In a cylinder application, a quick exhaust valve is a simple shuttle valve. This valve allows air that is coming out of a cylinder to be directed to atmosphere instead of flowing back through the directional valve. While this may seem like a simple change in the air release, it can have a big impact on performance. Quick exhaust valves can improve a pneumatic system in three ways: increasing speed, lowering backpressure, and reducing valve size. All of these benefits are achieved without loss in performance because the quick exhaust reduces wasted energy. This translates to savings – in both energy use and wear on your parts.
The speed of a cylinder is determined by where the incoming pressure can overcome the resistance of the load. However, there is a hidden force built into that resistance. That force is the energy needed to get the air on the opposite end of the piston out. The tubing and directional valve restrict this outgoing air until it reaches the exhaust port. This resistance is helpful when trying to slow a cylinder down. Flow control valves meter this outgoing air to control the speed of a cylinder.
Not all applications require this metering, however. Improving the outgoing flow of air in these applications will reduce cycle time. Even a 10% increase in cylinder speed can have a dramatic effect on a machine’s output. This speed can be destructive, so it is important to determine if the increased speed will increase stress on the cylinder, or push other components beyond their safe and reliable limits.
The installation of a quick exhaust valve on a cylinder port can reduce the force required on the incoming side of a cylinder. This can also reduce the pressure on the incoming side. Savings provided by these components aren’t obvious, because the application still uses the same incoming air from the compressor. Savings come from reducing the amount of energy consumed each cycle. Using 60psi instead of the incoming 90psi is a small change, but most pneumatic applications have a high cycle rate. Multiplying small per-cycle savings by the high cycle rate produces a significant savings in the long run. This can result in thousands of dollars in energy savings from lower compressor requirements, and maintenance and capacity savings on the compressor itself.
Reducing valve size
Pneumatic valves are sized based on the flow required to get incoming air to the cylinder and outgoing air to the exhaust port. The limiting factor on valve size is often the exhaust air. This is particularly true on the return stroke of a cylinder where the incoming area of the piston is smaller than the outgoing area. When a cylinder returns there is more air flowing out of it than into it because the rod is taking up some of the space. When the exhaust air is routed to atmosphere before the valve, it allows for the use of a smaller valve in the application.
All three of these factors are centered on reducing inefficiency. The cost of a quick exhaust is a small upfront price to pay for continuous savings on your pneumatic powered equipment.
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