Valves are represented by symbols because actual construction is quite complex. A symbol specifies function of the valve, method of actuation, no of ports and ways.
Pneumatic symbols have been standardised in ISO 1219-1:2006. (Fluid power systems and components – Graphic symbols and circuit diagram). Another standard ISO 1219-2:1995 establishes the rules for drawing diagrams of fluid power systems using symbols from ISO 1219-1. Port designations are described in ISO 5599.
Port markings: As per the ISO 5599, ports are designated using a number system. Earlier, a letter system was used to designate a port. Table 1.1 gives port markings.
Table 1.1: Port Markings of Direction Control Valve
Ports and position: DCVs are described by the number of port connections or ways they control. For example: Two way, three – way, four way valves. Table 1 shows the Port markings of DCVs and
Table 1.2 shows commonly used DCVs with old and new designations.
Table 1.2: Port designation of DCV