Kuhn power hammer problem

[john barron]

I recently aquired a used Kuhn CF-50 air hammer. It was not running and had no dies at the time. Upon setting it up in my shop and installing the dies, the hammer hits fine but stays at the lower end of the stroke fluttering up and down when I back off on the treadle. The owner's manual lists only 2 valves to adjust. I have loosened and tightened the regulating valve with no effect on this problem. The directions on the setting of the control valve do not match the accompaning illustration. My valve is set to the written directions, and I am hesitant to change it as it is physically impossible to completely match the illustration. There are 2 blocks locking onto 2 shafts that are connected by a rod. The directions call for one to be parrallel to the body and the other indexes to a mark on it's shaft. Setting it this way causes the second block to be about 20 degrees out of parrallel yet the picture shows them both parrallel. I would sure appreciate advice from anyone familiar with this machine.
Thanks, John Barron
john@barroncreations.com
530-333-1129

[Lynn Gledhill]

John, for what it's worth... A friend of mine acquired a used air hammer and had a similar problem to yours. Turned out the mud dawbbers had plugged the vent or exhaust port... Might check that.

[Larry L]

It very well could be that the ram is not sealing well in the cylinder...
First thing is does it have plenty of oil? the oil is needed not only for lubrication but also to help with the air seal... It should have a thin film of oil on the ram at the very least, I run my hammers so there is always a bit of oil that drips off the ram (not like runs off, but every once in a while you will get spot that gathers enough it will drip, In my mind oil is cheap and more is better
With the hammer off if you pick the ram up (might require a forklift or friend) and then drop it does it slowly drop or crash to the die? If it was coming all the way to the top when it ran you could just shut it off when the ram was up... but if its not coming up then you would need to lift it... It should take at least 5 seconds and maybe as many as 20 seconds for the ram to drop if the rings are good and its got plenty of oil If it just drops you need probably new rings and if you have to order new rings Id order a set for the compressor as well It also could mean that your valve is so far out of adjustment that its allowing air move between the upper and lower ports


Have you checked to make sure the linkage connection to the valve is properly set? where it attaches to the valve it should have some hash marks showing factory alinement.. You can move it slightly either way and it would allow slightly more or less air at a given treadle point... Might just be that you need more air coming in at idle

[Rob F]

I was able to get the exact symptoms of your hammer on my nazel #2 by pulling the stem of the check valve so it is disabled. It then oscillates at the lower end of its stroke and seems to hit like normal when pedal is depressed. That leads me to believe that you have a check valve problem. I can not remember if by pulling down the stem on nazel it is opening or closing the valve.
Very likely if it has been sitting for a while and dried oil or rust is keeping it from moving.

[Larry L]

Good theory but not the case. In a Nazel what your calling a check valve is actualy a bypass for the lower rotary valve (it is still a check valve but that implies are only is suppose to travel one direction, in this case air needs to flow one way sometimes and the other way the rest of the time). The lower valve has a port that feeds the bypass and how tight the spring is determens how much air gets to the ram, where the valve is also changes how much air is routed to the bypass. The hammer won't run with either the valve held closed or held open, would act the same either way. In a Kuhn there are no cylinder checks but rather bypass checks built into the compressor that allow the air to "vent" if the valves don't allow the air to reach the cylinder...

At least that's what I think I know ;-)

[Rob F]

Thanks for keeping my terminology correct. My understanding is that most self contained air hammers work on the same basic principles. My nazel has a bypass valve that if I manually hold it open the cylinder will oscillate untill pedal is pushed at which time it hits like normal, If I hold it shut the ram drops to the lower die and if I push the pedal it will then start to oscillate mid stroke (no hitting). Were the valve is located on a kuhn hammer that does this function does not matter, but it is somewhere and is suspect in my mind.
When I got my hammer years ago it had a similar problem due to stuck bypass valve and bergman pointed me to this answer.
Larry You are mistaken about the functioning of the bypass valve, Reviewing mark's book he states " The bypass valve is a one way valve or "check valve." It is important that the spring is strong enough to keep air from passing through it the wrong way but not so strong that it restricts air flow in the proper direction. "

[Larry L]

I just read what I wrote and it's not right either. The air only flows one way through the bypass it's where the air goes out of the bypass that changes. There is a circuit that routes the air either up or down depending on where the valves are... The bypass uses pressure from the lower valve to close thus routing a pulse of air to either the top or bottom depending on valve position... I think

[Rob F]

Bypass closes with the spring.

[Rob F]

It is raining here, stuck inside. Solidarity with the PNW

[Larry L]

Yes. I said that wrong, the spring holds it closed until it gets blast of air.. It also dosent or barely open when the hammer landing blows because all of the air is then directed to the ram, it's only at idle or when the ram is cycling in air that it should bypass ... That's why if it's stuck open or closed it won't retract the ram at idle... Anyway I guess my point no matter how poorly I described what was going on is there is no cylinder bypass on a Kuhn style hammer and if the compresser bypass was stuck the hammer wouldn't hardly run at all, and since it seems to hit fine that dosent sound like the case... I don't claim to be anything like an expert but I have done a fair amount of work on both Styles of hammers. Who knows though. Maybe they are not all the same. I know the early Say Maks have a much simpler air system with no balancing valve maybe there are other kinds of Kuhns as well...