Hi, I thought it might be useful to post some photos of a typical pump assembly from a classic brass tank stove: The pump is a clever design. The whole piston assembly is designed to "float" between the shaped radius at the end of the reduced section, and the small nut on the end of the pump shaft. On the push stroke the piston seats on the radius and this forms an air-tight seal. Air is pressurised and is forced through a non-return valve into the tank. On the pull stroke the piston assembly moves to the nut on the end of the reduced section, and air can now enter the cylinder past the radius section. On the majority of pumps, such as this one, the piston assembly is like a drilled bolt and nut, which traps the leather washer in the correct position, and slides on the reduced section of the shaft. One or two manufacturers used a simpler but adequate piston, where the leather "bucket" sits between two steel washers. This piston design relies on by-pass flow, past the periphery of the leather washer on the back-stroke. Best Regards, Kerophile.
Thank you George! It amazes me how much things change over the years but how many things stay the same. Many new pump use this idea ... sadly have gone with washers. Cheers, Jeff
Bloody hell, George, I'd not realised that was what was happening. Seriously. I guess I'd thought the air was getting past the cup washer on the 'pull' stroke!!! Bloody hell. Thanks for pointing that out. You have an un-erring eye for essential details. Brilliant. Thank you. John
G,,day, the smaller the pump tube diameter, the more important the floating cup is, the small diameter will let very little air past the leather cup. kerry
Many thanks kerophile, you revealed another gem of knowledge to light my journey through the world of stoves. Many thanks.
Some info that might help save a few pump rods. To change a pump leather, I don't usually remove the small nut at the far end of the pump rod. In my experience these are usually peened & you only have so many chances to remove the nut before the threads are knackered. If you remove the pump knob, remove any spring, grip the brass pump cup carrier with vice grips or screwdriver in the slot, you can remove the retaining nut and slide the old washer off the rod. Refitting the new pump cup is just the same in reverse.
That's exactly what I have done but I honestly think its the wrong size washer. Although it is smaller than the other one that came in the kit, I will get another kit for the 210 and try again. Thanks for your help redspeedster.
Hi We are sometimes asked about the significance of rising pump shafts on operating stoves. I provided some comments and explanation in this thread: https://classiccampstoves.com/threads/pump-rod-not-seating-completely.36795/#post-380254 Best Regards Kerophile.
Here in the US, Coleman stoves and the like let the air slip around the outside of the leather cup and piston, the piston doesn't use any float to make it work right. Moving your thumb off the pump knob vents any excess pressure, so once the piston is pushed down, it's down. Murph
“Going in from the top” Sometimes when stoves were manufactured, the only way to ensure that the retaining nut on the shaft will not come off in long-term use was to “peen” the bottom end of the pump shaft. This can make changing a pump leather very difficult, if not impossible. One solution, described by Ron, is to “go in from the top of the pump shaft: Replacing Leather Pump Cups Best Regards, Kerophile.
Thank you all for your comments. Kerophile, thanks for the photos. It took reading the information a few times before I got the concept, but now it all makes sense. Once again, this site is such a wealth of knowledge that is willingly shared among the members!
Thank you Kerophile for the original post and everyone for your comments. I came looking for this information as I'd recently found the mislaid parts for my Svea No 5 which I stripped down for refurbishment a couple of years ago. Everything else is ready now, barring the pump and I was wondering why the cup was free to slide back and forth against the end nut - I thought I must be missing a part. Your excellent explanation above made instant sense to me! I am missing the spring, which I assume is to dampen the force when you pull out the piston so it does not shock / damage the small end nut - I can pick up any suitable spring from the hardware store though, I assume.
Hi @Coffindodger Thank you for kind comments. Your pump will work quite happily without the spring, which is not an original maker’s part anyway but likely a later addition by a previous owner. Good luck with your Svea No.5. Best Regards, Kerophile.