Jeph
May 7th, 2014, 06:09 AM
I was putting together a Parker striped duofold vac mechanism recently. I tested the operation (section removed) against my finger and was really distressed by how little vacuum the filler drew on a stroke. I would depress the plunger, cover the end of the barrel with a wet finger, release the plunger and then pull my finger away. When I do this with something like a well maintained Pelikan piston I get a resounding "*POP*!" That echoes around the room. With the Parker I only got a wimpy little puff of air.
The next day I was thinking about this and did some rough calculations and figured that a Parker vac unit should pull about 4 psi of vacuum. (I later did some more precise calculations that were apparently less accurate as my answer was 3 1/4 psi.) I also felt that 4 psi of vacuum should be plenty for a good, strong gulp of ink with each stroke. But I didn't really have a good way to measure it. Then I remembered my Mityvac for bleeding my car brakes and decided that I could use it to give me a good reference vacuum on my finger for comparison. That was followed by the thought that the Mityvac has a gauge so with the right adapters I could just measure the vacuum directly. Not long after that my Fiancée looked at me like that and gave me an emphatic (and exasperated) "what in the world are you doing to those pens now?" comment.
What did I find out? The real answer was that my attempt to rebond the sac pellet cup to the filler button had failed. Once I (hopefully) got that joint to properly cure it worked well enough that the science experiment really was not needed. But I had too much momentum to stop so I did some tests anyway.
The only real takeaway from my testing is that even 1 psi of pressure differential is enough to reliably draw ink into the pen. We know that a (properly working) piston converter (1 psi) fills with ink with no problems. It does make me wonder more about fountain pens on airlines, but I have done some testing there and had no problems and now I am not sure why not. All tests were performed with the sections or nib and feeds removed. The Parker vac was tested the same way I was doing before only substituting the vacuum gage for my finger. The piston fillers are shown with the value for 1/2 turn of the filler knob. This is a realistic simulation of actual use as it is impossible to instantaneously turn the knob fully open and the pressure tends to equalize after each turn. Just for fun I added the value for if you could somehow instantaneously fully actuate the piston. There was no discernable difference for the at least 7 different brands of piston converters. I only had a pair of Waterman and one Parker squeeze converter not in use and although the Watermans had permanent set to their sacs they worked just as well as the Parker squeeze converter. The Sheaffer vac was a little more problematic. Because of the way that it works there was no way for me to attach the gauge at the instant that the vacuum released and if it was attached before the vacuum released the rod would not travel any further. As a compromise I pushed the filler rod just short of releasing the vacuum, installed the gauge and then let go of the rod and allowed the vacuum to force it back out. The amount of vacuum measured from that return stroke should be almost the same as the vacuum generated from a normal down stroke. Both the Parker and the Sheaffer vacs gave peaky readings and I did not have a follower needle but I am reporting the minimum confirmed value. The true value may be as much as 10% higher. All tests were performed at least 5 times and the results were consistent. I do find in practice that the Sheaffer vacs take the biggest gulp of ink from a single operation, but to get it nearly completely full takes at least one more stroke and that is bothersome to perform. I was not able to figure out a way to properly test a snorkel or touchdown with the adapters that I have but I might do that later if I get bored. I did not do any button fillers or lever fillers since I did not have any that were both un-inked and easy to get the nib and feed out of. I would expect them to be very close to the squeeze converters if in proper operating condition (and of good design.)
So now the useless results. Note that these are just results from my pens and converters and while they are all in like new or freshly restored (by me) condition they may not be truly representative.
Piston Converter (various) 1 psi per 1/2 turn (6 psi total)
Pelikan M200 Piston 1 1/2 psi per 1/2 turn (12 psi total)
Parker Vac 4 1/2 psi per stroke
Squeeze Converter 5 psi
Sheaffer Vac (thin) 10 psi
The next day I was thinking about this and did some rough calculations and figured that a Parker vac unit should pull about 4 psi of vacuum. (I later did some more precise calculations that were apparently less accurate as my answer was 3 1/4 psi.) I also felt that 4 psi of vacuum should be plenty for a good, strong gulp of ink with each stroke. But I didn't really have a good way to measure it. Then I remembered my Mityvac for bleeding my car brakes and decided that I could use it to give me a good reference vacuum on my finger for comparison. That was followed by the thought that the Mityvac has a gauge so with the right adapters I could just measure the vacuum directly. Not long after that my Fiancée looked at me like that and gave me an emphatic (and exasperated) "what in the world are you doing to those pens now?" comment.
What did I find out? The real answer was that my attempt to rebond the sac pellet cup to the filler button had failed. Once I (hopefully) got that joint to properly cure it worked well enough that the science experiment really was not needed. But I had too much momentum to stop so I did some tests anyway.
The only real takeaway from my testing is that even 1 psi of pressure differential is enough to reliably draw ink into the pen. We know that a (properly working) piston converter (1 psi) fills with ink with no problems. It does make me wonder more about fountain pens on airlines, but I have done some testing there and had no problems and now I am not sure why not. All tests were performed with the sections or nib and feeds removed. The Parker vac was tested the same way I was doing before only substituting the vacuum gage for my finger. The piston fillers are shown with the value for 1/2 turn of the filler knob. This is a realistic simulation of actual use as it is impossible to instantaneously turn the knob fully open and the pressure tends to equalize after each turn. Just for fun I added the value for if you could somehow instantaneously fully actuate the piston. There was no discernable difference for the at least 7 different brands of piston converters. I only had a pair of Waterman and one Parker squeeze converter not in use and although the Watermans had permanent set to their sacs they worked just as well as the Parker squeeze converter. The Sheaffer vac was a little more problematic. Because of the way that it works there was no way for me to attach the gauge at the instant that the vacuum released and if it was attached before the vacuum released the rod would not travel any further. As a compromise I pushed the filler rod just short of releasing the vacuum, installed the gauge and then let go of the rod and allowed the vacuum to force it back out. The amount of vacuum measured from that return stroke should be almost the same as the vacuum generated from a normal down stroke. Both the Parker and the Sheaffer vacs gave peaky readings and I did not have a follower needle but I am reporting the minimum confirmed value. The true value may be as much as 10% higher. All tests were performed at least 5 times and the results were consistent. I do find in practice that the Sheaffer vacs take the biggest gulp of ink from a single operation, but to get it nearly completely full takes at least one more stroke and that is bothersome to perform. I was not able to figure out a way to properly test a snorkel or touchdown with the adapters that I have but I might do that later if I get bored. I did not do any button fillers or lever fillers since I did not have any that were both un-inked and easy to get the nib and feed out of. I would expect them to be very close to the squeeze converters if in proper operating condition (and of good design.)
So now the useless results. Note that these are just results from my pens and converters and while they are all in like new or freshly restored (by me) condition they may not be truly representative.
Piston Converter (various) 1 psi per 1/2 turn (6 psi total)
Pelikan M200 Piston 1 1/2 psi per 1/2 turn (12 psi total)
Parker Vac 4 1/2 psi per stroke
Squeeze Converter 5 psi
Sheaffer Vac (thin) 10 psi