Pen Sac Co. Diaphragms

[fpn00b]

Today I ran into something of concern to me while putting a diaphragm into a vacumatic junior Duofold. The deb diaphragm I used from a batch purchased this summer acted nothing like ones I have used in the past. It was cantankerous to roll back on itself, more so than normal. The problem I ultimately had was when I finally got it on the taper of the inner collar and tried to test it out. The diaphragm won't extend correctly. I tried another one and the result was the same.

 

Looking at the wall thickness of the rubber it looks thicker, and compared to cuttings I have from old ones it feels thicker. Has anyone else had any issues with diaphragms they've used recently? I need to contact Pen Sac Co tomorrow to see if they have heard from any other people with the same problem.

 

PS it was a deb size sac so correct size for a Duo junior.

Edited November 24, 2014 by fpn00b

[mhosea]

I have recently started restoring vacs and have not had any similar problems. Considered as a set, the hundred or so latex sacs I've had, all from PSC, seemed to vary a lot in wall thickness. They're dipped, I guess, so one should probably expect a lot of variability in thickness, probably batch-to-batch. I don't see why the diaphragms should be any different.

 

I'm not surprised to hear that it was hard to roll back as a result of being thicker, but I am surprised to hear that it wouldn't extend properly. Could you elaborate on what that means, exactly? It seems to me that a thicker diaphragm, even if it might not actually work inside the barrel, ought to extend properly outside of the barrel, just with more resistance.

[FarmBoy]

Did you cut the diaphragm to the correct length?

[fpn00b]

1 1/16" IIRC, I use a piece of wood that I marked with the correct length years ago to cut them on. As far as explaining it is difficult. When the filler plunger is depressed the sac should unroll over itself at the leading edge where the sac is folded back onto the inner collar taper thus extending providing the expelling of proper air to be replaced by ink drawn back in. These diaphragms don't do this, all that moves out is the tip of the plunger and you can see the little white pellet as it extends to the tip of the diaphragm opening, when let up on it was actually binding up trying to retract to a resting position. Without a video clip it would be hard to visualize. I thought maybe I didn't put enough talc on it so it wasn't sliding well but it still does it even after retalc'ing.

[mhosea]

Too thick, I guess. I've not seen it in the ones I've purchased since June, so I would assume it's a "bad batch" thing. Maybe contact the Pen Sac Co. and discuss it with them.

[FarmBoy]

I buy rather large amounts of these. I dug through the box last night. Even the thickest one I have was no problem. I favor a problem other than a 'bad batch'.

 

FB

[mhosea]

I favor a problem other than a 'bad batch'.

 

You would know better than I. I'm just having trouble imagining what that's going to be, given that it's the right length and talc'd. I got the impression that it did this outside of the pen, when actuating the plunger just holding the edge of the diaphragm in place, but maybe I misunderstood.

[fpn00b]

It does this out of the pen. When put in the barrel it binds because the sac isn't extending so the plunger can't be fully depressed.

 

The filler seat is pristinely clean and this speed line filler is in superb working order. I've done enough diaphragm replacements to know what is normal and this is not. As stated the cut length is to spec. Ruling out all other factors at this point, the only variable left is the diaphragm.

 

Curious to know what your opinion of what might be the problem farm?

Edited November 25, 2014 by fpn00b

[FarmBoy]

Any pictures?

[Ron Z]

There are often variations in wall thickness, and it isn't critical. I had some this summer that were thicker than normal, but they worked just fine. The most noticeable result is that the blind cap nut doesn't screw down as far as it may have with the previous sac.

 

Is the area below the ring also clean? Parker didn't make these on a CNC machine, so there are variations in barrel and ring diameter diameter on occasion. Even with everything cleaned out, I occasionally have to press the plunger down while holding the diaphragm on the cone, and pop it into place with some pens.

 

Not assuming anything, so forgive me for asking - but does the blind cap nut spin freely on the cone? This has to be free to turn so that it doesn't bind and twist the diaphragm, which would cause the binding that you're experiencing.

[Ernst Bitterman]

I don't have anything to offer on the problem, but I'm curious to see if I'm understanding it properly. Let me grab a diagram...

http://dirck.delint.ca/beta/wp-content/uploads/2011/06/drawdiap-205x300.jpg

 

Let's call the cross-section of "at rest" a v-shape, and "extended" an I-shape. If I'm understanding properly, you're not getting an "I" but something more like a "Lazy s" or a "w"-- is that right?

 

As much as I'm given to parsimony, I'd try another diaphragm and see if the problem persists. I'd also (and I'll bet you already have) look into the mechanism itself just to make sure nothing has gotten into the spring.

[mhosea]

Ernst, I can't quite decipher your diagram, but my reading of it is that when the plunger is extended outside of the pen, the center of the diaphragm is pushed out, but instead of the diaphragm unrolling to the correct fully-extended shape, the fully-extended shape has an s-curve along the sides, and full extension can only be achieved by stretching the latex adjacent to the pellet cup. The same situation in the barrel might (and apparently does) prevent the pellet cup from having enough clearance to clear the leading edge of the folded diaphragm, preventing the s-curve from forming, and preventing the latex next to the pellet cup from stretching as it does outside the pen.

[ThomasB]

 

http://dirck.delint.ca/beta/wp-content/uploads/2011/06/drawdiap-205x300.jpg

 

 

 

Looks like the beginning of a Cialis commercial...

[fpn00b]

Bingo mhosea! All parts on pen and filler are spic and span Ron, and the filler is not spinning in the barrel when I tighten it in. I scrupulously check that on every installation. It does this out of the pen, being when I first noted it. By the way Ron thanks for the buna-N sheet from the Columbus show, resulted in great barrel seal! Unfortunately the Balance has a hairline in the celluloid near the cap threads.

 

Ernst your drawing looks like how it should be more than what this is doing. Once again it is outside of pen.

Note that if I wasn't holding the sac on the collar out of the pen it would pull free when it does this as it causes pulling because it isn't unrolling properly over itself.

Edited November 25, 2014 by fpn00b

[fpn00b]

Here is what it should roughly do in normal operation.

Edited November 25, 2014 by fpn00b

[Ernst Bitterman]

Well, as inscrutable as my diagram may be I think we may have an answer; that is, by my reckoning, a lot of fold left on the diaphragm at full extension.

 

BUT that may be mere artistic licence (I show mine as awfully tight). Your 1 1/16" is the same as the 28mm I aim for, so by that measure, that's not the problem. It's certainly ACTING too long, though.

[fpn00b]

Please don't take my drawing to be literally the way it looks, the saggy look to sac wall on the first image is my poor drawing. The side is actually taut when extended, as I say it wants to pull off the taper of the filler collar when the rod is depressed and it 'sticks'. At any rate I called PSCo and got a machine to which I left my info. Awaiting a return call.

 

Thanks everyone.

[FarmBoy]

How about a picture of the problematic filler and sac?