|The most important responsibility of a hydraulic technician is to make sure that there is no stored energy in a hydraulic system before performing service, repair, or troubleshooting, on a hydraulic system.
The hydraulic system MUST be equipped with some type of device which makes it safe and simple to remove stored energy without EVER having to discharge the oil to atmosphere and, more importantly, to verify that the hydraulic system is at a zero-energy state.
This critical procedure MUST be performed before loosening a connector, or removing a component.
In fact, its the law! According to OSHA, lockout/tagout regulations and procedures are designed to prevent injury due to unexpected energization or startup of machines or equipment, or the release of stored energy during servicing and maintenance.
In addition, the regulations and procedures state very clearly that the energy sources include, amongst others, hydraulics.
Also, the rules and regulations make it equally as clear that, lockout devices and tagout devices should: be durable; be standardized; be substantial; indicate the identity of the employee applying the device(s); and, not to be used for any other purpose.
Now that we have reviewed what OSHAs rules and regulations (the law) say about stored hydraulic energy, lets review a few hydraulic system manufacturers warnings and cautions about the hazards associated with NOT complying with the law:
NOTE: The OSHA regulation, and, machinery and equipment manufacturer's warnings and cautions seem to have some common ground. However, machinery and equipment manufacturer's troubleshooting and air-bleeding recommendations seem to contradict both the OSHA regulations, and, their own warnings about the hazards associated with discharging hydraulic oil to atmosphere.
Here are a few examples:
For the record: these examples originated in my hydraulic safety worrkshops. They were handed to me by students who were concerned about the apparent contradiction between what they were being taught and what manufacturers recommended.
|John Deere Company®
|Here is a warning about escaping oil under pressure from John Deeres Operation and Test Manual for a John Deere 643G and 843G Feller-Buncher (ref., TM1683 (06MAY97) Page # 9000-01-3:
Avoid High-Pressure Fluids
Escaping fluid under pressure can penetrate the skin causing serious injury.
Avoid the hazard by relieving pressure before disconnecting hydraulic or other lines. Tighten all connections before applying pressure.
Search for leaks with a piece of cardboard. Protect hands and body from high pressure fluids.
If an accident occurs see a doctor immediately. Any fluid injected into the skin must be surgically removed within a few hours or gangrene may result. Doctors unfamiliar with this type of injury should reference a knowledgeable medical source. Such information is available from Deere & Company Medical Department in Moline, Illinois, U.S.A.
|Its obvious, based upon the preceding warning, that John Deere® is acutely aware of the hazards associated with releasing stored hydraulic energy to atmosphere. Moreover, one cannot help but conclude that John Deeres warning offers no exceptions - or do they?
|Here is an excerpt from the same manual which covers the test for the machines steering valve:
The illustration accompanying the test shows a drawing of what appears to be a pipette being held adjacent to an open port (transmission line disconnected) in the machines steering valve (although the illustration does not show a hand, one can only assume it has to be held there). The pressure setting for the steering system is apparently 3410-PSI (235 bar) and the recommended oil temperature for the test is 130ºF (54ºC).
|The steering valve test procedure, as I see it, puts a persons face and hands within an arm's length of an unknown (if the valve is defective) amount of oil escaping to atmosphere (Figure 1) at extraordinarily high velocity - the extent of which is determined by oil escaping across a clearance (orifice) at 3410-PSI (235 bar).
In addition, a natural by-product of a worn hydraulic component is heat. The normal operating temperature of a mobile hydraulic system is generally above 160ºF (71ºC) well above the temperature which, will result in second and third degree burns.
|When this issue was presented to me by a concerned student during the workshop, I decided to take the matter up with the folks at John Deere.
I contacted Mr. Derek Boudrea Manager Technical Support Operations for John Deere Dubuque Works (September 3, 2002).
I wrote a letter to Mr. Boudrea, to which he sent me a reply. His reply dealt only with the technical merits of my enquiry, but completely avoided the issues addressing apparent conflict between John Deere's warnings and their practices.
He did not answer my second letter, return my telephone calls, or answer my e-mails regarding this matter.
John Deere is not the only company that would not open dialogue with me regarding the obvious conflict between their warnings versus their recommendations.
|Caterpillar Tractor Company®
|On two occasions I wrote letters to the Service Information Division of Caterpillar, Inc., at 501 SW Jefferson Ave., Peoria, Illinois, regarding similar issues however, both went unanswered!
|Heres an example (Caterpillar ® Ref. SENR2522-02):
Hydraulic oil, under pressures that can be higher than 34500kPa (5000 psi/345 bar) can remain in the hydraulic system on this machine after the engine and pump have stopped. Sudden movement of the machine or release of oil under pressure can cause injury to persons on or near the machine. To prevent possible injury, do the procedure that follows before testing and adjusting the hydraulic system.
|Step 5 states: Make sure all hydraulic pressure is released before any fitting, hose or component is loosened, tightened, removed, or adjusted.
This is a standard warning in the industry. However, there is no hydraulic system I am aware of in which the pressure status can be verified prior to loosening or disconnecting lines, or removing components.
Step 10 states: Carefully loosen bleed screws (1) at the rear of the tilt cylinders. When the oil from the bleed screws stops, tighten the screws.
Again, there is absolutely no way of safely verifying that the pressure in the tilt cylinders is zero before opening the bleed screws.
|Under sub-heading Leakage Checks in the same document the procedure for testing the pumps reads as follows:
|After the pump control tests are complete, it is known that the output of the pilot system pump is correct and the relief valve in the pilot system is correct.
If the output of either of the piston pumps is not according to specifications, it is probable that there is too much wear inside the pump. Leakage from the drain openings is an indication of the conditions inside the pump.
Disconnect one end of the drain and let the drain go into a bucket. Measure the amount of leakage per minute.
The chart accompanying the procedure shows the leakage rates at 100-PSI (6.9 bar) and 3250-PSI (224 bar). In other words, a person is holding the drain line into a bucket with a pressure drop across the pump clearances at up to 3250-PSI (224 bar).
Ironically, Caterpillar® offers a stern warning about oil containment in their document (ref NEEG2871):
Personal injury can result from fluid under pressure. Care must be taken to ensure fluids are contained during inspections, maintenance, adjusting, or repair of the machine.
|Letters and telephone calls to Tuboscope, (a manufacturer of Coil Tubing Machines based in Houston, Texas) about safety issues with respect to testing hydraulic components contained in their Coiled Tubing Handbook, (ref., 999-366), also fell on deaf ears.
|Tuboscopes (a manufacturer of coil tubing products) recommendation for testing a pressure control valve is surely, in my opinion, one of the most ill-advised troubleshooting recommendations ever written:
Procedure for Determining if the Problem is Systems Pressure Relief Valve or the Pump
Discharge from the relief valve must be observed. If possible disconnect the tank return line for the relief valve at point C. Attach a short length of hose to the relief valve outlet. Hold the open end of the hose over the tank filler opening where the flow rate can be observed. Start the pump and run the relief valve adjustment up and down while observing the relief valve discharge flow. If the pump is bad, a full stream of oil may possibly be observed when the relief valve is backed off but this stream will greatly diminish or stop as the relief valve setting is increased.
|If a person who understands hydraulic safety and/or hydraulic safety hazards thinks that the preceding recommendation was ill-advised, the best (or worst) is yet to come:
|If the relief valve discharge line cannot be disconnected, a person can place his hand near the discharge opening inside the tank and can detect a large change in the flow volume as the pressure is varied.
|Considering the fact that the oil temperature could be (and will in all probability be) well above 130ºF (54ºC), any person following this recommendation is likely to suffer severe burn injuries.
Oil injection injuries and burn injuries are both extraordinarily severe injuries, which can lead to death! Here is a picture of an operator who was burned whena hydraulic hose, which had been neglected during maintenance, burst, and spewed hydraulic oil - at normal operating temperature - over his entire body. Removing a hydraulic line from a component for the purpose of air-bleeding or testing and running the pump, is, in my opinion, identical to a burst hose - the ends, in both cases, are open, the temperature of the oil, in both cases is unknown, and, the discharge volume and resultant velocity, in both cases, are completely unpredictable!
Moreover, there is no telling where the pressure relief valve return line might be, or, what the respective velocities of the pressure relief valve return line, other return lines might be.
John Deere®, Caterpillar®, and, Tuboscope®'s service and repair manuals aren't the only place where there appears to be a conflict with safety warnings and troubleshooting procedures. Almost ALL machinery and equipment manufacturers, and, component manufactuers make recommendations which involve discharging hydraulic oil to atmosphere. There is overwhelming evidence that manufacturer's troubleshooting and air-bleeding procedures generally collide head-on with OSHA's recommendation. Fortunately for the industry, OSHA inspectors, and corporate safety personnel know little, or nothing, about hydraulic safety - so the problem is ignored!
Machinery and Equipment Manufacturers are both right and wrong!
Machinery and equipment manufacturers, and hydraulic component manufacturers are absolutely right when they warn about the consequences of discharging hydraulic oil to atmosphere. However, they are, in my professional opinion, dead-wrong when they recommend you to test hydraulic components, or air-bleed systems, by "cracking" or disconnecting transmission lines and discharging high-pressure hydraulic oil to atmosphere!
The irony is that there is a safe way to test EVERY hydraulic component, with very few exceptions, while it (they) are situated on a machine without EVER discharging hydraulic oil to atmosphere
There is also a safe way to bleed air out of a hydraulic system without EVER having to discharge hydraulic oil to atmosphere (www.safe-t-bleed.com).
Engineers have a moral and ethical responsibility to design SAFE and environmentally friendly hydraulic systems. Manufacturers have a moral and ethical responsibility to build and sell SAFE and environmentally friendly hydraulic machinery and equipment, and, the person(s) who work on and around hydraulic machinery have a right to be able to service, repair, and troubleshoot hydraulic systems without EVER having to compromise their safety, which they obviously do when having to "crack" connectors to de-energize a hydraulic system, or, remove transmission lines to test hydraulic components.
|Here are common myths that the vast majority of machinery and equipment manufacturers would like you to believe:
|The hydraulic system automatically bleeds down when the power supply is shut off.
Hydraulic system de-energization HAS TO BE independently verifiable. If you cannot verify that the stored energy is depleted DO NOT disconnect a transmission line or remove a component. CALL THE MANUFACTURER!
HERE IS A HYDRAULIC SCHEMATIC FOR A COPPER PRODUCTION MACHINE. THE EUROPEAN MANUFACTURER'S ENGINEERS INSISTED THAT THE HYDRAULIC SYSTEM AUTOMATICALLY DE-ENERGIZES WHEN THE PUMP IS SHUT OFF (Figure 4).
HOWEVER, AS YOU CAN SEE, THERE ARE DUAL COUNTERBALANCE VALVES IN THE CIRCUIT. All counterbalance valves have the inherent capability of trapping oil in a hydraulic component. If a person recommends that you reduce the pressure to its lowest setting, which will remove the stored energy, bear in mind that the lowest setting for the average counterbalance valve is 400-PSI. According to the Occupational Injuries Handbook, injection into the skin can occur at a pressure of 100-PSI.
Ironically, it would be inconceivable for a person to disconnect the oil transmission line from the port in a weight-loaded accumulator because an accumulator is, amongst other things, a storage device for energy.
This, begs the question, what is a vertically-mounted hydraulic cylinder bearing a load with oil trapped between the raised piston and a counterbalance valve? Answer - A weight-loaded accumulator - a storage device for energy!
Safe de-energization and verification of weight-bearing cylinders is absolutely critical!
|If there is stored energy trapped in a hydraulic system carefully crack a connector.
This recommendation is nothing less than fallacious. Loosening the most common hose-end connector in the industry, the JIC 37º type, while it is under pressure, lessens the thread count upon which it relies for strength. While this type of connector is being loosened, the connection is obviously growing progresively weaker. It will eventually reach a point, relative to the internal pressure, at which it will blow off unexpectedly.
Another common connector is the split-flange type, which in my opinion, presents a more serious hazard than a JIC connector. Since it has an O-ring seal which lies in a machined groovebetween the two metal surfaces, loosening the retaining bolt/s, while it is under pressure, to release stored energy is ludicrous.
This type of connector will not submit to leakage until the O-ring seal literally extrudes/bursts. This sudden and unexpected burst of hot pressurized hydraulic fluid exposed to victim to all the safety hazards which manufacturers warn about - including the potential for severe eye injury or eye loss.
A tapered pipe fitting also presents a clear and present danger simply because it is tapered. When a tapered pipe fitting is slowly loosened, not only does it offer continual resistance, but its holding strength rapidly decreases, until it unexpectedly blows out.
|Remove a valve cartridge to release stored energy.
It is hard to believe that a machinery or equipment manufacturer would be so grossly negligent as to tell a person to screw a cartridge valve out of its housing with the objective of removing stored hydraulic energy. In fact, I was recently talking to an applications engineer from one of the largest cartridge type valve manufacturers in the world. I asked what he recommends when people ask for his advice about removing stored energy from the downstream side of a counterbalance valve or a pilot-operated check valve - his reply "very carefully loosen and back-out the cartridge valve." In terms of safety hazards pertaining to hydraulics, this procedure is tough to beat!
This ludicrous practice apparently rears its ugly head in applications wherein a cartridge valve is contained within the body on a hydraulic cylinder typically a counterbalance valve, or a pilot-operated check valve.
NEVER submit to sacrificing your life because an engineer failed to do his/her job properly.
There are hydraulic components in the market place which, are designed for the exclusive purpose of removing stored hydraulic energy, and air-bleeding hydraulic systems, under any circumstances (www.safe-t-bleed.com).
Generally, manufacturers dont use them for two reasons: because no-one is complaining, and, because it erases precious profit!
You do the math!
A manufacturer saves approximately $15.00 (per actuator) for a component, which is designed for the exclusive purpose of saving a life. An injection injury, the size of a pin-prick, will cost $50,000.00 to $70,000.00 in surgery and hospital bills, and, keep you away from work for 5 months to a year while you suffer excruciating pain and undergo months of rigorous rehabilitation!
Machinery and equipment manufacturers warnings are absolutely correct, YOU COULD GET SERIOUSLY INJURED OR KILLED, if you exhaust stored hydraulic energy to atmosphere.
Follow their respective safety warnings to the letter dont exhaust oil to atmosphere under any circumstances! Don't use a piece of cardboard, as recommended by some manufacturers, to find a hydraulic leak - it doesn't work unless can can see the leak, which obviously makes the cardboard redundant! Use a proper microleak detector.
If you are unable to safely remove stored hydraulic energy, and/or verify that the stored energy is depleted CALL THE DESIGNER AND/OR THE MANUFACTURER AND ASK FOR THEIR ADVICE ITS THEIR PROBLEM NOT YOURS!!!
NEVER DISCHARGE HYDRAULIC OIL TO ATMOSPHERE FOR ANY REASON. IF OIL PENETRATES YOUR SKIN YOU WILL BE GOING FOR SURGERY. A HOLE THE SIZE OF A PINPRICK WILL GENERALLY PUT YOU OUT OF WORK FOR 6 - 12 MONTHS AND LEAVE YOU WITH A HOSPITAL BILL TOTALLING $50,000.0 TO $100,000.00. IS IT WORTH IT SIMPLY BECAUSE A MACHINERY OR EQUIPMENT MANUFACTURER SAVED APPROXIMATELY $40.00 UP FRONT? YOU BE THE JUDGE!
IF THE HYDRAULIC SYSTEM YOU ARE WORKING ON DOES NOT COMPLY WITH OSHA'S (MSHA'S) LOCKOUT STANDARD YOU HAVE A RIGHT NOT TO WORK ON IT - EXERCISE YOUR RIGHT! It is most unfortunate that the fluid power industry, OSHA, MSHA, and your own corporate safety personnel "look-the-other-way" when it comes to hydraulic safety.
I find it hard to believe that in the year 2009, hydraulics is still not recognized as an occupational hazard by any institution - other than the Fluid Power Safety Institute™. If you want to know anything about hydraulic safety call us!
Fluid power safety doesnt just happen, it has to be pursued."
Rory S. McLaren
Fluid Power Safety Institute
The Fluid Power Safety Institute welcomes constructive dialogue regarding our safety bulletins. Your comments are welcome.