Hi I have a question on the assembly and function of British No 12 Cooker pump. On the downward stroke, the pump is creating pressure, but on the upward stroke I am working against a vacuum because no air is able to fill the pump cylinder. I am familiar with the operation of a pump such as in the Optimus 111 but this one is of different construction. When the slotted brass nut is tightened (slots toward the c-shaped washer) there is virtually no play in the leather pump cup so there is a seal on both the up and down stroke. Are these the correct parts and is should they be assembled in a different order? I have pictured them in the order of disassembly. Thanks in advance for any information.
Hi @poncho455 You say that you are familiar with the type of pump assembly used in an Op.111 so this post will be revision for you: https://classiccampstoves.com/threads/typical-pump-assembly.14026/ I have just checked the pump on one of my Military No.12 stoves and it operates the same way as a classic Op.111, or as is described in the attached link. The piston assembly moves on the reduced segment of the pump shaft and seals against the radiused shoulder on the down stroke. On the upstroke it moves about 1/8 inch on the shaft allowing air to pass between the bore of the piston and the reduced shaft section, so no vacuum. The pump assembly you show in the photos is a different beast. The piston assembly is different to mine and the pump shaft has a shorter reduced section, and no radiused stop. Your pump is similar to that used in Heinze/Geniol pressure lamps and their NATO Military stove and relies on by-pass flow between the leather bucket of the piston and the pump tube bore on the back stroke when pumping: https://classiccampstoves.com/threads/heinze-geniol-military-stove-pump-fettling.31364/ I currently have three No.12 stoves and as far as I know they are all fitted with the "floating" piston design pump internals. Best Regards, Kerophile.
@poncho455 I don't own a No.12 but I wish I did. I would think the pump cup would float to let air pass by on the up stroke. Have you tried loosening the nut??
I would think that there has to be a reason for the slotted nut and the c-shaped washer other than just to hold the leather pump cup in place. It definitely is not working as assembled. Yes, I have tried loosening the nut to allow some play but that does not make a difference. There are barely enough threads on the shaft to hold the nut when tightened down because of the collared washer that sits on top and passes through the leather. I guess I will have to come up with a replacement or substitute pump.
Hi @poncho455 . Have a read of this thread: https://classiccampstoves.com/threads/optimus-111t-pump.28080/#post-286559 CCS Member kerry460 makes these replacment pump pistons to fit Optimus stoves with O-ring pump pistons (which are an abomination IMO). Best Regards, Kerophile.
More of the same: https://classiccampstoves.com/threads/pump-rod-design-pumping-efficiency.26319/ Best Regards, Kerophile.
