Pneumatic Quick Exhaust Valves

A pneumatic quick exhaust valve (QEV) is a specialised component used in pneumatic systems to increase the speed of a cylinder's return stroke by providing a rapid path for exhaust air. Also referred to as a quick-release valve, the QEV bypasses the directional control valve, allowing the compressed air to exit the cylinder directly into the atmosphere, rather than travelling back through the entire system. This significantly reduces backpressure, improving the overall performance and speed of the cylinder.

RS Australia offers a wide range of these valves, including options for high-pressure applications, to meet the needs of any industrial setting.

How Does a Pneumatic Exhaust Valve Work?

A pneumatic quick exhaust valve works by providing a direct and rapid escape path for compressed air from a pneumatic cylinder. The QEV is installed as close as possible to the cylinder's exhaust port. When the cylinder's piston rod is driven forward by compressed air from the control valve, a small amount of air pressure builds on the exhaust side of the cylinder, causing the internal shuttle of the quick exhaust valve to shift.

Once the directional control valve is shifted to its return position, the pressure on the drive side is vented. The pressure on the exhaust side, now higher than the drive side, forces the valve's shuttle to switch, opening a large port directly to the atmosphere. This allows the air to vent quickly and directly, significantly increasing the piston's retraction speed and overall cycle rate.

Types of Pneumatic Exhaust Valves

While all quick exhaust valves serve the same primary function, they are designed in different ways to suit specific applications and environments.

High-Pressure Quick Exhaust Valve

A high-pressure quick exhaust valve is specifically engineered to handle higher operating pressures than standard models. This type of QEV is constructed from robust materials and features a more durable design to withstand the greater forces and stresses associated with high-pressure systems. They are also crucial in heavy industrial applications where machinery operates at elevated pressures and a faster return stroke is still required for efficiency.

Adjustable Exhaust Valve

An adjustable exhaust valve provides the ability to control the rate at which air is exhausted from the cylinder. Unlike a standard pneumatic quick exhaust valve that vents air as quickly as possible, this type allows the user to fine-tune the speed of the piston's return stroke. This is particularly useful in applications where a rapid but controlled motion is necessary to prevent damage to the equipment or to precisely manage a process.

Connection Types

A pneumatic quick exhaust valve can be connected to the rest of the pneumatic system in several ways, including:

Female Thread: This is a common connection type where the quick exhaust valve has a female thread on its input and output ports. This also allows it to be screwed onto a male-threaded pipe or fitting, creating a secure and reliable connection.
Male Thread: A less common option, a male-threaded valve is screwed into a female-threaded port on another component, such as a cylinder.
One-touch Fitting: Also known as push-to-connect fittings, these allow for quick and easy tube insertion and removal without the need for tools. This type of connection is popular for its speed and convenience in applications where components are frequently reconfigured.
Tube: Some valves are designed to connect directly to tubing, either by a barbed fitting or by a push-in mechanism. These types of connections are ideal for applications with limited space or where a direct and simple connection is required.

Different Threaded Connections

Threaded connections are crucial for ensuring a secure and leak-free fit in a pneumatic quick exhaust valve. Here are some of the threaded connections you’ll usually encounter:

BSP / G Thread: This is a British Standard Pipe thread, where G-threads are parallel threads (BSPP - British Standard Pipe Parallel). This is also a very common standard in Australia and many other parts of the world.
NPT Thread: This stands for National Pipe Taper, a US standard. NPT threads are tapered, meaning they get tighter as they are screwed in, creating a seal. However, they are not interchangeable with BSP threads.
R Thread: This refers to a tapered male thread (BSPT - British Standard Pipe Tapered) that is often used in conjunction with Rc or Rp threads.
Rc Thread: This is a tapered female thread, used to create a pressure-tight seal when connected to an R thread.
Rp Thread: This is a parallel female thread, also used in conjunction with an R thread, which requires an additional sealant to create a pressure-tight connection.

Main Features of a Quick Exhaust Valve

A pneumatic quick exhaust valve has several key features that make it an essential component for optimising cylinder speed and efficiency:

A range of body materials, including forged brass, die-cast aluminium and nickel-plated brass
Industry-standard threads, BSPP, BSPT, NPT or Metric
Available with built-in silencers
A broad range of operating pressures
Available with ATEX approvals

Industrial Applications for Quick Exhaust Valves

Pneumatic quick exhaust valve systems are utilised across a wide range of industrial applications.

Oil & Gas

In the oil and gas sector, these valves are used to control the movement of large actuators and valves. The fast-acting nature of a pneumatic quick-release valve ensures that processes can be stopped or started rapidly.

Automation & Manufacturing

In automation and manufacturing, quick exhaust valves are integral to assembly lines and robotic systems. By improving the cycle time of pneumatic cylinder parts, they allow for faster production speeds.

Chemical Processing

In the chemical industry, QEVs are used in various control applications, including the operation of dampers. Their robust design, including options for a high-pressure quick exhaust valve, makes them suitable for handling a variety of fluids and environmental conditions.