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Author Topic: swing barrel fix?  (Read 2467 times)

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Offline krusty

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Re: swing barrel fix?
« Reply #20 on: July 07, 2018, 07:55:02 PM »
There was another explanation I found helpful on cylinder drift. If you put your arm in a full bucket of water, it would overflow based on the volume of your arm. Same with drift, if there is no fluid coming out the end of the cylinder somewhere you can see, it is coming out the valve body internally to the opposite side or tank. That applies to single or double acting. For the rod to move in or out at all the fluid needs to go somewhere. Either it leaks at the cylinder or at the valve. The bucket analogy finally made it click for me.

My valve bank is a Gresen 25P based on the casting numbers I found and logo after a nice spray of brake fluid to uncake sections of it. Turns out these shafts are machined to fit and dont have seals to fix them unfortunately. So if I really want to fix it I need a new section in my valve bank. Mine did not look overly worn I thought but I never measured it with a micrometer either. I am going to put a 1/2" hydraulic valve inline to the cylinder tomorrow to get a definitive answer in my mind. The valve bank part is not cheap. The 1/2" valves are relatively cheap and can seal the fluid to the cylinder.


Offline Skeans1

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Re: swing barrel fix?
« Reply #21 on: July 07, 2018, 08:50:30 PM »
Is this actually using cylinders or is it a rack setup?

Online Grandpa

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Re: swing barrel fix?
« Reply #22 on: July 07, 2018, 09:50:48 PM »
Is this actually using cylinders or is it a rack setup?
It is a rack gear with a piston on each end that a swing barrel goes over.


Offline Don P

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Re: swing barrel fix?
« Reply #23 on: July 07, 2018, 10:06:40 PM »
My leaky valves on the old Prentice are also Parker Gresen 25P's. Same setup on the swing, a rack with cylinders on each side. From what I've found so far the 25P's are obsolete and unavailable. That's as far as I've gotten with it other than being tempted to try 90 weight in it, I'm going to school on you.

Offline mike_belben

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Re: swing barrel fix?
« Reply #24 on: July 07, 2018, 10:23:56 PM »
Look to see that the detenting is still acurate and keeping each land located exactly where it should.  

Also pull the relief cartridge for that section and the overall relief to check for any signs of bypassing there.  Metal chip, grit, o ring chunk etc will all hold them open. 
Revelation 3:20

Offline mike_belben

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Re: swing barrel fix?
« Reply #25 on: July 07, 2018, 10:28:00 PM »

So as a basic order of troubleshooting, if a double acting cylinder is drifting, unless there is fluid coming out of the cylinder or other external leak, check the valves first?
Yes sir.
Mike, I would disagree with your answer, if a double acting cylinder is drifting the oil should return to the tank, as per the link you posted above.

If cylinder oil is reaching the tank when the valve is closed, we have a valve leaking.   
Revelation 3:20

Offline Jack S

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Re: swing barrel fix?
« Reply #26 on: July 08, 2018, 10:35:04 AM »
 from my experience with double acting cylinders if the seal on the piston is bad  drift will happen until the internal pressures equalize on each side of the piston. I have rebuilt many and the problem is cured. In fact I just did the crowd cylinder on my woods backhoe this year. Jack

Online Grandpa

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Re: swing barrel fix?
« Reply #27 on: July 08, 2018, 11:44:51 AM »
Mike
     In reply 4 you posted a link that says the oil returns to the tank via the port relief. Now you are saying it is a leaky valve. Can you clarify, keeping in mind the original question by DonP was troubleshooting a drifting double acting cylinder?

It has been my experience also that when a double acting cylinder drifts, it is most often the cylinder packing. Valves can and do leak, but it is much less common.

Of course all of this assumes no external leaks.

Offline mike_belben

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Re: swing barrel fix?
« Reply #28 on: July 08, 2018, 12:17:21 PM »
If the cylinder is not leaking externally, drifting all the way down is probably in the valve, but it isnt in the piston.  Even with piston seal removed, a cylinder without an external leak can only drift until pressures on both sides of the piston face equalize.  If no leak from rod seal or hose, that will not likely be a full cylinder stroke worth of drift before equalization occurs. 


Here is a quick crummy sketch to illustrate only the cylinder, lines and spool.  



Once the pressures above and below eqialize the drift stops even with no piston seal at all.  If drift continues its because something allowed one side to continue losing pressure.  Either the rod seal or a hose or a crack or the valve spool.  It cannot go from the cylinder to the exhaust port, or back through the pump when shutoff, without first going by the valve. Granted there are plenty of parts in a multisection valve to consider so thats a blanket answer but it does start narrowing down.  It could be a spool, a relief, a section O ring, a cracked section, a cracked fitting, a bad O ring on and SAE or ORFS connection etc etc etc.  But if it behaves like this under these constraints ...it aint the piston seal.  Thats the whole point.  One less part to needlessly rebuild.
Revelation 3:20

Offline Skeans1

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Re: swing barrel fix?
« Reply #29 on: July 08, 2018, 07:03:26 PM »
Iíve had cylinders with no external leaks drift off or fully let off issue was the piston packing.

Offline kiko

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Re: swing barrel fix?
« Reply #30 on: July 08, 2018, 09:55:45 PM »
What don't want to confuse things and I may repeat previous comments. The rack swing cylinders I have dealt with did not have a gland, just a piston on each side of the rack , so if the drift issue was caused a piston leak oil would be exiting around the rack.  So a rack swing cylinder is two single acting cylinders more or less.  As far as theory goes gravity will not let the pressures equalise on both sides of a piston untill it no longer a factor as with a boom cylinder where the boom had made to a stop or cylinder had bottomed out, or the swing has reached the low spot.   The spool seal leaking would not likely cause drift.  With the spool in neutral,  the oil must travel through the port relief before returning to tank and that back flow would not be applied the spool.  Also I have never seen a gresen valve with out spool seals, but that does not mean they don't exist. 

Offline kiko

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Re: swing barrel fix?
« Reply #31 on: July 08, 2018, 10:05:57 PM »
Kolstrand.com has spool seals for 25p valves.

Offline snowstorm

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Re: swing barrel fix?
« Reply #32 on: July 09, 2018, 06:09:01 AM »
i think he thought there would be seals sealing the spool to the valve body internally . i have had quite a few valves apart over the years never seen one built that way. spool to body machined fit only seal is for what oil may seep past that machine fit 

Offline mike_belben

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Re: swing barrel fix?
« Reply #33 on: July 09, 2018, 07:24:11 AM »
Same here.  All i can recall are ground finish spools and honed to size valve bores.  Dust seals on the end.  

I have seen a few crossleaks from bad sectional or end cap Orings. 
Revelation 3:20

Offline krusty

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Re: swing barrel fix?
« Reply #34 on: July 09, 2018, 10:07:55 AM »
I did see the seals  that Kiko has mentioned and they are cheap enough to order and try for phase #2 of the diagnosis. My fear is that if I cannot get this fixed I am at risk of the boom swinging around and either blowing the cylinder or knocking me off the platform.

Plus it has be in that "I must finally fix this problem out of principle" mode. I bought two ball valves to insert in the lines to the cylinders. They are 3/8" lines and due to back packaging of the valves, one was 3/8" one was 1/2" so will get the right one on the way home today. Even with just one valve it did still move a bit. Also noticed that when I cracked the line at the valve body, the fluid was highly aerated. Will also replace the suction line on the pump this week. If there is mucho air in fluid as I have seen, I would assume it would cause spongyness as well. There was enough air in the fluid to cause fluid to be pushed out of the hose at an alarming rate. The boom was grounded so there was no movement. Also the presser relieved by the valve in opening it in either direction.

Stay tuned........

Offline mike_belben

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Re: swing barrel fix?
« Reply #35 on: July 09, 2018, 10:53:28 AM »
Air throws my drift info out the window..  It will facilitate drift by its compressible nature.

 Its tough to know if its trapped air thats been in for years or if you have a rod seal thats letting air in every time you retract the cylinder.  


Revelation 3:20

Offline kiko

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Re: swing barrel fix?
« Reply #36 on: July 09, 2018, 08:49:21 PM »
Again, I was afraid I might confuse the issue.  I  Only call them spool seal because they go over the spool.  However ,the spool looks good and it seems the issue has been identified, or at least has to be addressed before moving foward .A cavitating pump will make a distinct sound.  Also check for a suction strainer when addressing the suction line.


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