Another Untrained Mechanic Is Almost Killed While "Testing" A Hydraulic Cylinder

An untrained mechanic and a hydraulic flow meter - a lethal combination!

Most maintenance people’s hydraulic diagnostic skills are acquired at the college of trial and error. Ironically, even the companies who design and manufacture flow meters don’t fully understand how, and where, to use their products to test hydraulic components safely and effectively.

The proper and safe use of a flow meter can only be achieved if a person is thoroughly trained in three disciplines:

1. Hydraulic safety.

2. Basic hydraulic laws and principles.

3. How to test hydraulic systems and components.

1. Hydraulic Safety - Hydraulic systems present a wide variety of unique safety hazards. An awareness of these safety hazards can only be garnered through training that focuses on all aspects of hydraulic safety.

2. Basic Hydraulic Principles and Laws - Every element of hydraulic component and system function is, in one way or another, tethered to a basic hydraulic principle or law. These principles and laws CANNOT be learned through on-the-job training - or more appropriately; trial-and-error.

3. How To Test Hydraulic Systems and Components - Once a person has a thorough understanding of hydraulic safety; principles and laws that govern hydraulics; the purpose of the primary components in a hydraulic system; and finally, the theory-of-operation of each of the primary components, they are ready to advance to learning and understanding how to execute safe and meaningful diagnostic procedures.

One of the challenging aspects of testing the volumetric performance of hydraulic components is knowing what the normal leakage rates of hydraulic components are. The question is: "how is it possible to determine what abnormal leakage rates are, if you don't know what normal leakage rates are, to begin with?"

This is again, where the hydraulic industry fails dismally. The few technicians that have instruments to test leakage, usually have no idea what they are looking for because they may not know what particular pump's volumetric efficiency is. Accordingly, if they don't know what normal is, they will have difficulty figuring out when a particular pump's leakage becomes marginal, and then unacceptable. It's safe to say that 99% of the time hydraulic components manufacturers leave the decision as to when to retire a hydraulic component at the discretion of the end user - very confusing to say the least!

In my book, "Performance Testing Hydraulic Components Using Leakage Path Analysis Methods," I provide normal, marginal, and unacceptable leakage rates for ALL hydraulic components.

Ironically, while the “health” of hydraulic components is determined by analyzing leakage rates, there is little or no comparative data available to support a technician’s findings.

In fact, while the industry marches out of step with regard to safety, it appears to march in-step with regard to component testing. For example, the entire industry embraces the case flow test for hydraulic pumps and motors. Yet, the so-called “case flow test” has a 95% margin of error. This proves that the vast majority of so-called “test procedures” floating around the industry are “plagiarized.” It is blatantly apparent that no-one has paused to question the merits of the many component test procedures.

Case In Point

A mechanic, with no formal training in hydraulics, was asked by his supervisor to determine why the bucket on the company’s front-end loader was drifting down when the directional control valve was in neutral. Although he had never personally used a flow meter, he had, during the course of his career, watched a person use a flow meter to test a pump. He found an inline, analog type, flow meter lying on a shelf, so he cleaned it off, installed the adaptors he needed to install the flow meter in the transmission line at the most accessible point, which in this case was the rod-end of the cylinder. He had no idea that the flow meter was designed to permit flow in one direction only. This was not shown anywhere on the flow meter, which is, in and of itself, a "failure to warn" issue.

Note: A flow meter is not the correct instrument for testing hydraulic cylinders. A MicroLeak test makes it possible to test cylinders with the power safely isolated. The test takes only 15-minutes.

Caution: Flow meter manufacturers (in-line analog type) generally do a very poor job of indicating whether a flow meter is a uni-directional type or a bi-directional type.

After the mechanic installed the flow meter, he asked the operator to start the machine, and cycle the cylinder so he could observe the flow meter. When the cylinder rod was retracting, all seemed well. As soon as the operator extended the cylinder rod, there was a thunderous explosion. Oil spewed from the cylinder at extreme velocity and pummeled his body. The force of the oil literally “blew” his hard-hat and safety glasses off, and filled his eye sockets with hydraulic oil.

The operator shut the machine down and rushed to his aid. The mechanic was fortunate in that he did not (this time) suffer a lost time injury. The mechanic initially thought the hydraulic hose had burst. Upon inspection, he found there was a gaping hole in the flow meter. Of course, he had no understanding why.

His supervisor, who was as equally ignorant about hydraulics as the mechanic, simply wrote the failure off as a being caused by a "defective flow meter." The company never conducted a formal investigation to determine the root cause of the failure. Moreover, even though the company had a near-miss reporting program, the accident was never recorded as a near-miss.

There is no doubt that training would have prevented this accident.

A course in basic hydraulics would have taught the mechanic about force, pressure, and area as it applies to a hydraulic cylinder. He would have learned that a double-acting, single rod hydraulic cylinder is, in addition to being a device which converts fluid energy into linear mechanical energy, is also a device, which can amplify flow and pressure.

Incidentally, less than 1% of America's technical colleges teach students how to use electronic flow meters. Ironically, over 99% of college's automotive departments teach students how to use state of the art tools and equipment like electronic wheel alignment, digital analyzers, etc.

Hydraulic system design engineers totally ignore the fact that hydraulic systems must be to incorporate ways that make it possible for technicians to safely perform routine component performance testing. Moreover, there is only one way to determine the volumetric efficiency of a hydraulic pump scientifically; and safely, and that's with a flow meter, which is equipped with a load cell.

Let me explain how a double-acting single rod cylinder amplifies pressure.

Let's say that a given cylinder has a rod-to-bore ratio of 2:1. This means that the major area of the cylinder piston is 10 square inches (25.4 cm) and the minor area is 5 square inches (12.7 cm). Let's also say that the system's pressure relief valve is set at 3000 PSI (207 bar).

The formula for cylinder force is: FORCE = PRESSURE x AREA, then 3000-PSI (207 bar) X 10 square inches (25.4 cm) = 30,000 pounds (1360.7 kg).

Now, let's focus on pressure. If the formula for pressure in a cylinder is: PRESSURE = FORCE ÷ AREA, and there are 30,000 pounds (1360.7 kg) pushing on the confined liquid in the rod end of the cylinder, if the piston's minor area is 5 square inches (12.7 cm), then the pressure is 6,000 PSI (414 bar).

Untrained people have no clue what they get themselves into when they "test" hydraulic components without the proper training. In this case, the maximum pressure rating of the flow meter was 3000 PSI (207 bar), and the untrained mechanic unknowingly subjected it to 6000-PSI (414 bar). Bear in mind, test equipment is always within an arm's length from a mechanic's face.

Here Is What Happened -

The type of flow meter the victim used was equipped with an internal check valve, which permitted flow in one direction only (see schematic below). When the operator was instructed to cycle the cylinder – retract and extend the rod – the check valve blocked the flow causing the pressure in the rod end of the cylinder to amplify to twice it's maximum rated pressure.

The photographs below show how the extreme pressure literally “blew” a gaping hole in the flow meter.

CONCLUSION:

Over 99% of America’s maintenance workforce that work on and around hydraulic systems have never received training in hydraulic safety. Over 80% have never received formal training in fundamental hydraulic.

Warning - Despite what the so-called "experts tell you, NEVER "test" hydraulic components by discharging hydraulic oil to atmosphere - it could severely injure or kill you. I have many more articles coming up that will make that abundantly clear.

If the college you are attending teaches you to "test" hydraulic components by discharging hydraulic oil into a "bucket," the instructor is literally teaching you how to injure or kill yourself.

If your supervisor refuses to purchase a flow meter because the irresponsible machine supplier recommends testing hydraulic components into a bucket, ask the supervisor if he/she is going to take volt meters away from the electricians. Moreover, if your supervisor tells you to "test" any hydraulic component, knowing full well you are not properly trained to perform the task, hand write a note to the effect, and have the supervisor sign it. If a supervisor is willing to sacrifice you to the production God's, you might just as well make it official.

If a machine or equipment manufacturer provides warnings about discharging oil to atmosphere stating that it can "cause severe injury, death, and/or severe property damage, and then tells you to "test" a hydraulic component by discharging oil to atmosphere, if, while you are executing the test, you get blasted in the face with hydraulic oil, take the warning, along with the procedure, to an attorney. I believe you have a good "ignored duty of care" case.

If you are not trained in hydraulics DO NOT work on hydraulic systems. It's only a matter of time before I will be writing a similar article about you.

Respectfully