This will be helpful. Also if you have low cracking effort you may need to replace the spring or shim it up.
Scubapro 108 High Performance -manual
1. Remove the two screws holding the retaining ring for the purge cover. They will be either a standard, Phillips or hex head screw - all three were used at various times. If they do not come out easily soak the reg in a 3% solution of hydrochloric or acetic acid to loosen any salt or corrosion.
2. Once the retaining bands are removed, remove the metal purge cover. They are sometimes stuck to the rubber purge cover underneath which is in turn often stuck to the diaphragm which is usually stuck to the metal case if the reg has not been serviced in a while, so proceed carefully and don't tear the diaphragm. Once you get them all off you can peel them apart. The diaphragm will be one of several colors from black to white to off white to orange, red or one of two shades of blue. The silicone diaphragms will all be comparatively flat while the original oldest style rubber diaphragm will have an edge about 1/4" in wide and then a deeply curved section around the flat center section.
Dry rot frequently occurs around the edge of the rubber purge cover where it is clamped between the metal cover and case. A little in isolated spots is ok, a lot around a significant portion of the circumference can cause problems and should be replaced. Inspect the diaphragm as well by stretching it against a backlight to spot any small pin holes. Gently wash the diaphragm with a mild soap to remove any crud and then rinse thoroughly.
3. Inside you will see either an all metal lever or a metal lever with a white plastic ball on the end (older style) Thisolder style is usually found with the older rubber diaphragm.
4. These older models are likely to have a non adjustable orifice. In either case, remove the hose (if you have not already done so) and look inside the fitting. If it is smooth and chrome plated, you have a non adjustable orifice. If it is flat and slotted for a standard screw driver, you have an adjustable orifice.
5. Unscrew the inlet fitting from the case with a suitable sized wrench. In some cases, the inlet fitting will come loose before the hose fitting and come out with it. If this begins to occur, just put a wrench on each nut on each side to the line where they separate and take them apart.
6. If the poppet assembly is dirty complete disassembly is recommended and is done by unscrewing the nut on top of the lever. Pressing up on the poppet assembly with a suitably sized object will remove the tension and if you do this do it before you remove the seat. If the poppet assembly is clean and/or if you lack a new nylock nut, you are better off leaving it assembled.
7. Under the nut will be a washer over the lever which is in turn over a brown resin washer that indexes in the poppet assembly with two arms and has a square hole to keep the poppet stem from rotating . The poppet stem is under spring pressure as the spring lies under the lead of the stem where the seat is held and is sandwiched between the head of the poppet and the aspirator body - be careful not to launch it across the room when you remove the nut.
8. When you reassemble things, get them in the correct order (spring place on the poppet stem, inserted into the aspirator body, with the poppet stem properly indexed in the square holed brown washer which is in turn properly indexed in the aspirator, followed by the lever, the metal washer and the nut. Again, pressing up on the seat end of the poppet will ease the tension and make it easier to install the new nyloc nut. There must be threads visible past the top of the nyloc nut, but do not expose more than 1 1/2 threads.
9. At this point replace the seat on the head of the poppet by using a pick to remove the old one and install a new one.
10. If the orifice is removable it should be removed by screwing it all the way out (you can feel it jump the top thread when it is all the way unthreaded. When this occurs take a relatively soft object (the plastic end of an o-ring pick works well, a plastic piston bullet is even better) and carefully push the orifice back out of the inlet fitting. Change the o-ring around the orifice. If they are older and red, they are often very crispy and will break on removal. If you do not have a new o-ring don't go there under the "if it ain't broke don't fix it" doctrine - but be advised they can leak if not in good condition.
Inspect the orifice by running your finger nail around the sharp edge. Any nicks that can be felt or seen are bad news and mean you need a new orifice.
11. Reinstall the orifice. Screw it all the way to the bottom and then back it off one and a half turns.
12. Carefully remove and re-lubricate the o-ring that seals the inlet fitting to the case. If you are not sure you can get it out without damaging it, a light coat of lubricant on top the o-ring will probably work and is better than damaging a part you don't have a replacement for.
13. Re-install the inlet fitting. Depress the lever to prevent the orifice from potentially cutting the seat.
14. Inspect and lubricate or if needed replace the o-ring in the swivel end of the LP hose. This is a more or less dynamic o-ring that can experience wear as well as exposure to salt and dirt.
14. Adjustment is much easier with an inline adjuster, but can be done in small increments (1/6 to 1/12 turn) with a screw driver, but doing it that way requires the stage to be removed from the hose (with the reg depressurized) to make each adjustment. If the reg freeflows when pressurized, screw it in farther, if it does not screw it out until it does.
15. Once you get it initially set hold the diaphragm and purge covers in place to ensure that it does not freeflow with the cover installed and that it purges easily with minimal depression of the purge. If it freeflows you need to lower the lever height by loosening the nut, if it requires excessive depression of the purge button or will not aggressively purge, you need to raise the lever height by tightening the nut.
On the non-adjustable models what you get is what you get with lever height as it is a single adjustment design. On the adjustable orifice modes it is a dual adjustment system and one adjustment affects the other, so any lever adjustment will most likely require an orifice adjustment.
16. Once the lever is adjusted and does not leak with the diaphragm and covers held in place, reinstall the diaphragm, purge covers and the retaining bands. DO NOT use silicone on the diaphragm as it will cause it to expand. Also make sure all the parts are dry as a wet diaphragm may slip out of the groove during assembly.
Proper etiquette requires the screw heads to be up so the band with the larger holes goes on top. Later SP used a single part with large hole on one side and small threaded hole on the other and with these you get one up and one down. Scandalous to a purist. Good form also dictates that the holes in the rubber purge are properly indexed with the upper hole centered - referencing the mouth piece works well to accomplish this - the "S" should be vertical with the arrow pointing down, and finally the joint between upper and lower bands should be in the middle of the case.
17. Once all this is done, turn the orifice in 1/12 turn farther to compensate for the seating groove that will develop in the seat - basically what you end up with is a reg that has an orifice 1/12 turn farther in past the point where any freeflow occurs with a lever that begins to release air with only a very slight depression of the purge button.
Normally when properly adjusted an adjustable orifice model will produce an inhalation effort in the 1.0 to 1.2" of water range but some with a very sharp orifice and very flexible diaphragm will have inhalation efforts as low as .8".
If you are using this on an unbalanced first stage like a MK 2, Mk 3, MK 200 or Mk 2+ be sure to make the adjustment with a full tank of the highest pressure you plan to use or else you will discover that it freeflows slightly with a full tank.
