FLUID POWER SAFETY INSTITUTE™ - Instructor Safety Bulletin

(Ref. No: ISB-002)

TO: All fluid power institutions, instructors, trainers, and consultants.

FROM: The Fluid Power Safety Institute™.

SUBJECT: Accumulator Safety - ball valves and "sound" don't cut the mustard!

ACCUMULATOR SAFETY -
Here are two examples of hydraulic systems that are designed with no means of verifying zero-energy state, other than by "noise."

EXAMPLE #1 - Rail-car, coal-loading facility:

This photo (opposite) shows four of six, 15-gallon accumulators that are incorporated in a hydraulic system that operates a rail-car, coal-loading facility.

The six massive accumulators provide the oil that operates the numerous actuators that operate the many gates and doors that distribute and unload the coal that is contained in large hoppers.

They also provide the stored energy that is critical in the event of an electrical power outage.

Located at the base of each one of the accumulators is a manual, lever-operated, two-way valve. The purpose of these valves is to provide a means to manually bleed-off stored energy to facilitate service or repair work.

According to the machine manufacturers recommendations, the steps for making the machine "safe" to work on are:

1. Lockout the prime mover.

2. Open the two-way valves and bleed-off the accumulators.

3. Proceed with the service or repair work when you can no longer hear the noise of the oil passing through the two-way valves.

EXAMPLE #2 - Giant earth-moving machine:

This photo (opposite) shows two 10-gallon accumulators that are integrated into the steering and braking systems of a giant, rubber-tired, earth-moving machine.

The accumulators in this hydraulic system are designed to automatically bleed-off approximately 60 seconds after the engine key-lock switch is turned off - providing there is electrical power. This is accomplished with an electrical timer, and an electrical solenoid-operated valve.

There are a number of inherent safety flaws in this design:

1. The use of an electric, sliding-spool, solenoid-operated valve for de-energizing a hydraulic system is not recommended, especially if de-energization is not verifiable. Sliding-spool valves have the inherent capacity to seize due to the dynamics of high pressure, silt, and small clearances.

Spool seizure is most likely to occur when pressure is held against a closed valve, for extended periods of time.

2. If the master switch is disconnected within 60 seconds of shutting off the engine, the automatic bleed-off system is rendered inoperative. This can easily occur because the master switch is located within three feet of the operator's cab.

If the operator turns off the key-lock switch, climbs out of the cab and turns off the master switch, the bleed-off system does not activate.

3. If the solenoid-operated, bleed-off valve fails to operate, there is no pressure gauge to show that there is stored energy in the system, and there is no redundant, back-up manual bleed-off system.

4. Bleed-off and verification is determined by "sound."

There are a number of convincing reasons why hydraulic system de-energization by "ear" could lead to severe injury or death:

1. If a person is wearing mandatory hearing protection, and does not hear the sound of the system de-energizing - there is no means of verification.

2. If a person is hard of hearing.

3. If the hand-lever on the two-way valve is stripped at the stem and fails to rotate the valve to the open position when the handle is turned (the damage is not always visible as the mechanism is generally covered with a washer).

4. If the two-way valve handle is removed and re-installed at a 90º angle from its original position ("open" is now "closed", and "closed" is now "open").

5. If a person opens the valve, hears the system bleed-down, and then leaves the area. A colleague is now assigned to the job but is unaware that the system has been de-energized. He/she opens and closes the two-way valve - no sound, and leaves the hand-lever in the "open" position. However, "open" is "closed" because the handle configuration was inadvertently changed.

Without any means of verification, the person assumes that the system is de-energized, and proceeds with the service work – the result, an accident!

Conclusion -
This Safety Bulletin provides further evidence of the safety problems facing the fluid power industry. As long as there are no safety design standards, there will be potential for accidents.

For the folks who design hydraulic systems, here are a few "do's" and "don'ts":

DO! Make sure the hydraulic system is designed to comply with OSHA’s standard for lockout with respect to de-energization and verification.
(Reference OSHA 3120)

DO! Design-in independent and reliable components to facilitate safe de-energization and verification. Include connect-under-pressure (CUP) connectors that permit the installation of a "master" pressure gauge to verify de-energization.

DO! Include detailed information on exactly how to de-energize a hydraulic system in the service and repair manuals.

DO! Specify manually-operated valves as opposed to solenoid-operated valves for de-energization. They are far more reliable than electrically-operated valves. Sliding-spool, solenoid-operated valves are prone to seizure due to silting.

DO! Specify manual valves with zero-error installation, angled hand-levers to avoid installation confusion.

DO! When using an "any-angle" hand-lever install, two-way valve, provide an illustration showing the relationship of the handle to the stem. This will avoid costly mistakes whenever re-installing a handle becomes necessary.

DO! Assume that the person who is going to work on the hydraulic system is untrained - design accordingly!

DON'T! Leave de-energization to chance. It must be safe and verifiable.

DON'T! Recommend "cracking" a connector to de-energize a hydraulic system. This standard, acceptable practice, is extraordinarily hazardous, and can lead to severe injury or death.

For the folks who work on and around hydraulic systems, here are a few "do's" and "don'ts":

DO! Consult with your safety department if you cannot find a way to safely de-energize a hydraulic system. DO NOT subscribe to "noise" as a means of verification - it is unsafe!

DO! Report to an emergency room if you ever get injected with hydraulic fluid - regardless of how insignificant the wound appears.

DO! Ask your supervisor to provide hydraulic safety training for you. If your supervisor declines, submit a letter of request to management. Place a copy of the request in your personnel file at work, and keep one at home. Remember, there are "supervisors" out there who believe that training is a waste of money - your safety is their responsibility!

DON'T! "Crack" a connector to de-energize a hydraulic system. It can lead to severe injury or death.

DON'T! Try to de-energize a hydraulic system by trial-and-error. If there is no safe, prescribed way to do it, consult your safety department or the machine manufacturer.

DON'T! EVER follow a manufacturer's recommendation to screw out a cartridge valve under pressure to de-energize a hydraulic system - this practice WILL kill you!

If you have machines that are similar in design to the ones discussed in this safety advisory, they are unsafe - bring this matter to the attention of your safety department, or safety committee immediately.

Waiver of Liability -

The Fluid Power Safety Institute™ does everything possible to ensure that the information and drawings contained in this safety notice are accurate, and the suggested 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 in conjunction with your safety department read these recommendations and make the necessary changes for your application.
The Fluid Power Safety Institute™ is not responsible for actions taken by untrained and/or unauthorized persons.
Trained, authorized persons only should do ALL fluid power system service, repair, and troubleshooting.