Distributer (automatism)

In the automated systems, the distributer is the element of the transmission chain of energy used to commutate and control the circulation of the fluids under pressure. Although certain sensors function on the same principles, one more particularly holds this term with the preactionnor then are equivalent of the relay for electricity.

Generally constituted of a drawer which slides in a body, it puts in communication openings (suitable for connection or not) according to several associations. The drawer can be actuated by a lever, a reel, a piston, or a return spring (for those having a neutral or stable position).

The drawer has a functional play which lets pass a light escape. The distributers with valve or the cartridges logical remove this disadvantage.

Classification and Representation

Types of distributers

One initially distinguishes the distributers by the number of the openings and the number of positions, then the nature of the orders, the management of the flow of power (" All or nothing " or progressive).

The number of opening is the number of contuites (suitable for connection or not) outgoing of the body of the distributer. There are thus at least two of them.

The number of positions corresponds to the number of situations of the component. For each position, the conduits are associated according to a different combination. Certain passive components (like the non-return valves or Pressure controller) are considered, from the point of view of the representation like distributers with a position. The current cases comprise two or three boxes.

The designation of a distributer is presented in the form of a fraction giving the number of opening then the number of positions.

The diagrammatic representation of the distributers is a juxtaposition of square boxes:

There are as many boxes as of positions.
For each position the arrows represent internal connections connecting the openings. The arrow gives the direction of flow. One finds in each box the same site for each opening. An orphan opening is marked by a stopper in form of T.

Connection

Outside, in the prolongation of the openings, one represents the conduits bringing the fluid.

They are obligatorily connected to the same box associated with the position with reference, called active position for the component but position intiale for the system.
the source of pressure and the exhaust are identifiable by their specific symbol which simplifies the total diagram.
the other conduits are represented by a simple feature connecting two components.
the auxiliary conduits are represented in stopped feature (dotted line).

Orders or pilotings

On with dimensions free one of the boxes, the control device is represented in the respect of conventions. The codes of representation are appreciably the same ones as for the electrotechnical components.

The nature of the orders can be very varied, simple or sometimes multiple:

hand drive operation by push rod, punch, lever or pedal,
electric drive by Solenoid,
hydraulic control or pneumatic,
power-control for the sensors,
order by spring (it is then about distributer monostable).

By defect, the central box corresponds to a stable situation, forced by one or more Ressort S.

Examples presented, and use

The image opposite gives the representation of very current cases, and their employment:

2/2 monostable NO per pushbutton: control knob.
3/2 NF sensor with roller: mechanical detection of presence
4/2 with pneumatic controls: jack supply for double purpose
5/2 with electric drives or manual: jack supply for double purpose, direct piloting by automat.
4/3 with lever driving and progressive exit (joy-stick): order hydraulic machine

Even if on the theoretical level, certain sensors or control knobs function like distributers, it are very different technologically from the components of power. In practice, one appoints by distributer only the préactionneurs charged to control energy sent to the jacks and other engines.

Direction of action

For the monostable distributers with two positions, therefore with recall by spring, one distinguishes two families according to whether the power is delivered by defect or on order:

normally closed Distributer (NF): the exit is not fed in absence of instruction.
normally open Distributer (NO): the exit is fed in absence of instruction. It is thus necessary to order the cut of energy.

Choice

The choice of the distributer is strongly related to its environment of establishment. It is necessary to take account of:

the nature of the fluid: air or oil,
of the power required by the controlled actuator, problem of possible flow,
of the nature of the energy of order: manual, electric, pneumatic or hydraulic
of the desired action: with or direction memorizing, by defect or on order.

The table below gives the most current technological choices, according to these criteria.

monostable Distributer
bistable Distributer
Center closed (4/3 or 5/3)
open Center (4/3 or 5/3)

Jack simple effect:

pneumatic: 3/2
hydraulic: 3/2 or 4/3 (closed opening)

Jack double effect:

pneumatic: 4/2, 5/2 or 5/3
hydraulic: 4/3

Principal distributers

Distributer 2/2
Distributer 3/2
Distributer 4/2
Distributer 5/2
Distributer 4/3
Distributer 5/3

Special distributers

Blockers 2/2
advanced Disconnecting switches
general Disconnecting switch
progressive Starter

Particular case

The piston of the Trumpets and other instruments of the brass family are actually of the distributers of the type 4/2 monostable. The role is to temporarily cause a prolongation of the Airstream.

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