and the nipple couplers also usually have a hex
collar for you can use a wrench or vise grip to tighten them.

Dave K 

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