I can't address the valves made by other companies, but I can tell you about the ones I make. They have been on many suits but not yours unless used as a replacement etc.
Nothing lasts forever, and so I placed a limit on things, intending the valves I made to last as long as the suit, the warranty would be limited to one suit and one owner. No, I'm not smart enough to design in a product life, but I felt the valve should be made as durable as the suit, ...but not necessarily two or three suits etc. Still, I did my best to design it to last and work well.
Imagine my surprise when some actually did come back!
Actually, way more than I would have liked.
The culprit?
Dirt, muck, dried salt crystals, ...one even came back pierced through the flap by a sea urchin spine.
On the exhaust valves I make, there are no user serviceable parts. Yes, they come apart if soaked in acetone for quite a while (don't do this.) But it would be difficult to teach someone how to glue them back together. No, it's not real tricky, it's just one of those things which you need to do a few times to get the hang of like playing the guitar. The glue used is a type of instant glue and in all likely hood the process would end up a sticky mess the first few times and result in the valve going back into the acetone to get cleaned again. The frustration this would cause the consumer is only exceeded by the worry I would have about it being done correctly too.
On the inlet valve there is either a c-clip or nut (possibly tagged with a drop of glue) which if removed will allow the button-shaft to come out the front. If an O-ring (there are two) is the problem, (you check by placing a rod of the correct diameter through the valve and pressurizing it and being careful not to poke your eye out) and dunking it in some water and looking for what my employees called Evil Bubbles.
O-ring removal is easy. Hook it with a bent pin and snag it out of the gland. To put it in you must first re-insert the rod used for the leak test, to the point where it reaches the other side of the gland, as if blocking the passage out of the gland. Bend the O-ring between your fingers to an ellipse, and cause it to form a slight U-shape. Stick the one end of this U-shape into the gland (it bottoms out on the rod you put in, and slides into the recess of the gland) and continue to press it in, followed by completely pressing it in with another similar rod.
Check it visually. The O-ring should not appear to have a twist and should be uniformly seated all around in the gland. If not, then yard it back out and do it again.
Putting in a new O-ring can be frustrating. I have watched folks try for half an hour and then just give up. (The O-rings go in amazingly quick easy when done by someone who has done a hundred.) Again, I don't recommend this. I'd rather have you send it back and if it's out of warranty then we really should all consider it time to retire that valve.
Silicone grease (at about fifty bucks a tube) is used to lubricate the inlet valve and should be used when putting it back together. Don't forget the spring.
I use a spool valve design and it requires more parts than my competition as the glands are separate parts. I like this design feature as it results in a better valve from my perspective, based upon my calc's regarding friction and flow. It's down side is that it is again an assembly and therefore can develop a leak through the assembly interface. We check for this here and if that's the case, then we fix it with a tiny drop of very thin and penetrating glue during normal assembly. Again, this is something I just can't recommend, as a touch too much glue may seep into the gland itself and then the valve would need to be soaked in acetone and be disassembled and cleaned. Re-gluing the glands together and positioning them correctly and gluing them back into place is not something which you can do without some custom tools.
Mounting the valves on the suit can be important too. If you remove them, then you might just start over and do it right. Lay a bead of silicone on the outside of the suit around the hole and (after coating the bottom of the valve with mold release) place it in the suit but don't tighten it up completely, leave a little gap for the silicone to make a formed in place gasket. After the silicone sets, remove the valve,and re-install it later after the silicone has had time to cure, and then tighten it down.
Air pressure keeps the inlet valve from allowing water to enter through the valve, but if the hose is disconnected, water can then get into the valve to later be injected into the suit when the diver re-connects the hose and inflates the suit. Just a drip really but could explain a mystery leak.
My best advice is to soak your valve in water for a while to dissolve any salt, then while holding the valve open, flush fresh water through it from the inside of the suit to the outside. Examine the flap edge all around to see if there is anything caught under it like a piece of seaweed or even just a hair.
Drysuit valves are not perfectly dry devices. When opened, the water can flow in if the flap is up, and the flap must be up to let air out. Current or other conditions can allow some water to leak back in while the air is rushing out. Water can even be hiding in the valve from the last time you rinsed it out. For the most part this should only be a drip or two and not soak your sleeve or chest.
If it's clean and tight and you are sure it is still not working right, take it back and demand a replacement or buy a better product Short of sea urchin spines destroying them, the parts such as the flap shouldn't need replacing unless made of inferior quality plastics.
Dive safely.
and is best done if your tanks have not yet been refilled after last dive:
