Sealing Hydraulic Cylinders?

[rockNmayhem]

Ok guys I'm calling in the expert and people with all the experience here. :p

As many have seen and know I've been working on building cylinders for my CAT conversion and I have the size and dimensions down but I'm running into operating problems.

My pump I'm running has no problem throwing out 165PSI all day long at full speed. I can turn it down simply by stick control through my esc. The problem I'm having is not getting my cylinders to seal around the shaft.

I started out with o-rings at the shaft and over sizing the shaft so it was a tight squeeze to get through it and it seemed to work for a bit but I still have some seeping around them. I then found some U-cup seals with the sizes I needed and I finally got one of them assembled and started testing it but I'm getting leaks out the front once again.

So now I'm dreading my options. I can keep experimenting till I get it right and hope they'll hold up or end up buying several cylinders from Rick and shelling out around $300 for the cylinders.

I'm really hoping with your guys help and from those of you who have cylinders already and know how they are assembled and able to seal up well can chime in.

I'm not sure if my tolerances are just too loose causing my leaks or what but I'm leaving less that thousandths at critical points so I'm not sure where to go.

Any help I can get would be greatly appreciated. Pictures do help as well. :D

Thanks guys,
Tyler

[Lil Giants]

http://i90.photobucket.com/albums/k246/RockNmayhem_2006/Bruder%20Cat%20963%20Loader/IMG_1277.jpg

What are your piston rods made from? This one looks like it's a little rough.. needs a greater polished finish.

From Ari's thread,

Yep, it's 1.4305 grade stainless.

A lot better finish on his piston rod (or so it seems from the pic).

http://i327.photobucket.com/albums/k471/Hemi1966/CAT%20374D%20L/IMG_0695.jpg


I've gotten some "cylinder kits" from Fumotec to make my own cyls any length I want, I just have to cut the barrels & the piston rods to suit my needs and do the necessary machining on the piston rod at each end. The finish on the rods, while looking at in my hands, is much smoother yet than Ari's pic above... whether it's just the picture or an actual difference.. don't know.

Whenever I have to do a repair to a piston rod, I wrap the rod with brass sheet before chucking up in the lathe, prevents any tool marks on the rod that could cause seal failure.

[rockNmayhem]

Joe, that piston is aluminum as thats what I had available. I will look at some stainless polished rod that hopefully has a better finish and I can try making that work as well.

My main thing is, how is the front of the ram sealed. Whether it be an o-ring or actual U-cup seal? Thats about the biggest obstical I'm having to over come.

Thanks for the information though.

Tyler

[ihbuilder]

Joe, that piston is aluminum as thats what I had available. I will look at some stainless polished rod that hopefully has a better finish and I can try making that work as well.

My main thing is, how is the front of the ram sealed. Whether it be an o-ring or actual U-cup seal? Thats about the biggest obstical I'm having to over come.

Thanks for the information though.

Tyler

Tyler , on a real 1 : O-rings with backup rings and a wiper seal . For what we do just an o-ring . Real 1's use chrome rods (polished) thats what you want to have . I use 304 L ss from online metals . From the mill it comes very smooth . Another issue could be your piston seals are too tight . Looking at you ram pics , def. too course . I should note , if your cap (gland) is cocked in the slightest way that will make it leak also .

[Lil Giants]

After taking apart a Leimbach cyl, they use a U cup seal in the end cap.

The Fumotec cyls use dual o rings in precut grooves.

I don't know the tolerences of either.

[rockNmayhem]

Tyler , on a real 1 : O-rings with backup rings and a wiper seal . For what we do just an o-ring . Real 1's use chrome rods (polished) thats what you want to have . I use 304 L ss from online metals . From the mill it comes very smooth . Another issue could be your piston seals are too tight . Looking at you ram pics , def. too course . I should note , if your cap (gland) is cocked in the slightest way that will make it leak also .

Steve thankyou for the metal link. I'm glad I now have a metal number to go off of. I know how to rebuild a larger cylinder no problem with all the seals and rings but for this size I figured a sealing o-ring and a wiper was all I needed but I will back it down to one.

Do you also think I can still use the U-cup seals in the front or should I just stick with cutting an o-ring grove in the cap and leave it at that?

Also do you thread your caps on? I had the first ones pressed on but I'm designing another ram where the caps thread on with 12mm x 1.25 threads and am thinnking that might help some with sealing them up and keeping them straight.

Lemme know if there's anything else I can do differently as this is kicking my rear trying to get these cylinders built.

Thanks,
Tyler

[ihbuilder]

use an x ring IOW , the profile will look like an x instead of O I get them off McM. thats what they're called . yes my glands are threaded . Next 1's will bolt like Ari's . If I where you , I'd ditch the Alum. all together and go brass . much easier to work with for making cylinders . It hones nicer you can buy the tube (seamless) make the ends and silver solder them together . What grade alum are you using ? If your going to stay with alum. use 6061-T65 or 7075 - ? (Slipped my mind ) . you get a much better finish then hardware grade crap .

[dirtpusher9]

Tyler, you may be seeping by on the tubing side you may want to hone it and cross hatch it a little if it is too smooth.

I have some pics on my dozer thread page 8 or 9 that shows how I built my cylinders that may help with design.

[Newcastle]

use an x ring IOW , the profile will look like an x instead of O I get them off McM. thats what they're called . yes my glands are threaded . Next 1's will bolt like Ari's . If I where you , I'd ditch the Alum. all together and go brass . much easier to work with for making cylinders . It hones nicer you can buy the tube (seamless) make the ends and silver solder them together . What grade alum are you using ? If your going to stay with alum. use 6061-T65 or 7075 - ? (Slipped my mind ) . you get a much better finish then hardware grade crap .

Do you have a website for McM. I'm interested in these seals. Thanks.

[ihbuilder]

Do you have a website for McM. I'm interested in these seals. Thanks.


www.mcmaster.com