High pressure hyd oil Danger!

This topic contains 11 replies and was last updated by ben 9 years 9 months ago
April 9th, 2012 12:35am
I know this is a long one but please take the time to read it, Thanks.

I was recently working on a Volvo 460 Excavator. It had a pinhole leak on the right boom cylinder hydraulic tube at the weld (this is for the barrel end of the cylinder) I knew I had to remove the tube to re-weld it. So, knowing the dangers of high pressure oil being released when I tried to remove the tube I refered to the operators manual for the proper procedures to relieve the pressure....

it said:

1: Remove the cap for the hyd tank (vent pressure)

2: Turn on the key (without starting the engine) and move the control levers and travel pedals for a few seconds

thats it....

This is a newer machine, all the hydraulic valves (except the ones for the travel motors) are electronically controlled (electronic + pilot) therefore simply turning on the key will not be sufficient to actually move the spool and vent the pressure from the cylinder!

I knew this before hand and took extra precautions (2 pairs of gloves, face shield, long sleeve shirt) I also wrapped several rags around the fitting I was going to remove and loosened the bolts furthest away from me.

When I did loosen the fitting enough the oil rushed out with enough force to split the o-ring, SHRED the rags and hit the cab so hard it sounded like someone had hit it with a hammer! this is extraordinarily dangerous!

Once back at the shop I discussed this with the safety manager, his response to me was that he had already run the manufactures procedures by the ministry ("of labour" I think) and that they were satisfied with it! Total BS!!!

My question is: Does anyone have a better way to do this? or some kind of safety device to contain the escaping oil?

(My idea was to build some kind of collar to contain the oil but this would not work in all applications...)

Thanks for any help

April 10th, 2012 2:21am
I am more familiar with Cat Equipment than Volvo, but I would expect Volvo to utilize a hydraulic lock lever at the cab entrance. This lock lever must be in the unlock position in order for your pressure release procedure to be effective. On Cat excavators, the lock lever is attached to the LH armrest and is used to control the lock solenoid in the pilot oil system. I'm surprised your pressure release procedure didn't mention this. Volvo has to use some sort of safety interlock to prevent operators from leaving the cab and accidently bumping a joystick on the way out. This would certainly explain why things happened the way they did for ya.

The reason that the key needs to be on, is so that the lock solenoid in the pilot oil system can do its thing, when activated by the lock lever in the cab.

If lock lever and solenoid are working correctly, perhaps your pilot oil accumulator lost its gas charge, rendering the pilot oil system ineffective. Did you see your boom/stick/bucket settle at all when you did your pressure release procedure?

You might want to think twice about welding on hydraulic line tubes or cylinder barrel tubes. In the Cat world, that's a big no-no and is not a dealership or factory authorized repair. When welding on hydraulic tubes, the weld heat can cause metal material to push into the flow passage, thus creating a flow restriction or in the case of a cylinder barrel, a surface imperfection that could cause seal failure and/or internal leakage. Additionally, the weld heat could change the metallurgy thus making the metal unable to withstand the pressures in the system which could create a dangerous condition.

By the way, I commend you for being conscientious about what you're doing. Thinking things through beforehand and during work is very advantageous. You obviously care about safety which is great.
April 10th, 2012 3:38am
yes there is an interlock and the procedure did instruct me to have it engaged (which I did) I forgot to mention that when I wrote the original post, sorry about the confusion.

The boom did not settle nor did I hear any of the valves moving or making any noise (like the hiss you're used to hearing when pressure is released through a valve)

as I said this is a newer machine so i would expect there to be accumulators on the pilot system... I'm sure there are in fact... However had they lost they're gas charge I would expect to see problems with the everyday operation of the machine (erratic or choppy controls etc..) we have not had any complaints. unless the system only uses 1 or 2 small accumulators that don't hold much volume of oil...

As for the welding I am aware of the dangers of welding on high pressure pipe fittings, this is something I expressed to the maintenance supervisor however being that he's an old school guy and has done this "lots of times" I was told to do it despite my objections so i did, and stood way back when the machine was started (not great, but that's the way these guys work... unfortunately) I wasn't worried about a restriction being caused because it was a 1" tube I would have seen it.

This fitting has been welded twice now, and the last time I took the initiative and ordered a replacement tube, I know that the metal has been overly stressed now and needs to be taken out of service.

I would never weld to the barrel of a cylinder, I've seen the result this has on the cylinder first hand and I know that CAT has had PLENTY of experience with this! lol

thanks for the pointers I appreciate you taking the time to read my post
April 10th, 2012 9:31pm
In order to have pressure like that you must of had pressure applied to the ram either the boom was off the ground too far or the stick was pushed into the ground with pressure on the ram.Another cause would be if you didn't have the outer boom far enough forward,in which the bucket would roll back when the main rams lost pressure and this would give you an increase in pressure when released.I usually strech the booms right out and curl the bucket all the way open and the lodge it on the ground,bleed off the tank and then the lines on the ram.Good to see you thinking ahead and that's what is going to get you through for years to come.
April 17th, 2012 9:28pm
Hello..If you did not hear any noise maybe you have a problem with accumulator for pilot circuit.Accumulator is used for lowering of implement when engine is dead...or some cylinders have boom lowering control valve which have valve for manualy lowering...
November 2nd, 2012 12:39am

you said you want to remove cylinder pipe welding. If you want to work on excavators for boom cylinders is to position the machine properly. I mean keeping the attachment position. extend the arm (stick) completely. so that the arm cylinder rod is completely inside the cylinder and lower the boom until the arm (stick) touches the ground. in this position the boom cylinders will not have any load because the arm cylinder cannot travel inside the cylinder and the arm connected to bucket should be resting on the ground. In order to release any pressure in the line, turn the key on (don't start) and unlock the safety lever and operate boom down and up. this should work if your accumulator working properly.
November 20th, 2012 5:16pm
restrictions and load can increase or create pressure !!

try this !! extract the fluid on which side u will repair !! by shifting the control lever allowing the trap fluid to return to the tank! before turning off the engine !! !!!! the system is open loop circuit spool travel controlled by pilot lines which is electronically commanded !! !!!

releasing the pressure in the tank !! as off !! !! hint ur cylinder is taking load !!

safety is knowing where the fluid is high or low !! where being restricted or not !! should know were the fluid is !! look at the position of the cylinder and boom !!

i agree with this guys !! check ur accumulator !! because the pilot line pressure could be insufficient to do the functions !! check the lever and the solenoid !!
December 5th, 2012 5:02am
I'm currently working on a 460b and had to flush the Hyd system, I did the exact same thing, set the machine in the correct position and wiggled the sticks with the safety lock up, I felt no movement whilst doing it, the only lines that had pressure when I was cracking them were the boom cylinder line's
December 17th, 2012 9:23pm
Good day Matt

There are a couple of options that appear to be overlooked 1/ loosen the port relief valve but make a good note of the original position. 2/ Remove the pilot couplings at the main valve adapt a nipple with a thread then force the spool to shift. If you need more details drop me your email address.


May 18th, 2013 11:45am
Hydraulic and diesel fuel systems operate at very high pressures, often 3,000 psi and above. If a loose connection or a defect in a hose should occur, a fine, high-velocity stream of fluid will result. Even for systems pressurized to as little as 100 psi, this fluid stream can penetrate human skin as if it were a hypodermic needle.

Initially, an accidental fluid injection beneath the skin may only produce a slight stinging sensation. There is a danger that one will ignore this, thinking it will get better with time. Most often it does not. Within a very short time the wound may begin to throb painfully, indicating tissue damage has already begun. Fluid injected directly into a blood vessel can spread rapidly through your circulatory system. The human body has little ability to purge these types of fluids. A fluid injection injury can become very serious or even fatal if not dealt with promptly and properly.

A medical doctor familiar with treatment of this type of injury must surgically remove the fluid within a few hours. The longer the delay in getting professional medical aid, the further the tissue damage can spread. If left untreated, the injury could result in disfigurement or amputation of the affected part.

Rachel !!!
May 21st, 2013 4:20pm
Hi Rachel, good information to know.....thanks for the post.
May 26th, 2013 10:54am
It looks to me that Metal is just asking if anyone knows if there would be a difference.

It really would be interesting to see if there was a difference given the same situation.

Would the outcome be the same if he was wearing the same PPE but was using a 5000+/-PSI system?

Has any manufacturers performed a test to identify the difference? If there is a difference,it would be a great selling point!!

Stay Safe!

Rachel !!!

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