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Chevron piston seal direction
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doctorcorey View Drop Down
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Joined: 17 Jul 2011
Location: S. KC Missouri
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    Posted: 29 Jul 2023 at 7:12pm
Proper direction of Chevron piston seals in loader lift ram. I just returned from my 'local hydraulic shop' with a new and expensive set of piston seals for my loader lift ram. They were wrapped up and installed on the piston I took for them to match up. When I got home and unwrapped the assy., I noticed that it had 4 seals, and the 'lips' all face in the same direction(toward the tail end). I haven't rebuilt many cylinders of this seal type, but I was under the impression that a double-acting cylinder needed to have seals facing both directions, that is, some facing the head end, and some facing the tail end. I have a OeM packing set for a HD7G bucket ram, and that set uses a female and male backing, and only two chevron rings. Being Saturday, I can't call them up and ask this question, so I'm counting on one of you to help. 
Semper Fi USMC    1958 HD6G, 1959 MF 203 loader, 1960 Case 420B Backhoe, MF 65 Tractor/Loader Diesel
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steve(ill) View Drop Down
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Joined: 11 Sep 2009
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Points: 77845 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 7:50pm
on chevron seals, the oil pushes on the outer WINGS and forces them into the cylinder wall and piston groove to seal.... Normally they are used on SINGLE acting cylinders and they all face DOWN the tube.......... If they are used on a DOUBLE acting cylinder, the piston should have two different grooves for the two directions...Normally "chevron" are not the seal of choice on a double acting cylinder.







Edited by steve(ill) - 29 Jul 2023 at 7:51pm
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doctorcorey View Drop Down
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Joined: 17 Jul 2011
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Points: 570 		Post Options Post Options   Thanks (0) Thanks(0)   Quote doctorcorey Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 8:06pm
Originally posted by steve(ill) steve(ill) wrote:

on chevron seals, the oil pushes on the outer WINGS and forces them into the cylinder wall and piston groove to seal.... Normally they are used on SINGLE acting cylinders and they all face DOWN the tube.......... If they are used on a DOUBLE acting cylinder, the piston should have two different grooves for the two directions...Normally "chevron" are not the seal of choice on a double acting cylinder.   





Steve, Chevron seals are original equipment on factory AC cylinder. This is what it came out with from the factory. Why would they use something that was not 'the seal of choice'?
Semper Fi USMC    1958 HD6G, 1959 MF 203 loader, 1960 Case 420B Backhoe, MF 65 Tractor/Loader Diesel
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steve(ill) View Drop Down
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Joined: 11 Sep 2009
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Points: 77845 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 8:10pm
could be used..... "MOST" new cylinders have flat seals / scrapers and o-rings in a combination... Single acting cylinders use chevron for ONE direction..... but as noted above in the drawing, can use chevron on a double acting, if it was DESIGNED that way... but there should be some type of division between the two directions.
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steve(ill) View Drop Down
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Joined: 11 Sep 2009
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Points: 77845 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 8:14pm
i am more familiar with this type seal in DOUBLE acting cylinders.. CHEVRON goes on the head since in only see pressure from within... PISTON has oil on both sides, so it is a combination of flat seal/ wipers / o-rings..... Very common in newer cylinders... see below.

Does you Piston have a DIVIDER between the two sets ?






Edited by steve(ill) - 29 Jul 2023 at 8:15pm
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Codger View Drop Down
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Points: 1799 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Codger Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 9:18pm
Poor rendition but all shown the same direction:
A career built on repairing and improving engineering design deficiencies, shortcomings, and failures over 50 years now.
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doctorcorey View Drop Down
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Joined: 17 Jul 2011
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Points: 570 		Post Options Post Options   Thanks (0) Thanks(0)   Quote doctorcorey Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 9:23pm
Originally posted by steve(ill) steve(ill) wrote:

i am more familiar with this type seal in DOUBLE acting cylinders.. CHEVRON goes on the head since in only see pressure from within... PISTON has oil on both sides, so it is a combination of flat seal/ wipers / o-rings..... Very common in newer cylinders... see below.

Does you Piston have a DIVIDER between the two sets ?




No divider. It has 4 seals, plus a female and male backing ring. If it used seals placed in both directions, with the appropriate backing rings, there would only be enough room for one seal for each direction. Don't chevron seals use their shape to force them to tighten against the cylinder as they are 'pushed' by the oil pressure?
Semper Fi USMC    1958 HD6G, 1959 MF 203 loader, 1960 Case 420B Backhoe, MF 65 Tractor/Loader Diesel
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steve(ill) View Drop Down
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Joined: 11 Sep 2009
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Points: 77845 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 10:01pm
Don't chevron seals use their shape to force them to tighten against the cylinder as they are 'pushed' by the oil pressure?............

. Yes, thats why they are very common on single direction acting cylinder.

Guess Codger has the drawing so that must be right.. Seals face the EXTEND direction for the cylinder ... Must figure the  "power down" is normally float or not heavily loaded . I have not seen that before.

Edited by steve(ill) - 29 Jul 2023 at 10:05pm
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doctorcorey View Drop Down
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Joined: 17 Jul 2011
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Points: 570 		Post Options Post Options   Thanks (0) Thanks(0)   Quote doctorcorey Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 11:08pm
Originally posted by Codger Codger wrote:

Poor rendition but all shown the same direction:


  I think my old 7G manual showed this cross-sectional view of the piston packing, but my 6G manual doesn't . This diagram will ease my mind. Thanks 
Semper Fi USMC    1958 HD6G, 1959 MF 203 loader, 1960 Case 420B Backhoe, MF 65 Tractor/Loader Diesel
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Joined: 23 Dec 2020
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Points: 1799 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Codger Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2023 at 11:56pm
Clearer rendition:
A career built on repairing and improving engineering design deficiencies, shortcomings, and failures over 50 years now.
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Joined: 14 Sep 2009
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Points: 29563 		Post Options Post Options   Thanks (0) Thanks(0)   Quote DMiller Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jul 2023 at 9:38am
Will add a context, Farm 'Loaders' are generally only One Direction Loaded, when Lifting, the other side is convenience to reposition the frame or attachment or to hold the frame or attachment when not moving.  I know of few farm loaders that have any purpose Powered Down. 

  Only time I have ever used Down pressure is scraping LIGHTLY on grade work.  Allis Loader Highlifts can dig but down pressure is not so much for Pressuring in as  dozer but just Pushing into materials.


Edited by DMiller - 30 Jul 2023 at 9:40am
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doctorcorey View Drop Down
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Joined: 17 Jul 2011
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Points: 570 		Post Options Post Options   Thanks (0) Thanks(0)   Quote doctorcorey Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2023 at 9:18am
Interesting read I came across while looking through the manual for my JD300 backhoe

Edited by doctorcorey - 31 Jul 2023 at 9:21am
Semper Fi USMC    1958 HD6G, 1959 MF 203 loader, 1960 Case 420B Backhoe, MF 65 Tractor/Loader Diesel
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Edited by doctorcorey - 31 Jul 2023 at 9:26am
Semper Fi USMC    1958 HD6G, 1959 MF 203 loader, 1960 Case 420B Backhoe, MF 65 Tractor/Loader Diesel
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It appears that the direction of the chevron seals is not important. They are not sealed by 'lip-cup action' nor are they omni-directional. This JD cylinder operates at over 2500 psi. 
Semper Fi USMC    1958 HD6G, 1959 MF 203 loader, 1960 Case 420B Backhoe, MF 65 Tractor/Loader Diesel
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