Sites: GlobalSpec.com | GlobalSpec Electronics | CR4 | Electronics360
Login | Register
The Engineer's Place for News and Discussion®

Previous in Forum: Small 100% Duty Cycle   Next in Forum: How to put ourselves to the top
Close

Comments Format:






Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







16 comments
Participant

Join Date: Nov 2008
Posts: 1

my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/11/2008 1:36 AM

I have a hydraulic dump trailer that raises and lowers. it was leaking hydraulic fluid so i fixed the leak and after that i raised the bed and it went all the way up but would not go back down. i finally got it to go down but now when i try to raise it it will not raise on its own you have to manually lift on the bed for it to go up. also when it is up it acts like there is not enough pressure in the cylinder and it starts inching slowly down so it will not hold in place now. any suggestions as to what may be the problem. just a fyi it is motorized and has a pump in the single container that holds the hydraulic fluid. the leak was actually around the area that looks like an oversized o ring which i fixed not replaced. thanks

Register to Reply
Pathfinder Tags: hydraulic problems
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
2
Guru
Brazil - Member - New Member Engineering Fields - Mechanical Engineering - New Member Hobbies - RC Aircraft - New Member Hobbies - Target Shooting - New Member Hobbies - Automotive Performance - Hey there... interested in exchanging information about car performance? Hobbies - DIY Welding - New Member

Join Date: Jan 2007
Location: Porto Alegre - RS - Brazil 30deg01'39.73"S 51deg13'43.45"W
Posts: 832
Good Answers: 28
#1

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/11/2008 5:59 AM

It seems that you have fixed the external leakage. But you still have an internal leakage that you must fix. It's not loosing hydraulic fluid, but allows the higher pressure fluid to pass to the low pressure side.

Just an idea to isolate the problem, you could install shutoff valves in the actuator, pressurize it and close valves. If the actuator can hold the load, the leakage is likely to be at the pressure regulator or return valves. If the actuator behaves as stated before, the leakage is in the actuator.

__________________
Humm... suspicious you are...
Register to Reply Good Answer (Score 2)
Guru
United Kingdom - Member - Not a new member!

Join Date: Jun 2008
Location: USA/Europe
Posts: 4632
Good Answers: 77
#2

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 12:09 AM

Hello desireedog2:

These are just thought and suggestions OK?

Check the bearing on the side which acts as the hinge. The bearing may be dodgy which may account for the bed not going down when empty.

As has been said, there must still be a leak but on the inside. It means you are not at full pressure and hence the symptom. The leak on the inside, depending on the pistons can be leaking into the piston itself and something will fail if it is left. I am assuming you have just one pump?...........

Fixed and not replaced. What does that mean? I think you may have used a filler or tape round the leaking area to temporarily stop the leak.

For your safety and every one else's, I suggest you should replace all the rings and seals, like NOW!It is a relatively small job on a vehicle with a single pump.

Good luck, and get working, with no 'short-cuts'! There is an awful lot of pressure in those pipes when it is working as it should, it will hurt if it suddenly blows!

Take care.............

__________________
Take it easy, bb. >"HEAR & you FORGET<>SEE & you REMEMBER<>DO & you UNDERSTAND"<=$=|O|=$=>"Common Sense is Genius dressed in its Working Clothes"<>[Ralph Waldo Emerson]
Register to Reply
Participant

Join Date: Nov 2008
Posts: 1
#3

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 12:35 AM

As stated by another reader please for SAFETY sake REPLACE not "fix". You could have a bypass of the piston seal in the cylinder.It could also be that your "fix" could have led to something being sucked into the control valve or a relief valve.

Register to Reply
Anonymous Poster
#4

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 1:53 AM

the answer is in these two bits of info

'after that i raised the bed and it went all the way up but would not go back down'

what did you do while fixing that would cause the sticking?

'i finally got it to go down'

consider how you did that. that info would help you troubleshoot.

if all else fails, take everything appart and inspect, then put it back together. if nothing else, it will be quite instructing.

Register to Reply
Anonymous Poster
#16
In reply to #4

Re: my hydraulic trailer will not raise unassisted, and will not hold once raise

08/15/2009 12:52 AM

I have a similar problem! Dump is going up(kinda slower then before but it won't stay up! It starts going down slowly(empty or loaded bed) it was working fine and sudendly starts acting up on me! Have no idea is it a control valve inside the cab or O rings in the pump

Register to Reply Off Topic (Score 5)
2
Guru
Hobbies - CNC - New Member United States - Member - New Member

Join Date: Feb 2008
Location: Mid-West USA
Posts: 502
Good Answers: 28
#5

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 7:38 AM

Here is your basic hydraulic circuit for a dump trailer with a self contained pump unit. The pump, typically gear style, draws oil from the reservoir and forces oil through the pressure relief valve. Relief valves have 3 ports: pressure in, regulated pressure out, and bypass. From there the pressurized oil will go to the directional spool valve. The position of the spool handle will determine which end of the lift cylinder receives pressurized oil. Most of these trailers have power up and power down lift cylinders. That way the circuit is closed to the outside elements. Some are power up and gravity down. If yours is gravity down then that might explain why it was stuck in the lift position. As mentioned before the bearings may be the culprit. An easy way to tell is by how many hoses go to the lift cylinder. 2 hoses of the same size and rating then it is power both ways. One hose to the bottom of the cylinder and a vent or smaller breather hose to the other end and it is gravity. NOTE You can gravity down either style with the pump turned off. You must look at the hoses and connections. Also the location of the filter can be on the suction or return side of the pump. Most typically I have seen them on the return at the tank. This reduces the pressure in the filter and allows the use of cheap spin on types.

Now for trouble shooting. You fixed a leaky o-ring. Did the trailer work before this? I mean the same day the repair was done. Not "well it worked the last spring when I used it". If it did then the problem, as stated before, is in how the repair was made. O-ring type fittings should never have teflon tape on them. The use of tape on hydraulic systems can cause problems and care must be taken. Never put teflon tape near the end of a thread. Skip the first 3-4 threads. Tape in that area will tear off during the install and contaminate your system. If the tape gets caught in the relief valve it can cause the spring and seat to not seal off completely resulting in reduced pressure. If it makes it to the spool valve then you may notice the bed not holding position and drifting downward. Either valve is simple to disassemble and clean. That would be a great time to replace all of the o-rings in them and flush out and change the oil.

SAFETY FIRST. If you are unable to readjust the pressure relief valve then take it to a good hydraulic shop to be repaired. When the setting is to low the bed will not lift and no one gets hurt, just frustrated. Set it too high and you can damage hoses resulting in damage to the trailer and yourself.

If the bed has not been used for a while and was not tested before the repair then the problem is likely to be in the spool valve and / or the lift cylinder. If the spool valve has a damaged o-ring it will not hold pressure and the bed will drift if it even raises at all. You said the bed was stuck in the lift position. The damage may have occurred when you tried to get it to lower. Also, the packing in the lift cylinder may be old and deteriorated. Any small cracks or abrasions to the packing will cause the bed to drift as well.

More information about what you have done exactly would be helpful.

Register to Reply Good Answer (Score 2)
Guru

Join Date: May 2007
Location: Ohio. USA
Posts: 564
Good Answers: 30
#7
In reply to #5

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 8:14 AM

I was going to suggest that desireedog2 generate a hydraulic schematic but you did this verbally. I have dealt with hydraulic systems but never a dump bed specifically. I was wondering if this system may have separate safety hold valves or ones that would be build into other devices in the system. That way the bed could not go down (or maybe even up) without a specific hydraulic signal.

A malfunctioning hold valve could cause confusing up/down problems.

An accurate hydraulic schematic is always the first step of diagnosing an odd hydraulic issue.

__________________
I won't belong to any organization that would have me as a member. Groucho Marx
Register to Reply
Guru
Hobbies - CNC - New Member United States - Member - New Member

Join Date: Feb 2008
Location: Mid-West USA
Posts: 502
Good Answers: 28
#8
In reply to #7

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 8:42 AM

I made the assumption that the system used a manually controlled spool valve. It might have relays and solenoids to allow the use of electric controls. Good point on your part. Now that you mention it I have seen a couple trailers with a remote pendant control. They might be more common than I am aware of.

Register to Reply
Power-User

Join Date: Dec 2007
Posts: 153
Good Answers: 3
#10
In reply to #5

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 10:58 AM

great reply to the post.

after reading the original enquiry i went back to basics as presented in the hydraulic circuits shown in my john deere repair manuals, and to look at some designs of offshore (aka t-i won) sourced hydraulic pressure pumps.these things came out of the search

one the seats of the check valves for the up down lever may not be smooth or the pressure of the open close spool valve springs may not be strong enough to allow the ball bearing to seat properly.

two apparently the springs in the offfshore sourced products have been designed for other applications but are used in the pumps as well

three the body of the pump itself may have a cavity which when pressure is applied leaks through the castings wall and into the internal cavity void or as suggested in the post right through the castings wall

four the suggestion duck tape or similar glue or actual fabric etc being sucked in and jamming the return valve cannot be avoided

five the hydraulic jack buiklt into the 5 ton cab over of the international was known as a hazard i think that is why the truck maker started putting in internal supports that kept the cab up whie the top part of the engine e.g. alternator waws worked on.

as stated VERY GOOD response

'da ber

Register to Reply
Guru
Hobbies - DIY Welding - pipewelder

Join Date: Apr 2007
Location: North Georgia, USA
Posts: 672
Good Answers: 33
#6

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 7:58 AM

These are some very good posts and I believe your answer is in them. I would like to add some personal experience about the safety when dealing with any type of hydraulics. I had a buddy that drove a cab over diesel truck several years ago. These older type trucks had a lever behind the seat that worked a valve to lift the cab up to gain access to the motor area. While he was lifting the cab a high pressure hose burst and injected hydraulic fluid into his thumb. After several weeks of trying to save his thumb they finally had to amputate it. it was a very strange and misfortune accident. I have found over the years it is way better and safer to replace things that seal rather than to fix them and hope for the best especially on the high pressure hydraulics systems. Please be careful!

pipewelder

__________________
pipewelder
Register to Reply Score 1 for Good Answer
Guru
Hobbies - CNC - New Member United States - Member - New Member

Join Date: Feb 2008
Location: Mid-West USA
Posts: 502
Good Answers: 28
#9
In reply to #6

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 8:46 AM

Another safety note.

Never stick your head or any part of your body between the raised bed and the frame without safety blocks or pins in place. Should the bed drop you will not likely react in time. Lots of needless injuries by not following this simple rule.

Register to Reply Score 1 for Good Answer
Guru
Hobbies - DIY Welding - pipewelder

Join Date: Apr 2007
Location: North Georgia, USA
Posts: 672
Good Answers: 33
#11
In reply to #9

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 11:03 AM

I just completed a major refurbish/retrofit on a dump truck a friend of mine bought. The first thing I did was to add a steel brace and pin to lock the bed up before doing any work underneath it. This is a basic rule I follow before working on any dump in my shop. If a truck does not have a bed lock system I will refuse to work on it unless the customer agrees to pay for me to add one. I have seen where people slide a large wood or metal beam under the bed to have a stop to block the bed from being able to come all the way down but I have also seen a bed fall because of bursting seals and push these stops all the way up or shear the wooden ones off to where they would not have done much good. Thank god no one was under the bed at the time!

pipewelder

__________________
pipewelder
Register to Reply
Participant

Join Date: Nov 2008
Posts: 1
#12

Re: my hydraulic trailer will not raise unassisted, and will not hold once raise

11/12/2008 11:26 AM

Hi,

I wrote a long post about the dangers of working on hydraulics if one is not trained in the hazards. But then I decided it would sound like a typical internet flame post, and would be easy to dismiss. But I do want to seriously raise the issue that hydraulics is a hazardous field, and can surprise you and injure you.

I recommend you go to this link first, then consider whether you want to go ahead:

http://www.fluidpowersafety.com/fpsi_alerts_enter.html

You will have to log in (it's free) and then you can read the safety alerts. Please do so for your safety and to make sure you come home intact and healthy to your loved ones.

Best wishes,

safetyguy

Register to Reply
Anonymous Poster
#13

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 11:57 AM
The most common problem with 12 VDC hydraulic pumps results from a bad/weak ground. Check your pump attachments to the dump trailer frame. Make sure all bolts are tight. Also, make sure your battery ground to the trailer frame is strong. If everything looks good, but the pump still seems weak, try connecting a jumper cable directly from the battery ground to the pump ground - thus bypassing the trailer frame. This works in 90% of the pump problems. Also, make sure you have a fully charged battery.

Also, the drifting down problem is usually a small spec of dirt on the check valve. This many times can be dislodged by jogging the up/down buttons a half dozen times.

Register to Reply
Anonymous Poster
#14

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 2:33 PM

You said you fixed a leak , did you bleed the system after repairing the leak ? Usually if fluid is leaking it is being replaced by air . If there is air in the system , the air will compress in a hydraulic system and give many odd effects . If the fluid is airated ( tiny bubbles ) it can take time to compress that air and give the inching down impression much like the brakes on your car that need bleeding , spongy . Also may give the effect of " not enough pressure " as the pump will be compressing the air as it pumps fluid .

Register to Reply
Guru
Popular Science - Weaponology - bwire Hobbies - Car Customizing - New Member

Join Date: Dec 2007
Location: Upper Mid-west USA
Posts: 7552
Good Answers: 98
#15

Re: my hydraulic trailer will not raise unassisted, and will not hold once raised???

11/12/2008 2:48 PM

From your description my first thought was their maybe air in the cylinder; you may need bleed or purge the air out.

__________________
If death came with a warning there would be a whole lot less of it.
Register to Reply
Register to Reply 16 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Alien (1); Anonymous Poster (4); babybear (1); barfnagler (1); bhrescobar (1); bwire (1); DaveB (1); pipewelder (2); safetyguy (1); The Mechanic (3)

Previous in Forum: Small 100% Duty Cycle   Next in Forum: How to put ourselves to the top
You might be interested in: Hydraulic Repair Services, Hydraulic Cylinders