windmill repair opinions needed

[12bolts]

This is a repair I have made once before, and was also probably done previously by other unknown parties i'm guessing.
There is a roughly 30ft long threaded steel rod running down to the pump. It has a steel joiner nut on it just finishing inside the riser pipe. The foot long rod that connects from the joiner nut to the pump piston is 1/2" brass rod threaded 1/2" whitworth.
It has previously come adrift from the piston after a brass cross pin sheared off and it unscrewed itself. I replaced the brass cross pin with a stainless pin and now the threaded section has broken. Not sure if the cross pin is standard. There is no locking used where the top end of the brass rod screws into the joiner nut, just nipped tight with pliers, but it never comes apart there. The piston is cast brass/bronze
Should I....
1: just rethread the brass rod and put it back together with a new cross pin.
2: screw it back together but lock it with a back up nut
3: use a new section of stainless threaded rod and cross pin it.
4: open to suggestion here...







Cheers Phil

 

[DAN_IN_MN]

I'll start by saying I've never done a repair like this.

That being said, I'd go with rethreading the existing rod, if there is enough length left to do the job, and skipping the cross pin but go with the lock nut as you suggested.

I'm wondering if the rod broke because the thread wasn't tight and all of the pressure was on the hole through the rod. The pin could have been put in there because the thread were stripped.

Are you planning on replacing the leathers?

I have the remnants of a windmill driven pump and am still using a pump jack to pump my water.



I just searched the net for wind mill and found several places that sell parts. I'd suggest calling one of these places and see what they recomend.

 

[DMS]

That pin seems pretty large relative to the diameter of the rod. I also agree with Dan, that all the stresses are going to fall on that pin if the threads are not tight enough to take some of the load. Brass is nice because is fairly corrosion resistant, fairly strong, and machines really nice. It's also non-sparking if that matters in this situation. If you have enough material left I see no reason why you couldn't re-use the existing material, but I think you need to make some changes or you will run into the same issues again.

One question I have is, is this piece in torsion, or is it just a linkage? If it is just a linkage (push pull), I would think that a tapered thread (like a pipe thread) would work better. Barring that, try to get a tight threaded fit. The pin should only be there to keep the thing from unscrewing, so you could get away with a simple cotter pin, or some stainless wire, and a much smaller hole in the shaft.

If this thing is in torsion, then hopefully it only goes in one direction, and that direction causes the thread to tighten. If that's the case, I suppose my advice doesn't differ much. Shoot for a tight thread, and drill the cross hole in place. If possible use a taper pin, and re-ream the hole before re-inserting the pin.

The thing about this assembly is that, as soon as the shaft starts to wiggle relative to the pin/threaded end it's going to end badly again.

I wish you luck, hopefully this is the last time you have to pull it apart; I imagine it's no fun

 

[DAN_IN_MN]

Thinking about this, I don't think the pin is stock. I'm thinking it was designed to have a tight thread.

I believe there isn't any torsional forces at play here.

 

[GK1918]

Myself I would not pin it, i'd use a lock nut. The load is on the upstroke. Or use bronze marine shafting.
We just did one this past summer.

 

[FanMan]

The threads on the shaft look pretty worn. I'm guessing the pin was original to prevent it from unscrewing, but the threads are now worn to the point that the pin is taking a load it was never intended to see.

Using a stainless pin may have been part of the problem, too. When the brass pin sheared, it acted as a fuse prevented other, more expensive, parts from breaking. The last time, the stronger stainless pin held, and the shaft instead broke. The stiffer stainless pin may also have put more stress on the material as it was driven into the hole.

 

[12bolts]

Thanks for the input.
Pretty sure there are no other forces apart from direct push pull. Its not that difficult to strip it down. Just the time. Did the leathers last time as it wasnt working when we bought the place. Got 2ish years out of the ss pin repair....

I decided to rethread the brass rod and make a couple of brass jam nuts for each end. No cross pin this time.
We will see how long this repair lasts........






Cheers Phil

 

[GK1918]

This is why pins are a bad idea. The wheel had a pin and a set screw. It egged itself so bad the wheel fell off. Good thing nobody was around it.
We welded the egged hole turned it milled the setscrew so it will "bite". (this was an old post on mine)
this is the mills mainshaft thats all that holds a 300lb wheel: what were they thinking???

 

[oldgoaly]

I haven't done a windmill pump but lots of hand pumps, I use the locking nut. some I have repaired have had rusty lower sections 2-3 long, cut them off, then thread add a section of s/s rod my pieces of s/s are 3' long if they are bad longer than that it gets a new steel rod. knock on wood haven't had one come apart, some have been used almost daily for 30 years.

 

[Bill C.]

That pin seems pretty large relative to the diameter of the rod. I also agree with Dan, that all the stresses are going to fall on that pin if the threads are not tight enough to take some of the load. Brass is nice because is fairly corrosion resistant, fairly strong, and machines really nice. It's also non-sparking if that matters in this situation. If you have enough material left I see no reason why you couldn't re-use the existing material, but I think you need to make some changes or you will run into the same issues again.

One question I have is, is this piece in torsion, or is it just a linkage? If it is just a linkage (push pull), I would think that a tapered thread (like a pipe thread) would work better. Barring that, try to get a tight threaded fit. The pin should only be there to keep the thing from unscrewing, so you could get away with a simple cotter pin, or some stainless wire, and a much smaller hole in the shaft.

If this thing is in torsion, then hopefully it only goes in one direction, and that direction causes the thread to tighten. If that's the case, I suppose my advice doesn't differ much. Shoot for a tight thread, and drill the cross hole in place. If possible use a taper pin, and re-ream the hole before re-inserting the pin.

The thing about this assembly is that, as soon as the shaft starts to wiggle relative to the pin/threaded end it's going to end badly again.

I wish you luck, hopefully this is the last time you have to pull it apart; I imagine it's no fun

I noticed the pin looked over-sized for the shaft too.