Although any "bang bang" valve is a valve that moves between two different positions (open or closed), it also applies to valves with three positions, such as a 4 / 3 solenoid operated directional valve. But in some cases, a true on-off valve provides the best solution to the problem.
The process industry uses the term "on / off" to describe a gate valve, ball valve, or butterfly valve simply to open or close the flow path. For fluid power systems, the 2 / 2 term is more common, describing a 2-way, 2-position valve, although the method of operation is not specified.
From a mechanical point of view, the most effective 2 / 2 valve is a poppet design that provides a low leakage seal over a wide pressure range and is easy to manufacture. The spool valve provides a smooth response, but it performs better in applications requiring metering or partial flow, such as proportional valves. However, since the clearance between the spool valve and the valve body must be sufficient for it to move smoothly, the spool itself is more likely to leak.
Two way two position valve has many uses in hydraulic circuit, but one of the more common applications is electric unloading valve. For the hydraulic system operated by fixed flow pump, closed center hydraulic circuit can be used. When the downstream valve is in the central position, the normally open 2 / 2 valve of the pump tee acts as the discharge valve, such as in conjunction with the pressure compensation pump.
Even if the fixed pump and discharge valve combination does not replace the variable displacement pump, it allows you to use a closed center valve, which has a better flow rate than a tandem center valve, which moves from pressure to the tank in neutral. The pressure drop of the tandem center valve accumulates with the number of valves in series, increasing the pressure drop across each valve. Compared with variable displacement pump, the combination of discharge valve and fixed pump can save thousands of dollars, making it a suitable alternative.
The drain valve can also be used for safety applications in different locations. The accumulator safety block will use a 2 / 2 normally open valve to drain the accumulator energy into the tank in case of power failure. Stored hydraulic energy is dangerous, especially if the technician is not aware of it. A similar discharge valve is used in the safety circuit of hydraulic press. A normally open drain valve will be parallel to the cylinder head bore of the press to discharge the pressure into the tank in case of emergency, preventing the possibility of accidental downward movement of the press under power.
On off valves are ideal for any application that requires fast switching between shut-off and flow. They can be installed on or inside the manifold block, or manufactured in inline valve bodies of different sizes and flows.