USD reserve washer question

[ScubaLawyer]

Quick question. As you can see from the schematic versus my manifold/valve, I am missing #21 washer. Is it mission critical to have it? Without it am I going to have a higher/lower pressure to indicate the reserve needs to be activated? If critical,  what thickness washer do I repace it with? (It's number 0517-06 in USD manual). As always, thanks for everyone's assistance. Mark

[luis]

Any washer / spacer there will increase the spring force and therefore the pressure required for the gas to push past the closing seat. In other words, the amount of the reserve may go up some.

[ScubaLawyer]

Any washer / spacer there will increase the spring force and therefore the pressure required for the gas to push past the closing seat. In other words, the amount of the reserve may go up some.

Thanks Luis, that is sort of what I figured but usually the more I try to visualize a concept the more basackwards it becomes in my feeble brain. I may look for a small washer that will fit the bill. M

[SurfLung]

A Story About That Washer - My favorite Twin 38s have always had a good functioning J-Valve until last winter when the manifold started leaking on the J-Valve side. Well, when I opened it up, I found the seat had 3-4 washers and the spring was busted in the middle. The leak was due to something else and apparently the J-valve worked fine in this broken spring with too many washers condition.

I took a new spring off one of my newer manifolds, put it together with one washer and re-assembled with a new J-valve seat. WOW. That J-Valve now works really great. It must be better than before but I was wondering: Did putting in too many washers make the old spring break? Or, was the old spring weak and the too many washers were used to make the J-valve work better?

[ScubaLawyer]

A Story About That Washer - My favorite Twin 38s have always had a good functioning J-Valve until last winter when the manifold started leaking on the J-Valve side. Well, when I opened it up, I found the seat had 3-4 washers and the spring was busted in the middle. The leak was due to something else and apparently the J-valve worked fine in this broken spring with too many washers condition.

I took a new spring off one of my newer manifolds, put it together with one washer and re-assembled with a new J-valve seat. WOW. That J-Valve now works really great. It must be better than before but I was wondering: Did putting in too many washers make the old spring break? Or, was the old spring weak and the too many washers were used to make the J-valve work better?

So your're saying its a chicken or the egg conundrum?

As to the soft washer (#19) I happen to have a NOS replacement but it is my last one. I've heard some folks just use an o-ring in place of that seal. Any clue as to what size o-ring would work? Just stuff i think about. Mark

[captain]

More than anything I believe the washer's purpose is to provide a flat seat for the spring to seat against.