What are the precautions for double valve failure?
Double solenoid valves for clutches and brakes for press machines have a double internal structure in consideration of safety. In fact, double valves have a point of caution that is often overlooked . From here, we will check the precautions for failure while looking at the diagram of the structure/operation of the valve.
Press Structural Standards/Japan (Revised in 1978)
(solenoid valve for clutch or brake)
Article 27 Mechanical presses that control clutches or brakes by pneumatic or hydraulic pressure shall be equipped with solenoid valves that comply with the following items. (Omitted below)
It must be a one-and-a-half type.
Must be a secondary closed type .
(3) Those controlled by air pressure shall be pressure return type .
(4) Those controlled by hydraulic pressure shall be of the spring return type.
With the single valve, if the valve fails to close after the power is turned off, the machine will not stop, and there is a danger that the press operator will be caught in a dangerous situation.
On the other hand, the double valve stipulated by the structural standards has a double structure of the valve body. When power is turned ON/OFF to the valve, the A/B valve discs open/close almost simultaneously.
Therefore, even if the B side fails (does not close when the power is turned off), the A side will close and the secondary side air will be exhausted reliably. The role of the double valve is to ensure exhaust even if one side fails.
At first glance, it is a double valve that looks safe. Some people may think that the double valve will automatically "stop" if it breaks down. In fact, the double valve will operate when the power is re-energized even if the B side is in a failed state. This is the same situation as operating with a “single valve” with only the normal A side opening and closing.
If you continue to operate with the B side broken, the normal A side may also break down at any time. And if both A and B fail...
Even double valves may cause the press to stop. Therefore, if one of the valve discs fails, it needs to be inspected and repaired as soon as possible. In fact, there are signs of a failure with one-sided return failure! Is it happening in your factory? Air leak from double valve exhaust port! This air leak is a sign of failure.
Air leaks should be noticed as soon as possible, but at actual manufacturing sites, they are difficult to detect for the following reasons...
There is a function that the valve itself will notify you of failures (recovery failure when the power is turned off) that are not usually noticed. That is a double valve with a monitor (monitoring device)! ROSS introduced the first monitored double valve in 1954, long before the standard was established.
Representative product of ROSS Double valve with monitor (monitoring device)
