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Function and Applications of Exhaust Valves

Exhaust valves increase the return speed of pistons in pneumatic cylinders by directly venting air at the cylinder's stagnation point. In industrial applications, targeted venting reduces dynamic air cushions, minimizes delays during piston reversal, and increases process cycle rates without additional control air or complex pneumatic valves. On your machine tool, robot axis, or packaging line, suitable exhaust valves ensure more precise end positions, reduced downtime, and consistent cycle times.

Principle and Designs

The basic principle is simple: a passage is restricted in the closed state so that when air flows in, it guides the piston in a controlled manner. When switching or depressurizing, the exhaust valve opens a defined exhaust path, which removes back pressure. Designs vary depending on the installation position and required exhaust performance: straight versions for inline mounting, L-shaped models for lateral accessibility, and compact angled variants for confined installation spaces. Parker Legris supplies these designs in standardized connection sizes that can be directly integrated into existing pneumatic lines.

Materials, Connections, and Seals

Material selection influences corrosion resistance, temperature range, and mechanical load capacity. Options include nickel-plated brass for high mechanical stability and moderate corrosion resistance, stainless steel (AISI 316/304) for aggressive environments and increased temperature resistance, and aluminum alloys for low mass with limited corrosion exposure. Connections are typically threaded sizes according to ISO/UNF or metric threads, and push-in or plug-in connections for flexible polyurethane and nylon tubes. Seals are usually made of NBR for general applications, FKM (Viton) for high temperature and oil resistance, or EPDM for good resistance to steam and many chemicals. The right combination of material, connection, and seal determines service life and fault-free operation.

Performance Criteria and Selection Criteria

Key parameters include flow coefficient (Cv or Kv), response time, maximum operating pressure, temperature range, and size. Parker Legris exhaust valves are designed to ensure defined release flows with minimal pressure loss. When selecting, ensure compatibility between the cylinder's operating pressure and the valve's nominal range; equally important is matching the flow performance to the cylinder cross-section and required piston speed. In pneumatic circuits, a valve that is too small reduces the exhaust effect, while an oversized valve can cause unwanted pressure conditions.

Application Examples – Structured Practical Cases

Example 1: Injection Molding Machine – Accelerated Piston Return
In an injection molding machine with an 80 mm cylinder diameter, delayed piston return occurred, increasing scrap. The installation of a Parker Legris nickel-plated brass exhaust valve with high flow characteristics at the cylinder end reduced return resistance and lowered the cycle time by 12%. Thanks to the nickel-plated surface, the valve remained impervious to corrosion even with fine cooling lubricant mist.

Example 2: Packaging Line – Space-Saving L-Shape
On a high-speed packaging machine, lateral space was limited. A Parker Legris L-shaped exhaust valve in stainless steel was used to keep the exhaust opening laterally accessible. The stainless steel design ensured reliability in the humid production environment, and the suitable FKM seal ensured resistance to oil vapors in the system.

Example 3: Robotic Handling – Precise Repeatability
In a pick-and-place robot, air cushioning in the gripping cylinders led to positional inaccuracies. The solution was a compact Parker Legris exhaust valve with a push-in connection, connected to a 6 mm polyurethane hose. The reduced back pressure improved the end position accuracy of the grippers by 0.3 mm, without the need for additional control logic.

Installation, Mounting, and Maintenance

Mounting is preferably in the exhaust direction towards open space, free from deposits and with sufficient accessibility for later maintenance. For threaded connections, the use of suitable sealants (PTFE tape or liquid thread sealant) compatible with the seal in the valve material is recommended. Filters before the exhaust valve protect against particulate dirt; regular visual inspection for corrosion, plus functional testing of the exhaust opening, reduces the risk of failure. For applications with aggressive media, the use of stainless steel and FKM seals, as well as cleaning and inspection interval documentation in the maintenance plan, is recommended.

Compatibility with Pneumatic Components

Parker Legris exhaust valves are designed for use in standard pneumatic systems and can be combined with cylinders, valve islands, and service units. Pay attention to matching the nominal size: valve connection, internal pipe diameter, and nominal cross-section of the cylinder must match to achieve the desired exhaust behavior. For integration into complex controls, more compact variants with defined response times and reproducible characteristics are advantageous.

Standards, Safety, and Documentation

Exhaust valves should be selected according to relevant standards for pneumatic components. Technical data sheets and material lists provide information on pressure and temperature limits, as well as compatible media. Safety-relevant applications require additional risk assessment: if exhaust air can carry potentially dangerous particles or gases, exhaust paths and extraction measures must be planned. Further technical information and application examples can be found under Technik and Anwendungsbeispiele on our website.

• Material overview: Nickel-plated brass, stainless steel (304/316), aluminum; Seal options: NBR, FKM, EPDM; Connection types: Threaded (metric/ISO/UNF), push-in, hose connection

Selection Check – Brief

Choose the version with suitable material for the environment, appropriate seal for media contact, the design for installation space, and a flow characteristic matched to cylinder size and desired cycle time. If unsure, use technical data sheets or our consultation pages.

FAQs

1. What is the difference between a nickel-plated brass exhaust valve and a stainless steel version?

Nickel-plated brass offers good mechanical strength and corrosion protection in moderately stressed environments; stainless steel (304/316) is required for aggressive media, frequent cleaning, humidity, or high temperatures. Stainless steel has a longer service life in corrosive environments but incurs higher acquisition costs.

2. Which seal should I choose if lubricants are present in the air?

When in contact with oils or lubricants, FKM (Viton) is preferable due to its high resistance to hydrocarbons and oxidative aging. NBR is suitable for general applications without heavy oil exposure; EPDM is suitable for steam and water contact but is not oil-resistant.

3. How often do exhaust valves need to be maintained in production lines?

Maintenance intervals depend on operating conditions. In dusty or dirty environments, a monthly visual inspection and a quarterly functional check are recommended. In clean laboratory or packaging environments, semi-annual to annual inspection intervals are possible. Supplementary measures such as inline filters extend the time until the next maintenance.