|Topic: Accident related to testing a hydraulic motor.
|Description of the accident:
A millwright suffered eye injury, minor burns, bruises, and abrasions, as a result of an accident he suffered while testing a hydraulic motor. He was following the test procedures that were included in the troubleshooting section of the machine manufacturer's service manual.
|How the accident occurred:
|The victim received a report that a conveyor had stopped unexpectedly and would not respond to the start/stop control switch on the operator's console.
|Upon his initial diagnosis, he noticed that the operating temperature of the oil had increased significantly from a normal of 110º F to approximately 170º F (43º C to 77º C).
|He also noticed that oil was leaking from the shaft seal in the motor.
|He referred to the troubleshooting section in the machine manufacturer's service manual for guidance. It stated that shaft seal leakage is a symptom of excessive internal leakage and gave general instructions on how to execute the leakage test. Here are the recommendations given by the manufacturer to perform the test:
- Disconnect the case drain line from the port at the motor housing.
- Hold the open end of the drain line in a receptacle.
- While holding the line, operate the machine through a load cycle.
- If a small amount of oil exhausts from the line, the internal leakage is satisfactory, and only the shaft seal needs to be replaced.
- If a large volume of oil exhausts from the line, the leakage is excessive, and the motor needs to be replaced.
|He locked the machine out in accordance with his company's lockout policy and proceeded with the test.
|He disconnected the transmission line that was connected to a port in the motor housing.
|The case drain line was too long, so he fabricated a short length of hose with which to execute the test and connected it to the motor. He placed the open end of the hose in an empty 5-gallon oil container.
|He was ready to execute the test, so he removed his lock from the breaker.
|Holding the hose into the neck of the container, he called the operator on his two-way radio and asked him to run the machine through a load cycle. When the test commenced, the conveyor was unloaded.
|As the motor began to turn, he pulled the hose away from the neck of the container so he could see the leakage. A stream of oil began to exhaust from the hose, into the container. According to the victim, at first the leakage appeared to be satisfactory. Then, without warning, the oil began to spray out of the hose with such intensity, that it jerked the hose violently, tearing it out of his hand. It jerked back and forth violently. The oil struck him in the face knocking his safety glasses off as the hose pulled away. As it jerked back the other way, it struck him against the chest knocking him approximately five feet backwards and over the edge of the platform upon which he was standing. He fell approximately three feet to the ground.
|The operator shut the machine off when he noticed the low oil level warning light flashing on the instrumentation console.
What caused the flow to increase so dramatically when the test appeared to be progressing well?:
First, you must understand two fundamental principles applicable to hydraulics:
One, pressure is a function of resistance to flow.
Two, the greater the pressure difference across an opening the greater the flow rate.
When the test commenced, the conveyor was running unloaded, so the system pressure was relatively low. Thus, even if a motor is worn or damaged, the leakage may be minor. However, when the load was placed on the conveyor, the pressure immediately increased to meet the load demand. High-pressure differential can force a large volume of oil through excessive clearances caused by wear or damage.
This is precisely why "testing" ANY hydraulic component to atmosphere can cause severe injury, death, or substantial property damage - IT SHOULD NEVER BE DONE!
Extent of injury:
The victim was taken to a hospital and treated for minor burns, abrasions, and had to have hydraulic fluid flushed from his eyes. He was thankful that he was wearing his safety glasses, because the oil exhausting from the hose hit his face with such brutal intensity, that the rims of his safety glasses bruised the perimeter of his eye sockets.
How this accident could have been prevented:
This motor test is probably one of the most simple, straightforward tests in the industry, and of course, it can be executed with the highest degree of safety - with a flow meter! Although, be aware, a case-flow test can be misleading - it does not always reflect true leakage in a pump or motor.
Training is the most significant vehicle for improving safety in all walks of life. Ignorance is the root-cause of almost all accidents associated with hydraulics, so TRAIN, TRAIN, TRAIN, until there is no more pain!!!
The fact that this test procedure was actually published in a service manual and probably found its way into the hands of who knows how many unsuspecting persons possibly all over the world, is testimony to the fact that ignorance in the fluid power industry is far reaching.
- Safety Information-
It was inevitable that someone following this procedure was sooner or later going to get hurt. However, the recommendations neglected to mention additional crucial safety information which, although not directly related to the task at hand, should always be reinforced:
Lockout and tagout- critical
Safety glasses- critical
Proper diagnostic tools- critical
Proper skills- critical
Names of contacts for technical assistance- important
- Do Not Offer a Compromise-
Machinery and equipment manufacturers will sometimes assume that the customer will not have the proper tools to do the job, consequently, they may offer a compromise. For example, remove a hose and "see" the flow, instead of using a flow meter. Or, crack a line to "see" for pressure, instead of using a pressure gauge. Manufacturers should state emphatically in their verbal and written communication, that if a person does not have the proper training and/or tools, they MUST NOT attempt to do the test. They should also point out the consequences of failing to follow safety recommendations.
- Job Safety Breakdown-
Machinery and equipment manufacturers should provide detailed Job Safety Breakdowns (JSA's) for the machinery they design and build.
- Lead by Example-
A technical representative from a machinery or equipment manufacturer is an extremely influential person. If he/she sets a good example for safety in the field, others will follow. Not only must they abide by their own safety rules and procedures, but they must also respect those of their customers.
If they service a customer's machine, they must have with them the proper diagnostic tools and equipment. If they are working with a customer's personnel, they must continuously reinforce safety, and tell what they are doing and why. The hard-working people in our plants and factories need all the help they can get - if you learn and know, share it with the world!
- Technical Schools and Colleges-
The greatest incubator for safety is where minds, young and old alike, go to learn - the classroom. Fluid power instructors must themselves learn how to execute safe test procedures so they can help others do the same. Teach students the value of safety. Stress it every day and each and every step of the way - and never give up! Demonstrate that you really care about safety, you may save a few lives. What could be more important than that?
|The accidents we report are real, and the victims are real. The safety guidelines we provide are to help companies and individuals work safely with hydraulics. All guidelines we provide are general, and are not intended for one specific hydraulic system or machine.
WHEN YOU PURCHASE HYDRAULIC-POWERED MACHINERY AND/OR EQUIPMENT, WE HIGHLY RECOMMEND THAT ONCE YOU DETERMINE THAT IT CAN DO THE WORK YOU WANT IT TO DO, YOU THEN DETERMINE HOW MUCH SAFETY HAS BEEN BUILT INTO IT BY THE MANUFACTURER. IN ADDITION, WE RECOMMEND THAT YOU, WITH THE INPUT FROM YOUR OPERATORS, MECHANICS, ENGINEERS, PRODUCTION PERSONNEL, AND SAFETY DEPARTMENT, FORMULATE A LIST OF MINIMUM SAFETY STANDARDS FOR THE EQUIPMENT YOU PURCHASE. ALTHOUGH WE LIKE TO BELIEVE THAT MOST MANUFACTURERS ARE CONCEREND ABOUT SAFETY, SOME BELIEVE THAT CERTAIN SAFETY MEASURES ARE AN UNNECESSARY EXPENSE. WE FURTHER RECOMMEND THAT ALL THE SAFETY STANDARDS AND RECOMMENDATIONS THAT YOU DEVELOP SHOULD BE REVIEWED BY YOUR SAFETY DEPARTMENT, ENGINEERING DEPARTMENT, AND BY THE RESPECTIVE MACHINE OR EQUIPMENT MANUFACTURER PRIOR TO MAKING THEM POLICY - TOTAL SAFETY CAN ONLY BE ACHIEVED WITH A TEAM EFFORT.
|The Fluid Power Safety Institute does everything possible to insure that the information and drawings contained in these documents is accurate, and the procedures are deemed safe and reliable. However, these are general recommendations only and might not be applicable to all situations.
You MUST have your engineering department and service department read these recommendations and make the necessary changes for your specific application.
The Fluid Power Safety Institute is not responsible for actions taken by untrained and/or unauthorized persons. ALL hydraulic system service, repair, and troubleshooting should be done by trained, authorized persons ONLY.