A manifold is a fluid or gas distribution system or device that serves to bring many junctions into one place or a single channel into an area where many points meet. Manifold systems range from simple supply chambers with several outlets to multi-chambered flow control units including integral valves and interfaces to electronic networks. Complex pneumatic and hydraulic circuits can utilize manifolds and manifold systems with interfaces to sophisticated electronic networks.

One piece manifold devices are simple in construction. Gas enters and exits through one or more ports as appropriate for an application.

Manifold systems are more complex, and incorporate a number of other components:

Pipe or tube - Vessels used to transport the fluid

Fittings - Tees, elbows, crosses, plugs, and other parts that fit pipe to manifolds.

Expansion chambers - Allows for a certain percentage of expansion in the piping line to prevent pressure increase in the system. This helps extend seal life and prevent leakage.

Valves - Used to control flow through the ports of the manifold

Flexible connectors - Braided connectors that bend and flex to attach containers to manifolds or manifolds to fixed equipment.

Instruments - Pressure gauges, switches, and other devices used to perform various system functions involving measurement.

Gas cabinets and distribution systems also contain manifolds as flow components which connect compressed gas cylinders and eliminate the need to repeatedly handle regulators during cylinder change-out. For information on selecting gas cabinets and distribution systems, visit GlobalSpec's Gas Cabinets and Distribution Systems Selection Guide.

Performance specifications, port and valve specifications, components and circuit style, and applications are all important parameters to consider when searching for manifolds.

Performance Specifications

Matching the performance specifications for manifolds and manifold systems to the needs of the application is important for proper selection.

Maximum pressure - Pressure describes the amount of force exerted on the system by the contained fluid. Most compressed gases will not exceed 2,000 to 2,640 pounds per square inch gage (psig), but some can reach pressures of 6,000 psig. The system's weakest point determines the pressure limit, so any parts weakened by heat, corrosion, or stress may potentially lower how much pressure the vessel can withstand, or may cause it to rupture.

Maximum flow - Flow rate describes the maximum rate of flow of the fluid through the system. If the fluid is a gas, it is typically measured in standard cubic feet per minute (scfm); for liquids, flow is commonly described using gallons per minute (gpm).

Temperature range - Temperature range is the full required range of safe ambient or fluid operating temperatures, given in degrees Fahrenheit or degrees Celsius.

Ports and Valves

Ports and valves are key components in manifolds and manifold systems, and their specifications are thus an important part of the selection process.

Port Types

Ports are openings in the manifold where the inlet and outlet connections are made. Each opening is either an inlet (supply) port or an outlet port; the number of each corresponds to the requirements of the application.

The number of supply ports defines the number of independent fluid supplies that can be interfaced with the manifold or manifold system.

The number of outlet ports determines the number of outlets in the system. This is frequently specified as number of ports or valves that are or can be attached to the manifold.  For example, a 6 point manifold has 6 ports or valves.

Ports are sized based on standardized National Pipe Thread (NPT) sizes. Dimensions for these sizes are given in inches; each is based on the nominal pipe size that corresponds to the connection.

Valve Types

Integral valves are integrally assembled with the manifold, as opposed to a base or subplate to which separate valves are attached. Integral valve types include manual, solenoid, and air pilot.

• Manual valves - valves are manually adjusted or actuated via a knob, lever, or other manual device.
• Solenoid valves - valves are opened and closed via a solenoid magnet activated by an electrical signal.
• Air pilot valves - valves are actuated by a pneumatic signal.

Materials

The materials used to construct manifolds and manifold systems determine fluid (gas or liquid) compatibility, and also play an important role in performance.

• Aluminum - A light and fairly corrosion-resistant metal which is typically anodized for increased corrosion and wear resistance. Aluminum has good temperature resistance, but is relatively weak compared to steel.
• Ductile iron - A variant of cast iron which retains its machinability and corrosion-resistance
• Plastic - Any of numerous thermoplastic or thermosetting polymers of high molecular weight. Different grades (such as nylon, acetal, and polycarbonate) have varying properties, but most have strong chemical and corrosion resistance.
• Steel - General purpose industrial metal with high physical strength and hardness. Steel is typically coated or finished to increase its corrosion resistance properties.
• Stainless steel - A steel alloy with excellent chemical and corrosion resistance most commonly used for liquid or corrosive gas distribution systems.

Features

Manifolds and manifold systems may be comprised of a number of additional features which are important for certain applications.

Adjustable chamber isolation - Supply chambers can be isolated or joined, depending on application or state of process cycle.

Feedback signal - Feedback signals are electrical or electronic signals used to signal the state of valves for indication or automated system response.

Filter or trap - Traps remove unwanted contaminants (typically oxygen, moisture, or hydrocarbons) from specialty gases before they reach the instrument. They also can be used as indicators of gas contamination.

Visual indicator - Indicators provide visual signals to describe the status of different parts of the system, such as LEDs used to signal valve state (open or closed). 

Applications

Manifold systems can be found in many systems and applications. Some of the most common types of manifolds include those for general purpose, pneumatic or compressed air, gas, water, hydraulic fluid, oil or fuel, food processing, or medical and pharmaceutical applications.

References

Applied Energy Systems, Inc. - Gas Man

Key Gas Components, Inc. - Custom Gas Manifolds

Magnaloy - Hydraulic Manifolds

Image Credit: Sigma-Aldrich