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Old 04-14-2013, 12:05 PM   #1
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Question Bleeding Air out of Hydaulic Slideout System

Does anyone know how to bleed the air out of a hydraulic slide-out system? Changed the seals/gaskets in Dewald pump & now the slide-out will not go in or out. Motor is running. I have a 1995 Aluma-Lite Holiday Rambler 5th Wheel. Trailer is kept inside when not in use. Changed seals due to the drifting of the slide-out. Dewald has sold out to PowerGear & their info has been helpful except they state to extract & retract room to purge air. The room does not budge. Thanks for any help.
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Old 04-14-2013, 12:39 PM   #2
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check your fluid level is it low or kind of milky looking if it is the fluid is full of air bubbles . if it is just let it set for an hour or two then fill the tank and try again. it will work out on its own by running the slide in and out but if the fluid has to much to much air in it the pump cant produce enough pressure to move the slide.
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Old 04-14-2013, 12:48 PM   #3
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Thanks for your reply. I have checked the fluid & it is not milky. After I changed the seals & reinstalled the pump, the slideout moved just a few inches, I checked the oil level, adding just to the fill level. Now the slide out will not go in or out, so the air does not bleed out.
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Old 04-14-2013, 01:01 PM   #4
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i assume that the only thing this runs is a single slide. how far apart did you have the pump
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Old 04-14-2013, 01:19 PM   #5
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Yes, all this runs is a single slide. Didn't quite catch that last question/comment.... Thanks.
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Old 04-14-2013, 01:26 PM   #6
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when you said you changed seals in dewald pump did you mean in the hyd cylinder or in the actual hyd pump that is located in the in the fluid tank attached to the dc motor
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Old 04-14-2013, 01:30 PM   #7
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Seals in the pump assembly.
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Old 04-14-2013, 01:47 PM   #8
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looking on line for break down of hyd pump dont know if you have done this yet but if you Google dewald hydraulic pump you will get the parts and service manual. sounds like you lost all pressure right away. i would start by making sure a o rig or seal was not cut when you reassembled it. if not follow the diagnostic procedure in the service manual
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Old 04-14-2013, 06:15 PM   #9
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Thanks....
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Old 04-14-2013, 07:52 PM   #10
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A quick way, if you can get at the hydraulic line attached to the hydraulic cylinder, loosen the nut on the line attached to the hydraulic cylinder, DO NOT REMOVE, just loosen a little bit turn on pump, if there is air in the line it will escape and be replaced with hydraulic fluid, if there is no air or no fluid your pump is not working. Now you have to do this at both the retract and extend end of the cylinders. The retract end is the fitting near the piston end of the cylinder. good luck
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Old 04-14-2013, 08:26 PM   #11
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That idea has crossed my mind, however, to get to the cylinder, I will have to cut open the bottom of the trailer. I did take off one of the hoses at the pump & had my friend press the button to the slide - red oil shot out of the hose. Not sure if that is a good sign, but I hope it means the pump is working.
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Old 04-14-2013, 08:44 PM   #12
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Quote:
Originally Posted by CajunGuy View Post
That idea has crossed my mind, however, to get to the cylinder, I will have to cut open the bottom of the trailer. I did take off one of the hoses at the pump & had my friend press the button to the slide - red oil shot out of the hose. Not sure if that is a good sign, but I hope it means the pump is working.
Here ya go, found this in another forum I read awhile back. This fellows answer and a total Hyd. pump overhaul. Lots of cooling time between cycles. 12 volt DC motor creates lots of heat.

"I had to run mine 6 8 times for 20 seconds, each time, to get the slides to start moving. I was concerned after about the fourth time and no movement, but I kept at it and once the pump got primed all was normal. Run it once for 20 seconds, wait 2 minutes to cool, the run it for another 20 seconds. Now wait 15 minutes for cool down and repeat above. "
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Old 04-14-2013, 09:08 PM   #13
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VinceU, I will try that approach first thing in the morning! Worth a try! Thanks for sharing.
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Old 04-14-2013, 09:11 PM   #14
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That idea has crossed my mind, however, to get to the cylinder, I will have to cut open the bottom of the trailer.
That seems a little extreme, what would one do if a cylinder had to be replaced? Are there no removeable panels underneath? It seems your pump is working? Then again it also requires pressure along with flow? However if the fluid leaked out from the cylinders while the pump was being rebuilt the air can only be removed by loosening the nut at the cylinder! Are you sure there is no mechanical interference preventing the slide from moving?
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Old 04-14-2013, 09:26 PM   #15
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The only way (clean unmessy way) to remove the air is to drive it with oil back to the reservoir tank with cylinder movements. Since the pump was open the air is somewhat more difficult to move until it primes. Positive Displacement pumps are self priming, just takes longer than when flooded as when a cylinder is replaced.
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Old 04-16-2013, 08:27 PM   #16
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Update: Pulled Pump/Motor Assembly back out & detached reservoir. Took a clear, clean tube & attached to both the retract & extract pump lines. Then using the manual hand pump, I primed the pump. The clear tube made it easy to see any air bubbles. Reattached reservoir (filling it back up with ATF), & connected to electrical & hydraulic lines. Slide-out now goes in & out as it should. Thanks for all of the help.
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Old 04-16-2013, 09:03 PM   #17
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Originally Posted by CajunGuy View Post
Update: Pulled Pump/Motor Assembly back out & detached reservoir. Took a clear, clean tube & attached to both the retract & extract pump lines. Then using the manual hand pump, I primed the pump. The clear tube made it easy to see any air bubbles. Reattached reservoir (filling it back up with ATF), & connected to electrical & hydraulic lines. Slide-out now goes in & out as it should. Thanks for all of the help.
Good shortcut!
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Old 10-12-2018, 07:28 PM   #18
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I know this post is a few years old. I found it while trying to resolve a hydraulic slide issue i am having on my Fifth wheel. How exactly did you hook these lines up and pump through them?
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Old 10-12-2018, 08:08 PM   #19
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Well, that was a long time ago. Tomorrow I will go out my trailer & look at the pump. I just can't remember how I hooked it up. Hope you can wait till then. Regards.
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Old 10-19-2018, 06:55 PM   #20
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Hydraulic systems using an open tank are self venting. The few times I did it simply start the system and reverse the slides or jacks multiple strokes until smooth. All devices should be purged. Most important is do not exceed pump/motor duty cycle of maybe 30 seconds with cool down periods in between each.
Most effective means to purge. Oil is pushed and pulled down each line while drained to tank.
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