Monty, The slot on the top in both bipolar and unipolar is an excellent way to go for more than one reason. The space across the top on a hole plate is wasted and must be subtracted from active area. With a narrow slot it actually gives you more active area (less to subtract), small amount more, but some, and of course the gas does not have to hunt, bounce of the top create more pressure and lower the level of the electrolyte and reduce the active area even more to get out. Also the errant ions that do not get used by the plate are bounced off the gasket back and hit other ions of the opposite charge neutralizing them reducing production. Easy out is one of the things that really helps. It does not need to be very big either, as narrow as you can make it unless you have a huge plate. Size should be related to volume of production in the cell. Make sure you have a small brace in the center to keep the plate from possibly bending and shorting from heat or vibration. The center brace is important especially when media blasting. There is one more thing that is splitting hairs to some but I have good evidence that it does make a small difference. The slot needs to be a 1/2 inch away from the side gasket that has the power connection. By giving up this small area on the unipolar (power) plates only you have less current leakage. Even though Weldon does one heck of a job the current density that close to the source is very high. I put Weldon on that area too. Remember it is only on the unipolar/power plates. I admit it is splitting hairs but every little thing helps when added together.
I must thank both Larry and Gus for the years of help they have given me!! Two unbelievable good guys!!
Gus, the only method of stopping the small leakage that I found besides the Weldon was a full gasket as you said. The others still had the same problem but less. It is very little, not noticeable unless you are looking for it, and not a real problem but it is robbing the end cell and the first cell in the next group of a little. The full gasket created other problems and you lost the extra pocket that helped maintain more even electrolyte levels in the group without have to run in a full flooded state all the time and added heat protection which is really not necessary unless you are in a climate where ambient is over 100ºF or the reactor is located in the engine compartment where ambient can be as high as 150ºF ambient or hotter on hot days. Ambient temperature and dry air is one of the reasons I have been in California as long as I have to solve some of the problems that are related to hotter dry climates compared to the cool and extreme cold of North Dakota. The pockets on either end of the groups have proved to make a measurable difference in warmer conditions. In colder climates not so much but still enough to keep them but for different reasons. In extreme colder climates the extra electrolyte besides helping maintain levels allows you to still operate in colder ambient without freezing solid or sit longer out in the cold before things begin to get slushy and you have to push the remote starter and let the engine warm up while shopping. LOL Larry knows what I am talking about.