Pneumatic function fittings perform needed control and safety operations

Appeared in print as "Multitasking pneumatics"

Pneumatic function fittings, as the name implies, do more than simply connect hose or tubing to a cylinder, valve, or other air-powered device — as is the case with conventional fittings. They perform additional control or safety operations, possibly eliminating valves and other devices from a circuit.

Flow-control regulator fittings use an adjustable restrictor to meter flow and control cylinder speed.

For pneumatic system designers, combining multiple capabilities into a single fitting offers compact size, greater design flexibility, elimination of potential leak paths, simplified installation, and potentially lower costs.

These fittings come in a variety of sizes, configurations, materials (such as brass, plastic, steel, and stainless steel), and with push-in connections or standard or metric threads. Here’s a look at some of the various types of function fittings available today.

Miniature ball valves
Mini ball valves come in 2/2 and 2/3 versions and let operators open and close a pneumatic circuit. Compact and light weight, they are suited to all types of installations, and a variety of mounting styles lets system designers select the best configuration for a particular application. A screwdriver slot allows closing and opening, even where access may be difficult. Full passage mini ball valves accommodate high flow with low pressure drop.

Mini ball valves let operators open or block pneumatic flow with the turn of a screwdriver.

Operating specs include a maximum pressure of 10 bar, vacuum capability down to 755 mm Hg (99% of vacuum), and working temperature of – 20° to 80° C.

Blocking fittings
Designed to offer maximum flow capacity, blocking fittings lock a cylinder’s piston in place by simultaneously cutting off the supply and exhaust air. Functional locks are more precise and rapid when blocking fittings are mounted directly on the cylinder, the volume of air in the piping is no longer a factor.

Removing the pilot pressure on this lockout valve causes a spring to reseat the pilot piston and close the valve.

Soft-start fittings let air pressure gradually increase on the first cycle of equipment operation.

They should be mounted in pairs, and some versions can fully swivel, providing flexibility in the design and installation of pneumatic circuits. Working pressure with compressed air ranges from 1 to 10 bar. Working temperature ranges from –20° to 70°C

Venting fittings
Fittings with venting capability come in several versions and configurations. Manually operated vent fittings can be used whenever a system must be frequently depressurized. They guarantee immediate isolation of the air line by venting to atmosphere when a simple manual lever is shifted.

These valves block the supply and vent system pressure with the flip of a lever.

Supply in the 3/2 version, for example, can be on the instant- connection side or on the threaded side — for instance, when mounted on a manifold. Maximum working pressure is 10 bar and temperature range is –10° to 80°C.

3/2 pneumatic sleeve valves may be used to bleed the air line by venting the system to atmosphere. Their in-line configuration permits compact mounting directly into the pipework. Moving the sleeve in one direction lets air freely pass through the valve. Moving it in the opposite direction shuts off the supply and exhausts downstream air. Temperature range is the same as for the manually operated vent fittings, but maximum working pressure is 16 bar, and flow direction is one way.

Pressure regulator
Pressure regulator fittings are used to stabilize the pressure applied to pneumatic actuators at a preset value, regardless of upstream pressure fluctuations. Outlet pressure is fully controlled by an adjustment screw. To aid pressure selection, the screw on fittings from some manufacturers is calibrated to show the pressure setting.

Pressure regulator fittings can be mounted downstream of the control valve to reduce pressure for one direction or mounted upstream of the control valve for reduced pressure in both directions. These fittings handle input pressure from 1 to 16 bar, and regulated pressure is 1 to 8 bar. Working temperature range is –10° to 70°C.

Pressure reducer
Pneumatic cylinders often require full force when extending to move a load, but only minimal force on the return stroke. Thus, applying full system pressure to retract the rod wastes energy.

Sensor fittings produce an output signal when a cylinder reaches the end of stroke and exhaust back-pressure disappears.

Pressure reducer fittings provide the cylinder with a pressure reduced to a value determined by manual adjustment, thereby increasing energy efficiency. These fittings can mount directly to a control valve or terminal block, or on the pipework between the control valve and cylinder (in-line version). Typical working pressure is 1 to 8 bar and temperature range is –15° to 60°C.

Soft-start fittings
Pneumatic soft-start fittings allow air pressure to gradually increase only on the first cycle of equipment operation. They prevent shocks to a pneumatic system or sudden movements when a machine starts up. For instance, a protected cylinder gradually returns to the position where it stopped when system was vented. Mounted on the FRL (filter-regulatorlubricator) outlet, they protect the entire downstream installation. When mounted to the control valve’s supply port or to the common supply line of several associated valves, they control all designated actuators.

Typical working specs for soft-start function fittings include pressures from 3 to 10 bar and temperatures from –15° to 60° C.

Non-return valves
Non-return valves are check valves contained in the body of the fitting. They let air pass in one direction while blocking flow in the other direction. The fittings typically mount upstream of the protected circuit. Their extreme compactness and light weight make them well suited as an easily installed safety item in compressed air circuits. Working pressure is 1 to 10 bar and temperature range is 0° to 70°C.

Sensor fittings
Sensor fittings detect pressure drop and are generally used to discern the end-of-travel of a cylinder. They produce a pneumatic or electric end-of-stroke signal when no exhaust backpressure in the cylinder exists. They can mount on the cylinder or on the control valve.

Typical specs include a temperature range of -15° to 60°C, working pressure from 3 to 8 bar, breaking pressure from 0 to 6 bar, and a response time of 3 msec.

Flow-control regulators
Flow-control regulators control the speed of pneumatic actuators. In the one-way version, an adjustable orifice restricts the exhaust or inlet air flow. The inlet or exhaust flow, respectively, is unrestricted. In a bi-directional version, they control both exhaust and inlet flow. Depending on the model, flow regulators can mount onto a cylinder or in the compressedair line.

However, flow regulation (and, therefore, control speed) is more precise and constant when the flow regulator is positioned near the actuator. This can minimize the elastic effect of the compressed air contained in the pipework between the control valve and actuator. Therefore, direct mounting of a flow regulator fitting onto the actuator is recommended. Typical operating range is 1 to 10 bar pressure at 0° to 70° C.

Snap connectors
Snap connector fittings are used to isolate a circuit without venting the entire system. They are designed for frequent connections/disconnections with complete safety. Connection is confirmed by an audible “click.” Working temperature is –20° to 80° C with a maximum pressure of 10 bar.

Rich Sachwitz is with Parker Hannifin's Fluid Systems Connectors Div., Otsego, Mich. Click here for more information on Parker's pneumatic function fittings.