When performing machine maintenance, it is very important to release the residual pressure (air) inside the machine. This is because accidents such as machine operation due to residual pressure and parts blowing off due to residual pressure can occur. However, at work sites in Japan, it seems that even if the pressure supply to the machine is stopped and the operation of the machine is stopped, inspection work is still carried out without releasing the internal residual pressure. On the other hand, in the US, OSHA standards require that residual pressure be released before inspection work is performed.
This time, we will introduce “residual pressure exhaust”, which is important for ensuring worker safety and efficient maintenance, along with examples.
Unexpected accidents that can occur due to residual pressure
"Residual pressure" is the pressure remaining in a machine after the pressure supply to the machine is stopped. When performing machine maintenance, if the residual pressure is not properly exhausted, it may lead to an unexpected accident. In the past, after turning off the power to the machine and stopping its operation, there was an accident where the machine started due to the residual pressure and the worker was injured. In addition, there have been reports of accidents such as breakage of parts and blow-off due to insufficient residual pressure release work during disassembly maintenance of pneumatic machinery.
For example, in April 2012, there was a joint inspection accident. The content of the accident was that the male worker was inspecting for air leaks in the hose joint without removing the residual pressure. As a result, it is reported that the high-pressure hose came off the joint and the residual pressure spouted out, and the man suffered injuries such as hypercorneal artifacts, right subconjunctival hemorrhage, and retinal concussion.
There have also been reports of accidents due to residual pressure in air cylinders. In the circumstances of the accident, the cylinder transfer unit got caught in the fixed frame, so the power was turned off and the transfer unit was grabbed with both hands. At that time, it was announced that the air cylinder suddenly operated due to the residual pressure in the machine, and an accident occurred in which the left middle finger was pinched.
As you can see from these examples, it can be said that the residual pressure exhaust work is an essential and important work for safe inspection. In addition to turning off the power to the machine, it is necessary to thoroughly exhaust the residual pressure.
Residual pressure release valve that helps prevent accidents
Residual pressure inside a machine that can cause various accidents, such as stopped machine operation, parts blowing off, and dangerous substances blowing out. Proper ventilation prevents these accidents and ensures the safety of workers. It is important to use a dedicated "residual pressure release valve" when releasing residual pressure from the machine.
In particular, a 3-way valve type valve can be used for inspection of pneumatic equipment because it is possible to cut off the pressure supply and exhaust it in one operation. Some can be equipped with a dedicated pressure gauge or pop-up indicator so that the residual pressure can be grasped when the valve is removed from the machine. The operation type of the residual pressure release valve can be roughly divided into three types, and each has a different type of manual type, electromagnetic type, and pneumatic type.
When performing residual pressure exhaust work, it is important to know where residual pressure tends to accumulate. Air tanks, check valves, 2-way valves, closed center 3-position 5-way valves, etc. need attention. When working with multiple people, it is important to use tags to attach warnings such as "There is a risk of residual pressure at this point" and to thoroughly share dangerous areas.
Don't let your guard down even if you stop the machine, be sure to exhaust the residual pressure
At worksites in Japan, there are many cases where the residual pressure inside the machine is not sufficiently exhausted. As explained above, residual pressure can cause parts to blow off, workers to fall, and hazardous materials to be ejected. In order to ensure the safety of workers, it is important not only to stop the pressure supply, but also to thoroughly exhaust the residual pressure.