For control valves that are mainly used for clutches/brakes in press machines, we recommend the "monitored double valve", which is essential in the United States and Europe, where safety management standards are high. By using a double valve with a monitor, it is possible to prevent accidents that cannot be prevented by workers' attention alone. Here, we will introduce how the double valve with monitor ensures safety compared to the conventional single valve and double valve without monitor.
Difference between single valve and double valve without monitor at the time of mechanical failure
First, let's compare how a single valve and a double valve without a monitor behave in the event of a failure.
Most failures in valves are valve body failures. In other words, it refers to a state in which the valve that plays the role of switching the supplied air stops working due to some kind of malfunction. This fault occurs both when the machine is switched ON and when switched OFF.
Failure when ON
ON failure is a failure in which the valve does not operate when the machine power is turned ON. In this state, air does not pass through the valve, so energy is not transmitted to the press. Therefore, the press does not operate and remains stopped. This is a characteristic common to both single valves and double valves, and any valve that fails when ON does not pose a risk of accident.
Failure at OFF
A failure at OFF is a failure in which the valve does not operate when the machine in operation is turned OFF. Differences in the operation of the press after failure appear between single valves and double valves. If the valve is not closed with a single valve, the air will continue to flow to the press and the machine will not stop. On the other hand, with double valves, even if one valve fails, the air can be exhausted from the other valve, ensuring safety by not transmitting energy to the press. This is a unique characteristic of a double valve that has two valves in one valve.
In this way, it can be seen that the double valve, which can ensure safety in the event of a single valve failure, has higher safety performance than the single valve.
Difference between without monitor and with monitor
As mentioned above, the double valve can safely stop the press even if one of the valve discs fails, but there is still the risk of overlooking the failure if the monitor is not installed.
When a double valve fails, it is easy to detect the failure on the spot if it fails when the valve is ON, and the machine does not operate, so you will know that immediate repair is required. On the other hand, in the case of an OFF-time failure, the valve is stopped with one side open, so when the power is re-energized, the valve on the normal side opens and the press can operate normally. This condition is very dangerous and may lead to a serious accident when the remaining normal valve is broken.
However, even if a failure occurs when the switch is OFF, it is not impossible for a person to detect it. Since air is continuously exhausted from the exhaust port in the event of an OFF-time failure, it can be confirmed in the form of an "air leak." However, if you don't look carefully at the valve, it's difficult to find an air leak, and if the valve is high up or the surroundings are noisy, discovery may be delayed. There have also been reports of dangerous cases of continued operation for some time in this state.
A double valve with a monitor is equipped with a function to detect failure of the valve body in both ON failure and OFF failure, and a function to prevent start-up when power is re-energized. Because the restart prevention function prevents the machine from running after a valve failure, it can be said to be safer than double valves without a monitor. In addition, since it will notify you of the failure, you can immediately send it for repair.
In order to protect the safety of workers in factories, it is important to install mechanisms with higher safety performance. A high degree of safety can be ensured by introducing a double valve with a monitor for the control valve of the press machine. Ross Asia's double valve can be retrofitted with a monitor, so if you are using a non-monitor double valve, please consider upgrading to a monitor that improves safety.