Manifolds simplify fluid power systems

Integrated valve manifolds provide many benefits, including the enhancement of system integrity and reliability, when employed in pneumatic and hydraulic systems. In addition, the reduction in the amount of piping and fittings results in low pressure drop and efficient operation. Early pneumatic and hydraulic control systems utilized valves that were individually mounted in or around the machin...

06/15/2002


Key concepts

Manifolds reduce piping, eliminating leakage and pressure drop.

Manifold-mounted valves are easy to replace, reducing downtime.

Valve cartridges are generally interchangeable, increasing availability.

Sections:
Piping requirements
Hydraulic manifolds
Flexibility via functionality
Pneumatic manifolds
Serial bus

Sidebars:
Benefits of integrated manifold technology
Hydraulic manifold disadvantages
Available stackable modules and valve cartridges


Integrated valve manifolds provide many benefits, including the enhancement of system integrity and reliability, when employed in pneumatic and hydraulic systems. In addition, the reduction in the amount of piping and fittings results in low pressure drop and efficient operation.

Early pneumatic and hydraulic control systems utilized valves that were individually mounted in or around the machine structure. Flexible hose or rigid tubing conveyed flow, and piping connections were made with traditional pipe thread or straight thread connectors. The source of power to the valves was the plant compressed air supply or a hydraulic power supply.


Fig. 1. Manifolds provide a clean, uncluttered look.

Piping requirements

In the case of pneumatic valves, air leaving the unpowered side of an actuator exits through the exhaust ports of the air valve to the atmosphere. In the case of hydraulic valves, fluid exiting the unpowered side of the actuator must be connected to the reservoir. Hydraulic valves require two lines — one for pressure flow and one for tank line flow — while pneumatic valves require a single pressure line.

To put the piping system in perspective, a hydraulic system with four control valves requires eight fluid lines — four for pressure and four for tank line flow. An additional eight fluid lines are required to convey the flow to the actuators. Considering the cost of materials and labor, it is apparent that a simpler, more cost-effective method of assembly is the integrated valve manifold .


Fig. 2. Hydraulic circuits require a return line to the tank.

Hydraulic manifolds

Three styles of functional components are available for integrated manifolds:

  • Cartridges that thread into the manifold

  • Cartridges that slip into the steel or aluminum manifold

  • Functional modules that stack on top of the manifold under the directional control valves.

    • Threaded cartridges consist of a body, poppet or spool, spring, and an operator such as a solenoid (Fig. 3). Pressure and flow cartridges usually have an external adjusting screw or knob. Simple check functions have no operators or adjustments. The valves are threaded on the outside diameter for simple installation into an integrated manifold.

      While there is no official dimensional standard for each size of cartridge, most major manufacturers have interchangeable designs. This standardization affords the user a choice of brands and reduces downtime should a specific brand of valve need replacement and not be readily available.

      Fig. 3. Threaded cartridge valves provide simplified installation into manifolds.

      Insert or slip-in type cartridges are held in place by a cover plate that bolts in place (Fig. 4). There is a worldwide DIN standard that delineates the dimensions for each size of cartridge. An older WERK standard type of insert cartridge may still be found in some plants, primarily in Europe.

      Fig. 4. Insert cartridges are made to a worldwide DIN standard for interchangeability.

      Stackable function blocks house the moving elements within an aluminum or steel module that stacks under the directional control valve . Longer bolts are used to accommodate the height of the stackable functions under each directional control valve.

      In the initial stages of development, valve manufacturers created their own manifold mounting dimensions and control port patterns. Their stackable valve modules were not interchangeable with other manufacturers.


      Fig. 5. Stackable valves mount under directional valves and provide additional control functions.

      Many users soon realized that in order to reduce downtime, they had to stock many brands of valves in their inventory. A standard was needed that would afford the ability to use any brand of valve on a manifold block. Hydraulic valve manufacturers were the first to adopt a directional valve standard.

      The National Fluid Power Association (NFPA) set a standard for hydraulic valves, and eventually an ISO standard was adopted for pneumatic valve manufacturers. The ISO standard for hydraulic manifolds followed the NFPA standard. Most stackable hydraulic valve modules today conform to the NFPA/ISO standard.

      Flexibility via functionality

      In general, hydraulic manifolds tend to use one of the three types of elements. In the case of the threaded or slip-in cartridges, there is no limit to the number or cartridges or the size of the manifold.

      Stackable modules are usually limited to four or five sandwich modules under each solenoid valve.

      Pneumatic manifolds

      Pneumatic manifolds are capable of handling many functions by offering sandwich-type control modules that mount under directional control valves. In a pneumatic system, the common additions to standard directional control valves are flow controls to regulate the actuator speed, and pressure regulating valves that allow for the reduction of pressure to one or both actuator ports.

      These functions, which were traditionally accomplished by mounting valves in the control lines to the actuator, can now be added as modules that stack under the directional valve. The modules provide easy access for troubleshooting or repair without disturbing any of the piping to the actuator.

      Another enhancement to pneumatic manifolds is the addition of integrated electrical wiring. The use of plug-in electrical connections on the valve and corresponding manifold means that no wiring need be touched when a valve is replaced. The removal of a valve from the manifold disconnects the electric power to the solenoids on the valves.

      Serial bus


      Fig. 6. Serial addressable modules dramatically reduce the control wiring in a system.

      A growing trend in the machine control arena is the use of serial bus systems. A serial bus system employs a five-wire cable that carries power and communication signals from the serial addressable module (SAM) to the control valves and other I/O devices in the system .

      The language of the serial systems is called a protocol and it denotes the manner in which the transmitted data is organized. The most popular systems are DeviceNet, Remote I/O, SDS, Interbus-S, and Profibus.

      The use of a single five-wire cable dramatically reduces the wiring on the system, and when used in conjunction with a valve manifold package, the system is esthetically and functionally appealing. In addition, the SAMs feature rugged construction to withstand hostile plant environments.

      Integrated manifolds make sense for users of hydraulic or pneumatic control valves. They can benefit from savings in labor cost, while enjoying the enhancements in system integrity and reliability that increase productivity.

      — Edited by Joseph L. Foszcz, Senior Editor, 630-320-7135, jfoszcz@cahners.com



      Benefits of integrated manifold technology

      Cost of labor to mount and pipe valves is reduced. Many equipment users can take advantage of this cost-effective technology when upgrading existing equipment.

      Reduced size and weight streamline installation.

      Ability to combine many functions for an actuator in a smaller package allows for placement close to the actuator. Many line-mounted operations, such as flow controls and counterbalance functions, can be integrated into a manifold that is mounted right on, or close to, the actuator.

      Fewer piping connections reduce the potential for leakage.

      Reduction in the amount of exposed tubing is an advantage in environments where piping may be exposed to mechanical damage.

      Efficiency is increased because the reduction in piping decreases pressure drops and heat generation in the system.

      Serviceability is improved because cartridges can be removed and replaced quickly without disturbing external piping.

      Hydraulic manifold disadvantages

      Cost—In the case of a custom manifold that uses threaded or insert cartridges, the volume must be high enough to offset developmental costs. Manifolds that use stacking modules are much simpler in design with a common pressure and tank gallery. The cost of the base manifold is low and offset by the slightly higher cost of the stackable modules.

      Nonrepairable cartridges—Most cartridges are assembled in a way that makes them nonrepairable and difficult to service. The only option available is a new replacement cartridge.

      Nonstandard cartridges—If a user selects a brand of cartridge that is not generally interchangeable with other models, then a cartridge failure can be a problem. If a replacement for the nonstandard cartridge cannot be obtained quickly, the user has no place to turn, and resulting machine downtime can be costly. Standardization—the ability to replace a given cartridge with many other brands—is "user-friendly."

      Logistics—Control valves should be mounted as close as possible to the actuator to reduce the capacitance in the piping between the control valve and actuator. Capacitance can reduce response time, which is not desirable in high-dynamic applications. These types of applications typically employ proportional valves or servo valves mounted on the valve manifold package close to the actuator rather than in a remote location.

      Available stackable modules and valve cartridges

      Flow control valves, both pressure and nonpressure compensated

      Check valves and shuttle valves

      Pilot-operated check valves

      Pressure reducing valves

      Relief valves

      Unloading valves

      Sequence valves

      Counterbalance valves

      Solenoid-operated two and three-way valves - poppet type

      Solenoid-operated two, three, and four-way valves—spool type

      Proportional flow and pressure control valves



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