Hydraulics overflow and a slow dump

[texasjohn]

Dump trailer hydraulics overflow and are slow.. .I wonder why?

OK.. more info...The facts are:

It's a 20 foot gooseneck PJ dump, I purchased it used, it's about 2 years old, was used to do Katrina cleanup. Cylinder is double acting... there is a hose that goes to each end of the cylinder.

When I bought it, I couldn't raise it all the way up because battery was low... but it did start and begin to move the dump bed up with no apparent difficulty.

I got it home, charged the battery, took a long time to charge... but it's a 1100 CCA CAT battery..12 V...I mean, it's BIG. It took a full charge.

Empty, I raised the bed and noticed it was kinda slow, but I'm not experienced and thus didn't know if this was the proper speed or not.. it went up at the same rate UNTIL the sound changed... fluid tank was empty.

Before starting, I had checked the tank... it was low, thus I put in about 2 quarts. I estimate the total capacity is one gallon. However, I had left about 1/2 inch air space (tank lays on its side) from liquid to top of tank. The fill plug is on the very top of the tank.

So, when it went dry, I figured that it needed to be completely filled up and added more fluid... maybe half a quart... ran dump up farther up and tank ran near dry again. Repeated this at least once more till dump was at maximum vertical extension. There was maybe .5 inch or less of fluid remaining in the tank at this point.

I figured that I now had a "full charge" of hydraulic fluid and let it down. To my surprise, I had a very significant overflow of hydraulic fluid from the tank... I began to surmise that the tank capacity and trailer capacity needs were mismatched... but this would be very surprising.... the prior owner had not indicated anything other than the hydraulics were strong... he said that the lift was capable of 20 tons... yes, 20 tons, not 20,000lbs.

Now, for the rest of the story...

I put a bout 1.5 yards of sandy material into the trailer... right over the rear wheels and mostly centered in the bed. I didn't want to overload it the first trip. When I went to raise it to dump, things went very, very slow... we're talking maybe 5 minutes of pumping to nearly empty the hydraulic tank... not wanting to pump air, I added more fluid... again... ran the pump for maybe another 5 minutes before the angle was sufficient to START the material to sliding down. I was, again, out of fluid and not at the top of the stroke, so added more fluid. Another 5 minutes or so of pumping (ever so slow progress, but it DID keep moving up) and I finally was able to complete the dump.

Again, lost a quart or more of fluid when letting the dump back down.

Fluid escaping looks creamy... what I added was clear fluid.

I see no evidence of recent replacement of any hoses, tank, motor, pump, solenoids, or cylinder. All are properly grungy to have been used together for quite some time. However, there is no evidence of ANY hydraulic leak other than what flows backwards out the fill opening which has an air escape cap. I looked carefully to see if there were any external leaks.. none visible at all, and no evidence of any.

So, it all looks factory original, although I do need to call PJ Trailers with the serial number and find out what was originally installed.

Current conclusions:

A) Hydraulic tank needs extra capacity to avoid fluid loss...
I have looked for an hydraulic overflow cap that I could use to replace the existing one and a matching overflow hydraulic tank... like what is used for radiator fluid... but haven't found anything so far... ideas??

B) Hydraulic system needs some repairs to increase lift speed:
I think I need to get a hydraulic pressure gauge to know what the pressures are. Where is the best place to get a hydraulic gauge?

Assuming that the pump can reach the required pressure (3300 lbs), I have read elsewhere that possible problems could be:
1) clogged filter.... haven't figured out where this is as yet.
2) hoses are reversed (hydraulic gauge will help here)
3) high pressure fluid is leaking past the cylinder (from wear, etc.) and dramatically reducing lifting efficiency. In which case we hope that replacement of seals is all that is necessary... and that the cylinder walls are not scored unduly.

If anybody sees a different analysis path or diagnosis, I'm listening. I have a college physics understanding of hydraulics, but no hands-on repair experience.

I have seen in other posts that people indicate that rebuilding a cylinder is not too difficult... the parts are not too much, it is the labor that adds up quickly.

 

[RonMar]

Do you have any pictures of the plumbing? Usually the reason for 2 hoses to a dump bed cylinder that lowers by gravity is to use the rod end of the cylinder as a reservoir for fluid. If this is done, the main reservoir only needs to be large enough to contain the ammount of fluid the rod would displace on a fully closed cylinder(pretty small ammount). If the reservoir is un-vented, this is to force fluid back to the rod end once full during lowering. The description of "creamy" fluid indicates to me the presence of air in the fluid or cavitation in the pump. Either the system is not primed, or their is a restriction in the supply path causing a suction and air to be induced thru a leak. It is far easier to draw in air thru a pinhole than move thick fluid thru a restricted pathway. This would explain the slow rise. A restriction of flow to-from the rod end of the cylinder would add a hydraulic load and also slow operation. The only filter on this HPU may be internal to the tank, a wire mesh suction strainer. A couple of pics would help a lot to get us all on the same page as to how yours is configured.

 

[texasjohn]

OK...will work on photos when it is next light.. thanks for the discussion... I can see you've been where I've yet to tread

 

[MikesTractor]

the prior owner had not indicated anything other than the hydraulics were strong... he said that the lift was capable of 20 tons... yes, 20 tons, not 20,000lbs.

Based on this statement and the facts that (1) It is extremely slow and (2) The reservoir does not hold enough fluid to complete the lift, It leads me to think that someone has replaced the cylinder with a larger one or replaced the pump/reservoir with a smaller one. I think I would look at this first and make sure that the two components are not mis-matched. Getting the specs from PJ Trailers would help confirm if they were right or wrong.

As RonMar said, pics would also help.

Mike

 

[RonMar]

I looked online and found a website for PJ trailers. They have the operating and spec documentation for their Hydraulic power Units online, including a hydraulic schematic... There was also a troubleshooting table. There are a couple valves involved with the plumbing of the HPU and a failure of one of these valves could be causing your problems. I forget the web address, just google PJ trailers and you should find their site.

 

[wushaw]

Yes pictures would help.
Is it a scissor lift type hoist?
My tank for my Colt 18K hoist is over 2 gallons and uses almost the whole tank.
It does take awhile for it to get to the full up position but not no five minutes.

You just may need a seperate tank that has a vented cap for the extra capacity.

 

[texasjohn]

All.. thanks for the ideas.. working on getting pictures... buddy with digital camera will drop by and assist...

Update... just now contacted P-J trailers, talked to Dave in warranty... nice guy... he amazed me with his explination... I yet have to try his solution to see if it works.

He suggests that the problem may be a low battery... try a fully charged batt.

He says that a trickle charger is needed to charge the battery that the traditional 12V car battery charger (10 amps or so) I have used will give it a charge, but the charge won't hold... not sure I fully understand this and I need to study it further.

Low voltage would explain why it is a slow pump and rise in the dump. I hadn't put a voltmeter on the battery since I had charged it overnight and the meter on my charger showed it at over 90% charged.

ALSO, apparently the pump is responsible for pumping the fluid from the tank into the other side of the cylinder on the down stroke when lowering the dump bed. Thus, if low voltage, slow pump, and the gravity down pressure flow gets ahead of the pump, thus excess fluid accumulates in the tank and overflows.

So, low voltage = slow pump = hydraulic overflow ..

 

[texasjohn]

OK... photos are taken, looking into the hydraulic bin in the front of the trailer, in order of increasing detail.

pump and connected motor and tank

pump connections

two hydraulic connections that go back to the big lift cylinder... they are the brassy looking fittings connecting into the steel pump housing




I have not yet tried a replacement battery, however, I put a voltmeter on the battery, which has had a trickle charger on it all day... 12.5 volts, no load. Then, I started raising (all too slowly) the dump and voltage dropped to 11.4 volts after a minute... front of dump had raised 4 inches. Does this voltage drop versus work done seem reasonable? Anybody with a dump trailer have any time versus distance traveled versus voltage information?

The above was without having the battery connected to a charging pickup alternator, or other charger, just running off of battery only.

The battery is a biggie, CAT 1000 CCA, 9X9720, 275 reserve capacity minutes at 25 amp output at 80 degrees F (about today's temp)

 

[wushaw]

That is one big ***** battery...

Mine is a Wally World special average size car battery, mine takes about two minutes to go to full dump position....and I thought that was slow..This battery has been working for three years.

You need to check the electrolyte level in each of the cells to see the specific gravity level, this will tell you what shape the cell is in.

Here is a pic of mine in full dump.
copy of dsc00010 pictures from friends & fun photos on webshots

 

[texasjohn]

OK, Wushaw, thanks for the comparison info...

The battery weighs 101 lbs wet according to the Cat specs. Fluid level in all cells was above the plates when I got the trailer and I've brought the level up to just under the filler cap with distilled water.

Nice looking trailer.... how do you charge your battery? Does it charge while connected to your pickup, or with a 110V charger when parked?

 

[wushaw]

Fluid level is one thing which is good when it is above the plate area. You still need to get a hydrometer to check the electrolyt level, this gives you a good indication of how healthy the cell is. Any parts store sell them for under 10 bucks.
The truck does all the charging, I have not had to charge seperately.
I am half owner of this trailer and the other owner now owns that truck in the picture ( a divorce causes one to sell things )

 

[Rara Avis]

Fluid level is one thing which is good when it is above the plate area. You still need to get a hydrometer to check the electrolyt level, this gives you a good indication of how healthy the cell is. Any parts store sell them for under 10 bucks.
The truck does all the charging, I have not had to charge seperately.
I am half owner of this trailer and the other owner now owns that truck in the picture ( a divorce causes one to sell things )

Speaking of those pictures...just a tip to protect your privacy...never have photos of your license plate numbers...you would be suprised what info you can get from DMV...

 

[wushaw]

Speaking of those pictures...just a tip to protect your privacy...never have photos of your license plate numbers...you would be suprised what info you can get from DMV...

Thanks

 

[diyDave]

2 things occur to me that have not been discussed yet. If the trailer came from Katrinaville, check to make sure that the fluid does not have water in it, as that would give it a creamy or milky color, and secondly- look at those electrical connections the jumper from the solenoid to the motor looks rusty, and a ground wire appears to have the end just wrapped around a bolt, no crimp on end. Also have you had that battery load tested, Interstate will do it for free, the tester they use hits the battery with a load, waits, hits it again, and measures the response to varying loads, a much better test than old hygrometer, or carbon pile load testers.

 

[diyDave]

A third thing just occurred to me check lines, hoses for kinks or inner liner separation.

 

[texasjohn]

Good ideas, all. I'm getting ready to do battle soon.. have acquired additional battery power to see if it is the battery. Also hydraulic pressure gauge to test output of the pump. Plan to replace hydraulic fluid. Will hunt for any strainer clogs, also loose wires. Now, I gotta get my hands really messy

 

[Wayne County Hose]

There is no way that the fluid return will lead the fluid output enough to explain the tank puking fluid. If the pump could not keep up to what the cylinder demands on the lowering side of the hydraulic circuit, there would be a vacuum created which would draw the fluid from the tank thru the pump into the cylinder. This vacuum would also draw air past the cylinder packings into the cylinder. These seals are designed to keep fluid in, not air out. Believe it or not, air is easily introduced into cylinders in a case like this.
The volume in the rod end of a cylinder is roughly half that of the base end because of the volume of the rod.
Here is what baffles me with the tech guys answer. In a double acting cylinder such as this, When you raise, more fluid is required (than lowering) because you are filling the bottom of the cylinder, the rod is in the top end. The rod takes up volume in the top of the cylinder which the bottom of the cylinder doesn't have. So, it does take more fluid to raise than to lower. If you are running out of fluid to raise, this tells me that the tank volume is way too small. Engineering snafu. So, when lowering, if the bottom of the cylinder pushes more fluid back to tank than the top requires, explain to me how the top can't fill up enough to keep up with the bottom? The pump should have more than enough flow to fill the top of the cylinder as the bottom empties. Except for a poorly engineered system.
Because of the weight of the dump unit on the cylinder, there is no pressure required whatsoever to lower this unit, only flow. If you cut the hydraulic line when the trailer is raised, it would drop like a brick. So, battery voltage would be a non-issue for slow lower. 12.5v sounds a little low for a resting, fully charged battery, but 11v under load isn't real bad. These pump units are traditionally slow. It's not pressure, but volume which controls the lifting speed, so a pressure gauge may not be much help. If you had low pressure, it wouldn't raise. Pressure is power, flow is speed. You need a flow gauge. These units have small pumps in them, not much you can do.
Total tank capacity about a gallon? If your cylinder is anything close to wushaw's, it takes way more than that to fill it for lift.
As far as your cylinder is concerned, lift the unit and make a mark on it somewhere for height. Come back in about 5 minutes and measure movement. You are checking for cylinder drift, a.k.a. internal seal leakage. No or little movement, o.k. Lots of movement, bad seals internally. You can also lift the unit and remove the line for lowering. There should be minimal flow as any flow is fluid leaking past the seals. If you do this, please be very careful as removing the wrong line can kill you.

This just sounds like a poorly engineered unit.

 

[texasjohn]

I fully charged (and proved it with a load tester) the 1000 CCA deep cycle battery, also hooked two 6V golf cart batteries in series, then in parallel with the 12V Cat battery... voltage before lifting was 12.5, during attempted lift... 11.4... and rock solid. Plenty of amps!

Same results, terribly slow lift, overflow on lowering the dump trailer bed.

Called PJ Trailers with that result, they put me in touch with KTI, the manufacturer of the hydraulic pump in Ca. Both fellows very courteous and knowledgable.

After checking model and serial number, (it's still in warranty) KTI current diagnosis is that they had initially used a plastic filter between the hydraulic fluid tank and the pump. This was a problem because when the motor heats up, the plastic filter gets hots, gets mushy, collapses and restricts the flow.. causes pump to work hard, inserts bubbles in the hydraulic stream, which don't compress very well. They will be sending me their new design... a metal filter and attachment elbow along with exploded parts view so I can disassemble tank from pump and replace the filter. The current belief is this will fix the problem and all should be well... so, am awaiting the shipment in the mail.

Stay tuned

 

[McSummation]

Yesterday John and I spent several hours working on his trailer. We pulled the pump assembly out of the trailer, dumped the fluid, removed the tank, cleaned all the crap out of the tank, replaced the filter, put it all back together, filled it with fluid and hit the "up" button. About 1/3 of the way up, it was getting low in fluid, so we stopped and topped off the tank. When we started up, there was much bubbling of air in the tank. We had to stop again and top off the tank before we got all the way up. Much air came out while going up. As we lowered the bed, we lost a small amount of fluid because we had no idea of how much to put in, with all the air that was coming out. We then cycled the unit again, without having to add any more fluid. When it was all the way up, we stopped while we sat down and drank some cold liquid. It didn't creep down so the seals all seem to be good and the check valves work. The comments about the tank only needing to hold enough fluid to account for the size of the piston rod also seem to be true.

This is an end view of the filter:
View attachment 87151

One side view:
View attachment 87152

Other side:
View attachment 87153

Anybody have any ideas why this filter didn't pass fluid.

The filter appears to be of the "fine brass mesh screen" type.

There was a magnet in the bottom of the tank. I'm not sure what good it does because the pump is made from aluminum. (Maybe the pump rotor is steel.)

 

[texasjohn]

James, good post.... dunno why photos didn't show.

All... had you seen the photos, you would have simply seen a glob of stuff completely covering the filter... preventing entry of all but an extremely small amount of fluid. I think that moisture/condensation over time got into the hydraulic fluid tank and turned it into mayonaise... it was creamy yellow, anyway, and there were lumps in it like curd...you know, like curds and whey

Conclusion... clogged filter resulted in all the problems. All seems fine now.
PJ Trailers and KTI the manufacturer of the hydraulic system were helpful. KTI sent me a new filter under warranty, no questions asked. None of the work was hard, just time consuming... and, 5 gallons of hydraulic fluid is about $25. I used all 5 gallons in diagnostics and repair.