In a Valve magazine article, Solenoid Pilot Valves for Valve Actuation, Emerson’s Bill Reeson defined a “pilot valve” as:
…an electromechanically operated valve. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports. Multiple solenoid valves can be placed together on a manifold.
…a three- or four-way solenoid valve that pilots or controls the flow of media, such as air or water, into an actuator, which in turn controls the movement of a valve connected to the actuator. In other words, the pilot valve drives or controls the main process or control valve in a process control system.
This article is a great primer on the terminologies and descriptions used for solenoids. Here’s an example:
Today there are many functions based on these two basic descriptions, and it is not uncommon to see descriptions such as 3/2 NC, 3/2 NO, 3/2 U, 3/3, 4/2, 5/2, and 5/3. While these designations may look confusing, they are actually quite simple. For a three-way pilot valve, for example, the expression 3/2 NC means:
- The number 3 signifies three ports on the valve.
- The number 2 designates that the valve has two positions. The two positions are energized or deenergized.
- NC stands for normally closed, which means that in the de-energized position, the process connection to the actuator is closed.
The first port is normally marked as P (pressure) or 1. This is the air supply to the valve. The second port is C (cylinder) or 2. This is the working port connected to the piston side of a spring-return actuator. The third port is designated 3 or E (exhaust). The exhaust port is where the air from the actuator is released when the pilot valve changes state from energized to de-energized.
Pilot valve islands or manifolds are used in the pharmaceutical and biotech industries to drive sanitation valves and are typically mounted inside an enclosure. This allows one place for the pneumatic supply and electrical connections to be made. ASCO Numatics 501 Series, 502 Series and 503 Series are examples of these solenoid pilot actuated valves and manifolds.
Traditionally, discrete outputs (DOs) from the control system have driven solenoid valve state changes. With the advancement of digital bus technologies, products such as the Numatics G3 Fieldbus Electronics add DeviceNet, Ethernet, PROFIBUS DP, CANopen, PROFINET and POWERLINK digital protocols to communicate between the control system and pilot valves.For process manufacturers and producers with DeltaV distributed control systems, a recent news item, Emerson Simplifies Pneumatic Valve Commissioning and Marshalling in I/O Cabinets introduced:
…the ASCO Numatics 580 CHARacterization Module (CHARM) node for easy solenoid valve integration into Emerson’s DeltaV S-series distributed control system (DCS) with Electronic Marshalling technology.
It directly links the 580 CHARM node and manifold to the CHARMs baseplate to support communications with up to 32 solenoid valves per 580 CHARM node. This eliminates the need to use individual DO CHARMs to drive each valve coil on the pilot manifold. The 580 CHARM node also provides:
- A single connection from the field to the DeltaV system
- Streamlined configuration and diagnostics in the DeltaV system
- Redundant communications and power
Altogether, programming and commissioning time can be reduced and savings in wiring and components up to 15% can be achieved.