Megalodon DSV Rebuild
After about a year or so of
use the Meg DSV becomes difficult to operate, especially with one hand. This is a good indicator to the diver of
service time. This article is
intended to give the user an overview of how to accomplish this. The process, if one has the correct
tools and supplies, takes about 30-60 minutes. This is an excellent time to replace the
mushroom valves too, and this process is included here as well. The parts will be referred to with the
following nomenclature.
DSV Body, Spool, Mushroom
valves (2), MV Carriers (Inhale and Exhale), Snap rings (2 or 4), screw, o ring
and Stud.
Tools and supplies required
to perform this service include, Safety glasses, combination screwdriver
(straight and Phillips #2), Snap ring pliers, 5/16(8mm) open end wrench or
pliers, new mushroom valves, Christolube, blue Loctite, shop towel, light
colored marker, and alcohol. Do not
attempt to do this procedure without a proper pair of snap ring pliers. Snap-On tools SRPC7000 is an excellent
tool at $17.75usd.
Pliers,
Retaining Ring, Fixed Tip, Convertible, 0°/.070" tips, 7 7/16"
It is highly recommended that
you read this article in its entirety, in detail, prior to picking up a single
tool. Be sure you have all supplies
and tools at hand before beginning.
If, after reading this, you are not confident in completing it,
don’t even start. This would not be a good procedure to start right
before a dive, wait until you have plenty of available time so there is no
rush. The DSV is an extremely important part of your ISC Megalodon closed
circuit breathing apparatus and if mis-assembled
could cause injury or death.
Contact ISC, info@customrebreathers.com
or 1-360-330-9018 for your nearest service center or authorized technician.
Above is a parts breakout of
all the pieces in a Meg DSV. There
are several versions of this system.
Early Megs have one Snap ring in each end; later versions have two on
each side to provide more sealing with lower rotating effort. Early DSV’s also have MV carriers
that will fit in either end of the DSV body, current units are sized different
(for CE compliance) and will fit in only one direction, the only exception to
this is with the new DSV fitted with a P port mouthpiece, on this unit the MV
carriers are universally sized to allow use on R2L flow loops.
DO NOT, UNDER ANY CIRCUMSTANCES, reverse the gas flow on your ISC Megalodon CCR, to
do so is foolish in the extreme.
Mark the DSV and hoses with a
bit of white marker so you can align the hoses when reassembling, ensuring that
the mouthpiece is still at the same angle in the diver’s mouth. You may want to code the marks to tell
the difference between inhale and exhale.
When you clean the parts with alcohol during the service procedure, be
sure not to remove the marks.
The elastic/nylon covers are
pulled back to reveal SS hose clamps (sometimes called jubilee clamps), these are covered with black electrical tape to protect
the nylon from abrasion. Remove the electrical tape and loosen and remove the
hose clamps. The hose clamp is
sized for a ¼ inch nut driver or straight blade screwdriver. There is another layer of electrical
tape below the hose clamps and if it is serviceable it may be left in
place. Pull the hoses off of the
DSV, the MV carriers will most likely stay in the hoses, remove them from the
ends of the hoses and set the hoses aside.
Wearing safety glasses,
compress and remove the snap rings from the ends of the DSV using the snap ring
pliers, using care as the rings can spring off the tool and go flying. There will be one, or two, in each end.
With the DSV in the open
position, insert a #2 Phillips screwdriver into the mouthpiece and index it on
the screw that holds the stud to the spool. Grasp the stud with the open end wrench
or pliers and turn the screwdriver counterclockwise to separate the two
pieces. Take note of the condition
of the orange O ring on the screw and replace if necessary.
Slide the spool out the end
of the DSV body and notice that it is seamed at the mouthpiece edge. The snap
rings sit inside this spool and apply distal pressure providing the spool with its
seal to the DSV body.
Inspect the mushroom valves
and be certain they are serviceable; they should be supple and lay flat on the
spiders. Look for any cracks or
tears in the top or the stem. Your
life depends on these valves; replace them if there is any doubt. Remove the mushroom valves (if they are
being replaced) by grasping the top and pulling away from the carrier, there is
a notch in the stem that indexes the valve into the carrier and the valve must
be pulled past this notch to be removed.
The valves are quite durable but can break during removal. If you cannot get hold of the valve,
push something gently through the carrier spider to fold it out and give you
something to grab. Discard the old
valves.
Clean all parts (except the
new mushroom valves) with a clean shop towel and isopropyl alcohol.
Inside the carriers, on the
end that the mushroom valve inserts from, you will feel a slight ridge raised
up from the surface the valve seals onto.
You MUST insert the new mushroom valves so they seat on this ridge. See
picture below.
Insert the stem of the
mushroom valve from the ridged side, then turn over and pull the stem through
the hole in the center of the spider. It may help to very slightly lubricate
the stem with Christolube to get it to snap into place and have the notch
seated. Other than that, the mushroom valves require NO lubricant.
Once installed properly, the
flat top of the mushroom valve will lay flat in the carrier.
This is a correctly installed
mushroom valve; notice the absence of ridge from this end. This is the exhale MV carrier and it
will seat on the left side of the DSV body. Proceed with the removal and replacement
of the mushroom valve into the inhale MV carrier. The rules concerning the ridge are the
same on that side even though the carrier is shaped differently.
Next we lubricate the bearing
surfaces on the outside of the spool and inside of the DSV body. This is probably the only liberal use of
Christolube you will ever encounter, rather than a light shiny coating, you
want a good coating as the lube is what is assisting the seal. Apply with a finger and smear the
surfaces.
Here is the spool with a good
coating of Christolube. Do the same
to the inside of the DSV body.
Align the spool with the DSV
body. The oval depression in the
spool is what allows the diver to clear the DSV prior to opening it. It must be aligned with the purge port
in the DSV body. If not aligned as in the picture below, flip the spool over.
Here is how the pieces align
(no lube in the picture for clarity).
If assembled incorrectly, the diver will not be able to purge water from
the mouthpiece prior to opening it.
Slide the Spool into the DSV
body and align the stud port directly opposite from the mouthpiece. Check the O ring on the screw and be
sure it is intact and a bit of lube on it is a good thing. Replace if
torn. Apply a very small amount of
Loctite to the end of the screw and set it on the end of the #2
screwdriver. Feed that through the
mouthpiece and into the hole in the spool and out the stud slot of the DSV
body. Spin on the Stud and tighten
the two pieces together snug. Align
the notches in the stud up and down with reference to the DSV; this gives
fingers a place to grasp when turning the DSV on and off.
Again, while wearing safety
glasses, install the snap rings into the grooves on the inside of the spool,
open ends toward the split in the spool for maximum expansion force. Test the DSV for proper operation and
smooth rotation of the spool. With
the DSV in the open position, place your palms against both ends and do a
positive and negative pressure check.
With the DSV in the closed position, be sure you can purge the
mouthpiece. If you cannot purge, you
have the spool inverted in the DSV body. If you have leaks while pressure
testing, check the mouthpiece for cracks or tears, and the O ring on the screw.
Verify that the assembled DSV
looks like the above picture, with the DSV in the open position; the open end
of the snap rings should face the mouthpiece and be centered over the split in
the spool. The snap rings should also be fully seated in the groove of the
spool. Check both sides.
Install the MV carriers into
the proper sides, if you have a DSV that will accept them in either side take
extreme care to install them in the correct side. Best way is to hold the DSV like you
would for diving, turn it on, be sure you can only inhale from the right side
and exhale out the left side. Lay
the DSV down in that orientation and slide the hoses over the carriers and up
over the clamping surface of the DSV body, aligning the marks you made prior to
disassembly. Be sure you fit the correct hoses on either side of the DSV,
recall that the T pieces have a slight angle off of straight (molded T pieces
only, the very early machined T pieces were straight). The diver is inside of the
“V” made by the angle of the T pieces. <diver>. The easiest way to set this up properly
is to put the DSV in your mouth, orientated properly and lay the hoses and T
pieces over your shoulders, check twice, assemble once! Remember that new megs
have thread keyed T piece nuts and head couplers, if you assemble the hoses
incorrectly the threads will not engage.
Don’t forget the HUD mount.
We like to set the hose clamps up so that they are screw drive down and
screw slot facing away from the diver and very tight. Place a layer of black electrical tape
over the screw drive and slide the elastic/nylon bands over the hose clamps
neatly. If the mouthpiece does not
lay correctly in the divers mouth, its usually easier
to loosen the hose clamps on the DSV side of the T piece, rather than disturb
the clamps at the DSV, and rotate the hoses there with the attempt to level the
DSV across the divers face with equal pressure on both lips. This really requires a spare person to get
it right. Make sure that all hose
clamps are securely tight and then do your breathing hose check to be sure you
have the mushroom valves in the right orientation. Inspect the mouthpiece for cracks or
splits and replace if necessary. A
common cause for a leaky DSV is a worn mouthpiece.
Here is the rebuilt DSV, you are looking at the inhale side with a correctly
placed mushroom valve and MV carrier inserted.
This is the exhale side of
the assembled DSV.
Here is the reassembled
I hope this has enlightened
the reader on the proper method of DSV servicing, feel free to contact me with questions
or comments on this article.
Ron Micjan
22MAY07