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Hydraulic System Safety: Assuming Will Cause Trouble ben lee

Counterbalance valves are an area that many of our clients are interested in. We’re not really sure why, but it’s a fact. If you’re new to this field, then let’s get you on the same page.

 

Counterbalance valves operate as safety devices. If pressure is lost in a line going to the cylinder, then they will stop a load from dropping. They will allow fluid to flow the one direction into the cylinder, but will prevent it from coming back out again unless there is an inversely proportional pressure in the pilot line of the valve. Although it’s possible to swap this this valve out with a pilot operated check valve, the method of checking for proportion is what keeps movement smooth as the cylinder piston retracts.

 

With the pilot operated valve, there will be some ‘chatter’ as it retracts. Although the counterbalance valve is useful and widely popular, there are some concerns with it. For example, over in the USA there has recently been a safety alert issued on the Fluid Power Safety Institute website by Rory McLaren. It’s been discovered that the counterbalance valve can create a form of deception when pressurized fluid is trapped between the cylinder and the directional valve.

 

With regards to safety, we understand that there was an incident with an engineer and a leaking rod seal. Following all the necessary safety precautions, the engineer needed to lower the load by shifting the directional valve, then de-energize the hydraulic power unit. He then needed to remove the power unit from the application as he was guided by the company’s hydraulic system maintenance process. Imagine his surprise to witness a high-velocity jet of fluid shooting out of the fitting that he was loosening.

 

Assuming that the lowering of the load would take out all the pressure from the hydraulic line makes sense. However, the counterbalance valve being in the line between the valve and the cylinder can create problems. Even if the cylinder is in the rest position with the machine shut off the pressure setting in the counterbalance valve is at its lowest pressure.

 

Unfortunately in the above situation, the pressure was set in the counterbalance at 1200 psi which means that the shot of oil is going to be expected. Although the engineer was injured, he fortunately, wasn’t killed by it – although this is an outcome that would have been entirely possible.  His action should have been to check that each of the lines were depressurized prior to opening them to atmosphere.

 

Here are our tips to ensure that you’re safe when performing this type of hydraulic system maintenance: 

 

1.   Take necessary actions and verify that the lines have been de-energised.

 

2.   The written maintenance process needs to contain a step to safely remove any pockets of hydraulic energy in the system. If there is a chance that the pressure could re-accumulate, then take steps to check that isolation is in operation until you have completed your maintenance or servicing or until it’s simply not possible for pressurisation to occur.

 

3.   Make it mandatory for all hydraulic system personnel to have lockout and de-energisation training.

 

4.   Create a written safety process for both lockout and de-energisation of machines.

 

5.   Schedule drills for de-energisation and lockouts to verify that all staff know what to do to make the machine safe to work on. Some situations can be more complex as more than one machine may need to be locked out for maintenance purposes.

 

6.   Make it a punishable offence to ‘crack’ connectors in order to remove stored energy.

 

7.   Don’t risk your life by tampering with a hydraulic machine that is not designed to safely de-energise. Don’t follow instructions to crack a connector as this could kill you.

 

8.   When purchasing any new machines, look for those that have de-energisation functions or facilities.

 

9.   Contractors will need to obey all safety rules and they should have a history of training and certification. This is particularly vital if they have been brought in for their skills and to mentor your employees.  You don’t want your employees picking up any behaviours that are not considered to be industry best practice.

 

Summary

All hydraulic machines must meet safety regulations when it comes to lockout and de-energisation.

If for some reason you cannot remove the energy from the system, then call the manufacturer for guidance. This is not the type of situation where you can use guesswork, or you could even lose your life or health when pressurised oil penetrates your skin.  Hydraulic systems can be dangerous with fatal consequences when not used correctly.




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